INFLUENCE OF BUOYANCY FORCES ON THE FLOW OF GASES THROUGH PACKED-BEDSAT ELEVATED PRESSURES

The flow of gases through packed-bed columns af elevated pressures was investigated by displacement experiments with a stepwise change in th e tracer concentration. The experiments with different tracers, flow r ates, pressures, particle sizes, tube diameters, and flow directions w ere used to illustrate the effect of buoyancy forces on the apparent f luid mixing in packed beds. The experimental results exhibit a strong influence of the density differences between the tracer and carrier ga s on the flow behavior at higher pressures. Axial dispersion significa ntly increases due ro hydrodynamical instabilities when the density in creases with the height, and is reduced in the presence of stable dens ity gradients. The effect of density differences on the fluid flow bec omes more pronounced with increasing tube diameters. It can be argued that in pressure equipment the usual correlations for mass and heat tr ansfer may not be valid any more and that plug flow in such equipment is hardly possible to achieve.