Abstract
This paper aims to find the relation between the air permeability of the unidirectionally oriented fiber assemblies at high porosity and these porosity, applying the Darcy's law to the onedimensional air flow through the fiber assemblies. According to the theory of hydrodynamics, the permeability for the bed of particles is proportional to ε3/ (1-ε) 2, where ε represents the porosity of bed, and inversely proportional to the Kozeny constant. However, it was clarified by E. Lord that the Kozeny constant of fiber assemblies depends on the porosity. So, we have to determine the relation between the permeability and the porosity experimentally.
Experiments were performed with the use of unidirectionally oriented fiber assemblies made of cotton fibers and polyester fibers in the porosity region of 96.0-99.9% and on two fiber-axis directions relative to air flow; parallel and perpendicular. From the experimental results, it was found that :
K=R·ε3/ (1-ε) β
where K represents the air permeability, R and β being experimental constants depending on the two kinds of fibers used on this experiment (specimen 1 : 2.2 d, 30mm, 1.54g/cm3, 80t/cm cotton fiber. specimen 2 : 1.25 d, 38mm, 1.36g/cm3, mean no. of crimp 4.5t/cm polyester fiber) and the relation between the fiber-axis direction to air flow.
These results do not qualitatively correspond to the Kozeny-Carman's law, but show good agreement with the Lord's results obtained for cotton fiber assemblies in the porosity region of 96.0-99.0 (%).
