MECHANICAL ENGINEERING INTERVIEW QUESTIONS
1.
Why Entropy decreases with incr ease in temperature?
An s.
ds =dQ/T Entropy is inversely proportional to the t emperature so, as temp. Increases, entropy d ecreases.
2.
Why different types of sound are produced in different bikes, though they run on SI Engines? Engines?
An s. Engine specifications specifications are different in different manufactures like as Bore Diameter (CC), Ignition timing. Also the exhaust passage takes more responsible for sound. 3.
How much Watt means 1Hp?
Ans.
746.2 W att
4.
Explain Bicy cle Rear Rear Wheel Sprock et worki ng?
An s.
Rear wheel sprocket works under the principle of ratchet and pawl.
5.
Defini Defini tion of Octane Number and Cetane Number? Number?
An s. Octane No.- Octane number is defined as the percentage, by volume, of iso octane in the mixture of iso octane and hheptane. It is the measure of rating of SI engine. Cetane No.- Cetane number is defined as the percentage, by volume, of n-cetane in the mixture of n-cetane and alpha methyl naphthalene. It is the measure of rating of CI engine. 6. Ans.
Which Mechanism is used in Autom obil e gearing System? Differenti al mechanis m
7. An s. 8.
When Crude Oil is Heated, Heated, Which Hydro Carbon comes first ? Natural gas (Gasoline)… at 20 Celsius How to calculate Bearing number ti Diameter Diameter of the inner and outer?
An s. Divide the shaft diameter size by 5, it will give last two digit of the bearing no. and according to type of load we have to choose the type of bearing and that will give prior number of the bearing. 9. An s. 10.
The Fatigu Fatigu e life of a part can be impr oved by? Improving the surface finish by Polishing & providing residual stress by Shot p eening. What happens if gasoline is used in a Diesel Engine, Siesel Engine will work?
An s. No, It will not work, as the Compression ratio of Petrol engine is 6 to 10 & that of Diesel engine is 15 to 22. 22. Thus on such high compression, gasoline gets highly compressed & it may blast. 11.
Poissons Ratio is Higher in, Rubber/Steel/Wood?
An s. When a material is compressed compressed in one direction, direction, it usuallytends to expand in the other t wo directions perpendicular perpendicular tothe direction of compression. This phenomenon is called thePoisson effect. Poisson’s ratio is a measure of the Poisson effect. For rubber = 0.5 For steel = 0.288 For wood < 0.2 Thus Poisson’s ratio is higher in RUBBER. 12. 12.
Why the Centrifug al Pump is called High Discharge pump?
An s. Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to push out the fluid. So the liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the liquid in high rate. It is given in the following formulae: 2
Centrifugal Centrifugal force F= (M * V )/R. Where, M-Mass V-Velocity
R-Radius
13. 13. How Cavitation can be eliminated by Pump? An s. • • • •
14.
Cavitation means bubbles are forming in the liquid. To avoid Cavitation, we have to increase the Pump size to One or Two Inch; To increase the pressure of the Suction Head, or Decrease the Pump Speed.
Why Cavitation will occu r in Centrifug al Pump and not in Displacement Pump?
An s. The formation of cavities (or bubbles) is induced by flow separ ation, or non-uniform flow velocities, velocities, inside a pump casing. In centrifugal pumps the eye of the pump impeller is smaller than the flow area of pipe. This decrease in flow area of pump results in increase increase in flow r ate. So pressure drop happened between pump suction and the vanes of the impeller. Here air bubbles or cavities are formed because of liquid vapour due to increase in temperature in impeller. This air bubbles are transmitted to pump which forms cavitation. 15.
Which Pump is more Effic ient Centrifug al Pump or Reciproc ating Pump?
An s. Centrifugal pump. Because Because flow rate is higher compared to reciprocating pump. Flow is smooth and it requires less space to install. Lower initial cost and lower maintenance cost. 16. 16.
Why Centrifugal Pump is not called as a Positive Displacement Type of Pump?
An s. The centrifugal has varying flow depending on pressure or head, whereas the Positive Displacement pump has more or less constant flow regardless of pressure. Likewise viscosity is constant for positive displacement pump where centrifugal pump have up and down value because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. When there is a viscosity change in supply there is also greater loss in the system. This means change in pump flow affected by the pressure change. One more example is, positive displacement pump has more or less constant efficiency, where centrifugal pump has varying efficiency rate. 17. 17.
What is the diff erence between Critic al Speed Speed and Whirling Speed?
An s. In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases increases system vibration. The resulting resonance occurs r egardless egardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft. 18.
How a Diesel Engine Works as Generator? Generator?
An s. Diesel engine is a prime mover, for a generator, pump,and for vehicles vehicles etc. generator is connected to engine by sh aft. mostly in thermal power plat ,there is an engine is used to drive generator to generate power. 19. An s. 20.
Explain Second Law of Thermodyn amics? The entropy of the universe increases over time and moves towards a maximum value. Compare Brayton Cycle and Otto Cycle?
An s. The heat addition and rejection processes in Otto cycle are of constant volume, whereas in Brayton cycle, they are of constant pressure. -Otto cycle is the ideal cycle for spark ignition engines. -Brayton cycle is the ideal cycle for gas power turbines. 21. An s. 22.
What is the purpo se of Scrapper Ring? scrap the excess lube oil from the cylinder walls. there by preventing oil from entering combustion zone. What is DTSI DTSI Technology ?
An s. DTSI stands for Digital Twin Spark Plug I gnition. The vehicles with DTSI Technology use 2 spark plugs which are controlled by digital circuit. It results in efficient combustion of air fuel mixture. •
Digital - Since the spark generation will be initiated by a microchip.
•
Twin - Since two spark plugs will be used.
•
Spark Spark ignition - Since the ignition will be done via a spark.
23.
How to Find, Ductile-Br ittl e Transiti on Temperature in Metals?
An s. The point at which the fracture energy passes below a pre-determined point for a standard Impact tests. DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. 24.
What is the impor tance of Thermodyn amics?
An s. All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers. 25. An s.
What is the diff erence between P11 and P12 Pipes? P11 the chromium molybdenum composition that is 1% ofchromium and 1/4% of molybdenum
P12 the chromium molybdenum composition that is 1% ofchromium and 2% of molybdenum 26.
State diff erence between AnitiFri ction Bearing and Journal Bearing?
An s. Generally, journal bearings have higher friction force, consume higher energy and release more heat, b ut they have larger contact surface, so normally used in low speed high load applications. In anti friction bearings friction is less. One object just rolls over each other. 27. 27.
What is the diff erence between Fan and Blower?
An s. Fan is an air pushing device. Either Axial or Centrifugal type systems are used to move the air in low pressure. It is rotated by a motor separately. When the fan is a housing of blades and motor, then it called as Blower. It directs the air in a single path with high pressure. 28.
What is Heat Heat Rate of Power Plant?
An s. Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output 29. An s.
What is Hydrody namic Cavitation? Hydrodynamic cavitation describes the process of vaporization in a constrained channel at a specific velocity.
Bubble generation and Bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in pressure. 30. An s.
What is Difference between Hardn Hardn ess and Toughness ? Toughness is the ability of a material to absorb energy.
Hardness is the ability of a material to withstand wear. 31. An s. 32.
What is the hott est part of Refrigerant in Refrigeratio n? Compressor What does F.O.F F.O.F Stand for Piping Design?
An s. Face of Flange, The F.O.F (Raised face and Flat face) is used to know the accurate dimension of the flange in order to avoid the minute errors in measurement in case of vertical or horizontal pipe lines. 33.
Where Multi stage Pump is Used?
An s. Pressure washing of Aircraft, Trains, Boats and Road vehicles as well as Spray washing of industrial parts and Electronic components. 34. An s. 35.
What does pump develop:- (a) Flow (b) Pressure A pump does not cr eate pressure, it only creates flow. Pressure is a measurement of the resistance to flow. How to measure temperatur e of Bearing?
An s. Normally the temperature range from 80 degree to 110 degree Celsius. So the following temperature measurement devices are used. · Dial T ype Bearing Temperature Detector · Stator W inding inding Temperature Detector · R esistance esistance Bearing T emperature emperature Detector (Bearing RTD)
· Specialized in Pin type RTD 35.
Difference between Perfor Perfor mance and Effici ency?
An s. The accomplishment of a given task measured against preset known st andards of accuracy, completeness, cost, and speed is called as Performance. Efficiency is defined as the input given and the work obtained from that input like money, time, labour etc. It’s the main factor of productivity. 36. 36.
What is Sentinel Relief Valve?
An s. It’s a special type valve system. The valve will open when exhaust casing pressure is excessive (high). The valve warns the operator only; it is not intended to relieve the casing pressure. 37. An s.
What is the diff erence between Specific ation,Codes, Standards? Specification is describing properties of any type of materials.
Code is procedure of acceptance and rejection criteria. Standard is accepted values and compare other with it. 38. An s. 39.
Which is heavier 1kg Cotton or 1kg Iron? Both of them have same weight. What is Auto Dosing?
An s. Auto dosin g is an aut omated system of feeding th e equipm ent with liquid products. It is the ideal way to ensur e the corr ect calibrated dose at the right time every time in auto. 40. An s.
What is the diff erence between Sudden Force and Impact Force? · An impact is a high force or shock applied over a short time period when two or more bodies collide.
· A f orce which applies applies on th e body (material) suddenly is known as sudden force. 41. An s. 42.
What is Geyser Pressure Valve? To release the pressure created inside due to evaporation of water. What is diff erence between Correct ive actions and Preventive actions ?
An s. Corrective actions are taken on discrepancies noticed during inspection of products/documents/process products/documents/process whereas pr eventive actions are taken to eliminate the possibility ofdiscrepancy in future. 43. 43. An s. 44.
How do you know air is fully saturated? saturated? In its Dew point. (100% relative humidity condition) What is the func tion of scoop in BFP (Boiler Feed Feed water pump) in Thermal Power Station?
An s. The Function of Scoop tube is regulating the varying amount of oil level in the coupling during operation of infinite variable speed. 45.
What is Operating Operating Pressure?
An s. The amount of pressure nearest the point of performing work at the output end of a pneumatic system. The system operating pressure is used to specify the capability of valves and actuators. 46. 46.
What is the diff erence between Technology and Engineering?
An s. Engineering is application of science. Technology shows various methods of E ngineering. A bridge can be made by using beams to bear the load,by an arc or by hanging in a cable; all shows different technology but comes under civil engineering and science applied is laws of force/load distribution. 47.
How to Measure Measure Temperature in Wet Bulb Thermometer?
An s. Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity.
48. 48.
What are the Advantages and Disadvantages of usin g LPG in Car?
An s. Ad van tag es 1. Complete c ombustion ombustion 2. Fuel saving 3. Homogenous combustion Disadvantages 1. As complete combustion is occurring ,more heat liberated,not advised for long journey, engine will be over heated 2. Installation is difficult 3. Reduce engine life life efficiency efficiency 49.
What is the diff erence between Speed and Economi c Speed?
An s. The rated speed tells us about the maximum speed which can be achieved by a vehicle or some other machine but the economical speed means the speed limit at which the machine works efficiently with least consumption of fuel.eg-in normal bikes(not racing),the max.speed limit shown on speedometer is upto 120 kmph but companies always advice their customers to drive such bikes at around 60 kmph to have maximum mileage. 50.
What is Powder Technology ?
An s. Powder technology is one of the ways of making bearing material. In this method metals like bronze, Al, Fe are mixed and compressed to make an alloy. 51. 51. An s.
State all the laws of Thermodynami cs? There are three laws of th e thermodynamics.
First Law: Energy can be neither created nor destroyed. It c an only change forms. In any process in an isolated system, the total energy remains the same. Second Law: When two isolated systems in separate but nearby regions of space, each in thermodynamic equilibrium in itself, but not in equilibrium with each other at first, are at some time allowed to interact, breaking the isolation that separates the two systems, and they exchange matter or energy, they will eventually reach a mutual thermodynamic equilibrium. The sum of the entropies of the initial, isolated systems is less than or equal to the entropy of the final exchanging systems. In the process of reaching a new thermodynamic equilibrium, entropy has increased, or at least has not decreased. Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum. 52. 52.
State the diff erence between Unilateral and Bilateral Tolerance?
An s. A unilater al toleranc e is toleranc e in which var iation is perm itted only in one direct ion from th e specified dir ection.e.g. 1800 +0.000/-0.060 Bilateral Bilateral tolerance is t olerance in which variation is permitted in b oth direction from the specified direction.e.g. 1800 +0.060/-0.060 53. An s.
What is the abbreviation of welding rod 7018? 7018? 7018 =
70=tensile strength 70000psi 1= welding position 8=current flux 54. 54. An s.
What is diff erence between Welding and Brazing? In Welding concentrated heat (high temperature) is applied at the joint of metal and fuse together.
In Brazing involves significantly lower temperatures and does not entail the melting of base metals. Instead, a filler metal is melted and forced to flow into the joint through capillary action. 55. An s.
Which has more Effici ency Diesel Engine or Petrol Engine? Diesel engine has the better efficiency out of two.
1. What is the difference between isotropic and anisotropic materials ?
Ans: If a mat erial exhibits same mech anical prop erties regar dless of load ing directi on, it is isotropic, e.g., homogeneous cast materials. Materials lacking this property are anisotropic. 2. What are orthotropic materials ? Ans: It is a sp ecial class of anisotrop ic materials w hich can be d escribed b y giving their prop¬erties in three perpendicular directions e.g. wood; composites. 3. What is view factor ? Ans: View fact or is dep endent upon geometry of the two s urfaces exc hanging r adiation. 4. What properties need to be considered for applications calling for following re¬quirements : (i) rigidity (ii) strength for no plastic deformation under static load (iii) strength to withstand overload without fracture. (iv) wear resistance (v) reliability and safety. Ans: (i) Rigidit y—Elastic modulus and yield streng th (ii) Strength (for no plastic deformation deformation under st atic loading)—yield loading)—yield point (iii) Strength (overload)—Toughness and impact resistance (iv) Wear resistance—Ha resistance—Hardness rdness (v) Reliability and safety—Endurance limit and yield point. 5. Explain the effects of alloying chromium and nickel in stainless steel. Ans: Addition of nickel and c hromium inc reases the t ensile str ength and incr ease in resistance to corrosion takes place. 6. Mention two types of dislocations. Ans: Dislocati on refers t o a break in the conti nuity of th e lattice. In edge disloc ation, one plane of atoms gets squeezed out. In screw dislocation the lattice atoms move fom their regular ideal positions. 7. What are the principal constituents of brass? Ans: Princip al constituents of brass are copp er and zinc. 8. What is Curie point ? Ans: Curie p oint is th e temperature at which f erromagnetic materials can n o longer b e magnetised magnetise d b y outside f orces. 9. Specific strength of materials is very high when they are in fibre size but lower when they are in bar form Wh y ? Ans: Crystal str ucture h as order ed, repeati ng arrang ement of at oms. Fibres are liable to maintain this and thus have high specific strength. As size increases, the condition of ordered and repeating arrangements can't be guaranteed because of several types of defects and dislocations and thus the specific strength gets lower. 10. What is the percentage of c arbon in cast iron ? Ans: 2.5%. 11. Which element is added in steel to increase resistance to corrosion ? Ans: Chromiu m. 12. Whether individual components in composite materials retain their characteristics or n ot? Ans: yes. 13. An elastomer is a polymer when its percentage elongation rate is ? Ans: Greater t han 100 %. 14. If percentage elongation of a material is more than 200%, it is classed as ? Ans: Rubb er. 15. Why is it that the maximum value which the residual stress can reach is the elastic limit of the material ? Ans: A stress in excess of elastic limit, with no exter nal force t o oppose it, will relieve itself by plastic deformation until it reaches the value of the yield stress. 16. Why fatigue strength decreases as size of a p art increases beyond around 10 mm? Ans: Perf ection of materi al conditions is possibl e at lower siz es and as size increas es, it is not possible to attain uniform structure of the material. 17. Distinguish between creep and fatigue. Ans: Creep is low and pr ogressive deformation of a materi al with time und er a cons tant stress at high temperature applications. Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading condition. 18. While normal c arburisin arburising g and nitriding surface treatments increase f atig atigue ue strength, excessive treatment treatment may decrease th e fatigue strength. Why ? .Ans: Normal carburising/nitriding carburising/nitriding treatments increase volume due to phase transformation at Surface and introduce residual compressive surface stress and thus increase the fatigue strength. By excessive treatment the high compressive stresses are introduced but th ese are balanced by high in¬ternal tensile stresses of equ al value and the s ubsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failure. 19. List at least two factors that promote transition from ductile to brittle fracture. Ans: Manner of loading, and the r ate of loadin g promote tr ansition fr om ductile to br ittle frac¬ture. A machine member may have ductile failure under static loading but may fail in brittle fashion when the load is fluctuating. Similarly a material may evidence ductile failure under tensile loading at ordinary testing speed but if load is applied at a high velocity then failure may be brittle.
