Criteria for choking in vertical pneumatic conveying lines

Abstract Choking in vertical pneumatic conveying lines is not a clear-cut phenomenon. Different definitions and criteria are available in the literature. They are first reviewed in this paper. A mathematical definition for choking first proposed by the author was refined and presented with additional data. The concept of continuity wave and cluster formation, which were successfully applied to predict the transition between the bubbling and the turbulent fluidization, were then introduced to derive the basic relationship expected at choking. A semi-theoretical equation similar to the Richardson and Zaki equation for particulate fluidization was obtained from the available literature data. Hopefully, this mechanistic approach will eventually lead to a unified theory for choking in vertical pneumatic transport lines.