Numerical investigation of single-blow transient testing technique

Abstract

The single-blow transient testing technique has been used for more than 50 years, and many correlations have been proposed from this technique. However, these correlations differ significantly from one another and the behind reasons are still unknown. In this study, we used numerical simulation to detect the detailed temperature evolution of an entire porous matrix during the single-blow experiment. The numerical simulation was performed on a three-dimensional geometry with idealized packed tetrakaidecahedron structures, and the numerical method was based on three-dimensional RANS equations. The initial and boundary conditions of the simulation were the same as those of the single-blow transient testing technique. The detailed temperature evolution of the sample and air stream was obtained. Computational results indicated a local thermal equilibrium region inside the porous matrix during the single-blow transient experiment. The local thermal equilibrium is affected by the sample thickness, superficial velocity, and thermal capacity. The “local thermal equilibrium” inside the porous matrix during the single-blow transient test contradicts the prerequisites of this measurement method. This finding is validated by experimental data and is crucial to heat transfer inside porous media, as well as to the design and optimization of heat exchangers, volumetric solar receivers, and thermal storage systems.