Search for: All records

We integrate quasi-liquid surfaces, nanovibration technology, and capacitive sensing to create an energy-efficient system for detecting and removing frost and ice without complete melting. 

Water harvesting from air is desired for decentralized water supply wherever water is needed. When water vapor is condensed as droplets on a surface the unremoved droplets act as thermal barriers. A surface that can provide continual droplet-free areas for nucleation is favorable for condensation water harvesting. Here, we report a flow-separation condensation mode on a hydrophilic reentrant slippery liquid-infused porous surface (SLIPS) that rapidly removes droplets with diameters above 50 μm. The slippery reentrant channels lock the liquid columns inside and transport them to the end of each channel. We demonstrate that the liquid columns can harvest the droplets on top of the hydrophilic reentrant SLIPS at a high droplet removal frequency of 130 Hz/mm 2 . The sustainable flow separation without flooding increases the water harvesting rate by 110% compared to the state-of-the-art hydrophilic flat SLIPS. Such a flow-separation condensation approach paves a way for water harvesting. 

Abstract Extensive research concerns dropwise condensation of low surface tension fluids to promote energy efficiency and decarbonization in thermal energy systems. However, it is challenging as these fluids typically result in filmwise condensation. Drawing inspiration from the Namib desert beetle that enhances condensation through patterned wettability, conventional beetle‐inspired surfaces excel in water condensation but flood when condensing low surface tension fluids. In this work, a patterned quasi‐liquid surface is reported that achieves exceptional dropwise condensation of low surface tension fluids. The surface consists of alternating stripes with low surface energy, that is, a perfluoropolyether (PFPE) and fluorinated quasi‐liquid surface (FQLS), that shows ultralow contact angle hysteresis for ethanol and hexane. The PFPE stripes are slightly more slippery, acting as slippery bridges that accelerate droplet coalescence and removal. It is experimentally demonstrated that the striped PFPE‐FQLS pattern exhibits a heat transfer coefficient 85%, 330%, and 550% higher than that of PFPE, fluorinated silane, and filmwise condensation, respectively. This study reveals that a high contact angle is desired to sustain dropwise condensation, irrespective of contact angle hysteresis. These findings provide a new paradigm for promoting the dropwise condensation of low surface tension fluids and offer valuable insights into surface design for energy sustainability. 

Abstract Massive studies concern the development of low‐carbon water and energy systems. Specifically, surfaces with special wettability to promote vapor‐to‐liquid condensation have been widely studied, but current solutions suffer from poor heat transfer performances due to inefficient droplet removal. In this study, the limit of condensation on a beetle‐inspired biphilic quasi‐liquid surface (QLS) in a steam environment is pushed, which provides a heat flux 100 times higher than that in atmospheric condensation. Unlike the beetle‐inspired surfaces that have sticky hydrophilic domains, the biphilic QLS consists of PEGylated and siloxane polymers as hydrophilic and hydrophobic quasi‐liquid patterns with the contact angle hysteresis of 3° and 1°, respectively. More importantly, each hydrophilic slippery pattern behaves like a slippery bridge that accelerates droplet coalescence and removal. As a result, the condensed droplets grow rapidly and shed off. It is demonstrated that the biphilic‐striped QLS shows a 60% higher water harvesting rate in atmospheric condensation and a 170% higher heat transfer coefficient in steam condensation than the conventional beetle‐inspired surface. This study provides a new paradigm to push the limit of condensation heat transfer at a high heat flux, which sheds light on the next‐generation surface design for water and energy sustainability.