Process Equipment and Plant Design
Number of evaporators which can be used in service in a multiple effect evaporation system is limited by the

Both A & B
Neither A nor B
Economic limit reached, when the plant cost exceeds the saving of steam
Practical limit reached, due to low heat transfer rate because of inadequate temperature difference

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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

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

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