Heat Transfer
Which of the following is the most widely used heat insulating material for pipelines carrying steam?

85% magnesia cement and glass wool
Cotton followed by aluminium foil
Fireclay refractory followed by aluminium sheet
Tar dolomite bricks followed by asbestos

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

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