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

The minimum pickup velocity (Upu) for pneumatic conveying is analogous to the minimum fluidization velocity (Umf) in fluidization systems in that both dictate the minimum gas velocity required and have important implications in gas-solid flows. However, Upu is not as well-understood as Umf. In this work, the impact of the width of lognormal particle size distributions (PSDs) and particle sphericity (φ) on Upu 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, Upu 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 Upu 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.