CSB,Csb C-factor at flood, given by Eq. (6.10), ft/s.

Cv Orifice coefficient in dry pressure drop calculation.

Cw Eddy loss coefficient through valves, dimensionless.

Cw A constant in the weeping rate equation, Eq. (6.35), dimensionless.

CBP Closed balance point for valve trays (Sec. 6.3.2).

CFS Vapor flow rate, ft3/s.

D Diffusion coefficient, ft2/s.

De Eddy diffusion coefficient, ft2/s.

Df Arithmetic average between tower diameter and weir length, ft.

dH Hole diameter, in.

Dt Tower diameter, ft.

dT Tower diameter, in.

dv Diameter of valve unit at narrowest opening, in.

dw Diameter of circular weir, in.

E Tray efficiency, fractional.

e Entrain men t rate, lb-mole/h.

Ew Murphree tray efficiency, fractional.

Ea Section efficiency. Similar to Eoc, but taken only over a section of column, fractional.

■®oc Overall column efficiency, fractional.

Eog Point efficiency, fractional.

Es Entrainment, lb liquid entrained/lb vapor.

f Friction factor in hydraulic gradient correlation [Eq. (6.50)] given by Fig. 6.24, dimensionless.

F^ The active area ^-factor. Same as Fs when Fs is based on the active (bubbling) area.

FH,Fh The hole F-factor, analogous to Fs but based on the hole area, defined by Eq. (6.3).

Fiv Flow parameter, defined by Eq. (6.7).

Fs The superficial F-factor, a parameter describing vapor load, de fined by Eq. (6.2), ft/s ^b/ft3

Fva Same as Fga.

Fw Weir constriction factor, used in Eq. (6.49).

fw Weep fraction, ratio of liquid weeping to liquid entering the tray

FF Fractional approach to flooding, defined by Eq. (7.20).

FPL Flow-path length (distance from the inlet downcomer edge to outlet weir), in.

Fr The Froude number, defined by Eq. (6.66) for froth regime clear liquid height calculation.

¥vh The Froude number, based on hole velocity, defined by Eq.

(6.33), for weeping rate calculation.

G Vapor flow rate, lb/h

Acceleration due to gravity, 32.2 ft/s2.

Gas flow rate per bubbling area AB, lb-mole/(s-ft2).

Liquid flow rate, gpm.

Henry's law constant, lb-mole/(ft3-atm).

Liquid head, in of liquid.

Froth head, in of froth.

Clear liquid height on the tray, in of liquid.

Clearance under the downcomer, in.

Clear liquid height at the transition from the froth to spray regime, in of liquid.

Clear liquid height at the transition from the froth to spray regime for the air-water system, in of water.

Dry pressure drop, in of liquid.

Head loss due to liquid flow under the downcomer apron, in of liquid.

Froth height on the tray, in.

Froth height over the outlet weir, Eq. (6.63), in.

Hydraulic gradient on the tray {high minus low clear liquid height), in of liquid.

Pressure drop through the aerated liquid on the tray, in of liquid.

Clear liquid height at the froth-to-spray transition, corrected for the effect of weir height on entrainment, given by Eq. (6.29), in of liquid.

Depth of notches in weir, in.

Liquid head over the outlet weir, in of liquid.

Residual pressure drop, i.e., total tray pressure drop less dry pressure drop less clear liquid height, in of liquid.

Tray pressure drop, in of liquid.

Valve thickness, in.

Maximum vertical travel of a valve on a valve tray, in. Outlet weir height, in.

Head loss due to bubble formation, given by Eq. (6.316), in of liquid.

Dimensionless vapor velocity used for correlating weeping rates, defined by Eq. (6.36).

Dimensionless weeping liquid velocity, defined by Eq. (6.37).

Dry pressure drop coefficient, defined by Eqs. (6.43) (sieve trays) and (6.44) (valve trays), in/(ft/s)2.

Mass transfer coefficient, ft/s.

Pressure loss coefficient through closed valves, in/(ft/s)2.

Ka Pressure loss coefficient through open valves, in/(ft/s)2.

Koa Overall mass transfer coefficient based on vapor, ft/s.

L Liquid flow rate per tray pass, "lb/h.

La Liquid flow rate, lb-mole/h.

Lf Length of flow path across the tray, ft.

Lm Liquid flow rate per bubbling area AB, lb-mole/<s-ft2).

LW,LW Outlet weir length, in (Note; In multipass trays, Lw is the total outlet weir length, i.e., the sum of lengths of all outlet weirs).

M Marangoni effect index, or Ai-index, Eq. (7.37), dyne/cm.

m A constant in the weeping rate equation, Eq. (6.35), dimension-


m Slope of the equilibrium curve.

n A parameter in the spray regime clear liquid height correla tions, given by Eq. (6.69), in.

N Rate of diffusion, lb-mole/s.

Na Number of actual trays in the column.

N0 Gas film transfer units.

Nl Liquid film transfer units.

JVmin Minimum number of theoretical stages for the separation.

JVOG Overall gas transfer units.

Np Number of liquid passes per tray.

N, Number of theoretical stages required for the separation minus the sum of theoretical stages provided by the reboiler, partial condenser, and intermediate heat exchangers.

Nu Number of valve units on a tray.

OBP Open balance point for valve trays, Sec. 6.3.2.

P Pressure, atm.

p Hole pitch (center-to-center tray hole spacing), in.

AP Pressure drop, in of liquid.

Pe Peclet number, defined by Eq. (7.26), dimensionless.

Qd Downcomer liquid load, defined by Eq. (6.8), gpm/ft2.

Ql Liquid load, defined by Eq. (6.6), gpm/in of outlet weir length.

R Reflux ratio (i.e., reflux rate divided by distillate rate), molar.

Rh Hydraulic radius in hydraulic gradient calculation, defined by

R^ Ratio of valve weight with legs to valve weight without legs, di mensionless.

S Tray spacing, in.


Separation parameter, defined by Eq. (7.30).

0 0

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