Porosity and permeametry at sub-atmospheric pressures


  • Dr.-Ing. Godwin J. I. Igwe

    1. Department of Chemical/Petrochemical Engineering, Rivers State University of Science & Technology, Private Mail Bag 5080, Port Harcourt/Nigeria
    Current affiliation:
    1. Visiting Professor, Texas A&M University, Department of Chemical Engineering, College Station, Texas 77843-3122, USA
    Search for more papers by this author


The Carman-Kozeny equation is applicable in the viscous flow regime but, as the powder becomes finer, this equation fails. The controlling factor is the ratio of the hydraulic diameter to the mean free path of gas molecules (rH/λ) and, as this approaches unity, “slip flow” occurs. This effect increases with (a) increasing fineness, i.e. rH reduced, (b) decreasing porosity, i.e. rH reduced, and (c) decreasing pressure, i.e. λ increased. In order to account for the enhanced flow arising as a result of this failure, a second term is introduced into the equation and this includes an unknown “constant” (δK0/K), the coefficient of slip. It was considered probable that this so-called constant was a function of (rH/λ), and an attempt was made to investigate this relationship.