Chapter 15: Q27CQ (page 549)
Can you cool a kitchen by leaving the refrigerator door open?
Short Answer
No, it is not possible to make a kitchen cool by leaving the door of a refrigerator open.
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Chapter 15: Q27CQ (page 549)
Can you cool a kitchen by leaving the refrigerator door open?
No, it is not possible to make a kitchen cool by leaving the door of a refrigerator open.
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An ideal heat pump is being considered for use in heating an environment with a temperature of 22.0ºC . What is the cold reservoir temperature if the pump is to have a coefficient of performance of 12.0?
What is the change in internal energy of a car if you put 12.0 gal of gasoline into its tank? The energy content of gasoline is 1.3×108 J/gal. All other factors, such as the car’s temperature, are constant.
(a) What is the hot reservoir temperature of a Carnot engine that has an efficiency of \({\bf{42}}{\bf{.0\% }}\)and a cold reservoir temperature of \({\bf{27}}{\bf{.0}}\;{\bf{^\circ C}}\)? (b) What must the hot reservoir temperature be for a real heat engine that achieves \({\bf{0}}{\bf{.700}}\) of the maximum efficiency, but still has an efficiency of \({\bf{42}}{\bf{.0\% }}\) (and a cold reservoir at \({\bf{27}}{\bf{.0}}\;{\bf{^\circ C}}\))? (c) Does your answer imply practical limits to the efficiency of car gasoline engines?
Why—other than the fact that the second law of thermodynamics says reversible engines are the most efficient—should heat engines employing reversible processes be more efficient than those employing irreversible processes? Consider that dissipative mechanisms are one cause of irreversibility.
Which cyclical process represented by the two closed loops, ABCFA and ABDEA, on the PV diagram in the figure below produces the greatest net work? Is that process also the one with the smallest work input required to return it to point A? Explain your responses.

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