Question:

Problem 1 (10 pts)

An insulated piston-cylinder device contains 0.05 m3 of R-134a at 0.8 MPa and initially as a saturated vapor. The R-134a is then allowed to expand until the pressure drops to 0.4 MPa. If the specific entropy does not change during the process, determine the final temperature in ◦C and the work done in kJ.

Problem 2 (10 pts)

Consider a Carnot heat-engine cycle using water as the working fluid and operating in a closed-piston cylinder. The cycle has a thermal efficiency of 30% and the water changes from saturated liquid to saturated vapor at 250◦C during the heat addition process. Draw this cycle on a T − ν diagram with respect to the saturation curve and indicating all heat transfers, the temperature of the cold thermal reservoir in ◦C, the net work output of this engine in kJ/kg, the amount heat supplied in kJ/kg, and the amount of heat rejected in kJ/kg.

Problem 3 (10 pts)

a) (2 pts) What is the maximum possible thermal efficiency of a heat engine operating between thermal reservoirs at 33◦C and 400◦C?

b) (3 pts) Is it possible for a heat pump to have a Coefficient of Performance of 5 and operate between thermal reservoirs at 250 K and 330 K? Justify your answer.

c) (3 pts) Two reversible heat engines operate between the same two thermal reservoirs. Heat engine A has a thermal efficiency of 0.30. Heat engine B has a heat input rate of 100 kW. Determine the power output of heat engine B.

d) (2 pts) What is the lowest TH for a refrigerator with a COP of 4, assuming that TL = 273 K?

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