20. Which theories of failure are used for (a) ductile materials, and (b) brittle materials ? Ans: For duct ile materials, theories of f ailure used are maximum sh ear stress t heory, an d maximum energy of distortion theory; while for brittle materials, theory of maximum principal stress, and maximum strain are used. 21. What does thermal diffusivity of metals signify. Ans: Thermal dif fusivity is ass ociated with t he speed of propag ation of h eat into solids during changes in temperature with time. 22. For conduction of heat, the instantaneous rate of heat flow is product of three factors. What are these ? Ans: (i) Area of the s ection of th e heat flow path, perp endicular t o the directi on of heat flow. (ii) temperature gradient, i.e. change of temperature w.r.t. length of path. (ii) Thermal conductivity of material. 23. How convective heat transfer is effected and on what factors it depends ? Ans: Convect ive heat tr ansfer is eff ected bet ween a s olid and fluid b y a combinat ion of molecularr c onduction within the fluid in combination with energy transport r esulting from the molecula motion of fluid particles. It depends on boundary layer configuration, fluid properties and temperature difference. 24. Which is the common element between brass and bronze ? Ans: Copp er. 25. What does following alloy designation indicate FG FG 250 ? Ans: Grey c ast iron with t ensile streng th of 250 MPa. 26. How is ceramic defined ? Ans: It is a s olid formed b y combination of metallic and non-metallic elements. 27. Give one example of metal classified as per structure as BCC, FCC, HCP and CCP. Ans: BCC (bod y centred c ubic) struct ure—Molybd enum FCC (face c entred cubic) structure—Aluminium HCP (hexagonal closed p acked) structure—Zinc CCP (cubic dosed packed) structure-Copper. 28. What is the name of s olid solution of carbon in alpha iron and delta iron ? Ans: Ferrite an d austenit e respecti vely. 29. Explain the difference between pearlite and c ementile ? Ans: Pearlite is eutectoid mixture of f errite and c ementile. Cemen tite is ch emical compound of iron and carbon. 30. Give one example each of the following proportion of materials dimensional, physical, technological technologi cal and mechanical. Ans: Rough ness, enth alpy, tough ness, and h ardness r espectively. 31. For which parts the W ahl factor and Lewis form factor used ? Ans: For sprin gs and g ears respec tively. 32. How oxygen can be removed from steel during melting? What are fully killed steels ? Ans: Oxygen c an be remov ed by addin g elements s uch as man ganese, s ilicon or alu minium which, because of their high affinity for oxygen, react with it to form non-metallic oxides which rise into the slag. Steels which have had most of their dissolved oxygen removed are called "fully killed steels". 33. Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ? Ans: Execessi ve hydrog en results in th e formation of small fissur es often des cribed as hairline cracks or flakes in the steel. Large forgings in alloy steel are particularly sensitive to this phenom¬enon. 34. What is allotrope ? In what forms of cubic pattern, iron exists ? Ans: Some elem ents exist in more than on e crystallin e form. Each f orm is known as "allotrope". Iron exists in two forms of cubic pattern, namely body centered cubic (bcc) and face-centered cubic (fee). 35. What is the difference between alpha iron, delta iron and g amma iron ? Ans: The bcc f orm of iron exists between room temperatur e and 910° C, and bet ween 1400°C and the melting point at 1539°C. The lower temperature form is known as "alpha"-iron and the higher temperature form as "delta"-iron. The face-centered cubic form existing between 910°C and 1400°C is referred to as "gamma-i "gamma-iron". ron". 36. Metals, in general are of low strength and do not possess required physio-chemical and technological technologi cal properties for a definite purpose. Alloys are therefore more than metals alone. Discuss the arrangement of atoms and structures of alloys. Ans: Alloys ar e produc ed by melting or sintering t wo ore mor e metals, or m etals and a nonmetal, together. Alloys possess typical properties inherent in the metallic state. The chemical elements that make up an alloy are called its components. An alloy can consist of two or more components. The phase and structures of alloys describe the c onstitut onstitution, ion, transformations and properties of metals and alloys. A combination of phases in a state of equilibrium is called a system. A phase is a homogeneous portion of a system having the same composition and the same state of aggregation throughout its volume, and separated from the other portions of the system by interfaces. For instance, a homogeneous pure metal or alloy is a singlephase system. A state in which a liquid alloy (or metal) coexists with its crystals is a two-phase system. Structure refers to the shape, size or the mutual arrangement of the corresponding
phases in metals or alloys. The structural components of an alloy are its individual portions, each having a single structure with its characteristic features. features. 37. What is th e difference between isotropic material and homogeneous material ? Ans: In h omogeneous mat erial the c omposition is s ame through out and in is otropic material the elastic constants are same in all directions. 38. Explain the difference between the points of inflexion and contraflexure. Ans: At points of inflexion in a loaded beam the bend ing moment is zero and at points of contraflexure contraflex ure in loaded beam the bending moment changes sign from increasing to decreasing. 39. What is th e difference between proof resilience and modulus of resilience ? Ans: Proof r esilience is th e maximum str ain energ y that can b e stored i n a material without permanent deformation. Modulus of resilience is the maximum strain energy stored in a material per unit volume. 40. What is the difference between column and strut ? Ans: Both c olumn and str ut carry c ompressive load. Column is al ways vertic al but strut as member of structure could carry axial compressive load in any direction. 41. Explain the difference between ferrite, austenite and graphite ? Ans: Ferrite is t he solid solu tion of carb on and ot her constit uents in al pha-iron. It is soft, ductile and relatively weak. Austenite is th e solid solut ion of carb on and other c onstituents in gamma- iron. It exists in ordinary steels at elevated temperatures, but it is also found at ordinary temperatures in some stainless steels. Graphite has a hexagonal layer lattice. ' 42. Explain the terms solid solution, eutectic, eutectoid and peritectic. Ans: Solid S olution. W hen a homogen eous mixtur e of two (or m ore) atomic f orms exists in solid state, it is known as solid solution. Eutectic. A mixture of two (or more) phases which solidify simultaneously from the liquid al¬loy is called an eutectic. Alloys in which the components solidify simultaneously at a constant temperature temperatu re the lowest for the given s ystem, are called eutectic alloys. Eutectoid. Eutectoid alloys are the alloys for which two solid phases which are completely soluble become completely insoluble insoluble on c ooling before a c ertain temperature called eutectoid temperature. Peritectic. A peritectic transformation involves a reaction between a solid and liquid that form a different and new solid phase. This three phase transformation occurs at a point called peritectic point. 43. What do you und erstand by critical points points in iron, iron-carbide diagram ? Ans: The temp eratures at which the ph ase ch anges occur are called critical points ( or tem¬peratures). 45. Why PERT is preferred over CPM for evaluation of project ? Ans: PERT is b ased on th e approach of multiple time estimates f or each acti vity. 46. What is the percentage of chromium in 18 : 4 : 1 IISS ? Ans: 4%. 47. What is stellite ? Ans: It is a n on-ferr ous cast alloy c ontaining c obalt, chromiu m and tungs ten. 48. Which rays are produced by c obalt-60 in industrial radiography radiography ? Ans: Gamma r ays. 49. What are killed steels and what for these are used ? Ans: Killed st eels are d eoxidised in the ladle with silicon an d aluminium. O n solidific ation no gas evolution occurs in these steels because they are free from oxygen. 50. What is critical temperature in metals ? Ans: It is th e temperatur e at which th e phase ch ange occurs in metals. 51. Car tyres are usually made of ? Ans: Styrene- butadine r ubber. 52. What is the structure of pure iron and whether it is soft or hard ? Ans: Ferrite an d it is soft. 53. Which elements increase the c orrosion resistance resistance of steel ? Ans: Chromiu m and nickel. 54. What causes hardness in steel ? H ow heat treatment alters properties properties of steel ? Ans: The sh ape and d istribution of t he carbides in the iron determine s the hard ness of th e steel. Carbides Carbides can b e dissolved in austenite is the basis of the heat t reatment of steel. If steel is heated above the A critical temperature to dissolve all the carbides, and then cooled, suitable cooling through the cooling range will produce the desired size and distribution of carbides in the ferrite, imparting different properties. 55. Explain the formation of microstructures of pearlite, bainite and martensite in steel. Ans: If aust enite contai ning about 0.80 percent carbon is sl owly coole d through t he critic al temperature, ferrite and cementite are rejected simultaneously, simultaneously, forming alternate plates or lamellae. This microstructure is called pearlite. At temperatures just belot the A1, the transformation from austenite.to pearlite may take an appreciable time to initiate and complete, but the product will be lameller pearlite. As the transformation temperature is lowered, the time to initiate transformation transformation shortens but the product is pearlite of increasing
fineness, and at temperatures approaching 550°C it cannot be resolved into its lamellar constituents. Further deerease in transformation temperature causes a lengthening of the ncubation period and a change in structure of the product to a form known as "bainite". If the temperature is lowered sufficiently, the diffusion controlled nucleation and growth modes of transformation are suppressed completely and the austenite transforms by a diffusionless process in which the cr ystal lattice effectively effectively shears to a new crystallographic configuration known as "martensite". This phase has a tetragonal crystal structure and contains carbon in supersaturated supersatu rated solid solution. 56. How with alloying of steel it is possible to a achieve properties which can not be achieved with heat treatment ? Ans: A prer equisite to t he harden ing of steels is that mart ensite sh ould be for med on cooli ng, but this can only be achieved if the rate of cooling is great enough to suppress the formation of pearlite or bainite and in plain carbon steels this can be achieved by quenching relatively relatively small specimens 57. What are the major effects of alloying elements? Ans: (1) T o alter the tr ansformati on temperatur es and times (2) To modify the room temperature and elevated temperature strengths of given structures by (a) stiffening the cr ystal ystals s and (b) introducing complex precipitates which tend to harden the steel. (3) To modify the type of oxide film formed on the surface of the steel and thereby affect its corrosion resistance. 58. What is th e difference between austenite stabilisers stabilisers and ferrite stabilisers ? Ans: Austenit e stabilisers have the effect of ext ending the t emperatur e range over which austenite is formed. Such elements are carbon, manganese, nickel, copper and cobalt. Ferrite stabilisers have the effect of extending the temperature range over which alpha and delta ferrite are formed, which consequently reduces temperature range over which austenite is formed. Such elements are silicon, chromium, molybdenum, tungsten, titanium and niobium. 59. What are the effects of carbon on the properties of steel. Ans: In gen eral, an incr ease in carb on content produces h igher ultim ate strength and hardness but lowers ductility and toughness of steel alloys. Carbon also increases airhardening tendencies and weld hardness, especially in the presence of chromium. In low-alloy steel for high-temperature applications, applications, the carbon c ontent is usually restricted to a maximum of about 0.15% in order to assure optimum ductility for welding, expanding, and bending operations. To minimize intergranular corro¬sion caused by c arbide precipitation, precipitation, the carbon content of austenitic (18-8 type) alloys is limited in commercial specifications to a maximum of 0.08%, or even less, i.e. 0.03% in the extremely low-carbon grades used in certain corrosionresistant applications. In plain carbon steels in the normalised condition, the resistance to creep at temperatures below 440°C appears to increase with carbon content up to 0.4% carbon, at higher temperatures temperature s there is but little variation of creep properties with carbon content. An increase in carbon c ontent less ens the therm al and elec trical con ductivities of s teel and increases increa ses its hardness on quenching. 60. What is the role of silicon as alloying element in steels ? Ans: Silicon c ontributes gr eatly to th e production of sound st eel becaus e of its deoxidi zing and degasifying properties. When added in amounts up to 2.5%, the ultimate strength of the steel is increased without loss in ductility. Silicon in excess of 2.5% causes brittleness, and amounts higher than 5% make the steel non-malleable. Resistance to oxidation and surface stability of steel are increased by the addition of silicon. These desirable effects partially compensate for the tendency of silicon to lower the creep properties of steel. Silicon increases the electrical resistivity of steel and decreases hysteresis losses. 61. Discuss the role of manganese in alloying steels. Ans: Mangan ese is an excellent deo xidizer an d sulfur neu tralizer, an d improves the mechanical properties properties of st eel, notably the ratio of yield strength to t ensile strength at normal temperatures. As an alloying element, manganese serves as an inexpensive means of preventing "hot shortness". It improves r olling properties, hardenability, hardenability, and resistance to wear. However manganese increases t he crack sensitivity of weldments, particularly particularly with steels of higher carbon content. 62. Define buckling f actor actor.. Ans: It is th e ratio of t he equival ent length of column t o the minimum r adius of g yration. 63. What do you und erstand by catenary cable ? Ans: A cabl e attached t o the supports and carryin g its own weig ht. 64. What is coaxing ? Ans: It is th e process of improving f atigue prop erties by f irst under-s tressing and then increasing the stress in small increments. 65. What is difference between conjugate beam and continuous beam ? Ans: A conju gate beam is an imaginary beam of s ame size as original beam and carr ying a distributed load in accordance with the bending moment diagram. A continuous beam is on e which is r esting on mor e than two s upports .
66. What is isotropic material ? Ans: It is a material havin g same elast ic constants in all directi ons. 67. Explain difference between modulus of resilience and modulus of rigidity ? Ans: Modulus of resilienc e is the maximu m strain en ergy stored i n a mater ial per unit volume and modulus of rigidity is the ratio of shearing stress to the shearing strain within the elastic limit. 68. What is the difference between basic hole and basic shaft ? Ans: A basic h ole is one w hose lower d eviation is z ero and in c ase of basic s haft the up per deviation is zero. 69. What for pyranometer is used ? Ans: It is us ed to measur e the total h emispherical s olar radiat ion. 70. Describe transfer machines in brief. Ans: It is an automatic mac hine in wh ich workpiec e alongwith fi xture is tr ansferred fr om one station to other automatically and several operation on workpiece are performed at each station. 71. What is burnt-out point ? Ans: It corr esponds t o maximum heat f lux at whic h transition occurs fr om nucleate boi ling to film boiling. 72. What do you und erstand by eutectic ? Ans: It is mec hanical mixtur e of two or mor e phases whic h solidify simult aneously f rom the liquid alloy. 72. Explain the difference between grey iron and white iron. What is mottled iron ? Ans: The c arbon in cast iron could exist at room t emperature as either ir on carbide, or as graphite which is the more stable form. Irons containing carbon as graphite are soft, easily machinable and are called "grey irons". Irons with carbon present as iron carbide are extremely hard, difficult to machine and are called "white" irons. Irons with fairly equal proportions proportion s of graphite and iron carbide h ave intermediate intermediate hardness and are called "mottled" irons. 73. The graphite in grey irons exists in the form of flakes which act as stress-raisers under tensile loading and consequently grey irons have r elative elatively ly low t ensile strength and ductility. Still grey iron is extensively used in engineering. Why ? Ans: Grey ir on is extensi vely used in engineer ing becaus e of following ch aracteristics. (a) Cheapness. (b) Low melting point and high fluidity making it suitable for castings of intricate shape. (c) Relatively good erosion and corrosion resistance. (d) High damping capacity, with respect to vibration. (e) Relatively good mechanical properties under compressive loading. 74. Under what condition a convergent divergent nozzle required ? Ans: When pr essure ratio is greater th an critical pr essure rat io. 75. What is endurance limit and what is its value for st eel ? Ans: Endur ance limit is th e maximum level of fluctuating stress whic h can be t olerated indefinitely. In most steels this stress is approximately 50% of the ultimate tensile strength and it is defined as the stress which can be endured for ten million reversals of stress. 76. How the net work to drive a compressor and its volumetric efficiency behave with increase in clearance volume ? Ans: Work r emains unalt ered and volumetric eff iciency decr eases. 77. What do you und erstand by sulphur print ? Ans: Sulphid es, when att ached with di lute acid, evolve hydrog en sulphide gas which s tains bromide paper and therefore can be readily detected in ordinary steels and cast irons. W hile sulphur is not always as harmful as is sometimes supposed, a sulphur print is a ready guide to the distribution of segregated impurities in general. 78. What is the different between brass and bronze ? Ans: Brass is an alloy of c opper with z inc; and br onze is alloy of copper with tin. 79. What is the effect of addition of zinc in c opper? What is the use of 70/30 brass ? Ans: By additi on of zinc in c opper, both tensile str ength and elongation i ncreases. T he 70/30 brass has excellent deep drawing property and is used for making radiator fins. 80, What for admirality brass used ? Ans: Admiralit y brass with 2 9% zinc and 1% tin has good corr osion resist ance and is us ed for condenser and feed heater tubes. Aluminium is also added to brass to improve corrosion resistance. 81. What is the maximum use of magnesium ? Ans: Magnesiu m is used t o alloy with aluminium and as an add itive for making SG (Spher oidal Graphite) iron. 82. What for zinc f inds applications applications ? Ans: Galvani zing consum es the larg est proportion of zinc. Zinc is r esistant t o corrosion b ut is attacked by acids and alkalies. Zinc alloy.s are suited for making die casting since the melting point is reasonably low. 83. Which factors influence the type of fracture in failure of a material ? Ans: Seven f actors influenci ng type of f ailure are : (i) Type of material (inherent structure properties),
(ii) Manner of loading (Static versus dynamic), (iii) Range of imposed stress, (iv) Strain rate (static, dynamic, impact), (v) Stress d istributio istribution n (discontinuity in material/ material/shape), shape), (vi) temperature, and (vii) surface treatment. 84. What is the name given to ratio of actual cycle efficiency and ideal cycle efficiency. Ans: Effici ency ratio. 85. List two effects of manganese in plain carbon steels. , Ans: Mangan ese increas es tensile str ength and h ardness. It d ecreases wel dability. 86. Name the strongest and weakest type of atomic bonds. Ans: Metallic b ond is stron gest and m olecular bon d also kn own as Van der Waals b ond is weakest. 87. In which process internal energy remains constant ? Ans: Isother mal process. 88. What is temper embrittlement in alloy steels and what are its effects ? Ans: Embrittlem ent attack is usually int ergranular i n metals, i.e. c racks pr ogress between the grains of the polycrystalline material. It imparts a tendency to fail under a static load after a given period of time in those alloy steels which are susceptible to embrittlement. 89. What are whiskers ? Ans: Whiskers are very smal l crystals whic h are virt ually free f rom imperf ections and dislocations. 90. What is Bauschinger effect ? Ans: Accordi ng to Bausc hinger, th e limit of prop ortionality of material does not rem ain constant but varies according to the direction of stress under cyclic stresses. 91. What is the difference between heat capacity and specific heat of a material ? Ans: The heat capacity of a material is the amount of heat tr ansformed t o raise unit mass of a material 1 degree in temperature. The specific heat of a material is the ratio of the amount of heat transferred to raise unit mass of a material 1 degree in temperature to that required to raise unit mass of water 1 degree of temperature temperatu re at some specified t emperature. For most engineering purposes, heat capacities may be assumed numerically equal to;specific heats. 92. Explain the rule to find specific heat of aqueous solutions. Ans: For aqu eous solutions of salts, th e specific h eat can b e estimated b y assuming t he specific heat of the solution equal to that of the water alone. Thus, for a 15% by weight solution of sodium chloride in water, the specific heat would be approximately 0.85. 93. What do you und erstand by latent heat ? Give four examples of latent heats. Ans: For pur e substanc es, the heat effects acc ompanying ch anges in s tate at cons tant pressure (no temperature change being evident) are known as latent heats. Examples Examples of latent heats are : heat of fusion, vaporisation, sublimation, and change in crystal form. 94. Define the terms free energy and free enthalpy. What is their significance significance and importance ? Ans: Free ener gy (or H elmholtz functi on) is defin ed as/= u -Ts . It is equal to the work during a constant-volume isothermal reversible nonflow process. Free enthalpy (or Gibbs function) is defined as g = h - Ts (where u = internal energy, h = enthalpy, T = temperature, s = entropy) Gibbs function is of particular importance in processes where chemical changes occur. For reversible isothermal steady-flow processes or for reversible c onstant-pre onstant-pressure ssure isothermal nonflow processes, change in free energy is equal to net work. 95.Which parameter remains constant in isochoric process ? Ans: Volume. 96. What is polytropi polytropic c process ? Under what conditions it approaches isobaric, isobaric, isothermal, and isometric process ? In which reversible process no work is done ? Ans: A polytr opic process is one that f ollows the eq uation pun = constant (ind ex n may ha ve values from - oc to + oo. This process approaches isobaric when n = 0, isothermal when n = 1, and isometric when n = . No work is done in isometric process. 97. Whether superheated steam can be treated like ideal gas ? Ans: Yes. 98. Out of constant pressure and constant volume lines on TS diagram which line has higher slope ? And whether slope is constant or variable ? Ans: Constant volume line. Slop e is variabl e. 99. Whether entropy is intensive property or extensive property ? Ans: Entrop y is extensive propert y. 100. In which process fluid expands but does no work ? Ans: Throttlin g process. 1. How How s hea hearr forces are incurred in fluid flo w ? Ans: Shear f orces betwe en fluid part icles and boundary w alls and b etween th e fluid partic les themselves, result from the viscosity of the real fluid.
