Forced convective heat tranfer in a metallic foam cylinder cooled by a slot jet flow and comparison with a smooth cylinder and a full flow

The aim of the present paper is to study experimentally the enhancement of heat transfer, due to the presence of a layer of aluminum foam covering a smooth circular cylinder. The measurements are carried on with the impingement of a rectangular jet of air, which has a transversal dimension equal or smaller than the cylinder diameter, or jet flow, and full flow (or uniform flow, which has a greater dimension than the cylinder diameter). Literature does not report any paper dealing with this multiple problem. Experimental heat transfer and fluid dynamics measurements are carried out at Reynolds number ranging from ReD=2200 to ReD=24,750. The layer of the aluminum foam, 8 mm thick, is glued onto the smooth cylinder, with an external diameter of D = 10 mm. The height of the slot jet is H = 10 mm, with a width of W = 135 mm. Jet flow visualizations are performed for the smooth and the foam-covered cylinder to explain the heat transfer results from the fluid dynamics point of view. The flow visualizations show that the jet flow always penetrates into the foam, wetting it completely, while the reattachment never occurs downstream. In the smooth cylinder, the jet completely envelops the cylinder, at greater Reynolds numbers and a distance of x/H = 7, with a small recirculation zone, showing that the rear surface also participates in the heat transfer. The heat transfer on the foam-covered cylinder increases, mainly, because of the large increase in the exchange surface, while it is somewhat penalized, at the higher Reynolds values and at the greater distance from the slot exit, because the rear surface is little involved in the heat transfer.