Exit flows from highly porous media

Abstract

This paper presents laser velocimetry measurements of the streamwise component of mean velocities and turbulence intensities measured downstream from the exit plane of porous ceramic foams through which air is flowed. The recent development and commercial availability of porous ceramic foams has lead to their application in many fields. Their uses have extended to combustion, high-temperature fluid filtering, biotechnology, and as support matrix for catalysts. These applications have created an interest in their pore scale fluid mechanics, both within the porous matrix and along surfaces open to flow. One emerging application is porous ceramic burners which combust liquid or gaseous fuels within the pore matrix or along the surface of the ceramic. The ceramic foams have pore sizes ranging from 4 to 12 pores per cm (ppcm) and porosities of 85%. Mean velocities between 0.3 and 1.5 m/s were examined. Radial distributions of mean velocities show a jet-like structure through the pores, with local mean velocities reaching maximum values over two times the area mean velocity. Negative mean velocities were often observed between pores, suggesting that recirculation zones are present above the web-like struts surrounding the pores. Levels of turbulence intensities normalized by the area mean velocity ranged from 0.05 to 0.6 for the various flow rates and pore sizes. Turbulence intensities were found to increase with increasing pore size for a given flow rate.