Minimum Allowable Vapor Velocity for Perforated Plate Column.

Abstract

When the vapor rate is small, the vapor passes sporadically through some of the holes of the plate even if the plate is horizontal. As the vapor rate increases, the part that the vapor passes through becomes wider. For the effective operation of the perforated plate column, it is necessary that the vapor rises uniformly through holes all over the plate.
Minimum allowable vapor velocity to satisfy the above condition is shown by the following equation,
It was found that the slope of the plate had little to do with the uniform passage of vapor, so long as the slope of the plate was not too large. Nomenclature
H =hold-up on the plate [g/cm²]
R' =overflow rate [kg/hr]
V' =gas or vapor rate [kg/hr]
z =height of weir [cm]
Δz =liquid head over the weir by the Francis' Eq. [cm]
c =coefificient of discharge
d =hole diameter [cm]
f =effective foaming fraction
g =acceleration due to gravity [cm/sec2]
h =foaming height [cm]
i =slope of the plate (tangent of angle to horizontal plane)
Δp =total pressure drop through a tray [g/cm²]
Δpd =pressure drop through a dry plate [g/cm²]
Δp_w =wet pressure drop (=Δp-Δpd) [g/cm²]
Δp_σ =pressure drop due to the surface tension acting on the hole [g/cm²]
u =gas or vapor velocity through the hole [cm/sec]
ρ_g, ρ_l=gas or vapor and liquid densities [g/cm³]
σ =surface tension [dyne/cm]
φ =equivalent length of plate in the direction of slope [cm]