Heat transfer in rectangular channels with porous wire mesh under impinging jet conditions

Detailed heat transfer distribution in a rectangular channel under an array of impinging air jets was experimentally investigated using transient liquid crystal technique. The jet-to-jet spacing was 4 and the jet-to-surface spacing was 3. The rectangular channel was fully or partially filled with porous wire meshes (filling ratios = 100%, 50% and 25%) and the jet Reynolds numbers ranged from 2500 to 7700. Although the literature data indicated that the porous material enhanced the overall heat transfer rate, the regional heat transfer on the target surface was degraded because of the blockage and breakup of the core jet flow. The heat transfer coefficient was further reduced with an increase in the filling ratio. For the partially filled channel, the porous wire mesh located near the target surface contributed to even lower heat transfer. All the cases demonstrated that the porous material decreased regional heat transfer on the target surface, and the average Nusselt number for the fully filled case was only 50% of the unfilled case. Although the impingement heat transfer was hindered, the reduced variation in Nusselt number could prevent the development of local hot or cold spots in engineering applications.