A few problems in porous media flows: From swimming cells to complex fluids
Professor Jeffrey S. Guasto, Tufts University
Fluid transport in porous materials regulates processes ranging from ecosystem dynamics and remediation in soils to filtration and extraction in industrial processing. In this talk, we will discuss several recent experiments pertaining to the transport of swimming cells and complex fluids through porous media, where we use microfluidic devices as model porous environments to precisely prescribe microstructure and flow. First, we examine the physical mechanisms underlying the transport of swimming bacteria through porous media flows. In such confined environments, we show that significant heterogeneity emerges in the spatial distribution of motile bacteria. Unlike scalar transport, we also demonstrate that the transverse effective diffusion of swimming bacteria is significantly reduced, which enhances the stream-wise transport coefficient through a dispersion effect. Second, we discuss the flow of a yield stress fluid through a random porous medium. We demonstrate that at a critical applied pressure, the initially solid microgel flows and percolates along distinct paths through the random microstructure. As the applied pressure increases further, the fluidized network grows, resulting in a highly inter-connected network with a nonlinear Darcy Law. Taken together, this work demonstrates that even at vanishingly small Reynolds numbers, porous media flows have surprising ways of enhancing or diminishing transport in a wide range of biological and physical systems.