VIII-6

E. Guazzelli, N. Nicolas and P. Duru

IUSTI, Technopole de Chateau-Gombert

E. J. Hinch

University of Cambridge

Abstract

When beds of particles are fluidized, they usually suffer voidage instabilities. In gas-fluidized beds, instabilities manifest themselves as bubbles, i. e., regions essentially devoid of particles which rise through the bed. Liquid-fluidized beds are less unstable and exhibit voidage instability waves. We have examined the spatial growth of these waves. Experiments are described which suggest that the instability is convective in nature. The wave is shown to saturate along the bed. The saturated wave can be described as a succession of concentration dips and plateaus which can be well fitted by a cnoidal wave. We also test the two-phase flow governing equations which have been used extensively over the past two decades to describe fluidized beds. The solid-phase viscosity and pressure which are unknown in the two-phase model are deduced form the shape of the saturated wave. The validity of the two-phase Newtonian model is then questioned.