THE RHEOLOGY OF POWDERS

This paper studies the slow flow of powders. It is argued that since powders can flow like liquids, there must be equations similar to those of liquids. The phenomenon of a variable density, dilatancy, is described by an analogue of temperature called the compactivity X. Whereas, in thermal physics T = partial E/partial S, powders are controlled by X = partial V/partial S. The equations for rho, nu, T of a liquid are replaced by rho, nu, X. An analogy for free energy is described, the solution to some simple problems of packing and mixing are offered. As an example of rheology, it is shown that the simplest flow equations produce a transition to plug flow in appropriate circumstances.