Measuring fluid pressure and the impact of friction in water flow through sponge-like media

The study of water flow through porous media often has direct implications across a broad range of problems in science and engineering. Lutz et al. devised an experimental apparatus to quantitatively study flow through rigid, reactive or deformable porous media.

The apparatus can simultaneously measure the pervadic pressure profile, fluid volume flux, and deformation in the material placed inside of the cylinder device as fluid is pumped through the material.

Using a column of soft latex foam disks as their test subject, the team investigated the two-way feedback that occurred between the deformation of the sponge and the pressure-driven flow of the water. The apparatus measures the fluid pressure at arbitrary points within the sponge alongside the sponge deformation and the total rate of fluid flow.

“We were surprised to discover how significant a role friction plays as the sponge rubs against the walls of the container, which opposes the sponge’s motion along the container and impacts the feedback mechanism,” said author Tyler Lutz.

As the edges of foam disks push against the inside wall of the cylinder, friction plays a non-trivial role in the experiment, but the alternative – using a narrower sample – would completely change the overall flow in the cylinder and compromise pressure measurements. While friction complicates the mathematical modeling, understanding its consequences is important to understanding real world analogs from biological flows within cells to large-scale groundwater flows, all cases where friction is unavoidable.

“The techniques could be used in future work to investigate different flow geometries, types of porous material, and flows of broader biological, geophysical, or industrial relevance,” said Lutz.

Source: “A method for measuring fluid pressure and solid deformation profiles in uniaxial porous media flows,” by Tyler Harrison Lutz, Larry Wilen, and John Wettlaufer, Review of Scientific Instruments (2021). The article can be accessed at https://doi.org/10.1063/5.0019519 .