Experimental investigation on the local heat transfer with an unconfined slot jet impinging on a metal foamed flat plate

Abstract

The objective of the present work is to measure the local heat transfer coefficient for an unconfined slot air jet impinging on a metal foamed flat plate having different pore densities using a thin metal foil technique. The enhancement of the heat transfer caused by the metal foamed flat plate in comparison with a smooth flat plate is measured. The experiments are performed for the Reynolds number (based on slot width) ranging from 5200 to 12,000, and nozzle to plate spacing varied from 2 to 10 times the slot width. Aluminium foams having a porosity of 92% and a pore density of 10, 20, and 40 pores per inch (PPI) are used. The thickness of the metal foam is 8 mm. An infrared camera is used to measure the local temperature distribution of the metal foamed flat plate. A metal foamed flat plate enhances the stagnation Nusselt number and the average Nusselt number compared to the smooth flat plate irrespective of the pore density. The local Nusselt number is highest in the stagnation region and decreases in the streamwise direction. A metal foamed flat plate with a pore density of 40 PPI results in lower augmentation of the stagnation and average Nusselt number compared to a metal foamed flat plate with a pore density of 10 PPI and 20 PPI. Metal foamed flat plates with a pore density of 10PPI, and 20 PPI show almost the same stagnation Nusselt Number and average Nusselt number. The average and the stagnation Nusselt numbers are less sensitive to the nozzle to plate spacing for a metal foamed flat plate. Empirical correlations for the local Nusselt number for three different regions based on the Reynolds number (Re), non-dimensional streamwise distance (x/b) and nozzle to plate spacing (z/b) are proposed.