EGR 334: Thermodynamics Review Problems Solutions

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Problem 1) A reversible power cycle operates between a thermal reservoir at 1540°F and 40°F.
a) What is the maximum thermodynamic efficiency of the cycle?

1. b) This cycle is found to have Wcycle = 50 Btu, what is Qout?

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Problem 2) An inventor claims to have devised a refrigeration cycle that at steady state requires a net power input of 0.8 hp to remove 13,000 Btu/hr of energy by heat transfer from the freezer compartment at -10°F and discharge energy by heat transfer to a kitchen at 65°F.
a) What is the maximum thermodynamic coefficient of performance for the cycle?

1. b) Is this process thermodynamically possible? Why or why not?

Problem 3) One kilogram of water executes a Carnot power cycle. The following table describes the thermodynamic cycle.

1. a) Complete the following tables
 State 1 2 3 4 Process Q (kJ) W (kJ) p (bar) 40 40 1.5 1.5 1 – 2 T (°C) 2 – 3 x 0.15 1 0.801 0.32 3 – 4 v (m3/kg) 4 – 1 u (kJ/kg) s (kJ/kg-K)

1. b) Draw the cycle on the p-v and T-s diagrams.

Problem 4) A 2 m3 ridged, insulated container is filled with 4.76 kg of air and fitted with a paddle wheel. The container and its contents are initially at 293 K. The paddle wheel does 710 kJ of work on the air. Treat the air as an ideal gas with cv = 0.72 kJ/kg·K.

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1. a) What is the initial pressure?

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1. b) What is the final temperature?

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1. b) How much entropy is produced?

Problem 5) Steam enters a turbine operating at steady state at 6 MPa, 600°C with a mass flow rate 125 kg/min and exits as a saturated vapor at 20 kPa. The turbine produces energy at a rate of 2 MW. Kinetic and potential energy effects are negligible. The rate of heat loss from the turbine occurs to the air around the turbine at 27°C.

1. a)   What the rate of entropy production for within the turbine?
2. b)   What is the isentropic efficiency of the turbine?

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