2. In In laminar flow, how di scharge is related related to v iscosity ? Ans: Discharg e varies in versely as viscosity. 3. What What is best hydraulic section ? Ans: Best hyd raulic s ection is one i n which for a given cross- section area, the ch annel section has least wetted perimeter. 4. What is best hydraulic trapezoidal section ? Ans: It is a h alf-hexagon in shape. 5. What is specific energy in a channel section ? Ans: It is d efined as th e energy h ead measur ed with res pect to th e channel b ottom at th e section. At any section, it is equal to sum of the velocity head and the water depth at the section. 6. What What is cr itical depth and critical flow ? Ans: Critical depth is th e depth, at which the d ischarge may be delive red through the secti on at minimum energy. Critical flow is the flow in open channel corresponding to critical depth. 7. What What causes bound ary layer separation ? Ans: An advers e pressure gr adient. 8. What What is th e improtanc e of Nose radius ? Ans: Nose r adius is favou rable t o long tool lif e and good surfac e finish. A sh arp point on the end of a tool is highly stressed, short lived and leaves a groove in the path of cut. 9. At what point below fr ee surface surface in a uniform l amina aminarr flo w in a channel the point velocity is equal to mean velocity velocity of flow ? Ans: At 0.577 depth of ch annel. 10.. What 10 What is the value of friction factor for smooth pil e when Reynolds Reynolds number is approxim ately = 10G 10G ? Ans: 0.01. 11.. How hydrauli c grade line and free surf ace of open channel flow r elated ? 11 Ans: They coinc ide. 12.What 12 .What are the firs t and last elements of to ol sign atures ? Ans: Back rak e angle an d nose r adius. 14.. What is open channel flow ? Explain 4 types of op en channel flows . 14 Ans: Open c hannel fl ow has a fr ee water surf ace which is nor mally subject t o the atmosp heric pressure. Steady open channel flow : In this case the d ischarge and water depth at any s ection in the reach do not change with time during the p eriod of interest. Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time. Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady. Varied open channel {low : In this case th e water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unstgeady (as in the case of flood waves or tidal surge). 15.. When does wake occur ? 15 Ans: It occurs after a s eparation p oint. 16. In straight polarity, to which terminal the electrode is connected ? Ans: Negative. 17. What is hydraulic radius ? Ans: It is th e ratio of flui d flow area/s hear peri meter. 18. Define flow work. Ans: Flow work is the amou nt of mechan ical energ y required t o push or f orce a flowing f luid across a section boundary. 19. What do you understand by dimensional analysis ? Ans: Dimension al analysis is the mathemat ics of dimensi ons and qu antities and provides procedural techniques whereby the variables that are assumed to be significant in a problem can be formed into dimensionless parameters, parameters, the number of parameters being less than the number of variables. 20. What is hydraulic depth for open channel flow ? Ans: It is th e ratio of area and th e top widt h of the ch annel secti on. 21. Which welding set will you select for welding both ferrous and non f errous materials. Ans: D.C. gen erator s et. 22. Which welding process is a combination of arc welding and gas welding processes? Ans: Atomic h ydrogen wel ding. 23. What is hydraulic jump ? Ans: It is a n atural phen omenon in open chann el. It is an abrupt red uction in f low velocity b y means of a sudden increase of water depth in the down stream direction. Through a hydraulic jump, and h igh-velocity su percritical fl ow is chang ed to a low- velocity s ubcritical flow. 24. What is gradually varied flow ? Ans: The ch anges in wat er depth in the open chann el take place very grad ually with
distance. Depending on the channel slope, the surface conditions, the sectional geometry, distance. and the discharge, these may be classified into five categories : steep channel, critical channel, mild channel, horizontal channel, and adverse channel. 25. Explain 5 types of channels. Ans: Steep c hannel : I n this case n ormal depth < critical dep th. Critical channel : In this c ase normal depth = critical depth. Mild channel : In this case, normal depth > critical depth. Adverse ch annel : In this case, th e slope of c hannel bed < 0 Horizontal channel : In this case, the slope of channel bed = 0. 26. Mention two major differences differences between shaper and planer ? Ans: Shaper Planer (a) The cutting tool reciprocates (a) W ork reciprocates reciprocates (b) The work is stationary (b) Tool is stationary (c) Meant for small work pieces (c) Meant for large work pieces (d) Only lighter cut can be taken (d) Heavy cuts can be taken (e) Tools are smaller in size (e) Tools are bigger in size 27. Differentiate between drilling and reaming ? Ans: Drilling Reaming (a) It is the operation of initiating hole (a) Reaming is the operation of finishing and sizing a drilled/bored hole (b) It can be done at relatively high speeds (b) It should be done only at slow speeds (c) Larger chips are produced (c) Less chips are produced (d) Drill has only two flutes (d) Reamer has more than 4 flutes (e) Drill has chisel edge (e) Reamer has a bevel edge 28. What is similarity between normal shock wave and hydraulic jump ? Ans: Both ar e analogous and irrevers ible. 29. For what purpose chills are used in moulds ? Ans: Chills ar e used to achieve direct ional solidif ication. 30. What is tumbler gear mechanism ? Ans: Tumbler g ear mechanis m is a mechanis m consisting of number of different sized gears keyed to the driving shaft in the form of cone and is used to give the desired direction of motion of the lathe spindle. 31. What is relative roughness of pipe ? Ans: It is th e ratio of t he size of th e surface imp erfections t o the inside d iameter of t he pipe. 32. What is conicity ? Ans: The rati o of the diff erence in di ameter of th e taper to its length is termed conici ty. 33. Under what condition the effect of compressibility of fluid can be neglected ? Ans: When M ach number is less than 0.4. 34. For which type of flow the velocity distribution in a pipe is parabolic. Ans: For unif orm laminar fl ow. 35. What is the relationship between center line velocity and average velocity for a laminar flow in a pipe ? Ans: Average velocity = 1/ 2 centre lin e velocity. 36. On which factor the friction factor for a smooth pipe in t urbulent flow depends ? Ans: Reynolds number. 37. What do you und erstand by pipe branchings ? Ans: When w ater is brou ght by pip es to a junct ion where more than t wo pipes m eet, them th e total amount of water brought by pipes to a junction must always be equal to that carried away from the junction by other pipes, and all pipes that meet at the junction must share the same pressure at the junction. 38. What is pipe networks and what are the condition for network ? Ans: Pipe net work compris es a number of pipes conn ected toget her to f orm loops and branches. For a network, (i) at any junction, Y.Q = 0 and (ii) between any two junctions the total head loss is independent of the path taken. 39. What is Hardy-Cross Method ? Ans: It is a c ommonly used c omputer progr am for a pipe networ k. 40. Explain water hammer. Ans: The forc e resulting fr om changing th e speed of the water mass (say in a pipe due t o sudden change of flow rate) may cause a pressure rise in the pipe with a magnitude several times greater than the normal static pressure in the pipe. Pressure head caused by water hammer = C (V velocity in pipe, C = celerity). 41. What happens to impuritie impurities s in centrifugal casting ? Ans: They g et collected at the center of the casting . 42. Define the terms hydraulic similitude and dimensional analysis. Ans: Hydrau lic similitude is th e principl e on which th e model studi es are b ased. Dimensional analysis is the analysis of the basic relationship of the various physical quantities involved in the static and dynamic behaviors of water flow in a hydraulic structure.
43. Explain the difference between geometric similarity, kinematic similarity and dynamic similarity. Ans: Geometr ic similarity : It i mplies similarit y of form. Th e model is a geometric r eduction of the prototype and is accomplished by maintaining a fixed ratio for all homologous lengths between the model and the prototype. Kinematic similarity : It implies similarity in motion. Kinematic similarity between a model and the prototype is attained if th e homologous moving particles have the same veloci velocity ty ratio along geometrically similar paths. It involves the scale of time as well as length. Dynamic similarity : It implies similarity in forces involved in motion. 44. Define Reynolds law ? Ans: When th e inertial f orce and th e viscous f orce are c onsidered t o be the only forces governing the motion of the water, the Reynolds number of the model and the prototype must be kept at the same value. 45. When a built up edge is formed while machining ? Ans: While mac hining ducti le materials at high speed . 46. On what factor the friction factor for a r ough pipe in turbulent flow depends ? Ans: Relative roughness . 47. What is unit power of a turbine ? Ans: PHP12. 48. How cavitation causes damage ? Ans: In a a c losed system ( pipelines, or pumps), water vaporis es rapidly i n regions where the pressure drops below the vapour pressure. This phenomenon is called cavitation. The vapour bubbles formed in cavitation usually collapse in a violent manner, which may cause considerable damage to the system. 49. In milling process, how the arbor torque can be smoothend ? Ans: Arbor t orque can b e smoothened by increasin g number of teeth, us ing higher s piral angle of teeth, using higher c utting depth. 49. What are webs in a twist drill ? Ans: Webs ar e the metal c olumn in th e drill which s eparates t he flutes. 50. What is bluff body ? Ans: It is a b ody with such shape that the flow is s eparated muc h ahead of its rear end resulting in a large wake, the pressure drag being much greater than the friction drag. 51. What is bulk modulus ? Ans: It is th e ratio of h ydrostatic str ess to volum etric strain within the el astic limits. 52. Define boundary layer. Ans: It is th e fluid layer in the neig hborhood of a solid boundary where th e effects of f luid friction are predominant. 53. What is creep flow ? Ans: It is fl ow at very low R eynolds nu mber wher e viscous f orces are lar ger than th e inertia forces. 54. What is T orricel orricellis lis theorem ? Ans: Accordi ng to it vel ocity of jet fl owing out of a small op ening is pr oportional t o the squar e root of head of liquid above it. 55. How does cavitation manifest itself in a centrifugal pump ? Ans: Usual s ymptoms of c avitation of pu mp are noise, vibration, a drop in h ead and c apacity with a decrease in efficiency, accompanied by pitting and corrosion of the impeller vanes. 56. What happens if centrifugal pump is operated at excessive speeds ? Ans: When a pump is oper ated at exc essive speeds, the diff erential pr essure devel oped increases and causes a powerful pulsating vacuum on the underside of the blade tips and each particle of water is pulled away from the blade, taking away with it a small particle of metal, producing pitting/grooved effect. Repeated erosive action results in complete honey combing and total destruction of blade, with resultant loss in pump performance. 57. On what parameters the head developed by a centrifugal pump depends ? Ans: It depen ds upon th e impeller di ameter and its r otative sp eed. 58. Which factors determine the s electio election n of electroly electrolyte te for electrochem electrochemical ical machining process ? Ans: Electrol yte should b e chemically st able and h ave high el ectrical cond uctivity. 59. What is the disadvantages of centrifugal pump having very low specific speed ? Ans: For a.c entrifugal pump having very low sp ecific speed, the impell er diameter is l arge and narrow having excessively high disc friction and excessive hydraulic losses. 60. On what factors the efficiency of pump depends ? Ans: Effici ency of a pu mp (centrifug al) depen ds on the s ize, speed, and proporti ons of th e impeller and casing. 61. On what factors the cavitation in centrifugal pumps is dependent ? Ans: Cavitati on in centrif ugal pumps d epends on the velocit y of water entering tne i mpeller and on the relatiave velocity of the impeller blades where the water is picked up. 62. What are the losses in a centrifugal pump ? Ans: The loss es in a centr ifugal pum p are : Fricti on losses du e to edd ies in flow, leak age, friction loss due to rotation of impeller in chamber of water, gland and bearing power losses. 63. What should be done to avoid cavitation in pumps ?
