Mechanics of Gas-Liquid Flow in Packed-Bed Contactors

Packed beds are typically tall cylindrical vessels filled with pieces of inert solid that have been dumped or stacked to leave considerable space for fluid between them (Leva 1 95 1 ). They are used to bring flowing gas and liquid into the intimate contact needed for rapid exchange of dissolved substances and, often, for chemical reaction as well. This use began nearly two centuries ago and is common in large-scale chemical processing; there are other applications too. Flow in packed beds is justly regarded as complex, irregular, even capricious, and scaleup from laboratory and pilot­ plant models to commercial sizes is notoriously risky (Ng & Chu 1 987). Despite this, packed beds have had relatively little fluid-mechanical study (Westerterp et a1 1 984, NRC Panel Report 1 986). This article reviews what appears most significant from what has been done. The point of view we take began to emerge in the mid-1970s in the course of research into how immiscible fluids flow together in the much finer, yet no less irregular, pore space of sedimentary rocks. The key idea was H. T. Davis's-that the way to approach macroscopic two-phase flow in porous media is with the statistical physics of network processes, then blooming in applications of so-called percolation theory (Larson et al 1977, 1981, Levine et al 1977). The basic ingredient was the essence of accumulated knowledge of the fluid mechanics of microscopic behavior in the individual passages, enlargements, and junctions of the pore space (Ng