Condensation Experiments on Wettability-Patterned Surfaces in the Absence of Non-Condensable Gases

Water vapor condensation is affecting many engineering applications, especially in the power industry. The main modes of this phenomenon are dropwise condensation (DwC) and filmwise condensation (FwC). In DwC, the condensate creates droplets that grow, coalesce and eventually get pulled by gravity to leave the surface, while in FwC, the condensate forms a liquid film. In terms of heat transfer rate, DwC's performance far exceeds that of FwC. DwC and FwC can be combined spatially on the same surface, with philic wedge-shape tracks facilitating FwC and capillary-driven condensate drainage, while the phobic background promotes DwC. This strategy is applied here in passive heat spreaders to effectively enhance their condensation heat transfer coefficient (HTC). An innovative experimental setup was designed and built to evaluate the HTC for wettability-patterned surfaces with diverse characteristics by generating water vapor and condensing it on a cooled wettability-patterned plate in an environment devoid of non-condensable gases. Significant differentiators for the investigated wettability-patterned surfaces include the ratio of philic to phobic domains, the length of the contrast line between the two wettabilities, the size and opening angle of the wedge track, and the number of low pressure wells where condensate accumulates before removal.