Ans: In ord er to avoid c avitation, th e suction lif t and the operating sp eed must b e carefull y chosen. 64. What will happen if speed of reciprocating pump is increased ? Ans: If speed of a recipr ocating pu mp is increased beyond a l imit, then atm ospheric pr essure would be insufficient to force water into the pump at the same speed as the piston. This would a break in the continuity of the water in suction pipe (cavitation) and give rise to vibration, noise, and chemical attack by any dissolved gases which may be released from the water owing to the high vacuum and the breaking of the water column. 65. What is the order of efficiency efficiency of c enetrifu enetrifugal gal and reciprocating pumps ? Ans: The eff iciency of c entrifugal pu mp is of the order of 45% whereas th at of reciproc ting pump is around %. 66. What are the basic operations performed performed in a slotter ? Ans: The dif ferent oper ations don e in slotter are : 1. Machining grooves 2. Machining cylindrical surface 3. Machining irregular profiles. 67. How the positive displacement is obtained in rotary pumps ? Ans: Positive d isplacement in rotary pumps is achi eved in two ways : (i) A rotor carries radially adjustable vanes, the outer tips of which are constrained by a circularr casing, whose centre is remote from that of the rotor. circula (ii) Various combinations of gears, lobes, helices, etc. within a casing arranged so that the lobes or teeth attached to each rotor pass in sequence through the same pumping space. 68. How a slotter differs from shaper ? Ans: Slotter Sh aper (a) Ram r eciprocate eciprocates s vertical vertically ly (a) Ram reciprocates horizontally (b) It has a circular table (b) It has a rectangular table (c) Suited for machining internal surfaces (c) Suited for machining external surfaces (d) Table can take less load (d) T able can take much load 69. Under what condition the flow and power of pump vary as square of the size ? Ans: The fl ow and power vary as size2 when the g eometric siz e changes as invers e of change of speed. 70. How the incidence of cavitation detected ? Ans: The incid ence of c avitation is d etected by t he following in order of appear ance. (i) stroboscopic observation observation of bubble appearance and size (ii) sensitive acoustic tests of cavitation noise (iii) reduction of efficiency and/or head of 3%. 71. How cavitation erosion is assessed ? Ans: Cavitati on erosion is assessed b y depth of attack or weight of met al removed. 72. At which temperature the cavitation erosion is negligible and why ? Ans: Cavitati on erosion is negligible at above 3 00°C bec ause the wat er and st eam have same densities at critical temperature of 374°C and thus there is no volume change or bubble collapse in the vicinity of this range. 73. What is an arbor ? Ans: An arb or is an accur ately machin ed shaft f or holding an d driving th e arbor typ e cutter. I t is tapered at one end to fit the spindle nose and has two slots to fit the nose keys for locating and driving it. 74. For a body to float in stable equilibrium where the e.g. should be located w.r.t. metacentre ? Ans: e.g. sh ould be b elow metacentr e. 75. What is the condition for a flow t o be fully developed through a pipe ? Ans: Ratio of maximum velocity t o averag e velocity shou ld be 2. 76. When a fluid is moving with uniform velocity, whether the pressure of fluid will depend on its depth and orientation ? Ans: No. 77. How much is the vertical component of force on a curved surface submerged in a static liquid ? Ans: It is eq ual to weight of the liquid above the c urved surf ace. 78. On which factors depends the friction factor in a rough turbulent flow in a pipe? Ans: It depen ds on pip e diameter an d the c ondition of th e pipe. 79. What does th e realisation of velocity potential in fluid flow indicate ? Ans: It indic ates that flow is irrotation al. 80. What is the difference between potential flow and creep flow ? Ans: Potenti al flow assu mes viscous f orces to be zero but s ame is consider ed larger th an inertia forces in creep flow. 81. For which application Mach number and Froude numbers are s ignificant ? Ans: Mach no. is significant i n the stud y of projectil es and jet pr opulsion. Fr oude numb er is significant in the study of ship hulls. 82. What is the difference between geometric, kinematic, and dynamic similarities between model and prototype ? Ans: Geometr ic similarity is mainly for s ame shape f or model and prototyp e, kinematic
similarity is concerned with stream line pattern, whereas dynamic similarity concerns the ratio similarity of forces. 83. A body is floating in water. If it is displaced slightly then about which point it will oscillate. Ans: It will osc illate about centre of buoyanc y. 84. Why uniform ramming is c onsidered desirable in green sand moulding process ? Ans: Unif orm ramming results in greater dimensional st ability of a casting. 85. On what account the friction drag is experienced ? Ans: Friction dr ag is exper ienced on s eparation of b oundary layer. 86. What is th e characteristic characteristic of centrifugally cast components ? Ans: These h ave fine gr ain structur e with high d ensity. 87, Under what condition the separation of flow occurs ? Ans: When pr essure gr adient chan ges abrup tly. 88. What is the criterion for shaping of streamlined body ? Ans: It is shap ed to suppr ess the fl ow separati on about th e body and to shift the boundary layer separation to near most part of body to r educe the wake size. 89. What do you und erstand by entrance length and what is its value for turbulent flow in smooth pipe ? Ans: Entranc e length of f low is the in itial length in which the fl ow develops f ully such th at the velocity profile remains unchanged downstream. For turbulent flow in smooth pipe, entrance length is taken as 50 x diameter of pipe. 90. Explain the difference between friction drag and pressure drag. Ans: Friction dr ag is the dr ag force exerted b y a fluid on th e surface d ue to friction action when the flow occurs past a flat surface at zero incidence. Pressure Pressure drag is the additional drag force on account of the differences of pressure over the body surface when fl ow occurs past a surface which is not everywhere parallel to the fluid s tream. Pressure drag depends u pon separation of bondary layer and the size of wake. Friction drag is due to shear stresses generated due to viscou viscous s action. 91. What do you und erstand by choking in pipe line ? Ans: When sp ecified mass f low is not ab le to take place in a p ipe line. 92. What is the difference between streamline body and bluff body ? Ans: In streaml ine body th e shape is such that s eparation in f low occurs past the n earmost part of the body so that wake formed is small and thus friction drag is much greater than pressure drag. In bluff body the flow gets separated much ahead of its rear resulting in large wake and thus pressure drag is much greater than the friction drag. 93. What is the difference between dressing and trueing of a grinding wheel ? Ans: Dressing is the proc ess used t o clear the c utting surf ace of the gri nding whe el of any dull grits and embedded swarf in order to improve the cutting action. Trueing is the process employed to bring the wheel to the required geometric shop and also to restore the cutting action of a worn wheel. 94. Whether hard grade or softer grade is required for internal grinding than external grinding? Ans: Softer graders of wheel are r equired f or internal gr inding than f or external grinding. 95. How is the velocity profile and stress distribution due to laminar flow of an incompressible flow under steady conditions in a circular pipe. Ans: Velocity p rofile is p arabolic with zero veloc ity at boun dary and maximum at th e centre. Shear stress distribution is linear, being maximum at boundary and zero at centre. 96. Where the maximum velocity occurs in open channels ? Ans: Near th e chann el bottom. 97. Define hydraulically efficient channel cross section. Ans: The sh ape of such s ection is that which pr oduces minimum wetted peri meter for a given area of flow and carries maximum flow. 9. What is follower rest ? Ans .For slen der work a t ravelling or follower r est is used. T his fits on th e lathe - s addle and travels to and fro with it. By this means support is constantly provided at the position of cut. Thus the work piece being turn is rigidly held against the tool. 99. What is the meaning of the term sensitive drill press press ? Ans: A sensiti ve drilling pr ess is a light, s imple, bench type machin e for light duty working with infinite speed ratio. 100. Why carburised machine components have high endurance limit ? Ans: In carbur ised machin e compon ents, the proc ess of carbur isation int roduces a compressive layer on the surface and thus endurance limit is increased.
1. What is anisotropy ? Ans: The ph enomenon of different properties in different directions is called anis otropy. 2. What is vapour pressure and when it becomes important ?
Ans: Vapour pressur e is the parti al pressur e created by the vapou r molecules when evaporation takes place within an enclosed space. It becomes important when negative pressures pressure s are involved. 3. Explain absolute viscosity ? Ans: It is th e ratio of sh ear stress and the gr adient of veloc ity with dist ance bet ween a fi xed plate and moving plate (Its unit is Pa . s). 4. Define surface tension ? Ans: Surf ace tension of a liquid is t he work th at must be d one to brin g enough molecules from inside the liquid to the surface to form one new unit area of that surface. (Its unit is Nm/m2 or N/m). 5. What is capillarity and when liquid rises or falls ? Ans: Capillari ty : The ris e or fall of a liquid in a capillary tub e caused by surf ace tension. The magnitude of rise or fall depends on the relative magnitudes of the cohesion of the liquid and adhesion of the liquid to the walls of the containing vessels. Capillarity is of importance in tubes smaller than 10 mm diameter. Rise of liquid : Liquids rise (in capillary tube) when they wet and adhesion of the liquid to the walls is greater than the cohesion of the liquid. Fall of liquid : Liquids fall (in capillary tube) when they do not wet and the cohesion of the liquid is greater than the adhesion of the liquid to the walls. 6. What is the difference between perfect and real fluids ? Ans: Perf ect fluids are tr eated as if all tangential f orces created by fricti on can be ign ored. Real fluids refer to the cases in which friction must properly be taken into account. 7. Which factors affect tool size ? Ans: Following f actors influenc e tool size : 1. Process variable (speed, feed and depth of cut) 2. Tool material 3. Tool geometry 4. Work piece material material,, its hardness, microstructure and surface condition 5. Cutting conditions. 8. When the motion of fluid is fully known ? Ans: The moti on of a fluid is fully known when the veloc ity of eac h of its p articles c an be specified. 9. Define fluid. Ans: A fluid is a substanc e that can't r emain at rest under th e action of any shear f orce. 10. How is the size of a vertical boring machine designated ? Ans: The sp ecifications of vertical boring machine are : (i) Column height (ii) Table size (iii) Floor area (iv) Weight of the job (v) Spindle of the motor. 11. What do you mean by drill sleeve and a drill socket ? Ans: The drill s leeve is sui table for h olding only one size of shank. If t he taper s hank of th e tool is smaller than the taper in the spindle hole, a t aper sleeve is used. When the tapered tool shank is larger than the spindle taper, drill sockets sockets are used to hold the tools. Drill sockets are much longer in size than the drill sleeves. 12. What is nonbarotropic fluid ? Ans: Fluid suc h as air f or which the d ensity is not a single-valu ed functi on of the pr essure (aerostatics). 13. On account of which property, the falling drops of rain acquire superical shape. Ans: Surf ace tension. 14. How you can definte standard atmospheric pressure ? Ans: By intern ational agr eement, th e standard atmospheric pressure is defined as 101.325 kN/m2. 15. What do you understand by acoustic velocity ? Ans: Accoustic velocity is the s peed of a small pr essure (soun d) wave i n a fluid. 16. Explain the difference between centipoise and c entistoke ? Ans: Centipois e is the unit of dynamic visc osity. It is equ al to 1/100 of poise, an d poise = 0.1 Pa . s. Value of dynamic viscosity of water at 20°C is approximately equal to 1 Centipoise. Centistoke is the unit of kinematic viscosity and is equal to 1/100 x stoke. Stoke is defined as 1 square centimeter per second. 17. What is s aybolt seconds universal ? Ans: Saybolt Seconds Uni versal (SSU) is the unit of viscosit y and is equ al to the time required for a gravity flow of 60 cc through saybolt universal viscometer. 18. Explain difference between cohesion, adhesion and capillarity ? Ans: Cohesi on is the attr action of lik e molecules. Adhesion is th e attraction of unlike mol ecules for eac h other. Capillarity is the elevation or depression of a liquid surface in contact with a solid. 19. Differentiate between gear hobbing and gear shaping with reference to various relative
motions and applications. Ans: Gear h obbing is a continuous i ndexing pr ocess in whic h both cuttin g tool (a hob) and work piece rotate in a constant relationship while the hob is being fed into work. Hob is also imparted a radial feed. Gear shaping uses a pinion type of c utter which is reciprocated with required cutting cutting speed along the face of workpiece and is gradually fed radially to plunge. Continuous generation motion is obtained by feeding cutter to full depth and rotating the cutter and workpiece slowly. 20. What is bulk modulus of elasticity ? Ans: It repr esents the c ompressibility of a fluid. It is the ratio of the ch ange in unit pressur e to the corresponding volume change per unit of volume. 21. What is is entropic exponent ? Ans: It is th e ratio of t he specific h eat of a g as at const ant pressur e to the sp ecific heat at constant volume. 22. The best shape of a runner in sand casting is an inverted frustum of a cone why ? Ans: Tapered s hape with big ger diamet er at top an d smaller at bottom ensur es avoid ance of entrainment or absorption of air/gases into the metal while passing through the runner. 23. Explain difference between ideal fluid and non-newtonian fluid. fluid. Ans: Ideal fl uid is one f or which resist ance to sh earing d eformation is zero. Non-netwtonian Non-netwton ian fluids deform in such a way that shear stress is not pr oportio oportional nal to the rate of shearing deformation. 24. Explain the difference between poise and stoke. Ans: Poise is t he unit of viscosity in CGS unit and is measured in dyne sec/cm 2.1 poise = 10_1 Pa s. Stoke is the unit of kinematic viscosity in CGS units and is measured in cm2/s. 25. How does the pressure in an isothermal atmosphere behave ? Ans: It incr eases exponen tially with elevation. 26. The centre of pressure for a plane surface immersed vertically in a static liquid compared to centroid of area is always ... ? Ans: Below. 27. What is buoyant force equal to ? Define centroid of the area. Ans: Volume of liquid displac ed. Centroid of the area : The point at which the area might be concentrated and still leave un¬changed the first moment of the area around any axis. It is also the centre of gravity. 28. Define vapour pressure and on what parameters it depends ? Ans: The press ure exert ed when a s olid or liquid is i n equilibriu m with its ow n vapour is called vapour pressure. It is a function of the substance and its temperature. 29. Explain the difference between steady flow, one dimensional flow, two dimensional flow and three dimensional flow ? Ans: If at every point in the continu um, the local velocity and other fluid pr operty, r emains unchanged with time, it is referred to as steady flow. One dimensional flow is one in which a line is necessary to describe the velocity profile. Two dimensional flow is one in which an area is necessary to describe the velocity profile. Three dimensional flow is one in which a volume is necessary to describe the velocity profile. 30. What is aquifer and explain difference between confined and u nconfined aquifers. Ans: Ground water occurs in permeable, water-b earing geolog ic formations known as aquifers. Confined aquifer : It is a relatively high-permeable, water-bearing formation. Unconfined aquifer : It is a water-bearing formation with a free water table, below which the soil is saturated. 31. What do you und erstand by flurial hydraulics hydraulics ? Ans: The ch annels may b e classified as rigid bou ndary or mobile bound ary channels. Mobile boundary channels include rivers and unlined alluvial canals, the b oundarie oundaries s of which are made of loose soil which can be easily eroded and transported by flowing water. The study of flow of water in mobile boundary channels is dealt in flurial hydraulics. 32. By which instruments the shear stress in fluids can be measured directly ? Ans: By Stant on tube or Preston tub e. 33. On what factors does the pressure at a point as a static mass of liquid depends upon? Ans: Specific weight of liqu id and the depth bel ow the fr ee liquid surfac e. 34. What is th e difference between hoop or longitudinal tension and circum-ferencial tension ? I Ans: Hoop tension is created in the walls of a cylinder subjected to internal pressure. For thin walled cylinder (t < 0.1 d), hoop stress = pressure x radius/thickness. Longitudinal tension tension in t hin-walled cylinders cylinders closed at the ends is equal to half the hoop tension. 35. How much force is exterted by liquid ? Ans: Force e xerted by a liquid on a plane ar ea A is equal t o the prod uct of the un it weight pg of the liquid, the depth hcg of the centre of gravity of the area, and the area. 36. State standard point angle and helix angle of a twist drill. Ans: Standar d point an gle of twist dr ill is 118° an d helix angl e varies fr om 16° to 30° depending as diameter of hole.
