Process Equipment and Plant Design
In a double pipe concentric heat exchanger, the equivalent diameter of annulus for heat transfer would be (where, D₁ and D₂ are I.D. of inner and outer pipes)

None of these
(D₂² - D₁²)/D₂²
D₂ - D₁
(D₂² - D₁²)/D₁²

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Process Equipment and Plant Design
Mc Cable Thiele method used for finding theoretical stages in a distillation column assumes that the

Trouton's rule is applicable
Liquid/vapor loading across the column remains constant
All of these
Sensible heat differences are small, because the temperature changes from tray to tray is small

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