Heat Transfer
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

(COP)R = 1.5; (COP)HP = 2.5
(COP)R = 2.5; (COP)HP = 1.5
(COP)R = (COP)HP = 2.5
(COP)R = (COP)HP = 0.6

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Heat Transfer
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

Average temperature of the fin
Constant temperature equal to that of the base
Surrounding temperature
Temperature of the fin end

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Heat Transfer
If Prandtl number is greater than the Schmidt number, then the

concentration boundary layer lies inside the thermal boundary layer
thermal & concentration boundary layers are of equal thickness
none of the listed here
thermal boundary layer lies inside the concentration boundary layer

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