Liquid impingement dynamics on superheated superhydrophobic surfaces

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Characterizing heat transfer from a solid plate to a liquid is important in multiple applications where cooling, condensation, or cleaning properties are necessary. Superhydrophobic surfaces can be self-cleaning and thus present an immediate advantage for their use when in contact with liquids. Water will sit atop the micro/nano structures, leaving an air gap in between the structures and allowing for water to bead up almost completely into a ball on the surface. The water will then roll from the surface and thus it becomes self-cleaning. Although the liquid dynamics of impingement on a superhydrophobic surface are fairly well known, the understanding of heat transfer from these surfaces with micro-scale air gaps to an impinging liquid is not well characterized. Impinging liquids are able to remove heat by the constant replenishing of new, cooler liquid. This study will explore the capability of impinging water droplets or impinging water jets to remove heat from a superhydrophobic surface while still effectively being self cleaning. Superhydrophobic surfaces are generated by combining microscale structuring and a hydrophobic coating such that liquids are often only in contact with a fraction of the solid surface. Impinging processes are rich in fundamental fluid flow and thermal transport physics and represent an excellent test bed to consider with superhydrophobic surfaces since superhydrophobicity exerts enormous influence on the liquid-solid surface tension, which is dominant in impinging processes. It is expected that thermal transport physics of liquid impingement on superhydrophobic surfaces will experience greater departure from classical behavior than has been observed hydrodynamically. The objectives of this work are to characterize the transport for: 1) impinging droplets (normal and oblique impingement angles), and 2) liquid jet impingement (normal and oblique impingement). The proposed research plan includes coupled experimental and analytical approaches. The processes that will be explored have significance in next generation high efficiency condensers, desalinization processes, self-cleaning surfaces, and easily maintained spray cooling systems.