Scaling Laws for the Influence of Gravity and Its Gradient on Dropwise Condensation: A Simulation Study.

Gravity is essential for the shedding of condensed droplets on hydrophobic surfaces, whose influences on condensation parameters under unconventional gravity conditions remain unclear and are hard to probe through experiments. A simulation framework is designed here to investigate such phase-change processes. We find clear scaling laws between heat flux Q, residual volume V, gravitational acceleration g, and nucleation density N0 with Q ∼ g1/6N01/3 and V ∼ g-1/2N00. We also identify a critical gravitational acceleration determined by nucleation density, above which a counterintuitive trend emerges: the heat flux decreases with increasing gravitational acceleration. This deviation is attributed to the sharp decrease in heat flux contributed by droplets larger than the effective radius. In addition, for zero-gravity scenarios, a centrifugal strategy is proposed to simulate Earth's gravity by introducing artificial gravity with a spatial gradient. We reveal that the gradients have a significant influence on the residual volume but a minor one on the heat flux. The conclusions are informative for the estimation and design of condensation heat transfer systems for future space applications.

Copper-based electro-catalytic nitrate reduction to ammonia from water: Mechanism, preparation, and research directions.

Global water bodies are increasingly imperiled by nitrate pollution, primarily originating from industrial waste, agricultural runoffs, and urban sewage. This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions. Electro-catalysis, especially utilizing copper-based catalysts, known for their efficiency, cost-effectiveness, and eco-friendliness, offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia. In this review, we systematically consolidate current research on diverse copper-based catalysts, including pure Cu, Cu alloys, oxides, single-atom entities, and composites. Furthermore, we assess their catalytic performance, operational mechanisms, and future research directions to find effective, long-term solutions to water purification and ammonia synthesis. Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management. As to the application, challenges regarding complexity of the real water, the scale-up of the commerical catalysts, and the efficient collection of produced NH3 are still exist. Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.