37. Explain the difference between horizontal and vertical components of hydrostatic hydrostatic force ? Ans: The hori zontal comp onent of th e hydros tatic forc e on any surf ace is equal t o the nor mal force on the vertical projection of the surface and acts through the center of pressure for the vertical projection. Vertical component component of the h ydrostati ydrostatic c force on any surface is equal to the weight of the volume of liquid abaove the area and passes through the e.g. of the volume. 38. What should be diameter of capillary tube to avoid correction for effect of capillarity in manometer ? Ans: Greater t han 6 mm. 39. How much hydrostatic pressure acts on a curved surface ? Ans: The hori zontal comp onent of th e total hydr ostatic pr essure f orce on any s urface is always equal to the total pressure on the vertical projection projection of the surface, and can be located through the center of pressure of this projection. The vertical components of the total hydrostatic pressure force on any surface is always equal to the weight of the entire water column above the surface extending vertically vertically to the free surface, and cvan be located through the cemntroid of this c olumn. 40. How much is the horizontal component of force on a curved surface ? Ans: Force on a vertical pr ojection of th e curved surf ace. 41. State Archimedes principle. Ans: Any weig ht, floating or immers ed in a liquid, is acted upon by a bu oyant forc e equal to the weight of the liquid displaced. This force acts through the center of buoyancy, i.e. the e.g. of the displaced liquid. 42. What do you und erstand by center of buoyancy ? Ans: Center of buoyanc y is the c enter of gr avity of the disp laced liqui d and bu oyant force acts through it. 43. How one can establish stability of submerged body and floating body ? Ans: A submer ged bod y floats in st able equilibri um when the c enter of gravity of th e body lies directly below the center of b uoyancy. 44. What is neutral equilibrium ? Ans: A submer ged bod y is in neutral equilibrium f or all positions when the cent er of gravit y of body coincides with the center of buoyancy. 45. On what factors the stability of floating objects depends ? Ans: Stability of floating objects depen ds upon wh ether righti ng or over turning moment is developed when the center of gravity and center of buoyancy move out of vertical alignment due to the shifting of position of center of b uoyancy. 46. State two products each produced by f orward extrusion and reverse impact extrusion. Ans: Two examp les of products made by dir ect extrusi on are : g ear pr ofile, solder wire. Two examples of reverse impact extrusion are : Short tubes of soft alloys, tooth paste containers. 47. What are the best ge ometrica ometricall shapes suggested for sheet metal drawing and spinning? Ans: Cup sh ape is best su ited by drawi ng operat ion. Conic al shape is easiest to pr oduce by spinning operation. 48. What are the c onditio onditions ns for stability of buoyant bodies ? Ans: A floatin g body is st able if the c enter of gra vity is below t he metacentr e. A submerged body is st able if the c enter of gr avity is below t he center of buoyancy. 49. Define pipe flow ? Ans: It ref ers to full wat er flow in cl osed conduits of circular cr oss section under a c ertain pres¬sure gradient. 50. How much is vertical component of pressure force on a sub merged curved surface ? Ans: The weig ht of liquid vertically ab ove the cur ved surfac e. 51. Multiple coated, disposable carbide tips have more-or-less replaced brazed carbide tipped tools in CNC application applications. s. Why ? Ans: Dispos able tips ar e usually ind exable typ e and have a number o f cutting ed ges. Very convenient gripping devices for holding such inserts on tool holders are available. A wide variety of ready made inserts are available which require no grinding or adjustment. 52. State, sequentially elements of a canned CNC drilling cycle. Ans: Cann ed cycles are f ixed cycles f or general s equences of operati ons. For drillin g operation, sequence of operations will be movement of drill or workpiece to position of actual drilling, movement of drill downwards till it is in the proximity of workpiece, then movement of drill at desired feed rate to sufficient depth of hole, retracting the drill above the workpiece. 54. Explain the difference between one and two dimensional flow ? Ans: True one-dimension al flow occu rs when th e direction and magni tude of th e velocity at all points are identical. Velocities Velocities and acceleration accelerations s normal to t he streamline are negligible. Two dimensional flow occurs when the fluid p article articles, s, move in planes or parallel planes and the stream-line patterns are identical in each plane. 55. What is t he difference between irrotational and rotational flow ? Ans: Irrotati onal flow : An ideal fluid f low in which no shear str esses oc cur and h ence no torques exist. Rotational motion of fluid particles about their own mass centers can not exist. It can be represented by a flow net. Rotational flow occurs when the velocity of each particle varies directly as the distance from
the center of rotation. 56. Explain the difference between steady and unsteady flows. Ans: In stead y flow, at an y point, th e velocity of s uccessive f luid parti cles is the s ame at successive periods of time. Flow is unsteady when conditions at any point in a fluid change with time, 57. What is the difference between uniform and non-uniform flows ? Ans: Unif orm flow occurs when the m agnitude an d direction of the vel ocity do n ot change from point to point in the fluid. Non uniform flow occurs when velocity, depth, pressure, etc. change from point to point in the fluid flow. 58. Explain the difference between stream lines and stream tube. Ans: Stream lin es are imagin ary curves drawn throu gh a fluid t o indicate th e direction of motion in various sections of the flow of the fluid system. There can be no flow across a streamline at any point. Stream tube represents elementary portions portions of a flowing fluid bounded by a group of stream¬lines which confine the flow. 59. What is the advantage of independent jaw chuck ? Ans: Irregul ar job can be fixed. 60. Define vorticity ? Ans: It equals twice the angular vel ocity. 61. What is irrational How ? Ans: If a f low is unifor m in one region (without r otation), this property is cons erved as the f luid moves into a region of space where the motion is not uniform, and the flow is termed irrotational flow. 62. What is one-seventh power law ? Ans: Accordi ng to one-s eventh pow er law of tur bulent, velocity variati on corresp onds to a much favoured velocity profile and the mean velocity increases as the one-seventh power of the distance from the b oundary wall. 63. Mention the major difference between drilling and boring ? Ans: Drilling B oring (a) It is the operation of initiating a hole Boring is the operation of enlarging a drilled hole (b) It can produce only standard holes W e can produce non-standard hole (c) Drill is a multi point tool A single point tool is used 64. What is the magnitude of buoyant force and where does the line of action of buoyant force act ? Ans: It is eq ual to the volume of the l iquid displac ed. The line of action of buoyant f orce acts through the centroid of the displaced volume of the fluid. 65. What is metacentre ? Ans: Metacentr e is the poi nt at the int ersection of the buo yancy with th e vertical axis of the body. 66. Define Prandtl's pitot-static tube. Ans: It is a c ombination of p ressure pr obe and pitot tube. It is widely used for pr essure measurements in wind-tunnel installations. 67. Define the term f luid friction. Ans: The def ormation of r eal fluids is r esisted b y forces c aused by intern al friction or viscosity. Viscosity is that property of a real fluid which creates shear forces (fluid friction) between two fluid selements. 68. Why are hydrodynamic bearings used for grinding machines in preference to ball or roller bearings ? Ans: Hydrod ynamic beari ngs are more suitable at high sp eed, better tolerances, quiet operation, higher capacity to withstand shock, lesser space requirement, better life under fatigue conditions etc. 69. Distinguish between a jig and fixture. Ans: Jig clamps and locates p arts in positi ve manner and guides cutt ing tools ( drills, reamers , taps etc). Fixture is bolted or fixed securely to the machine table so that work is in correct location ship to the cutter. Fixtures are used for mass milling, turning and grinding, etc. 70. State the similarities and differences between a fixture and a jig. Ans: Both jig and fixture positively l ocate, hold and clamp th e workpie ce. Jigs guid e the tool for drilling etc but fixture has no facility to guide the cutting tools. Jigs are used for drilling etc and fixture for mass milling, turning, grinding, etc. 71.Explain the difference between relative density, viscosity and kinematic viscosity ? Ans: Relative density is t hat pure n umber which denotes t he ratio of the mass of a body t o the mass of an equal volume of a substance taken as a standard. This standard is usually water (at 4°C) for solids and liquids, and air free or C02 or hydrogen (at 0°C and 1 atmosphere = 1.013 x 105 Pa pressure) for gases. Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force. It is due primarily to interaction between fluid molecules. Kinematic viscosity is the ratio of absolute viscosity and mass density. (Its unit is m2/s). 72. A right hand helical gear is being cut on a milling machine. What changes in machine
settings have to be made to cut a left hand helical gear of same pitch and number of teeth ? Ans: For cutti ng right han d helical gear right sid e of milling tabl e is tilted up f rom normal position by the helix angle. For cutting left hand helical gear, right side of table needs to be tilted down at helix angle, all other settings remaining unchanged. 73. Explain what you understand by the term hydrostatic paradox ? Ans: Hydrost atic paradox is the ph enomenon th at the floor l oad of wa ter in vessels of different shapes shapes carrying water at s ame level depends only on the area of the bottom surface and not on the shape of the vessel. 74. Define buoyancy in brief. Ans: Buoyanc y is the vertic al force exerted on th e body by t he fluid at rest. The buoyancy of a submerged body in a fluid at rest is equal to the weight of the fluid displaced by the body and it acts upward through the c enter of gravity of the displaced volume (the center of buoyancy). 75. What is the necessary condition for a body to float in stable equilibrium ? Ans: Meta cent er should be above t he center of gravity. 76. If liquid rotates at constant angular velocity about a vertical axis as a rigid body, then how its pressure varies at various radial distances ? Ans: As squ are of the r adial distanc e. 77. How does the velocity vary along radius in a few vortex ? . Ans: It decr eases with rad ius. 78. What type of flow will occur when liquid discharges at constant rate through a long, straight tapering pipe ? Ans: Steady non-unif orm flow. 79. What does c ontinuity equation represent ? Ans: It relat es mass rate of flow alon g a stream t ube. 80. Under what condition steady flow occurs ? Ans: When c onditions d o not chang e with time at any point. 81. Why a drill can not drill deeper than its flute length ? Ans: If flute s ubmerges in a drilled h ole, the chi ps disposal passage i s blocked an d the drill will get jammed in the hole. 82. When do you rec ommend the use of straight fluted drill ? Ans: Drills us ed for brass and other s oft materials an d thin sheets need n ot be provid ed with any helix angle, to prevent the lips digging into the workpiece. 83. Explain velocity distribution for laminar and turbulent flows. Ans: In cas e of laminar fl ow, the vel ocity distribu tion follows a parabol ic law of variat ion. The maximum velocity at center of pipe is twice the average velocity. For turbulent flow, more uniform velocity distribution results. 84. In which type of flow the stream lines, streak lines and path lines are identical ? Ans: In stead y flow. 85. Under what condition a drill may not cut ? Ans: When th e cutting lips are not provi ded with cl earance angles. It will cut if 12° c learanc e angle is ground. 86. Some drills have straight shanks and some have tapered shank. W hy ? Ans: Small drills ( less than 12 mm diameter) are provided with straig ht shanks w hich can b e held in Dniren chucks. Bigger drills have tapered shank using self holding Morse tapers which prevent gravitational fall of drill. 87. What are the main factors that are r esponsible for the formation of built up edge ? Ans: The main f actors that ar e responsib le for the f ormation of bu ilt up edge are : 1. Extreme pressure in the cutting zone 2. High friction in the tool chip interface 3. High local temperature. 88. In which type of flow the Navier-strokes equation is useful ? Ans: Viscous f low. 89. Explain the difference between energy line and hydraulic grade line ? Ans: The en ergy line is a graphical r epresentati on of the energy at each section. Hydraulic grade line lies below the energy line by an amount equal to the velocity head at the section. 90. What is the characteristic of equipotential line ? Ans: It has n o velocit y component t angent to it. 91. How specific cutting pressure behaves with feed rate and what conclusion can be drawn from this ? Ans: As feed r ate increas es, the sp ecific cutting pressur e decreases. It leads to c onclude that feed rates be maximised in metal cutting process. 92. What is hydraulically rough pipe ? Ans: When Re ynolds numb er is very s mall, friction f actor f bec omes indepen dent of th e Reynolds number and depends only on the relative roughness height. Such a pipe behaves as hydraulically rough pipe. 93. What are the qualities of ideal tool material ? Ans: It should be hard t o resist flan k wear and deformation , have hig h toughn ess to resist fracture, be chemically inert to the workpiece, be chemically stable to resist oxidation and
dissolution, and ha ve good resistance to th ermal shocks. dissolution, 94. What are the factors to be considered while evaluating the machinability machinability ? Ans: 1. Tool life 2. Rate of metal removal 3. Power required 4. Surface texture and size of component 5. Temperature of tool (or) chip. 95. Which equation is satisfied by ideal or real, laminar or turbulent flow ? Ans: Continuit y equation . 96. How to judge the unsatisfa unsatisfactory ctory performance of cutting tool ? Ans: Uns atisfactory perf ormance of c utting tool leads to l oss of dimen sional accur acy, increase increa se in surface roughness and increase in power requirements. 97. What are t he criteria for judging machinability ? Ans: Cutting s peed, tool life, surfac e finish, cutti ng force/ energy req uired, teasp erature r ise at cutting point. 99. What is critical velocity ? Ans: It is th e velocity b elow which all turbulenc e is damped ou t by the viscosity of the f luid. 100. What is laminar flow ? Ans: In lamin ar flow the f luid particles move along s traight, p arallel pa ths in layers or laminae. Laminar flow is governed by the law relating shear stress to rate of angular deformation i.e. the product of the viscosity of the fluid and velocity gradient.
1. What What parameters influ ence the tool life ? Ans.- 1. T ool material 2. Work material 3. Speed, feed and depth of cut 4. Tool geometry work system 5. Cutting fluid 6. Built up edge 7. Vibration behaviour of the machine tool. 2. Mention the fun ction of interm ediate stage in a generalised measurement system.. system (i) Amplify signal without affecting its waveform (ii) Remove unwanted noise signals that tend to obscure the input (iii) Capable of doing other conditioning like differentiation/integration, A/D conversion etc. 3. What What is a sign al flow gr aph ? A signal fl ow graph of a system is a gr aphical mod el in which n odes repr esent th e system variables variable s and directed branches between the n odes represent relationship between the variables. variable s. In a signal flow graph, a forward path originate originates s from the input mode and terminates at output mode without encountering any mode more than once. 4. Explain the difference between rotational and irrotational flow. In rotational flow the vorticity is non zero and in irrotational flow it is zero. In irrota¬tional flow the net rotation of a fluid element about its own mass centre is zero as it moves from one place to another. For it, dv/dx = du/dy. 5. Define the term stability of a feed back control system ? A system is s aid to be stab le if the out put of a s ystem after fluctu ations, variations or oscillations, settles at a reasonable value for any change in input. 6. What is meant by precision ? Precision is defined as the ability of instrument to reproduce a certain set of readings within a given accuracy. 7. What is boundary layer ? Boundary layer is the fluid layer in the neighbourhood of a solid boundary where the effects of fluid friction are predominant. 8. On what account the boundry layer exists ? Boundary layer m fluid flow exists on account of fluid density. 9. Explain the difference between laminar flow and turbulent flow . In laminar flow the fluid particle particles s move along smooth, regular paths which can be pre¬dicted in well advance. Turbulent flow is c haracterise haracterised d by r andom and erratic movements of f luid particles resulting in formation of eddies. For flow to be laminar in a pipe, the Reynold's number is less than 2000 and for flow to be turbulent it is greater than 4000. 10.. What is the dif ference between path lin e and stream lin e ? 10 A path line is a curve tr aced by a sin gle fluid p article durin g its motion . A stream line is an imaginary line drawn in a flow field such that a tangent drawn at any point on this line represents the direction of the velocity vector. There is no flow across the stream line. 11. What is the difference between steady and unsteady flow ? In steady flow the velocity at a given point does not c hange with time whereas in unsteady flow it changes with time. 12. What is stagnation point and stagnation pressure ?
