Experimental investigation of moist air condensation on hydrophilic, hydrophobic, superhydrophilic, and hybrid hydrophobic-hydrophilic surfaces

This study experimentally investigates the condensation performance amid hydrophobic, hydrophilic, superhydrophilic and hydrophobic-hydrophilic hybrid patterned surfaces with air velocity ranging from 0.5 m/s to 4.0 m/s and relative humidity of 85%, 60% and 40%. The hybrid novel surface employs inverted V shape channels design with alternate hydrophilic and hydrophobic channel to direct condensate, and the accumulated condensate is gathered at vertical hydrophilic channel for further effective condensate removal. It is found that the heat transfer coefficient for hydrophobic surface is higher than that of hydrophilic surface irrespective of the operational velocity and relative humidity. Dropwise condensation prevails for the hydrophobic surface and a twig-like structure of condensate is seen for the hydrophilic surface, and this phenomenon becomes more pronounced when the relative humidity is increased. The superhydrophilic surface shows the worst heat transfer performance due to filmwise condensation. The hybrid surface shows superior heat transfer performance over other surfaces. The heat transfer coefficient obtained is around 3-9% higher than that of hydrophobic surface and is about 6-16% higher than hydrophilic one. The proposed novel design offers a shorter cyclic condensate removal time and better condensate drainage. It is found that the maximum diameter for the hybrid surface is about 80-90% smaller than the hydrophobic surface and the droplet size before falling off is relatively independent of operational velocity.