Ah. Benneker et al., INFLUENCE OF BUOYANCY FORCES ON THE FLOW OF GASES THROUGH PACKED-BEDSAT ELEVATED PRESSURES, AIChE journal, 44(2), 1998, pp. 263-270
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.