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[curious_cat]

In a multi-effect evaporator a common design thumb rule is that the deltaT across an effect is inversely proportional to the product of the Heat Transfer Coefficient ( U)  & Heat Transfer Area  (A) for that effect. 

 

Does it matter how the deltaT is distributed between the three effects? Why?

 

e.g. Say we have a triple effect with steam temp. is 120 C & the boiling point corresponding to the best vacuum effect (3rd effect) is 60 C. Does it matter if the individual deltaT's are equal, i.e. Effects at 100 C, 80 C & 60 C?

 

Or is an assymetric delta T equally good. i.e. 100 C, 90 C, 60 C. 

 

From fundamentals I find it hard to see why shooting for an equal delta T is good?

 

i.e. Q=U A deltaT

 

so long as the product remains same for each effect (which it automatically does by adjusting the delta T) shouldn't the system run equally well? 

Edited by curious_cat, 30 August 2015 - 11:38 PM.