Heat and Mass Transfer
According to Prevost theory of heat exchange

Heat transfer by radiation requires no medium
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
All bodies above absolute zero emit radiation
It is impossible to transfer heat from low temperature source to t high temperature source

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Heat and Mass Transfer
Film coefficient is defined as Inside diameter of tube

Equivalent thickness of film
Film coefficient × Inside diameter Thermal conductivity
Thermal conductivity Equivalent thickness of film Specific heat × Viscosity
Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity

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Heat and Mass Transfer
A steam pipe is to be insulated by two insulating materials put over each other. For best results

Better insulation should be put over pipe and better one over it
Both may be put in any order
Inferior insulation should be put over pipe and better one over it
Whether to put inferior OIL over pipe or the better one would depend on steam temperature

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