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Exam 6: The Second Law of Thermodynamics

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Question 1

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Consider a Carnot heat engine and a refrigerator operating between the same two thermal energy reservoirs. If the thermal efficiency of the heat engine is 0.80, the COP of the refrigerator is

A) 1.25
B) 0.20
C) 0.25
D) 0.80
E) 2.50

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Question 2

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A Carnot heat pump supplies heat to a house at a rate of 48000 kJ/h to maintain its temperature constant at 20°C. If the temperature of the outdoors is 5°C, the power required to operate this heat pump is

A) 0.68 kW
B) 10 kW
C) 13 kW
D) 26 kW
E) 0.72 kW

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Question 3

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A refrigerator with an average COP of 2.8 is used to cool a well-insulated container whose contents are equivalent to 12 kg of water from 40°C to 10°C. When running, the refrigerator consumes 400 W of electric power. The length of time the refrigerator must run to accomplish this cooling is

A heat pump absorbs heat from the cold outdoors at 3°C and supplies heat to a house at 20°C at a rate of 30,000 kJ/h. If the power consumed by the heat pump is 3 kW, the coefficient of performance of the heat pump is

A refrigerator that consumes 3 kW of electricity when running and has a coefficient of performance of 1.5 is placed in a well-sealed room, and is plugged in with its door open. The rate of cooling or heating this refrigerator will provide to the air in the room when running is

A heat engine operates between the temperature limits of 1200°C and 300°C. If heat is supplied to the heat engine at a rate of 200 kJ/s, the maximum power output of this heat engine is

An air-conditioner is removing heat from a room at 20<°C at a rate of 9000 kJ/h and rejecting the waste heat to the outdoors at 35°C. If the coefficient of performance of the air-conditioner is 3, the power consumed by the air-conditioner is

A heat engine cycle is executed with steam in the saturation dome. The pressure of steam is 2 MPa during heat addition, and 0.1 MPa during heat rejection. The highest possible efficiency of this heat engine is

A heat engine receives heat from a source at 800°C and rejects the waste heat to a sink at 40°C. If heat is rejected from this engine at a rate of 80 kJ/s, the maximum power this heat engine can produce is

Air is flowing steadily through a cooling section where it is cooled from 30°C to 15°C at a rate of 0.25 kg/s. If the average COP of the air-conditioner is 2.8 and the unit cost of electricity is $0.07 per kWh, the cost of electricity consumed by this air-conditioner per day (a period of 24 hours) is

An air conditioner running with R-134a on a cycle executed under the saturation dome between the pressure limits of 0.8 MPa and 0.12 MPa. The maximum Coefficient of Performance of this heat pump is

The hot water needs of an office are met by heating tab water by a heat pump from 16°C to 50°C at an average rate of 0.2 kg/min. If the COP of this heat pump is 2.8, the required power input is

A heat pump cycle is executed with R-134a under the saturation dome between the pressure limits of 1.6 MPa and 0.2 MPa. If the power consumption of the heat pump is 4.2 kW, the maximum rate of heat supply to the heated space is

An air-conditioner with an average COP of 2.5 consumes 15 kWh of electricity during a certain day. The amount of heat removed by this air-conditioner that day is