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)
1
(R₁/R₂)2

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Heat Transfer
In a shell and tube heat exchanger,

There is no relationship between temperature drop and resistance
The relationship is not generalised
The temperature drop is inversely proportional to the resistance across which the drop occurs
The temperature drops in the two fluids and the wall are proportional to individual resistances

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