Experimental analysis of steam condensation over conventional and superhydrophilic vertical surfaces

•A new experimental apparatus for investigation of condensation of pure steam is presented.•Filmwise condensation is investigated over untreated and superhydrophilic aluminum surfaces.•The effect of wall subcooling and vapor velocity is experimentally and theoretically analyzed.•The heat transfer coefficient decreases when increasing the wettability of the surface.•At high vapour velocity, the effect of the wettability increase on the heat transfer is reduced. Nano-engineered surfaces have been recently studied as a promising solution for many heat transfer applications. In particular, it is known that superhydrophobic surfaces, obtained by combining low surface free energy with micro-/nano-scale surface roughness, can promote dropwise condensation mode, while superhydrophilic ones, obtained for example by roughening the substrate to a micro-/nano-scale morphology, showed promotion of film formation during condensation. In the open literature there is a lot of information regarding the fabrication and characterization of these surfaces, but very few results on the heat transfer performance are reported. In this paper, a new experimental apparatus for investigation of condensation of pure steam, flowing at different velocities, is presented. Filmwise condensation is investigated over untreated aluminum surfaces placed inside a rectangular narrow channel. The effect of wall subcooling and vapor velocity on the two-phase heat transfer coefficient is experimentally and theoretically analyzed. Condensation tests are also performed over a superhydrophilic surface, aiming at analyzing the effects of the wetting properties of the substrate on the process. A comparison between the heat transfer coefficients measured on the superhydrophilic surface and the ones obtained on the untreated sample shows a penalizing effect of the hydrophilic treatment.