Process Equipment and Plant Design
For a cylindrical shell, (subject to the thickness of uppermost course being more than the minimum for diaofthe tank in question), the thickness of the courses of shell

Decreases upwards
Increases upwards
May decrease or increase upwards depending upon whether vacuum or positive pressure would be maintained inside the shell
Remains same throughout

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Process Equipment and Plant Design
A forced circulation long tube vertical evaporator as compared to the natural circulation evaporator

Is economical in operation
Employs high velocity, high heat transfer rate and less heating surface requirement
Employs a centrifugal pump placed between external downtake from vapor drum and inlet to tube bundle
Both B & C

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