Abstract
The present study is concerned with an experimental investigation of the local heat transfer coefficient for an air jet impinging on a metal foamed flat plate having different pore densities using a thin metal foil technique. The augmentation of heat transfer caused by the metal foams in comparison with heat transfer on a flat plate is quantified. The experiments are performed to measure the temperature distribution of the metal foamed flat plate with the help of an infrared themal camera. Alunumium metal foams having 8 mm thickness and pore densities of 10, 20 and 40 pores per inch (PPI) are studied. The porosity and thickness of the each aluminum metal foam is 92 %. The range of the Reynolds number (based on the nozzle diameter) covered in the study is 10000 to 25000 and the nozzle to plate spacing varied from 2 to 10 nozzle diameter. The local Nusselt number is highest at the stagnation region, and it decreases in the radial direction away from the stagnation point. Metal foamed flat plate enhances the heat transfer performance compared to a smooth flat plate irrespective of metal foam pore density (pores per inch). The stagnation Nusselt number and average Nusselt number for the metal foamed flat plate is consistently higher compared to the smooth flat plate. A metal foamed flat plate with a pore density of 10 PPI results in higher augmentation of the stagnation and average Nusselt number compared to metal foamed flat plates with a pore density of 20 and 40 PPI. Metal foamed flat plate shows little decrement in the stagnation Nusselt number with an increase in the nozzle to plate spacing irrespective of the pore density. The average Nusselt number seems to be insensitive to the nozzle to plate spacing. Region wise semi-empirical correlations of the local Nusselt number based on the Reynolds number (Re), non-dimensional radial distance (r/d) and non-diamnesional nozzle to plate spacing (r/d) are proposed.
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