Moist air condensation heat transfer enhancement via superhydrophobicity

•Moist air condensation on vertical superhydrophobic surface is tested.•Condensate departure mechanism in hydrophilic surface is gravity driven sliding.•Direct and bounced jumping are the departure mechanism in superhydrophobic surface.•Superhydrophobic surface offered a 36% enhancement in heat transfer coefficient.•Influence of subcooling temperature on heat transfer coefficient is predominant. The main objective of the present study is to experimentally investigate the moist air condensation behavior subject to hydrophilic and superhydrophobic surface with a much broader operating conditions such as different relative humidities (RH = 40 – 85%) and degree of subcooling (ΔTsub= 1 – 16 K). The flow visualization of condensation behavior showed that the main condensate departure mechanism of the hydrophilic surfaces is gravity-driven sliding. In contrast, the primary mechanisms for the superhydrophobic surfaces are direct jumping and bounced-jumping caused by the coalescence induced phenomena. The superhydrophobic surfaces yielded a maximum of 36% improvement in heat transfer coefficient at 85% relative humidity over the hydrophilic surfaces, while the enhancement is about 16% for 60% and 40% relative humidities. Similarly, the maximum heat transfer coefficient of 37 W m-2K−1 is attained at the subcooling temperature of 16 K, and it is reduced to 31 W m-2K−1 and 20 W m-2K−1 respectively when the subcooling is reduced to 6 K and 1 K.