STEADY FLUIDIZATION OF FINE PARTICLES IN A FIXED-BED OF COARSE PARTICLES

This work addresses the steady fluidization of small particles (diamet ers of 0.15, 0.2, 0.3 and 0.4 mm) within a randomly arranged fixed bed of bigger particles (diameters of 2, 3 and 4 mm). The research is rel evant in the field of comminution, where crushing processes and materi al transport phenomena are integrated features. Here measurements are made of fine particle bed height, solid volume fraction of both specie s, and liquid flow rate. The results show that existing correlations f or mono-disperse fluidization in vertical pipes (Richardson and Zaki [ 1]) provide a qualitative description of fluid velocity in this new co nfiguration, when using the effective diameter of the coarse pore spac e. The effective diameter is defined as the ratio of pore volume to we tted surface. The present results are correlated within a new proposed equation. The correlation maintains the form of the Richardson and Za ki correlation, but one of the empirical coefficients is modified to o btain a better fit. A simple model is proposed to explain the underlyi ng physical principles. In this model the hindering effects of the coa rse bed on the fluidization of the fines are explained in terms of a s ize exclusion mechanism.