Dropwise condensation heat transfer on superhydrophilic-hydrophobic network hybrid surface

摘要

Superhydrophilic-hydrophobic (SHPi-HPo) network hybrid surface was designed to investigate the condensation heat transfer using stainless steel as substrate material. The SHPi-HPo surface was comprised of superhydrophilic network grooves and hydrophobic regions. Hydrophobic (HPo) surface was prepared with fluorocarbon coating using polytetrafluoroethylene (PTFE) as the matrix resin and micro-nano silicon dioxide (SiO2) as additive to control surface roughness. Three kinds of SHPi-HPo surfaces were tested, having a grid spacing of 1.5, 2.5 and 3.5 mm and named as SHPi-HPo-1, SHPi-HPo-2 and SHPi-HPo-3, respectively. To study the effects of the wall subcooling, steam mass flux, cooling water temperature, cooling water mass flow rate and grid spacing, a series of experiments were conducted and a high speed camera was used to visualize the condensation process. The results show that SHPi-HPo surface can well control condensate droplet diameters and its condensation heat transfer performance is better than that of smooth hydrophilic (HPi) and HPo surfaces. This is attributed to SHPi-HPo surface sucking away droplets in time and limiting the growth of large condensate droplets through the superhydrophilic grooves. At wall subcooling Delta T-w = 6.3 K, the heat transfer coefficient of SHPi-HPo-2 surface is 2.7 and 3.4 times that of HPi and HPo surfaces, respectively. For SHPi-HPo surface, there is optimum grid spacing between superhydrophilic grooves to enhance condensation heat transfer. Among three SHPi-HPo surfaces, the heat transfer coefficient of SHPi-HPo-2 surface has the best condensation heat transfer performance, about 0-10% higher than that of SHPi-HPo-1 surface, and at Delta T-w = 9 K, the heat transfer coefficient is 1.7 times that of SHPi-HPo-3 surface. (C) 2018 Elsevier Ltd. All rights reserved.