Process Equipment and Plant Design
For annular flow of a fluid, the ratio of the equivalent diameter for pressure drop calculation to the equivalent diameter for heat transfer calculation is

D1/(d1 + d2)
(d1 + d2)/d2
D2/(d1 + d2)
(d1 + d2)/d1

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

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

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