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

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

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Process Equipment and Plant Design
A forced circulation long tube vertical evaporator as compared to the natural circulation evaporator

Employs a centrifugal pump placed between external downtake from vapor drum and inlet to tube bundle
Employs high velocity, high heat transfer rate and less heating surface requirement
Is economical in operation
Both B & C

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Process Equipment and Plant Design
In case of design of a shell and tube heat exchanger,

Minimum cleaning lane of 6.5 mm is provided, when tubes are on a square pitch
O.D. of the tube is 6 to 40 mm while the tube lengths used are 0.5, 2.5, 3.0, 4.0, 5.0, 6 metres
Minimum tube sheet thickness (in which tubes are fixed) is equal to the O.D. of the tube upto 15 mm tube diameter; and for > 15 mm tube diameter, tube sheet thickness is smaller than tube diameter
All of these

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