Process Equipment and Plant Design
In actual operation of distillation column, the vapour is not distributed uniformly among the bubble caps, primarily because of the

Liquid gradient on the tray
Small downcomer liquid seal
Lower skirt clearance
Lower static submergence

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Process Equipment and Plant Design
In a shell and tube heat exchanger, the clearance of the tube is generally

Equal to the tube diameter
Not less than one-fourth of the tube diameter or 3/16"
More in case of triangular pitch as compared to the square pitch tube layout
More than the tube diameter

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Process Equipment and Plant Design
In a shell and tube heat exchanger, triangular pitch arrangement as compared to square pitch arrangement

Facilitates easier shell side cleaning; hence is more suitable for handling high dirt factor shell side fluid
Results in higher shell side pressure drop
Can accomodate less number of tubes for a given shell diameter
Creates relatively lower turbulence on the shell side resulting in lower shell side heat transfer co-efficient

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