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Quick revision for iit jee physics chapters
1
ME 361 Fall 2012
Exam 3
Solution
11/19/2012
Problem 1 (10 pts) Refrigerant-134a enters an adiabatic compressor compressor as saturated vapor at 0.24 MPa at a rate of 2 kg/s, and exits at 1.2 MPa and 80C. Find the rate of entropy generation in the turbine. Solution
Problem 2 (15 pts). Liquid kerosene with a specific heat of 2.0 kJ/kg. C enters an adiabatic piping system at 15 at a rate of 3 kg/s. The water temperature rises by 0.8 C during flow due to friction. Find the rate of entropy generation in the pipe.
Problem 3 (15 pts) Refrigerant-134a enters an adiabatic turbine steadily at 40C and 900 kPa, and leaves at 140 kPa. Find the highest possible percentage of mass of R134a that condenses at the turbine exit and leaves the turbine as a liquid. Solution The percentage of mass of R134a condensing in this case will be highest for the isentropic process,
The highest possible percentage of mass of R134a condensing in this case will be 1.42 %
Problem 4 (15 pts) Refrigerant-134a expands in an adiabatic turbine from 1.0 MPa and 45C to a pressure of 120 kPa at a rate of 3 kg/s. Find the maximum power output of the turbine. Solution The power output of the turbine will be maximum for the isentropic process,
Problem 5 (15 pts) The temperature of a cold orange with an average mass of 0. 3 kg and average specific heat of 3.42 kJ/kg. C rises from 5C to 25C as a result of heat transfer from the surrounding air. What is the entropy change of the orange. Solution
Problem 6 (15 pts) Argon gas (k = Cp /Cv = 1.667) is compressed from 100 kPa and 15 C to a pressure of 900 kPa adiabatically. Find the lowest temperature of argon after compression. Solution The exit temperature will be lowest for isentropic compression,
Problem 7 (15 pts) Consider a Carnot heat engine and a refrigerator operating between the same two thermal energy reservoirs. The thermal efficiency of the heat engine is 0.80. What is the COP of the refrigerator? Solution
Extra credit problem 1 (20 points) Ideal gas undergoes a cycle which consists of isoentropic, isothermal, and isobaric process, as shown in Fig. 1. Express the cycle efficiency through = T2 /T1.
O l l pc w p b S(T) = αT w α w constant. As the result of the process the temperature of the gas changes from T1 to T2 . Find specific heat C associated with this process as a function of T. Express the amount of heat Q absorbed by the gas α T1 and T2.