Abstract
An equation for powder discharge from a vertical tube is derived theoretically by combining the Janssen equation of the pressure distribution with a dynamic balance equation of forces for falling non-cohesive powders. The derived equation is similar in form to Shirai's equation, which is based on an empirical pressure equation and an orifice equation. In cohesive powder systems, it is assumed that a cylindrical block of a certain height is formed at the bottom of the tube from which it emerges. The height of the block is calculated from a dynamic force balance. A periodic discharge of powder is predicted. This is similar to the results of Tanaka who analysed the motion of powder by using different values for static and dynamic Rankine's coefficients.
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