Coalescence-induced droplet jumping behavior in moist air condensation on superhydrophobic surfaces

This study provides a systematic experimental investigation of coalescence-induced droplet jumping during moist air condensation on superhydrophobic surfaces (SHS) under three subcooling temperatures (ΔT = 1.0, 5.5, and 10.0 °C). First, we present a large-scale statistical analysis of droplet size distribution and jumping probability, revealing that droplets <30 μm constitute ∼80% of the population and that jumping events of 10–30 μm droplets account for ∼77% of all events. Notably, the jumping probability at ΔT = 1.0 °C is significantly higher than at higher subcooling, especially for large droplets. Second, we quantitatively distinguish binary from multiple-droplet jumping: binary jumping dominates (50%–60% of events) with a wide size range (15–500 μm) but low size-mismatch tolerance (minimum radius ratio ∼0.46), while multiple-droplet jumping occurs in a narrower range (20–150 μm) with higher mismatch tolerance (minimum ratio ∼0.39). Finally, a new prediction model of the heat transfer coefficient of moist air condensation is established that incorporates relative humidity, subcooling, contact angle, and Reynolds number, exhibiting reliable predictive performance with an average prediction error of ∼8% for SHS.