Time-dependent heat transfer in a non-uniform porous body in thoughflow

Abstract

The time-dependent heat transport phenomena in the non-uniform porous media, which are frequently encountered situations in the modern technological applications of the porous media, is investigated by the experimental endeavors. A study is made of the thermal response of heterogeneous porous body cooled by steady throughflow. In the transient cool-down of the homogeneous porous media packed with spheres, the temperature of the air flow in the porous media are represented by the dimensionless time τ in the convection dominant flow. As Reynolds number decreases, the heat conduction to the upstream becomes dominant and causes the local nonuniform heat transport in the porous media. The cool-down characteristics of heterogeneous media are strongly affected by the geometrical and compositional arrangement and thermophysical properties of the components of porous materials. The impact of the conditions in the upstream-side region on the behavior of the downstream-side region is noticeable, but not vice versa. However, the overall heat transfer between the entire porous body and the throughflow is less affected by the local conditions of the make-up and properties of the media. For the sake of operational cost, the present homogeneous and heterogeneous porous body is to be run over times until τ~O(1) after the start-up, since the major transient process is accomplished over the characteristic time scale τ~O(1). The effect of pulsating flow on the transient cool-down of the homogeneous porous body is delineated. The temperature evolutions inside the porous medium indicate that the global heat transfer characteristics are little changed by the introduction of flow pulsation if the amplitude is small so that no reverse flows are induced. For the parameter ranges of present concern, the existing heat transport correlations based on the conventional non-pulsating flows can produce adequate approximations. When the pulsation amplitude is large so that reverse flows are pr...