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

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
Results in higher shell side pressure drop
Facilitates easier shell side cleaning; hence is more suitable for handling high dirt factor shell side fluid

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Process Equipment and Plant Design
For a cylindrical shell, (subject to the thickness of uppermost course being more than the minimum for diaofthe tank in question), the thickness of the courses of shell

Decreases upwards
May decrease or increase upwards depending upon whether vacuum or positive pressure would be maintained inside the shell
Remains same throughout
Increases upwards

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