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

(R₁/R₂)2
R₂/(R₁+R₂)
1

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Heat Transfer
Prandtl number is the ratio of

Thermal diffusivity to momentum diffusivity
Momentum diffusivity to thermal diffusivity
Momentum diffusivity to mass diffusivity
Thermal diffusivity to mass diffusivity

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Heat Transfer
A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because

Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
Total heat transfer area of all the effects is -less than that in a single effect evaporator system
Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system
Boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system

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