Heat Transfer
Thermal diffusivity of a material

Is the ratio of thermal conductivity to thermal capacity
Has the unit m² /sec
Is defined as K/ρ . Cp
All of these

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Heat Transfer
Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

Shell and tube heat exchanger with air inside tubes and steam on shell side
Shell and tube heat exchanger with air on shell side and steam inside tubes
Finned tube heat exchanger with air inside and steam outside
Finned tube heat exchanger with air outside and steam inside

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Heat Transfer
A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,

Both the spheres will emit equal amount of radiation per unit time in the beginning
The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
Both will absorb equal amount of radiation from the surrounding in the beginning
Both B & C

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