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

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Process Equipment and Plant Design
For turbulent flow (NRe > 2100) of low viscosity fluid (μ > 20cp) in steel pipes, the optimum inside pipe diameter is given by(where, Q = fluid flow rate, ft³/sec.ρ = fluid density, lb/ft³ μ = fluid viscosity, centipoise Di = optimum inside pipe diameter, inches)

Di, opt = 3 Q0.36 . μ0.88
Di, opt = 3.9 Q0.45 ρ0.13
Di, opt = 4.7 Q0.36 . μ3.2ρ0.13
Di, opt = 3.9 Q0.45 . μ0.95

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