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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces
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Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces

机译：在纳米结构表面上同时进行液滴撞击动力学和传热

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摘要

This study examines the hydrodynamics and temperature characteristics of distilled deionized water droplets impinging on smooth and nano-structured surfaces using high speed (HS) and infrared (IR) imaging at We = 23.6 and Re = 1593, both based on initial drop impingement parameters. Results for a smooth and nano-structured surface for a range of surface temperatures are compared. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. The near surface average droplet fluid temperatures are evaluated for conditions of evaporative cooling and boiling. Also included are surface temperature results using a gold layered IR opaque surface on silicon. Four stages of the impingement process are identified: impact, boiling, near constant surface diameter evaporation, and final dry-out. For the boiling conditions there is initial nucleation followed by severe boiling, then near constant diameter evaporation resulting in shrinking of the droplet height. When a critical contact angle is reached during evaporation the droplet rapidly retracts to a smaller diameter reducing the contact area with the surface. This continues as a sequence of retractions until final dry out. The basic trends are the same for all surfaces, but the nano-structured surface has a lower dissipated energy during impact and enhances the heat transfer for evaporative cooling with a 20% shorter time to achieve final dry out.
机译：这项研究使用高速（HS）和红外（IR）成像技术，在We = 23.6和Re = 1593的基础上，基于初始液滴撞击参数，研究了撞击在光滑和纳米结构表面上的蒸馏去离子水滴的流体动力学和温度特性。比较了一系列表面温度下光滑和纳米结构表面的结果。测量液滴的冲击速度，瞬态扩散直径和动态接触角。对于蒸发冷却和沸腾的条件，评估了近表面平均液滴流体温度。还包括在硅上使用金层IR不透明表面的表面温度结果。确定了撞击过程的四个阶段：撞击，沸腾，接近恒定的表面直径蒸发和最终变干。对于沸腾条件，先进行成核，然后剧烈沸腾，然后蒸发至接近恒定直径，导致液滴高度缩小。当在蒸发过程中达到临界接触角时，液滴会迅速缩回到较小的直径，从而减小与表面的接触面积。这将继续进行一系列收缩，直到最终变干。对于所有表面，基本趋势都是相同的，但是纳米结构表面在冲击过程中具有较低的耗散能量，并提高了蒸发冷却的传热效率，缩短了20％的时间以实现最终干燥。

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