Flow Regimes on Trays 641 The common flow regimes

The classic hydraulic model (Sec. 6.2.1) oversimplifies tray action. There are five main flow regimes on distillation trays (12,99). These regimes (Figs. 6.25 to 6.28) may all occur on the same tray under different liquid and vapor flow rates (Fig. 6.29). An excellent overview of the fundamentals and modeling of these flow regimes is presented by Lockett (12).

Bubble regime (F/g. 6.25a) or "deep pool" occurs at low vapor velocities. Discrete noncoalescing bubble swarms rise through quiescent liquid, which has a very clear surface. For the air-water system, Wallis (100 > showed that this regime is unlikely to occur when vapor velocities exceed 0.15 ft/sec, and therefore, in industrial columns. It may occur in bench-scale and pilot columns where outlet weirs are tall. If this regime occurs in a test unit, caution is required in data scale-up.

Cellular foam (Figs. 6.25b, 6.26a) is a wall-stabilized foam. Bubbles grow to an extent which limits the liquid to thin films between the jojooott o a c. 0 . o 5 ç ^ ÇJ o O o 0 $ Î 0 0 a î C G 1 -J ÏV


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