Condensation heat transfer is widely used in water and energy systems. Despite being extensively studied, since 1973, the models for dropwise condensation have strongly relied on the droplet size distribution. In this study, we report that the classical models underestimate the heat transfer performance of dropwise condensation on a hydrophilic liquid-infused surface, on which the meniscusmediated coarsening droplets lead to a previously unachieved droplet coverage ratio down to 30%. We found that the time-averaged classical models have overlooked the coarsening-induced disappearing droplets. Moreover, these models cannot be used to determine the instantaneous heat transfer coefficient on the sheddinginduced water-free surface under steam condensation. Thus, a dynamic model is developed for dropwise condensation by considering the disappearing droplets induced by both coarsening and shedding, which shows good agreement with the experimental validation. Such a dynamic model provides a theoretical foundation to design surfaces for condensation, giving rise to an advanced design guideline for water and energy systems.

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.

Massive studies concern the development of low-carbon water and energy systems. Specifically, surfaces with special wettability to promote vapor-toliquid 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 beetleinspired 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.

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