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If a 35.0%-efficient Carnot heat engine (Fig. 21.2) is run in reverse so as to form a refrigerator (Fig. 21.4), what would be this refrigerator’s coefficient of performance? Figure P21.2 Schematic representation of a heat engine. Figure P21.4 Schematic representation of a heat pump.

 

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Kath
KathLv10
8 Dec 2020

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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

A. Consider two arbitrary heat engines. Engine A hasanefficiency of 60%. Engine B absorbs the same amount ofheat from theheat reservoir as Engine A; however, it exhauststwice as much heatto the cold reservoir as Engine A. Findthe efficiency of EngineB.


B. Consider a nonreversible heat engine that operatesbetweentemperatures Th and Tc, whereTc =1/3 Th. The engine absorbs anamount of heatQh from the heat reservoir in order to doan amount ofwork W.

1) If the engine discards an amount of heat Qc= 3/5Qh to the cold reservoir, determine the efficiencyofthis engine.

2) How much work, in terms of Qh, would beavailableto a Carnot heat engine operating between the same twotemperatures?What would the efficiency of this Carnot enginebe?



C. A freezer with a coefficient of performance of 4 isused toconvert 2kg of water to ice in one hour. The waterstarts at atemperature of 20°C, and the ice that is producedis cooled to atemperature of -5°C.

1) How much heat must be removed from the water for thisprocessto occur?

2) How much electrical energy does the freezer use duringthishour of operation?

3) How much heat is discarded into the room that housesthefreezer?

A. Consider two arbitrary heat engines. Engine A hasanefficiency of 60%. Engine B absorbs the same amount ofheat from theheat reservoir as Engine A; however, it exhauststwice as much heatto the cold reservoir as Engine A. Findthe efficiency of EngineB.


B. Consider a nonreversible heat engine that operatesbetweentemperatures Th and Tc, whereTc =1/3 Th. The engine absorbs anamount of heatQh from the heat reservoir in order to doan amount ofwork W.

1) If the engine discards an amount of heat Qc= 3/5Qh to the cold reservoir, determine the efficiencyofthis engine.

2) How much work, in terms of Qh, would beavailableto a Carnot heat engine operating between the same twotemperatures?What would the efficiency of this Carnot enginebe?


C. A freezer with a coefficient of performance of 4 isused toconvert 2kg of water to ice in one hour. The waterstarts at atemperature of 20°C, and the ice that is producedis cooled to atemperature of -5°C.

1) How much heat must be removed from the water for thisprocessto occur?

2) How much electrical energy does the freezer use duringthishour of operation?

3) How much heat is discarded into the room that housesthefreezer?

A heat pump delivers 20 kW to heat a house.
The outside temperature is -25C and the
inside temperature of the hot-air supply for
the heating fan is 50C.
What is the coefficient of performance of a
Carnot heat pump operating between these
temperatures?

B) Find the minimum power of the engine needed
to run the heat pump.
Answer in units of kW.

C) If the COP of the heat pump is 40% of its
Carnot value, what is the minimum power of
the engine?
Answer in units of kW.

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