EXPERIMENTAL-STUDY OF DARCEAN FLOWS THROU GH RANDOMLY PACKED-BEDS OF MONODISPERSE FIBERS - INFLUENCE OF POROSITY

Experimental studies have been carried out on fluid how through porous media made up of randomly packed monodisperse fibers. The fibers of f ixed diameter have an aspect ratio (L/d) varying between 4 and 70 give n porosities of the porous media varying between 0.35 and 0.90. The re lationships between friction losses and superficial velocity have been systematically determined for each porous medium. A detailed analysis is carried out for low fluid velocities. The influence of how directi on on pressure drop is studied along two perpendicular directions: it is found that fibrous media behave globally in isotropic manner. The p ermeability and the Kozeny Carman parameter k(k) are deduced from expe rimental results. The variations of the permeability increase exponent ially with the porosity. The Kozeny Carman parameter k(k) is a decreas ing function of the porosity epsilon(L/d) and tends asymptotically to a value close to that deduced from a modified Ergun relation. The impo rtant decrease, observed for small aspect ratios, is certainly an effe ct of the cut sections of fibers. This effect becomes negligible for l arger aspect ratios. The results in terms of permeability and of Kozen y Carman parameter k(k) are systematically compared to those deduced f rom various theoretical models. Generally, these models consider cylin ders arranged in simple network, the flow being either parallel or per pendicular to the axis of cylinders. The variation laws of the paramet er k(k), deduced from different models, present important discrepancie s with our experimental results. The theoretical models, established f or regular arrays of fibers do not correctly describe the behavior of randomly packed fibers.