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the mechanisms of liquid flow over outlet weirs of distillation and
absorption trays (Wijn, 1999). Rao, Goutami, and Jain (2001) pre-
sented a method that used the tray efficiency matrix directly in
simulations. The tray efficiency matrix used in the simulation was
obtained frompoint efficiencymatrix. They used the direct incorpo-
ration of efficiencymatrix in the Naphtali Sandholmmethod (1971)
and reported that their modified method had better convergence
characteristics than the original Naphtali Sandholm method for
distillation, absorption and extraction columns. Wang, Li, Wozny,
and Wang (2003) proposed a model to express the startup behav-
iors of batch columns starting from an empty cold state. They
verified their model through experiments on a pilot batch plant
with a bubble-cap tray column to separate a methanol/water mix-
ture.
Due to progresses in computer hardware and software and con-
sequent increase of the calculation speed, the Computational Fluid
Dynamics (CFD) modeling technique would be a powerful and
effective tool for understanding the complex hydrodynamics in
many industrial processes.Mehta, Chuang, andNandakumar (1998)
analyzed the liquidphaseflowpatterns ona sieve tray by solving the
time-averaged governing equations ofmass andmomentumfor the
liquid phase. In their study, interactions with the vapor phase were
taken into account using the interphasemomentumtransfer coeffi-
cients determined fromempirical correlations. The two-phase flow
behavior on a sieve tray column was studied by Yu, Yan, You, and
Liu (1999) using a two-dimensional model. They focused on the
description of the hydrodynamics along the liquid flow path while
variations in the direction of gas flow along the height of the dis-
persion were ignored. van Baten and Krishna (2000) developed a
CFD model for describing the hydrodynamics of sieve trays. They
modeled the gas and liquid phases in the Eulerian framework as
two interpenetrating phases. The interphasemomentumexchange
coefficient was estimated based on the Bennett, Agrawal, and Cook
(1983) correlation. In their study, several three-dimensional tran-
sient modelings were carried out for a 0.3m diameter sieve tray
by varying the gas superficial velocity, the column weir height and
liquid loads. Their CFD model reflected chaotic tray hydrodynam-
ics and revealed several liquid circulation patterns, which had true
three-dimensional characteristics. They reported that the predicted
clear liquid height obtained from their models was in good agree-
ment with the Bennett correlation.
Gesit, Nandakumar, and Chuang (2003) employed the commer-
cial CFX package to predict the flow patterns and hydraulics of
a commercial scale 1.22m diameter air–water sieve tray. In their
investigation, the velocity distributions, clear liquid height, froth
height, and liquid holdup fraction in froth were predicted for var-
ious combinations of gas and liquid flow rates. In their model,
each phase was treated as an interpenetrating continuum hav-
ing separate transport equations and interaction between the two
phaseswas considered via an interphasemomentumtransfer. They
claimed that CFD could be used as a valuable tool in tray design and
analysis. A CFD model using the commercial CFX code was intro-
duced by Hoffmann, Ausner, Repke, and Wozny (2005) in order
to model two and three-phase transient film flow in packed tow-
ers. An Euler–Euler algorithmformultiphase calculationswith free
surfaceswas used. Similar to the VOFmethod, averaged phase frac-
tions inside the finite volume cells and the surface tension was
implemented in themodel. The turbulencemodelingwas not taken
into account due to the relatively low range of the Reynolds num-