Surface property effects on dropwise condensation heat transfer from flowing air-steam mixtures to promote drainage

In this study, the effect of a partially structured Ti-coated plate surface on droplet drainage and heat transfer in dropwise condensation in a compact plate heat exchanger is investigated. In the presence of high concentrations of inert gases, heat transfer is governed by vapor diffusion and condensate drainage is of major importance. A structured coating of the condenser plates is applied to create two coexisting dropwise condensation patterns. The structured Ti-coating constrains drainage and introduces directed surface energy “gradients”, 1-D binary patterns. The condenser with the partially structured coating is compared with two equally sized condensers: a full PVDF and a fully Ti-coated PVDF condenser. It is found that drop drainage is promoted by oriented Ti-coated tracks with a width of approximately the diameter of the maximum drop size to such a degree that the heat transfer performance is practically the same as that of a fully Ti-coated exchanger. Design recommendations are given.

► Titanium tracks were coated in a drainage promoting pattern.
► Dropwise condensation occurred with different patterns and drainage processes.
► Droplets roll-off with a smaller size and more frequently on Ti-coated tracks.
► Heat and mass transfer enhancements were up to 50% as compared to a PVDF condenser.
► The Ti-tracks have the same enhancement as a homogeneous Ti-surface.