A visualization study of the flow dynamics of a single round jet impinging on porous media

The use of high surface area foamed metals in heat sink design is desirable to improve thermal performance and there have been a number of studies which investigated the heat transfer aspects of jet impingement on foamed metals. However, an understanding of the fluid dynamics is also crucial to optimize the convective flow and heat transfer performance. In this experimental study, smoke-wire flow visualization is employed to investigate the behavior of a single round jet of 21. mm and 41. mm diameter issuing from a straight tube and impinging on a foamed aluminum heat sink. The permeability of the foamed aluminum is varied and the effect on the flow dynamics of the impinging jet is examined. The effects of jet-to-surface spacing and Reynolds number are identified. Recirculation regions and flow deflection patterns are identified. Flow deflection is found to be more significant for low jet exit-surface spacing and for low permeability foams. Thus, an increase in jet-exit-to-surface spacing allows more of the flow to evenly penetrate the heat sink. It is also found that an increase in Reynolds number from a laminar to a turbulent jet allows the flow to penetrate the porous media more evenly and reduces the recirculation region at the exit of the foam.