Enhancing condensation on heat exchange plates in vacuum membrane distillation evaporators for hybrid ocean thermal energy conversion cycles

Recent advancements in superhydrophobic surfaces have demonstrated improvements in condensation efficiency by promoting droplet detachment. However, the effectiveness of these surfaces in the low-temperature and low-pressure conditions typical of ocean thermal energy conversion (OTEC) systems remains underexplored. This study addresses that gap by developing a superhydrophobic surface modification scheme to promote dropwise condensation under low-temperature and low-pressure conditions. Superhydrophobic surfaces were created on 304 stainless steel samples using a spray method with nano SiO2+PDMS (polydimethylsiloxane), achieving a maximum contact angle of 154°. On the OTEC-VMD (vacuum membrane distillation) platform, the modified plate with SiO2 and PDMS mass fraction of 3.66%, an inlet temperature of 29°C, and a vacuum pressure of 1.77 kPa achieved a condensation enhancement ratio of 34% and an overall heat-transfer coefficient of 1043.2 W/(m2 ·K), a 33.65% increase relative to the unmodified plate. Under conditions of a SiO2 mass fraction of 2.47%, PDMS mass fraction of 3.66%, steam generation rate of 23 L/h, inlet seawater temperature of 29°C, and vacuum pressure of 1.77kPa, the modified plate achieved a condensation enhancement ratio of 36.7%, accompanied by a water-production flux of 7.78 kg/h/m2. Steam generation rate and vacuum pressure significantly influenced water production.