Measurement of Velocity and Temperature Distributions in a Highly Porous Medium

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Abstract
In the present article, the experimental results on the velocity and temperature distributions in a highly porous medium are reported. The highly porous medium used in the present study is made of aluminum oxide ceramic and has a porosity of about 87.5%. The velocities at the downstream end of the highly porous medium were measured using a laser Doppler velocimetry. Temperature within the highly porous medium was measured using a matrix of chromel-alumel thermocouples of 100 μm diameter. The following conclusions were drawn from the results obtained in the present study. Higher velocities were measured in the pore regions, whereas lower velocities were measured in the frame region. From the microscopic aspect, the highly porous medium has an ability to change the velocity distribution with its mesh frame. The velocity distributions at the upstream side of the highly porous medium were almost parabolic in the area average. However, the area averaged velocity distributions at the downstream end of the highly porous medium were homogeneous. From the macroscopic aspect, it can be concluded that the highly porous medium has an ability to make the flow velocity distribution homogeneous. The high temperature region was established in the highly porous medium. The stored energy in the highly porous medium was about 100 times larger than that for a medium that was not highly porous medium. It is presumed that the heat energy in the highly porous medium was maintained not only in the flow channel but also in the highly porous medium itself by convection in the complex flow path, as the heat capacity of the highly porous medium is about 180 times larger than the heat capacity of air. It can be said that the highly porous medium can retain much thermal energy by the complex three-dimensional slim mesh frames and the fact that it has a higher heat capacity than air. The facts obtained in the present study therefore suggest that the highly porous medium can be used in high-performance energy-conversion devices.

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