Minimum pickup velocity: The transition between nano‐scale and micro‐scale

The transport of nano‐scale particles has become increasingly important, but the knowledge base available is limited. This study aims to bridge the knowledge gap between the nano‐ and micro‐scales for pneumatic conveying. A key parameter is the minimum pickup velocity (U pu ), which is the minimum fluid velocity required to initiate motion in a particle originally at rest. The U pu values of nine alumina particles with particle diameters (d p ) ranging from 5 to 110,000 nm were determined using the weight loss method, then compared against the established pickup Zones (analogous to the Geldart Groups). Results indicated that: (1) U pu varied non‐monotonically with increasing d p , thus revealing the missing link between the nano‐ and micro‐scales; (2) the intermediate particle diameters surprisingly did not agree with any pickup Zone; (3) Zone III (analogous to Geldart Group C) is inadequate for all the nano‐scale particles, so new boundaries and a new Zone are proposed. © 2016 American Institute of Chemical Engineers AIChE J , 63: 1512–1519, 2017