EXPERIMENTAL-STUDY OF DARCEAN FLOWS THROUGH 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 fixed diameter have an aspect ratio (L/d) varying between 4 and 70 given porosities of the porous media varying between 0.35 and 0.90. The relationships 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 direction on pressure drop is studied along two perpendicular directions: it is found that fibrous media behave globally in isotropic manner. The permeability and the Kozeny Carman parameter k(k) are deduced from experimental results. The variations of the permeability increase exponentially with the porosity. The Kozeny Carman parameter k(k) is a decreasing function of the porosity epsilon(L/d) and tends asymptotically to a value close to that deduced from a modified Ergun relation. The important decrease, observed for small aspect ratios, is certainly an effect of the cut sections of fibers. This effect becomes negligible for larger aspect ratios. The results in terms of permeability and of Kozeny Carman parameter k(k) are systematically compared to those deduced from various theoretical models. Generally, these models consider cylinders arranged in simple network, the flow being either parallel or perpendicular to the axis of cylinders. The variation laws of the parameter k(k), deduced from different models, present important discrepancies with our experimental results. The theoretical models, established for regular arrays of fibers do not correctly describe the behavior of randomly packed fibers.