Process Equipment and Plant Design
Overall distillation column efficiency for most of the refinery columns can be given by (for μ = 0.07 - 1.4 cp and relative volatility < 4) (where η = overall column efficiency, % μ = molal average viscosity of feed at average column temperature and pressure, cp Δp = pressure drop per tray, psi)

Η = 0.25 log μ - 1.67
Η = 17 - 61.1 log μ
Η = 24.6 (Δp/μ)
Η = 1.66 - 0.25 log μ

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Process Equipment and Plant Design
When one of the fluids is highly corrosive and has fouling tendency, it should

Flow outside the tube, when the flow is counter-current and inside the tube when the flow is co-current
Preferably flow inside the tube for its easier internal cleaning
Flow at a very slow velocity
Perferably flow outside the tube

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Process Equipment and Plant Design
Mc Cable Thiele method used for finding theoretical stages in a distillation column assumes that the

Trouton's rule is applicable
Liquid/vapor loading across the column remains constant
All of these
Sensible heat differences are small, because the temperature changes from tray to tray is small

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