Experimental characterization of thermal and viscous powers in porous media under oscillating flow

Porous materials are integrated components across various industries, offering unique properties such as high surface area, low density, and good permeability. They have a wide range of applications including energy conversion, with relevance in sound absorption and thermoacoustic phenomena. Understanding the intricate energy conversion mechanisms within the microstructure of porous materials under oscillating flows, such as sound waves, is paramount for optimizing their performance in these applications. The techniques currently used for testing porous materials enable the characterization of the behaviour of the porous matrix when subjected to an acoustic wave, without consideration to energetic quantities. Here, this paper presents two novel measurement techniques allowing for the experimental quantification of the power dissipated within the porous material, by making an explicit distinction between thermal relaxation and viscous dissipation effects. The study involves a model to quantify the viscous and thermal energetic behaviours from which analytical expressions guiding the elaboration of the proposed experimental techniques are derived, and finally validated through experimental data. Experimental tests have been carried out on three different samples (polyester fibers, wire mesh and triangular pores sample) largely used both in acoustic and thermoacoustic fields. The experimental data compared with the theoretical prediction for each sample allow to validate the measurement methodologies. By bridging theoretical modelling with experimental validation, this work contributes to the broader understanding and utilization of porous materials in energy conversion applications.