COCURRENT DOWNFLOW IN NETWORKS OF PASSAGES - MICROSCALE ROOTS OF MACROSCALE FLOW REGIMES

Contending trickling, spray, pulsing, and bubbling regimes in cocurrent downflow in packed beds differ hydrodynamically and so also do holdups, pressure drops, transfer rates, and reaction performance. Uncertainties about the flow regimes and competition between them contribute to unreliability of existing design and scale-up methods for trickle beds. We report flow visualization of microscale hydrodynamics in the spaces between packing particles—the void space of the bed—where gas and liquid compete, and of macroscale flow behavior in nearly two-dimensional packed beds confined between parallel transparent walls. The macroscale regimes are the same as those that have been widely reported from beds with transparent walls. We show that these regimes result from an enormous set of interacting microscale regimes, themselves the outcome of local competitions between liquid and gas for enlargements and junctions of the void space network, on the one hand, and constrictions, on the other. © 1990, American Chemical Society. All rights reserved.