Chapter 5, Problem 5.39P

A heat pump maintains a dwelling at 68°F. When operating steadily, the power input to the heat pump is 7 hp, and the heat pump receives energy by heat transfer from 55°F well water at a rate of 500 Btu/min.(a) Determine the coefficient of performance.(b) Evaluating electricity at $0.08 per kW · h, determine the cost of electricity in a month when the heat pump operates for 300 hours.

An ordinary household refrigerator receives electrical work from its surroundings while discharging energy by heat transfer to its surroundings. Is this a violation of the Kelvin-Planck statement? Explain. Discuss about factors causing irreversibility.

By removing energy by heat transfer from a room, a window air conditioner maintains the room at 20°C on a day when the outside temperature is 28°C.(a) Determine, in kW per kW of cooling, the minimum theoretical power required by the air conditioner.(b) To achieve required rates of heat transfer with practical sized units, air conditioners typically receive energy by heat transfer at a temperature below that of the room being cooled and discharge energy by heat transfer at a temperature above that of the surroundings. Consider the effect of this by determining the minimum theoretical power, in kW per kW of cooling, required when TC = 16°C and TH = 32°C, and determine the ratio of the power for part (b) to the power for part (a).

Two reservoirs maintained at 600°F and 50°F are used to operate a Carnot engine. The rate of work done by the engine is 6.23 Btu/s. Determine the heat loss at 50°F in Btu/s.

A heat pump is used to extract heat from the outside atmosphere to heat the inside of a building. On a day when the outside air temperature is Tc°C, the heat pump is operating to a COP of 2.7, maintaining the inside temperature of the building at Th°C. If the building is losing heat at the rate of 62,893 kJ/hour in these conditions, determine how much power (kW) must be supplied to a heat pump.

Two identical metal blocks of mass 20 kg and specific heat 0.4 kJ/kg are at an initial temperature of 50 degree Celsius .A reversible refrigerator receives heat from one block and rejects heat to the other. Find the work required by the refrigerator to cause a temperature difference of 150 degree Celsius between the two blocks.

(b) A heat engine with a thermal efficiency of 40 percent rejects 1000 kJ/kg of heat. Determine the amount of heat it receives.

A household refrigerator with a COP of 1.25 removes heat from the refrigerated space at a rate of 90kJ/min Determine (a) the electric power consumed by the refrigerator and (b) the rate of heat transfer to the kitchen air.

In a given process, a heat engine requires 2500J of energy and exhausts 1200J of heat. What is its efficiency?