(67a) Transport through Partly Saturated Beds of Fully Wetted Hydrophilic Fibers

Fluid-saturated beds of hydrophilic fibers find numerous modern technology applications, including many in new energy and environmental systems, such as titanium dioxide light-irradiated superhydrophilic fibers used in photocatalytic decomposition of airborne pollutants and wastewater remediation, lignocellulosic cotton fibers used in diesel oil sorption from water, and environment friendly composite materials utilizing the hydrophilic fibers in natural polymers, such as starch, protein, and cellulose. Hydrophobic fibers are the material of preference in fuel cell gas diffusion and catalyst layers as they facilitate water removal from the cell stacks. Nonetheless, hydrophilic fibers are also utilized in certain fuel cell applications, since they enhance the dispersion of the catalyst particles, hence also the catalytic activity and fuel cell efficiency, while helping maintain the electrolyte wet in systems operating at low relative humidity conditions. The high hydrophilicity and electrical conductivity of sintered stainless steel fiber felt gas diffusion layers are credited for enhancing the performance of air-breathing direct methanol fuel cells. Not surprisingly, hydrophilic fibrous media have been investigated alongside hydrophobic ones in a number of recent experimental and theoretical fuel cell studies.

Our experimentally validated earlier and recent numerical methods for estimating effective mass, energy, and momentum transport properties of various types of fibrous media were modified to account for flow through beds of fully wetted hydrophilic fibers of various porosities and saturation levels. The numerical predictions for the effective diffusivity and viscous permeability of such beds are in agreement with earlier analytical predictions and experimental data of the literature for flow through partly saturated fibrous media and packed beds of cylinders. Further modification of our algorithms is under way, to derive the effective thermal and electrical conductivity and magnetic permeability of such systems.