HW 9 - Due Wednesday, April 1

ME 200 Homework #09 - Spring 2015
Homework Due: Wednesday, April 1, 2015
HW09(1)
During the isothermal heat addition process of a Carnot cycle, 900 kJ of heat is added to the
working fluid from a source at 400 oC. Determine:
(a) The entropy change of the working fluid;
(b) The entropy change of the source;
(c) The total entropy change for the process. (Answer: 0 kJ/K)
HW09(2)
The radiator of a steam heating system has a volume of 20 L, and is filled with superheated water
vapor at 150 kPa and 200 oC. At this moment,both the inlet and the exit valves to the radiator are
closed. After a while the temperature of the steam drops to 80 oC as a result of heat transfer to
the room air. Determine the entropy change of the steam during this process, in kJ/K.
(Answer: -0.0526 kJ/K)
HW09(3)
Two large bodies, one at a temperature 50 oF and the other at 400 oF, are exchanging heat at a
rate of 13500 Btu/h. Assuming the temperatures are uniform throughout each body and don’t
change during the process, compute the entropy change per second of
(a) The warmer body,
(b) The cooler body,
(c) A system comprised of the warmer and cooler body. (Answer: 10.77 Btu/h·oR)
HW09(4)
A 18 ft3 rigid tank contains refrigerant-134a initially at 30 psia and 40 percent quality. Heat is
transferred now to the refrigerant from a source at 100 oF until the pressure rises to 60 psia.
Determine:
(a) The entropy change of the refrigerant;
(b) The entropy change of the heat source;
(c) The total entropy change for this process. (Answer: 0.254 Btu/oR)
HW09(5)
Argon in a piston-cylinder assembly is compressed from state 1, where T1 = 540 oR, V1 = 35 ft3,
to state 2, where T2 = 360 oR. If the change in specific entropy is s2 – s1 = -0.0645 Btu/lbm·oR,
determine the final volume, in ft3. Assume the ideal gas model with k =1.67. (Answer: 17.5 ft3)
1
HW#9(6)
An insulated rigid tank initially contains 2.7 kg of carbon dioxide gas at 100 kPa and 27C. A
rotating paddle wheel adds 200 kJ of work into the system.
Assume that specific heats for carbon dioxide are constant at their 27C values.
(a) What is the final temperature (C) of carbon dioxide?
(b) Calculate the entropy change (kJ/K) for carbon dioxide during this process.
(Answer: 0.566 kJ/K)
Now consider that specific heats for carbon dioxide are not constant.
(c) What is the final temperature (C) of carbon dioxide?
(d) Determine the entropy change (kJ/K) for carbon dioxide during this process.
(Answer: 0.570 kJ/K)
HW09(7)
A 12 kg iron block initially at 350 oC is quenched in an insulated tank that contains 100 kg of
water at 22 oC. Assuming the water that vaporizes during the process condenses back in the tank,
determine the total entropy change during this process. (Answer: 1.95 kJ/K)
HW09(8)
An inventor claims that the device shown in the figure
generates electricity while receiving a heat transfer at
the rate of 250 Btu/s at a temperature of 500 oR, a
second heat transfer at the rate of 350 Btu/s at 700 oR,
and a third at the rate of 500 Btu/s at 1000 oR. For
operation at steady state, evaluate this claim
2