Heat Transfer
For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is

Nu = Gz
Nu = 2Gz0.5
Nu = Gz
Nu = 0.023 Re0.8 . Pr0.4

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Heat Transfer
The advantage of backward feed multiple effect evaporators over forward feed units is that

Equal heat transfer co-efficients exist in various effects
Most concentrated liquid is at highest temperature
Heat sensitive material can be handled
There is no additional cost of pumping

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Heat Transfer
Leidenfrost point is a term concerned with the

Concentration of a corrosive solution by evaporation
Heat transfer between two highly viscous liquids
Boiling of a liquid on a hot surface
Condensation of the saturated vapor on a cold surface

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