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

Results in higher shell side pressure drop
Creates relatively lower turbulence on the shell side resulting in lower shell side heat transfer co-efficient
Can accomodate less number of tubes for a given shell diameter
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
Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele's method, this method

Facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method
Is more accurate in finding the number of equilibrium stages
All of these
Accounts for the enthalpy changes in the process

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