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In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package,
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FLUENT6.2has beenusedtomodel the gas–liquidflowina valve tray column. The effect of valveweighthas
been investigated using three valves having differentweights. An experimental Perspex column equipped
with a single valve tray, a weir and two downcomers has been used. A fluctuating plate has been utilized
for measuring the quality of gas distribution inside the liquid phase. In order to prove the repeatability
and consistency of themeasurements, the results were analyzed using two-stage nested designs. Bubble
size distributions obtained from photographs confirm that more bubble dispersions can be obtained
using heavier valves with cost of higher pressure drops, which is quantified by interface–pressure drop
performance. The CFD predictions, using upward momentum integral (UMI) parameter, also show that
the produced gas–liquid interface increases by employing heavier valves.7679
1. Introduction
Mass transfer tray columns are gas–liquid contact devices that
are widely used in the oil refining and chemical industries (Branan,
1976). Their design, performance and optimization are therefore
thoroughly studied topics. In a trayed column, liquid flows down
the column through downcomers and then across the tray deck,
while vapor flows upward through the liquid inventory on the
tray.
Several well known trays have been proposed for use in these
columns. Sieve trays were in widespread use since 1950 (Wijn,
1996). Distillation columns provided with sieve trays were shown
to enable much higher column throughputs than columns with
bubble-cap trays, which had been in use before. The leakage of liq-
uid through the holes upon lowering the vaporflowrate is one of the
operating limits in sieve trays. As sieve tray was introduced com-
mercially in the chemical industries, some research was devoted to
this topic and the valve tray was proposed. A valve tray is a sieve
tray with large holes, having a disc mounted over each hole, which
can move. At a sufficiently high vapor flow rate, the valve is lifted
by the vapor flow and the holes will be opened. In contrast, as the
vapor flow decreases, the disc return back and closes off the hole
and stops the liquid leakage.Gas and liquid interaction on the tray may generate certain
regimes, depending on loads and physiochemical properties of
both and these regimes, in turns, determine how the fluids will
behave. Hence, the gas–liquid interface and the efficiency of trays
are strongly affected by fluid hydrodynamics upon them.Numerous
studies were carried out to understand the gas–liquid hydrody-
namics on the trays and the effect of various parameters on the
efficiency of these devices. Wijn (1996) investigated the role of
downcomer layout on the large-diameter trays. He developed a
model based on the multi-branch/multi-cell approach to predict
the effect of downcomer positioning patterns on the tray effi-
ciency. He reported that various downcomer layout patterns had
significant effect on the efficiency. In continuing his study (Wijn,
1998), he described the lower operating flow rate limits in the
sieve and valve tray columns. The author presented a model for
predicting the weeping range and their effects on the column
efficiency. His model included the simultaneous solution of two
equations describing the liquid flow across the tray and over the
outlet weir, as well as countercurrent liquid flow through the free
hole area of the tray. He claimed that the model could be used
for calculating the gas flow rate of the weep and seal point. He
also reviewed the two-phase flow regimes on the trays describing