Homework Problems
1 The radiator of a steam heating system has a volume of 20 L and is filled with superheated water
at vapor at 200 kPa and 150oC. At this moment both the inlet and exit valves to the radiator are
closed. After a while the temperature of the steam drops to 40oC as a result of heat transfer to
the room air. Determine the entropy change of the steam during this process in kJ/K.
2 A well insulated rigid tank contains 2 kg of a saturated liquid-vapor mixture of water at 100 kPa.
Initially, three quarters of the mass is in the liquid phase. An electrical resistance heater placed in
the tank is now turned on and kept on until all the liquid in the tank is vaporized. Determine the
entropy change of the steam during this process.
3 A piston-cylinder device contains 2 lbm of refrigerant-134a at 120 psia and 100oF. The refrigerant
is now cooled at constant pressure until it exists as a liquid at 50oF. Determine the entropy
change of the refrigerant during this process.
4 An insulated piston-cylinder device contains 0.05 m3 of saturated refrigerant 134a vapor at 0.8
MPa pressure. The refrigerant is now allowed to expand in a reversible manner until the pressure
drops to 0.4 MPa. Determine (a) the final temperature in the cylinder and (b) the work done by
the refrigerant.
5 A piston-cylinder device contains 1.2 kg of saturated water vapor at 200oC. Heat is now
transferred to the steam and the steam expands reversibly and isothermally to a final pressure of
800 kPa. Determine the heat transferred and the work done during this process.
6 A 50-kg copper block, initially at 80oC, is dropped into an insulated tank that contains 120 L of
water at 25oC. Determine the final equilibrium temperature and the total entropy change for this
process.
7 An insulated piston-cylinder device contains 0.05 m3 of saturated refrigerant 134a vapor at 0.8
MPa pressure. Find the maximum work that can be done if the refrigerant expands to a pressure
of 0.4 MPa in an adiabatic process.
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