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    In the present study, the volume of fluid (VOF) method implemented in the commercial CFD package,
    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
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