A stagnation point is on e at which velocity is zer o. Stagnati on pressur e is the su m of static pressure and dynamic pressure. 13. What is the hydraulic-grade line ? It is the line which shows tne variation of piezometric head. 14. Under what c ondition the thickness of thermal boundary layer and hydrodynamic boundary layer is same ? When Prandtl number is equal to unity. 15. What keeps the shaft in floating condition in hydrodynamic journal bearing ? Hydrodynamic pressure developed in the lubricant. 16. Why the elements of higher pairs must be f orce closed ? This is necessary to provide completely constrained motion. 17. What is the value of c oefficie oefficient nt of friction for ball bearing ? Ans: 0.1 t o 0.25. 18. Why belts are subject to creep ? Due to uneven extension and contraction of belt. 19. What is th e ratio of damping c oefficie oefficient nt to critical damping coefficient called ? Damping factor. 20. In which type of lubrication the starting friction is low ? In hydrostatic lubrication. 21. Whether Bernoulli's equation is applicable for streamline straight and r otational flows ? Ans: Yes. 22. When a plate slides over a parallel plate, what is the relationship between vis¬cous force and the lubricant thickness ? They are directly proportional. 23. How the stability of empty ship increased. By adding ballasts at the bottom level. 24. Define Froude number. It is the square root of ratio of inertia force to gravity force. 25. What for Maning's formula used ? It is used to determine velocity of flow in pipe. 26. What is the maximum efficiency of power transmission through a pipe ? Ans: 66.67%. 27.. What 27 What is the necessary necessary and suf ficient condition f or bodies in f loata loatation tion to be in stable equilibrium equilibrium ? Centre of gravity of body should be located below metacentre. 28. Under what condition the thermal boundary layer thickness will be equal to the hydrodynamic hydrodynami c boundary layer thickness ? When Prandtl number is unity. 29. How laminar boundary layer thickness varies on a flat plate ? It is proportional to the square root of the distance from the leading edge. 30. Name the axial flow reaction turbine with adjustable vanes. Kaplan turbine. 31. Define the degree of reaction of a turbomachine. It is the ratio of total pressure change in t he rotor to that in the stage. 32. What is meant by relative stability ? If the system is found to be stable, then it is necessary to know the stable strength or degr ee of stability which is called relative stability. Phase margin and gain margins are the measures of relative stability. 33. On what factors the efficiency of a centrifugal pump depends ? The efficiency of a centrifugal pump depends on size, speed and type number. 34. Define transducer ? Transducer is an element which converts the signal from one physical form to another without changing the information content of the signal. 35. A 200 mm impeller of centrifugal pump develops discharge head of 2 kg/cm2. If discharge head is required as 8 kg/cm2, what should be diameter of impeller. Ans: 400 mm. 36. Why thin-plate orifice is frequently recommended for flow measurement in most of the cases ? It is recommended because of its high accuracy, low cost, and extreme flexibility. 37. How the water flow from a hydrant in a city water system measured ? It can be measured by allowing the flow of water from a hydrant and noting down the horizontal distance (x) where jet strikes the ground and the vertical distance (y) of outlet from ground. Then flow = area of hydrant x 38. For the same size, length and condition of pipe, how the friction head loss changes if pipe size is varied. Under same flow conditions the friction head loss increases increases as th e size change to the 4.8th power. 39. How does the c apacity changes changes in p ipe flow with increase in pipe diameter if head is constant ? At constant head, c apacity is prop ortional t o d25. . 40. How does the head chang e in pipe flow with change in diameter, if capacity is is
constant. At constant c apacity, head is proport ional to 41. How head varies in pipe flow with change in flow, if pipe diameter is same. At constant diameter, h ead is prop ortional to (f low)2. 42. Give some properties of errors ? (i) Errors give the difference between the measured-value and the true value (ii) Accuracy of a measurement system is measured in terms of error (iii) A study of error helps in finding the reliability of the results. 43. Define the term contraction coefficient. The ratio of area of jet (contracted) and the cross section of the orifice. 44. What for pycnometer is used ? Pycnometer is used to measure specific gravity of the liquid. 45. How may types of bonded strain gauges us ed ? (a) Fine wire strain gauge (b) Metal foil strain gauge (c) Piezo resistive gauge. 46. Name various functional elements of an instrumental system ? (1) Primary sensing element (2) Variable conversion (or) tr ansducer element (3) Variable manipulation element (4) Data transmission element (5) Data processing element (6) Data presentation element (7) Data storage and playback element. 47. Name the three stages of a generalised measuring system. (i) Sensing and converting the input to a c onvenient and practicable form. (ii) Processing/manipulating Processing/manipulating the measured variable. (iii) Presenting the processed measured variable in quantitative form. 48. How is a Pelton turbine braked ? A pelton wheel is brak ed by a noz zle directing a jet on t he back of the buck ets. 49. What is static pressure ? How is it measured. The pressure caused on the walls of a pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to walls of the pipe is called static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid so that the tube is at right angle to the fluid flow path. 50. What are the requirements of a c ontrol system ? Stability, accuracy and speed of response are the three requirements of control system. 51. What is the difference between weir, and submerged weir. Any obstruct ion of a str eamflow over which wat er flows is weir. W hen the downs tream water level rises over the weir crest, it is called submerged weir. 52. What is th e difference between spillway and siphon spillway ? Spillway is an essential part of a large dam and provides an efficient and safe means of releasing flood water that exceeds the design capacity of the r eservoir. Siphon spillway is spillway designed to discharge water in a closed conduit under n egative pressure. 53. What is th e difference between culverts, stilling basin, and standpipe ? Culverts are built at the points of lowest valley to pass water across the embankments of highways or railroads. Stilling basin is transitional energy dissipating structure to avoid the damaging process by a highly accelerated spilled water. Standpipe is used principally for alleviating the transient pressures in large pipeline system. It also works as a pressure relief valve for the upstream pipe during the turbine shut off. 54. What do you und erstand by run-of-river run-of-river scheme in hydro p ower generation ? A scheme in which the disc harge is varying and only that muc h water c an be utilis ed for conversion as available in the river. 55. What is the difference between firm power and secondary power in hydro power plants ? The approximate constant and continuous power which is assured at power station and would be available throughout the year is called firm power. In run-of-the river schemes which are generally designed for % availability of water, the firm power would be available for at least % of the years during the life of the scheme. However in some years discharge in the river may be more than % availability discharge and some extra power known as secondary power can be generated. 56. What is the criterion for determining economic diameter diameter of power tunnel ? The economic diameter of a power tunnel is determined such that the total value of following two factors is least (i) annual loss of revenue on account of power head lost due to friction. (ii) recurring annual expenditure. 57. What are the three functions served by a surge tank in a hydro plant ? The three functions served by a surge tank are (i) flow regulation - act as a reservoir for acceptance or delivery of water to meet
requirements of load changes. requirements (ii) water-hammer relief or pressure regulation. (iii) improvement improvement in speed regulation. 58. What is the criterion to determine the economic diameter of penstock ? The economic diameter of a penstock required to carry a discharge is the one at which annual costs due to the greater investment do not exceed the annual value of resulting increment energy output. 5. If jet ratio for a pelton wheel is 12 then number of buckets should be .... ? 0.5 x 12+ 15 = 21. 60. What is th e difference between anti-friction and hydrostatic bearings ? In anti-friction bearings bearings r ollin olling g c omponen omponents ts are introduced between the sliding surfaces. In hydrostatic bearings lubricant is supplied at a high pressure to a pocket in the bearing. 61. What is inviscid fluid ? It is the frictionless fluid. 62. State law of conservation of momentum ? The ratio of change of momentum of a mass of fluid is equal to the vector sum of all external forces acting on it. 63. Define turbulent flow ? Flow in which adjacent layers mix continuously, so that the flow pattern is unsteady, full of eddies, and apparently without any mathematically expressible regularity. 64. Define Reynold's law of similitude ? Two geometrically similar flow systems subject only to friction and inertia forces are dy¬namically similar if both have the same 'Reynolds' number. 65. What is th e difference between boundary lubrication and fluid film lubrication ? In boundary lubrication condition the ratio of thickness of lubrication film to surface roughness (CLA value) is less than 1 and for fluid film lubrication condition this ratio is greater than 5 and less than 100. 66. A bearing in which hydrodynamic pressure is generated due to rotation of jour¬nal is called... ? Journal bearing. 67. For a journal running in a bearing clockwise at steady state, where will be the minimum clearance ? To the left of the load line. 68. Out of impulse and reaction type hydraulic turbines, which has higher specific speed ? Reaction turbine. 69. What is order of the system. The order of the system is the order of the highest derivative of the ordinary differential equation with constant coefficients which defines the system mathematically. 70. What is Bode plot ? Bode plot is a logarithmic plot used to represent transfer functions. The Bode plot consists of two plots namely. (i) The plot of magnitude in db (on linear scale) vs. frequency to (on log scale) (ii) The plot of phase angle in degrees (on linear scale) vs. frequency co (on log scale) 71. Navier stokes equation represents the c onservatio onservation n of which quantity ? Momentum. 72. What are t he characteristics of precision ? (i) If a number of measurements are made on same true value, the degree of closeness of these measurements gives precision (ii) It is a measure of the degree of repeatability or reproducibility of the measuring system. 73. What is meant by loading ? During the act of measurement the measuring instrument takes energy from the signal source or measured medium and thus the signal source is altered. This effect is called loading. 74. Give two uses of Bode plots. (i) They are the logarithmi logarithmic c plots used to represent transfer functions (ii) They are used in the calculation of gain margin and phase margin. 75. What is the name of nondimensional group for ratio of inertia force to gravity force. Froude number. 76. The head loss in a f ully developed laminar flow in a circular pipe due to friction is directly proportional to ... ? Square of mean velocity. 77. For what type of flow, the streamlines, pathlines and streaklines are virtually identical ? Steady flow. 78. How the streamlines and equipotential lines are related in a flow field ? They are orthogoial everywhere in the flow field. 79. Under what kind and condition of a fluid the velocity potential exists ? Irrotational flow. 80. Where should centre of gravity of a body lie for it to float in stable equilibrium ? e.g. should be located b elow the metacentre. 81. For fully developed flow through a pipe, what is the ratio of maximum to average velocity ?
Ans: 2. 82. Out of centrifugal, axial and positive displacement pumps, which has maximum specific speed and which has minimum ? Axial pump h as maximum spec ific speed an d reciproc ating pump has minimum. 83. Specific speed of a turbine is 800. What type of turbine is this ? Kaplan turbine. 84. In which type of lubrication system the starting friction is low ? Hydrostatic lubrication. 85. At which point the cavitation is most likely to occur in a hydel plant ? At turbine r otor exit. 86. What is the difference between lower pair and higher pair ? In a kinematic pair, if the elements have surface contact when in motion, the pair is called lower pair and if elements have line or point contact the pair is called higher pair. 87. What do you und erstrand by inversions inversions and how many inversions inversions are possible in a kinematic chain having 'n' links ? Inversions are different mechanisms obtained by fixing different links in a kinematic chain but keeping relative motions of links unchanged with respecat to one another. A kinematic chain with 'n' links can have 'n' inversions. 88. What is th e difference between basic kinematic chain and compound kinema kinematic tic chain ? What is the criteria for a chain to be constrained ? A basic kinemat ic chain c onsists of four kinematic links and a compo und kinematic c hain is a constrained chain of more than four links. A chain is constrained if no. of binary joints and half of number of higher pairs is equal to 3/2 of no. of links minus 2. 89. What is the difference between a machine and a mechanism ? A mechanism c onsists of lin ks forming a c onstrained k inematic ch ain. Its function is ba¬sic ally to transmit or modify motion. A machine is a mechanism but here we are concerned with forces to be transmitted and it is used to modify mechanical work. 90. In which type of motion, acaceleration is directly proportional to displacement ? SHM. 91. What is the function of a transducer element ? The function of a transducer element is to sense and convert the desired input into a more convenient and practicable form to be handled by measurement system. 92. What is th e direction of tangential acceleration ? The direction of tangential acceleration may be same or opposite to that of angular velocity. 93. What is the number of degr ees of freedom constrained in each case by the kinematic pairs. (i) Itevolute pair, (ii) cylindrical pair, (iii) Screw pair, (iv) Spherical pair. Ans: (i) Rev olute pair— single degr ee of freed om. (ii) cylindrical pair—two degrees of freedom. (iii) Screw pair—one degree of fr eedom. (iv) spherical pair—three degrees of freedom. 94. What is the purpose of D-slide valve in steam engines ? It controls the piston position for cut off of steam, for release of steam and compression position for steam in cylinder. 95. What is the purpose of Corliss valve in place of D'-slide valve in steam engine ? Corliss valve reduces condensation, provides independent control on admission, cut off, release and compression, and reduces driving power r equirements. 96. On what factor the size of cam depends ? Size of cam depends on base circle. 97.. If base circle diameter of cam in creases, what happens to press ure angle ? 97 It decreases. 98. If angular speed of cam is increased two times, how much jerk will be increased ? Eight times. 99. Define primary and secondary transducers ? A primary trans ducer s enses a physic al phenomen a and con verts it to an analogous output. The analogous output is then converted into an electrical signal by secondary transducer. 100. What is the relationship between (i) axes of spin, precession, and applied gyroscopic torqu e and (ii) in between their planes ? The axes of spin, precession, and applied gyroscopic torque are contained in two planes perpendicular to each other, and planes of spin, precession, and applied gyroscopic torque in the three planes perpendicular to one another.
1. Why excess air is required to burn a fuel completely ? Ans: Excess air is required to ensur e adequ ate mixing of f uel and air, avoid smoke, mini mize slagging in coal burning, and to ensure maximum steam output. 2. What is factor of evaporation ? Ans: It is th e ratio of h eat chang e from feed water to steam and the heat of vaporizati on of steam at atmospheric pressure.
3. Materials which absorb neutrons and produce fissionable material are called ? Ans: Fertile materials, such as U28 and T h22. 4. What is the process which produces fissionable material from a fertile material ? Ans: Breeding . 5. What is burn up in connection with fissionable material ? Ans: Burn u p corresp onds to des truction of f issionable m aterial when it underg oes nuclear fission. 6. What kind of nuclear fuel is used in Narora, Kalapakkam and Rana Pratap Sagar nuclear plants ? Ans: Natural uranium. 7. Which type of plant will you recommend for remote location if power is required in six to twelve months time ? Ans: Diesel engine power plant. 8. Under what condition a nuclear reaction is said to be critical ? Ans: For critic al condition, t he reacti on should c ontinue at a s teady ra te which is p ossible when rate of production of neutrons is same as the combined rate of absorption of neutrons and the rate of leakage of neutrons. 9. If a nuclear reactor generates more fuel that it consumes, it is called ______ ? Ans: Fast br eeder react or. 10. Natural uranium contains contains only 0.7% U 25 which is capable of switching chain nuclear reaction. How this percentage is increased ? Ans: Perc entage of U25 in natural ur anium is incr eased by a process c alled uraniu m enrichment. 11. Why the vane passages are gradually increased in size in successive wheels in steam turbine ? Ans: The veloc ity of steam decreas es in successi ve stages and to acc ommodate same f low per unit time, the area of flow must increase. 12. At what pressure and temperature the density of water and steam is same ? Ans: At 225 k g/cm2 and 74.6° C. 13. What is the latent heat of evaporation at critical critical point ? Ans: Zero. 14. How much space steam will occupy at atmospheric pressure corresponding to 1 kg of water ? Ans: 100 times the spac e occupied b y 1 kg of wat er. 15. What is meant by quality of steam ? Ans: It ref ers to amount of unevapor ated moistur e in steam. If steam is p erfectly dry, it's quality is 100%. 16. What is diagram efficiency in steam turbine ? Ans: Diagr am efficienc y = Change in K .E./kg / Ener gy suppl ed/kg. 17. What do you understand by effectiveness of heat exchanger ? Ans: Effecti veness of h eat exchan ger = actual heat trans fer/maximum p ossible heat tr ansfer. 18. If superheat and condenser temperatures are unchanged and if pr essure of steam is increased, increa sed, then what happens to dryness fraction of steam after isentropic expansion ? Ans: It will d ecrease. 19. As pressure of steam is increased, why r eheating is necessary? Ans: As pr essure is incr eased, the dryness fr action of steam lowers on is entropic expansion. Therefore, steam has to be reheated after partial expansion so that dryness fraction remains within limits after expansion. 20. What is boundary layer thickness in free convection case ? Ans: Velocity of fluid flow at solid surf ace is zero and it increases rapidly as distance f rom solid surface becomes greater, reaches a maximum value and then decreases to that of undisturbed fluid. The distance between the solid surface and point where boundary layer velocity equals undisturbed flow (edge) is called boundary layer t hickness. 21. What do you und erstand by forced convection ? Ans: When c onvection h eat transf er occurs bet ween a s olid body and a fluid and wh ere circulation of fluid is caused and controlled by some mechanical. 22. In radiative heat transfer, a gray surface is one whose emissivity is _____ ? Ans: Indepen dent of wavelength. 23. What is the effect of water injection and steam injection in gas turbine of heat rate and power output ? Ans: Water inj ection r esults in high er mass flow r ate through turbine section and as rich electrical output output is increased. However it increases gas turbine heat rate because of th e additional heat consumption required to vaporise the water. Steam injection increases power output and decreases heat rate because of its higher energy entering the combustion zone. 24. Water/steam injection in gas turbines increases power output. What is the limit and reasons for same ? Ans: Water/st eam injection is not allowed b eyond 5% of compress or flow to a void flame out in combustion and to minimise operating cost and impact on inspection intervals. 25. What are the advantage advantages s and drawbacks of centrifugal compressor compressor and axial flow
