Process Equipment and Plant Design
A perforated plate has holes of diameter dh arranged in a pitch ph. Each hole has a tube of I.D. dt passing through it. The ligament efficiency is given by

(ph - dt)/ph
(ph - dh . dt/2)/ph
(ph - dh)/ph
(ph - dh)/dh

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

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