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)
Same as that for fluid flow
More than that for fluid flow
Less than that for fluid flow

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Process Equipment and Plant Design
A head comprises of straight flange section, corner torus, section and central dished section. Crown radius and knuckle radius in a head is related respectively to the

Straight flange section and corner torus section
Central dished section and straight flange section
Central dished section and corner torus section
Corner torus section and central dished section

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