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

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

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Process Equipment and Plant Design
The function of manholes provided in the shell of a distillation column is to

Keep a check on the liquid gradient over the plate by direct visual observation
Guard against foaming & entrainment by dumping antifoaming agent through it
Give access to the individual trays for cleaning, maintenance and installation
All of these

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