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

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Process Equipment and Plant Design
Weep holes provided in the plates of a distillation column

All of these
Must be large enough (usually 1/4" to 5/8" dia) to prevent plugging but should not deliver excessive amount of fluid during operation
Facilitate draining out liquid from a tray when the unit is not in operation
Are normally located near the overflow weir so that any delivery of liquid during operation follows approximately the same path as the overflow fluid

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

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