Experimental study on thermal dependence of the permeability of heat-generating porous medium
Authors: Sidorov Aleksandr 
Published: March 2022

&lt;p&gt;The work is devoted to the experimental determination of basic filtration characteristics for a heat-generating porous medium. The results of measuring the permeability of fibrous porous medium by the convective method are presented.&lt;/p&gt;&lt;p&gt;Porous media are widespread materials in nature and technology. Such media are saturated with liquid or gas, therefore, flow regimes within them have been studying for a long time. The majority of research works to date has been devoted to porous media consisting of compact solid formations (grains of sand, granules, balls, etc.). Fibrous porous media are often created artificially. They are rarely found under the natural conditions. An example of such a medium is cuttings, which form during storage and drying processes. In industry, fibrous porous media are used to control heat transfer, chemical or radioactive reactions. Heat can generate as a result of biological processes, chemical or nuclear reactions. Heat release in the porous medium causes the onset of convective vortex flows. To compare theoretical calculations and experimental data adequately and successfully, one should know the main filtration properties and volumetric heat source strength of heat-generating porous materials.&lt;/p&gt;&lt;p&gt;The convective method for measuring the permeability of porous medium is applied. It is known that convective flows are excited in a threshold-like manner inside the cavity heated from below and filled with liquid or gas. For a horizontal layer with a porous medium, the threshold for the onset of convection is characterized by the critical dimensionless Rayleigh-Darcy number. Using this parameter, it is possible to find permeability through the critical temperature difference across the layer.&lt;/p&gt;&lt;p&gt;The fibrous porous medium is made up of 0.9 mm thick fibers. A single fiber consists of a thin nichrome wire of a 0.09 mm diameter with plexiglass coating. Such fibers are woven in one direction into a polymer frame composted of the cubic cells with a 1.7 mm side. The total size of the frame with fibers is of 100&amp;#215;100&amp;#215;10 mm&lt;sup&gt;3&lt;/sup&gt;. The effective thermal conductivity of a fiber can vary by a change in the thickness of plexiglass coating. The volumetric heat generation is due to the Joule heat induced by an electric current passing through the fibers. The pore volume can be calculated through the solid volume fraction of porous matrix. The entire porous medium configuration is placed between the heat exchangers combined with heat flow sensors.&lt;/p&gt;&lt;p&gt;Several samples of fibrous porous media with distinct pore volume fractions are prepared. A convective experiment is carried out with each sample. The diagrams of the Nusselt number versus the temperature difference over the porous layer are plotted. The diagrams are used to find the critical temperature difference, at which convective vortex flows initiate in the cavity. Applying the threshold Rayleigh-Darcy formula, permeability of the porous layer is calculated under the convective conditions and the thermal dependence of permeability is investigated.&lt;/p&gt;&lt;p&gt;The reported study was supported by the Russian Science Foundation (Grant No. 21-71-10045), https://rscf.ru/en/project/21-71-10045/.&lt;/p&gt;