The transport of gases in macroporous α-alumina supports

The infiltration of fluids through the voids of porous materials is common place to several well established and emerging technologies, and optimizing their performance relies heavily on developing a deeper understanding of how the fluid flow is affected by the topology of the pore space. This is particularly challenging when the medium is unconsolidated, since it is not only the pore size distribution and pore network connectivity that must be considered, but also the pore aspect ratio distribution will often assume importance. In this work, we introduce a modified effective medium theory (EMT) where the effect of non-vanishing aspect ratios is considered in order to describe the transport mechanism of several light gases through unconsolidated macroporous α-alumina tubular supports. It is confirmed that the tortuosity is not just a property of the medium, but also depends (weakly) on the operating conditions due to the combined effect of viscous and Knudsen contributions. The coordination number and average pore length are the only adjustable parameters in the theory, which allowed adequate prediction of the variation of the apparent tortuosity with temperature for the investigated gases.