Process Equipment and Plant Design
In a shell and tube heat exchanger having square pitch, the shell side equivalent diameter is given by (where, P = pitch, d = outside diameter of the tube)

4(P² - πd²/4)/πd
(P² - πd²/4)/πd
4P²/πd
Πd/4P²

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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

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

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