Heat Transfer
A sphere of radius 'R₁' is enclosed in a sphere of radius 'R₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

R₂/(R₁+R₂)
(R₁/R₂)2
1

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Heat Transfer
In sub-cooled boiling,

Temperature of the heating surface is more than the boiling point of the liquid
Temperature of the heating surface is less than the boiling point of the liquid
Very large vapour space is necessary
Bubbles from heating surface are absorbed by the mass of the liquid

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