Heat Transfer
Which of the following situations can be approximated to a steady state heat transfer system?

10 kg of dry saturated steam at 8 kgf/cm² flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C
Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C
A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C
A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmosheric air at 35°C

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

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Heat Transfer
Nusselt number is the ratio of the

None of these
Temperature difference to the temperature gradient at the wall
Heat flux at the wall to that across the entire pipe
Temperature gradient of the wall to that across the entire pipe

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