Process Equipment and Plant Design
Vertical condenser is advantageous to the horizontal condenser from operation point of view, when

Only the function of condensation is to be carried out
Both the functions of condensation & sub cooling are carried out in a single unit
Sub cooling of condensate is desired
Hydrostatic head is required for refluxing the condensate

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Process Equipment and Plant Design
In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be

D₂ - D₁ (D₁ and D₂ are I.D. of inner and outer pipes respectively)
Less than that for fluid flow
Same as that for fluid flow
More than that for fluid flow

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

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

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