A FLOW VISUALIZATION STUDY OF THE JET DYNAMICS IN A ROUND JET IMPINGING ON A FOAMED ALUMINUM POROUS MEDIA

The high surface area of foamed metals makes them an attractive choice for impingement heat sinks. If the jet can effectively penetrate the foam, the high surface area will lead to enhanced thermal performance. However, if the jet fails to effectively penetrate the foam, the surface enhancement effect will be reduced. Previous studies have suggested that for high density foams, the jet does not effectively penetrate the foam and under certain flow conditions may in fact deflect off the foam. In this study, the flow dynamics of round jets impinging on both aluminum foams and solid cubes are studied using smoke wire visualization to identify the effects of Reynolds number and jet exit to surface spacing. The differences in the impinging jet dynamics between the foams and the solid cubes are identified. It is found that the penetration of the impinging flow into the porous media is significantly affected by permeability. As permeability decreases, flow deflection off the impact surface of the foam increases, approaching the fluid dynamics behavior of impact on a solid cube. The jet-exit-to-surface spacing and Reynolds number are also found to significantly affect the flow dynamics.