Effect of micro- and nano-structural effects in condensation heat transfer
讲座名称：
Effect of micro- and nano-structural effects in condensation heat transfer
讲座时间：
2016-12-07
讲座人：
Daniel Orejon
形式：
校区：
兴庆校区
实践学分：
讲座内容：
报告题目：Effect of micro- and nano-structural effects in condensation heat transfer
报告时间：12月7日（周三），15：00-17：00
报告地点：东三楼东汽报告厅
报告人：Daniel Orejon博士
报告摘要：
The effect of micro-texture heterogeneities, spatial distribution, and surface wettability on wetting and on liquid propagation have been extensively addressed, nonetheless the role of nano-scale roughness has received lesser attention. In this talk I will address first the effect of micro-pillar density and then that of nano-roughness orientation on condensation dynamics. On a completely hydrophilic micropillared configuration the spacing between pillars is found to have a strong impact on the dynamics of condensation and on the heat transfer performance. Micropillared surfaces with short spacing between pillars allow for the continuous liquid propagation between pillars and condensation takes place in a mixed dropwise and filmwise condensation fashion. On the other hand, in the case of large spacing, the condensate is able to grow above the pillars and the final condensation behavior is that of filmwise condensation. Next, for the same micropillar geometry, different condensation mechanisms are observed for different orientations of the nano-roughness imprinted on the pillars. Longitudinally oriented nano-ridges (perpendicular to liquid propagation) are found to suppress the liquid propagation between pillars whereas circumferentially oriented ones (parallel to liquid propagation) facilitate the propagation of the condensate. As a result of the liquid propagation suppression, the liquid interface is constrained in an upwards direction rising above the micropillars’ height eventually flooding the substrate, i.e., filmwise condensation. On the contrary, in the case of circumferentially aligned nano-ridges the condensate does not rise above the micropillars. In this latter case, condensation takes place as filmwise condensation with active dropwise condensation at the micropillars’ tops. Differences observed in liquid propagation and on the final condensation behavior are solely induced by the nano-roughenss orientation. In addition, a thermal resistance based model is proposed to account for the different theoretical heat transfer performance depending on the micropillar density and on the nano-roughness orientation. We point out to the importance to account for nano-scale roughness orientation for the effective design of surfaces for condensation and microfluidics applications.
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