compressors compressor s in gas turbines? Ans: Centrif ugal compr essors have f ollowing advan tages : —short len gth due t o high pr essure ratio attained in a single st age. —simple in d esign, eas y to manuf acture, rugg ed in constr uction, less costly. —more reliabl e in oper ation under all operat ing condition . —less susc eptible to th e effects of deposits left on flow pat h. —less sensiti ve to the f ouling of th e flow path. —Good eff iciency over a wide ran ge of op eration. Drawback is larger cross-section area for s ame capacity and its unsuitability for high pressure ratios. Axial flow com pressor is mor e popular du e to high d elivery capac ity, high compr ession rati o due to many stages, high efficiency (85-90%), low cross sectional area. Its drawback is sophisticated sophisti cated design and appreciable length due to large number of stages, narrow operating range for good efficien efficiency, cy, higher weight and cost, high starting power. 26. What is the difference between pinch point and approach point in connection with heat recovery steam generator (IIRSG) ? How they affect performance of IIRSG ? Ans: Pinch p oint is the tem perature difference b etween th e gas turbin e exhaust l eaving the evaporator section and the saturation temperature of st eam at corresponding pressure (drum operat¬ing pressure). pressure). Approach point is the temperature difference between the temperatu temperature re of steam corre¬sponding to drum operating pressure and water temperature leaving the economiser. Both these vari¬ables affect the steam production and the cost and effectiveness of HRSG. If pinch point is lower, total heat recovered in HRSG in higher and st eam generation is also high. However lowering pinch point requires more heat exchange surface and increase in cost and draft side loss. Its optimum value is 8-10°C. Lower is approach temperature, higher is st eam production in economiser due to flashing which needs to be avoided for long life of tubes. Higher approach temperature increases increases the surface in evaporator section and assures higher stability. 27. How the efficiency of heat recovery in IIRSG increased ? Ans: It can b e increased by gen erating steam at more than one press ure. Further improvement improvement is possible b y heating make up water/conden water/condensate sate in HRSG, generating low pressure saturated steam or dearation steam in HRSG using a low pressure evaporator, preheating the make up water in a heat exchanger before it enters deaerator, and circulate more water than n ecessa ecessary ry through the economiser and recirculate excess to the deaerator. 28. NO.,, reduction in gas turbines is challenge to meet environmen environmental tal regulations. What measures measure s are taken in this regard ? Ans: NO* in g as turbin es is controll ed by (a) i njecting wat er/steam into c ombustor, (6) us ing selective catalytic catalytic redaction (SCR) and non-catalytic reduction system (NRS), and (c) b etter combustor design. 29. What is the difference between fuel NOx and thermal NOx ? Ans: Fuel NO* is formed by t he gas p hase oxid ation of ch ar nitrogen (CN~ compoun ds) in the fuel and thermal NO* is formed by high temperature reaction between the nitrogen and oxygen in the c ombustio ombustion n air. 30. How steam/water injection in combustion zone lowers NOx formation. Ans: It lowers the flame and gas temp eratures. 31. What are disadvantage disadvantages s of injecting steam/water steam/water in c ombustio ombustion n zone in gas tur¬bine ? Ans: —Incr eased CO at lower loads —Increas ed fuel consu mption —Loss of ext ensively tr eated water —Increas ed complexity of engine c ontrol —Short lif e of major turb ine componen ts. 32. What for water/steam is injected in combustion zones of a gas turbine ? Ans: Water/st eam is injected to limit the amount of NO x formed b y lowering the f lame and g as temperatures. 33. What are improved low NOx combustors ? Ans: Dry low NO x combustors result in i mproved air/f uel mixing and reduc ed flame temperature. temperatu re. The main type are lean premixed combustors, combustors, rich/quench lean c ombusto ombustors rs and catalytic combustors. Variable guide vanes are used to control the fuel-air mixture. In one design combustion chamber is designed into a series of small, lean pr emixe emixed d chambers. 34. What is selective catalytic reduction reduction (SCR) method for NO* control in g as turbines ? Ans: SCR is a p ost combustion method in which a c atalyst is installe d in flue g as where temperature could be of the order of 15-400°C. It enables vaporised NH to react with NO* in exhaust gas to form N2 and H20. Vaporised NH is injected into exhaust gases before it passes through the catalyst bed. This process can achieve in excess of 90% NOx reduction. 35. What catalyst is used in SCR process for c ontrol of NOx in gas turbines ? Ans: V2O5 s upported b y titanium or a mixture of titanium and si lica is gen erally used as catalyst. Oxides of Ti and Mo are often incorporated as moderators. 36. Measure to minimise formation of NOx inhibit complete combustion and this results in formation of CO and voltatile organic compound (VOCs). How these are controlled ? Ans: Catalytic oxidation, a p ost combustion treatment at 470°-600 ° temper ature is us ed to
reduce emission of CO and VOCs. 37. It is usual practice to report performance characteristics of gas turbine at ISO conditions. What are these ? Ans: ISO c onditions f or GT perf ormance are : A mbient dry bulb temper ature : 15°C, R elative humidity - 60%. Ambient berometric pressure 1.0 kg/cm2. 38. Which parameters influence influence the heat r ate of gas turbines and how ? Ans: Various parameters affecting h eat rate of G T are : (i) Lower the gas turbine inlet temperature, lower the heat rate. (ii) Higher the compression ratio, lower the heat rate. (iii) Higher the turbine firing temperature, lower the heat rate. (iv) Lower the exhaust temperature, lower the heat rate. (v) Exhaust gas flow, inlet pressure loss, exhaust pressure loss also affect heat rate. 39. Which parameters influence the performance of gas turbines ? Ans: Ambient c onditions, inl et/exhaust pressur e losses, fuels, and wat er/steam injection flow rates'influence rates'in fluence the performance of gas turbines. 40. Why the efficiency of superheat Rankine cycle is higher than that of simple Rankine cycle ? Ans: Becaus e the mean t emperatur e of heat ad dition is hig her for su perheat c ycle. 41. A Carnot cycle is to be designed to attain efficiency of 0.75. If temperature of high temperature reservoir is 727°C, then low temperature reservoir will have to be maintained at______°C ? Ans: - 2°C. 42. A gas having a negative Joule-Thompson coefficient, when throttled, will become .... ? Ans: hott er. 43. What is boundary layer thickness in turbulent boundary layer ? Ans: In eas e of turbul ent bound ary layer, b oundary lay er thickness is defined as the dist ance from solid surface at which the fluid velocity is 99% of the undisturbed free stream velocity. Near the surface of solid, there is laminar flow which changes to buffer zone and finally turbulent region. 44. Stirling cycle with regenerative arrangement and Carnot cycle operate within same temperature limits. What can be said about thermal efficiencies of these two ? Ans: Thermal n of both will b e same. 45. How does the stagnation temperature behave along a streamline in adiabatic flow with friction ? Ans: It remai ns constant. 46. What is the frequency of secondary imbalance in four-stroke engine ? Ans: Two times t he engine s peed. 47. What would be the order of boundary layer in pipe flow (i) laminar (ii) transition, and (iii) fully turbulent ? Ans: In lamin ar flow, boun dary layer extends r ight from surf ace upto centre. In f ully turbulent it may extend 5-10% of radius only whereas in transition flow, boundary layer may be from 5060% of radius of pipe. 48. In general how the boundary layer and local film coefficient coefficient of heat transfer are r elated ? Ans: In g eneral, the thi nner the boundary l ayer, high er the valu e of local heat transf er film coefficient. 49. Out of constant volume and constant pressure line, which line on T-S diagram has higher slope ? Ans: Constant volume. 50. A heat engine and a refrigeration cycle operate between two temperature limits limits T1 and T2(T1 > T2). The product of efficiency of heat engine and COP of refrigeration cycle will be ? Ans: T2/TX. 51. A refrigerator and a heat pump are working on the reversed Carnot cycle between the same temperature limits. limits. How COP of r efrigerato efrigeratorr and heat pu mp related ? Ans: COP of r efrigerator = COP of h eat pump -1. 52. For a given set of operating pressure limits limits of a Rankine cycle, for which cycle the efficiency will be highest ? Ans: For reg enerative c ycle which ap proaches C arnot cycl e. 1 53. A steam pipe is to be insulated by two different insulating insulating materials of same thickness. What arrangement is preferred ? Ans: Materi al with lower th ermal conduct ivity should be used f or inner l ayer and mat erial with higher thermal conductivity for the outer layer. 54. Why steam is in open sp ace and water inside tube in condensers used in p ower plants ? Ans: Overal l heat transf er coefficient c an be incr eased by incr easing velocity of water in tube. Further steam needs more space due to higher specific volume. 55. A condenser of a refrigeration system rejects heat at a rate of 60 kW, while its compressor consumes a power of 15 kW. What will be the coefficient of performance of this system ? Ans: . 56. Why a refrigeration compressor designed to operate with R22 refrigerant can't be
operated with R12 ? Ans: Cond ensing pressur e of R22 at any given t emperatur e is higher than that of R12. 57. Leakage of Freon-12 refrigerant can not be easly detected, still it is preferred for airconditioning. Why ? Ans: Leakag e of Freon- 12 can't att ain total c oncentration but it h as all desirabl e characteristics characteri stics as good refrigerant. 58. In which season the process of humidification and in which season dehumidifi-cation is used in air-conditioning ? Ans: Humidific ation in summer and dehum idification in winter. 59. What is the name given to c ombined process of cooling and humidifying humidifying ? Ans: Evaporat ive Cooling. 60. Which refrigerant is used for ice plant and transport refrigeration ? Ans: Ammonia and CO2 r espectively. 61. Which cycle is used in vapour compression and gas cycle refrigerantion system ? Ans: Brayton c ycle, and Bell-C oleman cycle. 62. In what connection Wilson line and Willan's line used ? Ans: Wilson li ne repres ents saturati on line on t he Mollier diagram. W illan's line is conn ected with determination of frictional power in IC engines. 63. How the characteristics of fuel like front end volatility, mid-range volatility and tail end volatility affect S.I. engines ? Ans: These ch aracteristics affect SI engines in c old starting, icin g of carb urettor and dilution in crankcase respectively. 64. What would be the approximate air fuel ratio at time of cold start, part load operation, full load, and idling ? Ans: 10, 12.5 and 16 res pectively. 65. Name pressure compounded and velo velocity city compounded turbine. Ans: Rateau and Curtis r espectively. 66. What is the nature of c urve in case of transfer of heat b y conduction through a cylindrical wall and through a spherical wall ? Ans: Logar ithmic and h yperbolic. 67. What is radiosity ? Ans: It is th e rate at whic h radiation l eaves a s urface. 68. When the compressibility effects become significant in heat transfer problems in high speed flow ? Ans: Compressi bility effects us ually becom e signific ant at gas fl ow velocities greater th an 0.5 times the velocity of sound. 69. What is the name given to process of removing non condensables in steam and other vapour cycles ? Ans: Deaer ation proc ess. 70. We often come across use of jet pumps in process industry ? What is the reason for this ? Ans: Jet pu mps are eas y to maintain and can b e used to trans port gas es, liquids an d mixtures of both. 71. When it can be s aid that a fluid is Newtonian ? 9/24/13 Mechanical Engineering Engineering Interview Questions and Answers Set3 - Preparation for Engineering www.engineeringkings.com www.engineeringkings.com/2012/11/mechani /2012/11/mechanical-engineering cal-engineering-interview_48 -interview_4878.html 78.html 7/9 Ans: When th e shear str ess is direcl y proporti onal to velocity gradient . 72. Why alcohol can't be used in diesel engine ? Ans: Alcohol h as low cetan e number an d thus its i gnition is pr evented by c ompression. 73. Out of 2 stroke SI engine, 4 stroke SI engine, and 4 stroke CI engine, how the brake thermal efficiency efficiency behaves if these are to be used for road vehicle vehicles s? Ans: 4 strok e CI engin e has high est brake th ermal efficienc y followed b y 4 stroke SI engine and the 2 stroke SI has lowest brake thermal efficiency. 74. A jet engine is used to drive a vehicle. When its mechanical efficiency will be maximum ? Ans: It will b e maximum when vehicle speed approach es the relat ive velocity of gases at nozzle exit. 75. The knocking tendency in a S.I. engine can b e reduced by increasing ? Ans: Speed 76. How you define the emissivity of a body ? Ans: Emissivity of a body is th e ratio of t he emitted r adiant energ y flux densit y to the emit ted radiant energy flux density of a blackbody at the same temperature. 77. What is gray body ? Ans: When th e emissivity of m aterial does not chang e with temp eratur e, it is called gra y body. 78. Define fin efficiency for extended h eat transfer surfaces. Ans: Fin eff iciency is defin ed as the r atio of th e mean temper ature diff erence from sur face to fluid divided by the temperature difference from fin to fluid at the base or root of the fin. 79. What are the harmful effects of sulphur in coal used f or power generation ? Ans: Sulphur i n coal gi ves rise to n umber of ec ological prob lems rang ing from acid mine drainage to ash waste problems and air pollution due to SO2 emission. Emission of S02 is the cause of acid r ain and is r esponsible for severe environmental damage.
80. What do you understand by microbial desulphurisation ? Ans: Sulphur f rom coal can be removed by physic al, chemical and microbial meA ns: Microbial means has a number of advantages over other methods. Thiobalilius ferroxidans is the most widely used micro organism studied for coal desulphurisation. This bacteria can remove 90-98% of pyritic sulphur from coal. The reaction, of course, is slow and may take several days to several weeks t o complete the reaction. 81. What causes rotation of steam turbine rotor ? Ans: Rotation of turbin e rotor is c aused by centrif ugal f orce created d ue to chang e of direction of fast flowing jet of steam. 82. What do you und erstand by the term coagulation ? Ans: Impurities in water are usually in f inely divid ed state wh ich takes l ong time to s ettle and these usually pass through the filtering media. B y adding certain chemicals (coagulants), gelatinous gelatinou s substances are f ormed which cause small particles to c oale oalesce sce into groups large enough to be checked during filtering. 83. What is equivalent evaporation in a boiler plant ? Ans: It is th e amount of water th at would be e vaporated fr om water at 100°C to s team at 100°C by the same amount of heat which was actually absorbed by water and steam under operating conditions. 84. What is meant by balanced draft in boiler ? Ans: Balanc ed draft ref ers to combin ation of f orced and in duced dr aft fans c ontrolled to k eep the furnace under slightly vacuum condition. 85. How is dryness fraction of steam measured ? Ans: By using t hrottling c alorimeter. 86. What is th e difference between isentropic process and throttlinglprocess ? Ans: In isent ropic pr ocess, heat tr ansfer takes pl ace and in throttling process, en thalpy before and after the process is same. 87. What is th e difference between pyrometer, pyranometer and pyrheliometer. Ans: Pyromet er measures temperatur e by radi ation principl e. Pyranomet er is used t o measure total hemispherical solar solar r adiatio adiation. n. Pyrheliometer is used to measure beam intensity by collimating the radiation. 88. What is the name given to useful part of available energy which is available for conversion to useful work ? Ans: Exerg y. 89. Does the area on PV diagram for a process represent work for bo th reversible and nonreversible process ? Ans: No. Same is true f or only revers ible proc ess. 90. Why work is considered as high grade of energy and heat as low grade energy ? Ans: While work can b e completely c on¬verted to heat, heat can't be converted fully to wor k. 91. When coluomb friction comes into existence between two surfaces ? Ans: When th ere is relati ve motion bet ween them. 92. Under what condition a number of forces acting at a point are in equilibrium ? Ans: When su m of the r esolved par ts in any t wo perpend icular direc tions is zer o. 93. What happens to two equal and opposite coplanar couples ? Ans: They b alance eac h other. 94. To slide a heavy block over a rough floor by a rope with minimum force by a man, at what angle the rope should be inclined with the level of floor ? Ans: He sh ould incline t he rope with horizont al at angle of friction b etween fl oor and bl ock. 95. A body is dropped from a certain height. If same body were to move down a smooth inclined plane from same height, which parameters parameters will be same on r eaching the ground ? Ans: Velocity, kinetic en ergy and momentum. 96. A test specimen is stressed slightly beyond the yield point and then unloaded. What happens to its yield strength ? Ans: It will incr ease. 97. Out of circular, square, channel, I sections, which is most economical for a component subjected to bending ? Ans: I section. 98. What does the area under t he stress-strain curve represent ? Ans: Energ y required to cause f ailure. 99. A tension member of certain diameter is to be replaced by a square bar of the s ame material. Side of square compared to diameter will be ? Ans: Smaller. 100. A circular bar subjected to tension is designed for a particula particularr safety factor. If both load and diameter are doubled, then factor of safety will be _____? Ans: doubled 1. What is t he diff erence bet ween scaven ging and su perchargin g ? Ans: Scaven ging is proc ess of flushin g out burnt gases fr om engine cylin der by intr oducing supplying higher mass of air by compressing the atmospheric air. 2. What are the names given t o constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes.Ans: Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively.
