Mixed dropwise-filmwise condensation heat transfer on biphilic surface

Condensation heat transfer on biphilic surface is investigated. The surface periodically populates hydrophobic stripes each having a coating layer thickness delta(p) and a width W-DWC, and hydrophilic stripes each having a width W-FWC. The proposed model includes dropwise condensation on hydrophobic stripe, filmwise condensation on hydrophilic stripe, and droplet detachment radius r(max) criterion for heat-mass coupling between the two wettabilities regions. The r(max) is the minimum of detachment radii determined by droplet removal modes of double-sides-suction DSS, one-side-suction OSS and sliding, where DSS is a special case of OSS for droplet located at hydrophobic stripe centerline. Simulation results matched the measured heat transfer data well. Optimal width of hydrophobic stripe W-DWC(o) is found to be dominated by delta(p) and W-FWC, but other parameters weakly influence W-DWC(o). Interfaced by a delta(p)-W-FWC transition curve, a heat transfer regime map is presented to contain Regime I for possible heat transfer enhancement and Regime II for heat transfer deterioration. Regime I enhances heat transfer if W-DWC approaches W-DWC(o), but may deteriorate heat transfer if W-DWC deviates W-DWC(o) too much. The maximum heat transfer enhancement ratio is 1.67 compared with purely hydrophobic surface. Regime ll always deteriorates heat transfer. Our work provides a general guideline to design biphilic surface for performance improvement. (C) 2019 Elsevier Ltd. All rights reserved.