Experimental study of flexible, unstructured metal foams as condensation structures

•Low cost porous-media based water recovery process.•Non-structured porous media as a condensation surface.•External condensation on vertical cooled, finned tubes.•Effect of the porous media density of the water vapor recovered. This paper experimentally considers the use of non-structured (i.e., flexible) metal foams as a way to increase the amount of water vapor recovered from a humidified air stream. For that, a dedicated experimental setup consisting of three sub-systems (i.e., air pumping, air humidification, and air dehumidification) was developed. In the dehumidification section, different test sections (condensation structures) were installed and the amount of water recovered from the saturated air stream was recorded and correlated with each of them. Four main types of test sections were tested: (i) bare copper tube (used as base line), (ii) copper tube assisted by metal foam, (iii) finned tube and (iv) finned tube assisted by metal foam. Refrigerated fluid was circulated through copper tubes within a close loop and served as heat sink, allowing vapor phase change. The results show that the amount of water recovered increases with the surface area of the test section and with the temperature difference between the saturated air stream and the cooled surface. Also, it was shown that, above a certain quantity of metal foam within the test section, the amount of condensate produced is basically unaffected. Differently, the results indicate that the use of fins, which were properly brazed to the copper tubes, increases significantly the amount of water recovered from the saturated air stream.