3. In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and condenser pressure same, what will happen to dryness fraction of steam after expansion ?Ans: It will decrease. 4. Why entropy change for a reversible adiabatic process is zero ? Ans: Becaus e there is n o heat transf er in this proc ess. 5. What are two essential conditions of perfect gas ? Ans: It satisf ies equation of state and i ts specific h eats are c onstant. 6. Enthalpy and entropy are functions of one single parameter. Which is that ? Ans: Temper ature. 7. Why rate of c ondensatio ondensation n is higher on a polished surface compared to rusty surface ? Ans: Polished s urface pr omotes drop wise condens ation and d oes not w et the surf ace. 8. How much resistance is offered to heat flow by drop wise condensation ? Ans: Nil 9. What is the relationship between COP of heating and c ooling ? Ans: COP of h eating is one( unity) more t han COP of cooling. 10. How much is the work done in isochoric process ? Ans: Zero. 11. When maximum discharge is obtained in nozzle ? Ans: At the cri tical pressur e ratio. 1. Under what condition the work done in r eciprocatin eciprocating g compressor will be least ? Ans: It is least when compress ion process approach es isothermal. For this pur pose, attempts are made to cool the air during compression. 13. What is th e difference between stalling and surging in rotary compressions ? Ans: Stalling is a local ph enomenon an d it occurs when How br eaks away f rom the bl ades. Surging causes complete breakdown of flow and as such it affects the whole machine. 14. Why the electric motor of a fan with backward curved blades is never got overloaded under any condition ? Ans: The maxi mum power is c onsumed at ab out 70% of maximum flow in c ase'of fan wit h backward blades. For higher flow, power c onsumption gets lower. 15. Why the work per kg of air flow in axial flow compressor is less compared to centrifugal compressor for same pressure ratio ? Ans: Isentrop ic efficiency of axial fl ow compressor is higher. 16. What is the name given to portion of thermal energy to be necessarily rejected to environmentt ? environmen Ans: Anerg y. 17. What is pitting ? How it is c aused ? Ans: Non un iform corros ion over th e entire met al surface, b ut occurin g only in sm all pits is called pitting. It is caused by lack of uniformity in metal. 18. What is caustic embrittlement ? Ans: It is th e actual ph ysical chang e in metal th at makes it extr emely brittle and filled wit h minute cracks. It occurs particularly in the seams of rivetted joints and around the rivet holes. 19. Which impurities form hard scale and which impurities soft scale ? Ans: Sulphat es and chl orides of li me and magn esium form hard scale, an d carbon ates of lime and magnesium form soft scale. 20. What is the difference between hard water and s oft water ? Ans: Hard wat er contains excess of sc ale forming impuriti es and s oft water c ontains very little or no scale f orming substances. substances. 21. Which two elements in feed water can cause corrosion of tubes and plates in boiler ? ' Ans: Acid an d oxygen i n feed wat er lead to c orrosion. 22. What should be done to prevent a safety valve to stick to its seat ? Ans: Safety valve should be blown off periodic ally so that n o corrosion c an take place on valve and valve seat. 23. Why large boilers are water tube type ? Ans: Water t ube boilers raise steam f ast becaus e of large heat transfer area and p ositive water circulation. circulation. Thus they respond faster to fluctuations in demand. Further single tube failure does not lead to catastrophy. 24. What type of boiler does not n eed a steam drum ? Ans: Super-c ritical press ure boiler. 25. Why manholes in vessels are usually elliptical in shape ? Ans: Elliptic al shape has m inimum area of opening and thus pl ate is weaken ed the l east. Further it is very convenient to insert and take out the cover plate from elliptical opening. 26. Low water in boiler drum is unsafe b ecause it may result in overheating of water tubes in furnace. Why it is unsafe to have high water condition in boiler drum ? Ans: High dr um level does not allow st eam separat ion to b e effective an d some water c an be carried over with steam which is not desirable for steam turbine. 27. Why boiler is purged everytime before starting firing of fuel ? Ans: Purging ensures th at any unbur nt fuel in fur nace is remo ved, oth erwise it may l ead to explosion. 28. What is th e principle of mechanical refrigeration ? Axis. A volatile l iquid will boil under th e proper c onditions and in so d oing will abs orb heat fr om
surrounding objects. 29. Why high latent heat of vaporisat vaporisation ion is desirable in a r efrigeran efrigerantt ? Ans: A high l atent heat of vaporisati on of refri gerant res ults in small amount of r efrigerant and thus lesser circulation system of r efrigeran efrigerantt for same tonnage. 30. What is the critical temperature of a refrigerant ? Ans: Critical t emperature is the maximum t emperature of a refriger antrat whic h it can be condensed into liquid and beyond this it remains gas irrespective of pressure applied. 31. Maximum combustion temperature in gas turbines is of the order of 1100 to 10°C whereas same is around 00°C in I.C. engine ? Why ? Ans: High tem perature i n I.C. engi ne can be t olerated bec ause it las ts for a f raction of second but gas turbines have to face it continuously which metals can't withstand. 32. Why efficiency of gas turbines is lower compared to I.C. engines ? Ans: In g as turbines, 70% of the output of gas turbine is c onsumed b y compress or. I.C. engines have much lower auxiliary consumption. Further combustion temperature of I.C. engines is much higher compared to gas turbine. 33. What do you understand by timed cylinder lubrication ? Ans: For eff ective lubric ation, lub oil n eeds to be i njected bet ween tw o piston rin gs when piston is at bottom of stroke so that piston rides in oi during upward movement. This way lot of lub oil can be saved and used properly. 34. What is IIUCR in relation to petrol engine ? Ans: HUCR is h ighest us eful compress ion ratio at which the fu el can be us ed in a specif ic test engine, under specified operating c onditio onditions, ns, without kn ocking. 35. In some engines glycerine is used in place of water for cooling of engine. Why ? Ans: Glycerin e has b oiling point of 90°C which increases its heat c arrying capacit y. Thus weight of coolant gets reduced and smaller riadiator can be used. 36. Why consumption of lubricating oil is more in two-stroke cycle petrol engine than fourstroke cycle petrol engine ? Ans: In two-str oke engin e lub oil is mixed with petrol and thus s ome lub oil is blow n out through the exhaust valves by scavenging and charging air. There is no such wastage in four stroke petrol engine. 37. As compression ratio increases, thermal n increases. How is thermal n affected by weak and rich mixture strength ? Ans: Thermal n is high f or weak mixtur e and it decr eases as mixture str ength becomes r ich. 38. How engine design needs to be changed to burn lean mixture ? Ans: Engine t o burn lean mixture us es high c ompression rati o and th e highly tur bulent move¬ment move¬me nt of the ch arge is produced by the geometry of th e combustion chamber. 39. Horse power of I.C. engines can be expressed as RAC rating, SAE rating, or DIN rating. To which countries these standards belong ? Ans: U.K., USA and German y respecti vely. 40. What is the use of flash chamber in a vapour compression refrigeration refrigeration cycle to improve the COP of refrigeration cycle ? Ans: When li quid refriger ant as obt ained fr om condenser is throttled, there are s ome vapours. These vapours if carried through th e evaporator will not contribute to r efrigerati efrigerating ng effect. Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and f ed back to the c ompre ompression ssion process. The throttling process is then carried out in st ages. Similarly compression compression process is also d one in two s eparate compressorr stages. compresso 41. Why pistons are usually dished at top ? Ans: Pistons are usually hol lowed at t op to (i) pr ovide great er spa'e f or combustion, ( ii) increase increa se surface f or flue gases to act upon, and (iii) better distribution of stresses. 42. What is the function of thermostat in cooling system of an engine ? Ans: Thermost at ensures optimum cooling because excessive c ooling decr eases the o verall efficiency.. It allows cooling water to go to radiator beyond a predetermined temperature. efficiency 43. What are the c ause auses s of failure of boiler tubes ? Ans: Boiler tu bes, usual ly are mad e from carbon steel and are subj ect to (a) h igh rates of heat transfer, (b) bending stresses due to uneven heating, especially at expanded or welded joints into h eaders or dr ums, (c) ext ernal eros ion from bur ners and f lue gas, ( d) possibl e corrosion on the boiler side, and (e) occasional manufacturing defects. Failure Failu re may occur due to following reasons : (a) High thermal ratings may lead to rapid failure if the internal fluid flow is reduced f or any reason. The resultant overheating leads to a failure by creep, characterised by the bulging of the tube with the eventual development of a longitudinal split. (b) Fatigue cracking due to bending stresses occur. These are associated with change of section and/or weld undercut, where tubes are expanded or welded into headers. (c) Failure may arise due to overstressing of a reduced section of metal. (d) Sudden failure of the boiler tube due t o corrosion arises from embrittlement embrittlement of the carbon steel due to interaction between atomic hydrogen from the corrosion process and the iron carbide present in the steel. (e) Defects in tube manufacture, although far from being a regular occurrence, can be a cause of serious trouble. Lamination in boiler tubes or score marks arising from the cold
drawing of tubes, give rise to premature failure and may promote corrosion at these regions. 44. What are the c ause auses s of failure of superheater tubes ? Ans: Superh eater tub es are subj ected to t he most sever e combin ation of stress, temperatur e and corrosive environment. In addition to high-temperature strength, resistance to corrosion is also important. For example, low-alloy ferritic steel such as -1/% Cr, 1% Mo would not be used at metal temperatures above 580°C because of inadequate resistance to corrosion and oxidation over a full service life of 100,000/150,000 hr. Failures in superheater tubes may arise fr om : (a) Prior fabrication history (b) Faulty heat tr eatment (c) Consequences of welding (d) Overheating of the tube metal (e) Gas-side corrosion (f) Stress corrosion (austenitic steels). 45. Why supercritical boilers use less amount of steel compared to non-supercrit non-supercritical ical boilers ? Ans: Supercr itical boilers do not he ad heavy dr um for sep aration of st eam from mixtur e of water and steam. 46. Out of electric heater and heat pump, which is economical in operation ? Ans: Heat p ump. 47. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag? Ans: Cyclon e furnace. 48. How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ? Ans: Ratio of t heir thickn ess = (Prandt l number)-1/ 3. 49. What is the effect of friction on flow of steam through a nozzle ? Ans: To decr ease both mas s flow rat e and wetn ess of steam. 50. Why gas turbine power plant needs efficient compressor ? Ans: Becaus e a large portion of tur bine work is eaten awa y by compress or and its inefficiency will affect net power output and cost of generation. 51. Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon ? Ans: Liquid hydrogen has higher burning velocity. 52. Why axial flow compressor is preferred for gas turbines for aeroplanes ? Ans: Becaus e it has low f rontal ar ea. 53. What is the effect of inter cooling in gas turbines ? Ans: It decr eases therm al efficienc y but increases net outp ut. 54. Why iso-octane is chosen as reference fuel for S.I. engine engines s and a llotted 100 value for its octane number ? Ans: Iso- octane permits highest c ompression wit hout causin g knocking. 55. Why thermal efficiency of I.C. engines is more than that of gas t urbine plant ? Ans: In I.C. engine maximu m temperatur e attained is higher th an in gas tur bine. 56. Which are the reference fuels for knock rating of S.I. engines ? Ans: n-hept ane and I SO-octane. 57. When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle ? Ans: Temper ature incr eases and pr essure d ecreases. 58. Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called ? Ans: Intensi ve propert ies. 59. The amount of radiation emitted per scm per sec is called .... ? Ans: Emissive p ower. 60. In c onvectio onvection n heat transfer, if heat flux intensity is doubled t hen temperature difference between solid surface and fluid will ? Ans: Get dou bled. 61. How you can define coal ? Ans: Coal is a naturally occurring h ydrocarb on that cons ists of the f ossilised remai ns of buried plant debris that have undergone progressive physical and chemical alteration, called coalification, in the course of geologic time. 62. Which pollutant is major greenhouse gas and what is its effect ? Ans: CO is maj or greenh ouse gas an d it traps th e radiati on of heat fr om the sun w ithin earth's atmosphere. 63. In order to increase efficiency and reduce CO emissions and other emissio emissions, ns, clear coal technologies are receiving major attention. What are these ? Ans: (i) Ad vanced pul verised and pressuris ed pulveris ed fuel combus tion. (ii) Atmospheric fluidised bed combustion and pressurised fluidised bed combustion. (iii) Supercritical boilers. (iv) Integrated gasification combined c ycle systems. (v) Advanced integrated gasification, including fuel cell systems. (vi) Magneto hydrodynamic electricity generation. 64. What are t he important operational performance parameters in design of fuel f iring equipment ? Ans: Fuel fl exibility, electric al load followi ng capabil ity, reliabilit y, availabilit y, and mainten ance ease.
65. What is the differenc between total moisture and inherent moisture in coal ? Ans: The moist ure cont ent of the bul k as sampl ed is referr ed to as tot al moisture, and that of the air dried sample is called inherent moisture. 66. Proximity analysis of coal provides data for a first, general assessment of a coal's quality and type. What elements it reports ? Ans: Moisture, volatile matter , ash and f ixed carb on. 67. Ultimate analysis of coal is elementary analysis. What it is concerned with ? Ans: Carbon , hydrog en, nitrog en, and sulp hur in c oal on a weigh t percent age basis. 68. Explain the difference between AFBC, BFBC, PFBC and PCFB in regard to fluidised bed technologies. Ans: AFBC (Atmos pheric fluidis ed bed c ombustion) pr ocess consists of forming a bed of in ert materials like finely sized ash or ash mixed with sand, limestone (for sulphur removal), and solid fuel particles particles in a c ombustor and fluidising fluidising it by f orcing combustion combustion air up through the bed mixture. The gas flows thorugh bed without disturbing particles significantly but gas velocity is high enough to support the total weight of bed (fluidisation). At slightly higher velocity excess gas passes through the bed as bubbles (fluidised bed) and gives the bed the appearance of a boiling liquid. Bubbling fluidised bed combustion (BFBC) has a defined height of bed material and operates at or near atmospheric pressure in the furnace. Pressurised Pressuri sed fluidised bed c ombustio ombustion n (PFBC) system operates the bed at elevated pressure. Exhaust gases have sufficient energy to power a gas turbine, of c ourse, gases need to be cleaned. In fluidised combustion, as ash is removed s ome unburned carbon is also removed resulting in lower efficiency. In circulating fluidised bed combustion (CFBC) system, bed is operated at higher pressure leading to high h eat transfer, higher combustion efficiency, and better fuel feed. Circulating fluidised beds operate with relatively high gas velocities and fine particle sizes. The maintenance of steady state conditions in a fast fluidised bed requires the continuous continuou s r ecycle of particles removed by the g as stream (circulating bed). The term circulating bed is often used to include fluidised bed sys¬tems containing multiple conventional bubbling beds between which bed material is exchanged. 69. What for Schmidt plot for is used in h eat transfer problems ? Ans: Schmidt p lot is a grap hical method for deter mining the temp erature at an y point in a body at a specified time during the transient heating or cooling period. 70. In which reactor the coolant and moderator are the s ame ? Ans: Pressuris ed water r eactor. 71. Which reactor has no moderator ? Ans: Fast br eeder react or. 72. What are thermal neutrons ? Ans: Thermal n eutrons ar e slow neutr ons (having energy bel ow 1 eV) whic h are in th ermal equilibrium with their surroundings. 73. What is big advantage of fast breeder r eactor ? Ans: It has r apid self br eeding of fis sile fuel duri ng the op eration of the react or, and thus, it offers about sixty times the output with same natural uranium resources through ordinary nonbreeder nuclear reactor. 74. What is the purpose of biologica biologicall shield in nuclear plants ? Ans: Biologic al shield of h eavy concr ete prevents exposure to neutrons , beta rays and gamma rays which kill living things. 75. Which two elements have same percentage in proximate and ultimate analysis of coal? Ans: Moisture and ash. 76. On which analysis is based the Dulong's formula for the heating value of fuel ? Ans: On ultim ate analysis. 77. Which element causes difference in higher and lower heating values of fuel ? Ans: Hydrog en. 78. Which heating value is indicated by a calorimeter and why ? Ans: Gross heating valu e because st eam is cond ensed and h eat of vapour formed is recovered. 79. State the difference between ultimate and proximate analysis of coal ? Ans: In ultimat e analysis, c hemical det ermination of following elements is mad e by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S. In proximate analysis following constituents are mechanically determined by weight. Moisture, volatile matter, fixed carbon and ash. Heating value is due to fixed carbon and volatile matter. 80. What is fuel ratio ? Ans: Fuel rati o is the rati o of its % age of fixed c arbon to v olatile matter. 81. How the analyses and calorific values of fuels can be reported ? Ans: It may be r eported as (a) as received or fired (wet) basis (b) dry or moisture free basis (c) combustible or ash and moisture free basis 82. What is th e difference between nuclear fission and fission chain reaction. Ans: The proc ess of splitt ing of nucl eus into two almost equal f ragments accompanied by
re¬lease of heat is nuclear fission. Self sustained, continuing, continuing, sequence of fission reactions in a con¬trolled manner is fission chain reaction. 83. Explain difference between fissile and fertile materials. Ans: The materi als which c an give nuclear fission e. g. U 35, Pu 39, U 33 are fissile materi¬als. Fertile material itself is not fissionable, but it can be converted to a fissionable material by irradiation of neutrons in a nuclear reactor. 84. What do you und erstand by fuel cycle in nuclear plants ? Ans: Fuel cycle a series of s equential steps involved in su pplying fu el to a nucl ear power reactor. The steps include : Mining, refining uranium, fabrication of fuel elements, their use in nuclear reactor, chemical processing to r ecover remaining fissionable material, re-enrichment of fuel from recovered material, refabrication of new fuel elements, waste storage etc. 85. What is heavy water and what is its use in nuclear plants ? Ans: Water c ontaining h eavy isotopes of hydrogen (D euterium) is k nown as h eavy water . Heavy water is used as a moderator. Heavy water has low cross section for absorption of neutrons than ordinary water. Heavy water slows down the fast neutrons and thus moderates the chain r eaction eaction.. 86. What is a c onverter reactor ? Ans: A react or plant which is design ed to prod uce more fu el than it c onsumes. Th e breeding is obtained by converting fertile material to fissile material. 87. Explain nuclear reactor in brief. Ans: A plant which initiates , sustains , controls and maintains nuclear f ission chain r eaction and provides shielding against radioactive radiation is nuclear reactor. 88. What is th e difference between conversion and enrichment ? Ans: The proc ess of c onverting the non fissile U 38 to fissile U -35 is als o called "Con version". The material like U 38 which can be converted to a fissile material by the neutron flux is called "fertile material". material". The conversion is obtained within the nuclear reactor during the chain reaction. Enrichment is the process by which the proportion of f issile uranium isotope isotope (U-35) is increased above 0.7% (original % in natural uranium). The concentration of U-35 in the uranium hexafluoride is increased from the 0.7% in natural uranium to to 4%. This is called enrichment and is accomplished in an enrichment plant. 89. Disposal of radioactive waste materials and spent fuel is a major and important technology.. How the waste radioactive material is disposed off ? technology Ans: Nonus able fission pr oducts are r adioactive an d take sh ort/medium/lon g time for radioactive decay to reach safe level of radioactivity. Accordingly three methods of disposal are : (a) Zero or low radioactivity material is dispersed or stored without elaborate shielding. (b) Medium radioactivity material is stored for short duration of about 5 years to allow decay of radioactivity. (c) High radioactive material. They are stored in water for several months to permit radioactive decay to an accepetable low level. 90. Which nuclear reactor uses water as a c oolant oolant,, moderator and reflector ? Ans: Pressuris ed water reac tor. 91. Which reactor produces more fissionable material material than it consume consumes s? Ans: Breeder reactor. 92. Which reactor uses natural uranium as fuel ? Ans: Gas c ooled reac ator. 93. Which reactor uses heavy water as moderator ? Ans: CANDU. 94. Which reactor requires no moderator ? Ans: Breeder reactor. 95. Which reactor uses primary coolant as fluoride salts of lithium, beryllium, thorium and uranium ? Ans: Molten s alt breeder reactor. 96. Why an increase in area is required to produce an increase of velocity in case of supersonic flow ? Ans: Incr ease in area f or increase i n velocity f or supers onic flow is r equired bec ause the density decreases faster than velocity increases at supersonic speeds and to maintain continuity of mass, area must increase. 97. Under what circumstances would there be an increase in pressure in a diver¬gent nozzle ? Ans: For subs onic flow at inl et section of a diffus er a lower vel ocity and hi gher pr essure will exist at the exit section. For supersonic isentropic flow at the inlet section a higher velocity and lower pressure will exist at the exit but if a shock wave occurs in the diffuser then a higher pressure will exist at the exit. 98. Why water can't be used as refrigerant for small refrigerating refrigerating equipment ? Ans: The r efrigerant sh ould be such that vapour volume is l ow so that pu mping work will be low. Water vapour volume is around 4000 times compared to R- f or a given mass. 99. Which parameter remains constant in a throttling process ? Ans: Enth alpy. 100. What is the difference between isentropic process and throttlinglprocess throttlinglprocess ?
Ans: In isent ropic pr ocess, heat tr ansfer tak es place and in throttling process, en thalpy before and after the process is same.
