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Porosity and permeametry at sub‐atmospheric pressures
Author(s) -
Igwe Godwin J. I.
Publication year - 1989
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/ceat.270120135
Subject(s) - porosity , fineness , constant (computer programming) , slip (aerodynamics) , slip ratio , thermodynamics , flow (mathematics) , mechanics , materials science , chemistry , mathematics , mineralogy , geotechnical engineering , physics , geology , composite material , computer science , programming language , shear stress
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 ( r H /λ) and, as this approaches unity, “slip flow” occurs. This effect increases with (a) increasing fineness, i.e. r H reduced, (b) decreasing porosity, i.e. r H 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” (δ K 0 / K ), the coefficient of slip. It was considered probable that this so‐called constant was a function of ( r H /λ), and an attempt was made to investigate this relationship.