Sustaining High-Performance Dropwise Condensation of Low-Surface-Tension Fluids on Multiscale Additively Manufactured Slippery Surfaces

Achieving long-term stable dropwise condensation in industry has been a long-standing goal over the past few decades. However, due to irreversible wetting state transition and insufficient material durability, the delicate dropwise condensation (DWC) mode rapidly deteriorates to the filmwise condensation mode (FWC) after hours or days of operation, a phenomenon commonly referred to as flooding. The slippery lubricant-infused surface (SLIPS), also known as a liquid-infused surface (LIS), was found to have great promise for enabling DWC not only for steam but also for low-surface-tension fluids such as ethanol or hexane. While numerous studies have focused on the chemical properties of the infused lubricants to improve DWC performance, the role of substrate roughness morphology has received far less attention. In this study, additive manufactured (AM) aluminum alloy AlSi10Mg was employed to create multiscale micro- and nanoroughness for SLIPS. For the first time, a modified Wilhelmy plate setup was developed to probe the capillary force induced by contact angle hysteresis for comparing the dynamic wettability of differently structured AM SLIPS with macroroughness. The two-tier hierarchical structured SLIPS exhibits significantly improved dynamic wetting stability, thus enhancing antiflooding performance for ethanol dropwise condensation under high subcooling conditions and long-term operation. Its heat transfer coefficient was maintained between 7000 and 7300 W/m²·K over a logarithmic mean temperature difference range of 8 to 28 K, which is approximately 280% of that measured for FWC (2500 to 2700 W/m²·K). During long-term testing, no significant degradation was observed after 100 h of a continuous high subcooling operation in pure vapor. In contrast, other single-tier structured surfaces rapidly transitioned to the FWC either under high subcooling conditions or after short-term operation within 10 h. This work highlights that micro/nanoscale roughness plays a pivotal role in antiflooding performance, offering important guidelines for the future design of durable antiflooding DWC systems for low-surface-tension fluids.