Impact of continuous particle size distribution width and particle sphericity on minimum pickup velocity in gas-solid pneumatic conveying

The minimum pickup velocity (U_pu) for pneumatic conveying is analogous to the minimum fluidization velocity (U_mf) in fluidization systems in that both dictate the minimum gas velocity required and have important implications in gas-solid flows. However, U_pu is not as well-understood as U_mf. In this work, the impact of the width of lognormal particle size distributions (PSDs) and particle sphericity (ϕ) on U_pu was determined by the modified weight loss method. Three Geldart Group B materials (namely, glass, aluminum oxide and plastic), with various PSD widths and different particle sphericities (ϕ), were investigated. Two observations are worth highlighting: (i) as PSD width increases, U_pu surprisingly exhibits a non-monotonic behavior (namely, decreases then increases), and (ii) the lower the particle sphericity (ϕ) is, the greater the extent of the non-monotonic behavior becomes. The discrepancy between the U_pu values of the experimental data here and values predicted by available correlations underscores the non-negligible impact of PSD width and particle sphericity, which thereby warrants more understanding and the incorporation of such effects to improve the predictive capability of gas-solid pneumatic conveying.