Process Equipment and Plant Design
Fouling factor must be included in the calculation of over all design heat transfer coefficient, when the liquid

Is highly viscous
Is of high specific gravity
Containing suspended solids flows at low velocity
Containing suspended solids flows at high velocity

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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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