13-mm insidediameter tube was investigated using 329-micron spherical glass beads in air. The gas Reynolds number varied from 0 to 30,oOO with solids-loading ratios of up to 20 at a gas Reynolds number of l0,oOO. The frictional pressure drop for downflow was found to be a weaker function of the solids-loading ratio than the upflow case using data reported in the literature. Empirical correlation of the t w q h a s e friction factor, in terms of the gas Reynolds number and a dimensionless parameter, C D E~D / [ (~ -E')dp], showed that at high solids loadings, particles tend to stabilize the suspension flow. The dimensionless parameter seems to be applicable to a universal pressure drop correlation for solids-fluid systems, but requires further investigation. University of Utah Depl. of Chemical Engineering Salt Lake City, UT 84112 the literature are in conflict. Several pressure-drop correlations proposed for vertical-upflow systems cover a very limited range of variables, and they cannot be safely extrapolated outside the range of the experimental data.

13-mm inside diameter tube with uniform heat-flux boundary conditions was investigated using 329-pm spherical glass beads in air. The gas Reynolds number varied from 0 to 30,000 with solids-loading ratios of up to 20 at a gas Reynolds number of 10,000. The suspension Nusselt number, defined in terms of the wallto-gas mixed-mean temperature difference, decreased with increasing solidsloading ratio at high Reynolds numbers, while it changed little from the value for gas alone at low Reynolds numbers. A possible explanation is given by considering the effects of particles on the fluid mechanical properties of the gas. Asymptotic Nusselt numbers in downflow are compared with results of other investigations for upflow.