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Two refrigerators M and N operate in series. The refrigerator M absorbs energy at the rate of 1 kW from a body at temperature 400 K and rejects energy as heat to a body at a temperature T. The refrigerator N absorbs the same quantity of energy which is rejected by the refrigerator N from the body at temperature T, and rejects energy as heat to a body at temperature 800 K. If both the refrigerators have the same C.O.P., what is the value temperature T?

Correct Answer: 565.68 K
GiveT1 = 400 K, T2 = 800 K, C.O.P. of M = C.O.P. of N C.O.P. of refrigerator M = T1 / (T2 − T1) = 400 / (T − 400) C.O.P. of refrigerator N = T1 / (T2 − T1) = T / (800 − T) Equating both the C.O.P. we get, 400 / (T − 400) = T / (800 − T) T2 = 400 x 800 T = √320000 T = 565.68 K.

A Carnot heat engine receives heat at 750 K and rejects the waste heat to the environment at 300 K. The net work output of the heat engine is used to drive a Carnot refrigerator, whose COP is 6.14. If the heat removal rate from the refrigerated space is 6.6 kW, determine the rate of heat supply to the heat engine?

A Korean refrigerator is bought to maintain the cool space at 8°C and a Japanese refrigerator is bought to main the cool space at -20°C in a laboratory room having constant temperature of 25°C. If the both refrigerators run on a reversed Carnot cycle, state the refrigerator that delivers maximum COP.

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are

Which of the following statements are true/false?
1. A minimum rate of wages for the time spent by employees for the production of output is minimum time rate.
2. Minimum piece rate is the rate based on the quantity of the output employees have produced.
3. The guaranteed time rate is a minimum rate of remuneration to apply in the case of employees employed on piece work for the purpose of securing to such employees a minimum rate of wages on a time work basis.
4. A minimum rate of remuneration to apply in the case of employees employed on piece work for the purpose of securing to such employees a minimum rate of wages on a time work basis is overtime rate.

The food compartment of a refrigerator is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2kW, determine the rate of heat rejection to the room that houses the refrigerator.

S1: Different countries show different pattern of growth.
P: Many others have a high birth rate with a low death rate.
Q: Some have a high birth rate and still have a high death rate.
R: The developing countries show the most rapid growth rate.
S: Some others like the European nations, have a low birth rate and a low death rate.
S6: Compared to this in Europe the growth rate is low.

The Proper sequence should be:

A refrigerator with a 2 kW motor for powering the compressor gives 6000 kJ of cooling to the refrigerated space during 30 minutes of operation in a thermally insulated kitchen. Calculate the change in internal energy of the kitchen if the condenser coil behind the refrigerator rejects 8000 kJ of heat to the kitchen over the same time period.

In a thermally insulated kitchen, a refrigerator with 2 kW motor for running the compressor provides 6000 kJ of cooling to the refrigerated space during 30 min operation. If the condenser coil placed behind the refrigerator rejects 8000 kJ of heat to the kitchen during the same period, calculate the change in internal energy of the kitchen.

A heat pump is used to meet the heating requirements of a house and maintain it at 20°C. On a day when the outdoor air temperature drops to 2°C, the house is estimated to lose heat at a rate of 80,000 kJ/h. If the heat pump under these conditions has a COP of 2.5, determine the rate at which heat is absorbed from the cold outdoor air.

Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow and k = Thermal conductivity of the body)