Abstract
Since gas permeation through a powder bed is affected by molecular flow, applicability of the Kozeny-Carman equation neglecting this effect is limited to powders coarser than about 10μm. ΦB=ΦV+δΦM is a general expression of some permeability equations for finer powders, where ΦB denotes the permeability of a bed, ΦV the term of viscous flow and ΦM the term of molecular flow. δ is the constant for adjusting molecular flow effect. It was more than 40 years ago that δ=0.515 was proposed by Rigden, 0.97 by Lea & Nurse and 1.125 by Carman. Such a big discrepancy of δ is one of the reasons why the Kozeny-Carman equation is still in use. δ=0.82 was proposed as a reasonable value through the least squares analysis of Rigden's data and reference of the Knudsen's equation of capillary permeation. Using δ=0.82, more reasonable measurement of powders down to about 1μm may be possible.
