多尺度沟槽结构梯度表面的自驱动珠状冷凝传热机理研究

The gradient surface is of significance to the droplet growth and removal so as to enhance the dropwise condensation. Inspired by the process of fog harvesting with cactus spines, this project introduces the multiscale groove structure of gradient surface for the cactus spine to enhance heat transfer performance during dropwise condensation process. Based on the fractal description of gradient surface topography with multiscale groove structure, the project will develop a theoretical model of transient dropwise condensation with a consideration of surface topography, wetting condition, heat and mass transport occurring at interfaces as well as interfacial motion and transformation. The lattice Boltzmann method is employed to numerically solve this model. The project will fabricate the gradient surface by micro 3D Printing technologies, measure the heat transfer performance of dropwise condensation on the gradient surface, and conduct visualization experimental investigation on the dynamic evolution of flow regime via high speed microscope camera. The coupled thermodynamics and kinetics mechanisms of droplet initial formation, growth, departure, self-propelled motion and coalescence during the dropwise condensation process are explored and analyzed, in effort to elucidate the surface effect, multiscale synergistic effect, coupled mechanisms of heat and mass transport as well as interfacial motion and transformation. This project will reveal the microscopic heat transfer mechanism of dropwise condensation on gradient surface essentially and obtain a functional condensation surface with the integrated optimization of fast droplet growth and high efficient removal, which will provide theoretical bases for the optimization design of miniature phase change heat exchanger.

梯度表面对于促进珠状冷凝液滴快速生长与高效脱除，强化冷凝换热具有重要的作用。受仙人掌刺从雾气中高效收集水分的现象启迪，本项目拟将仙人掌刺多尺度沟槽结构梯度表面拓展应用于强化优化珠状冷凝传热。本项目将在分形描述多尺度沟槽结构梯度表面形貌的基础上，建立考虑表面形貌、润湿状态、相间热质传递及相界面演化的非稳态珠状冷凝理论模型并采用格子Boltzmann方法进行数值求解；采用微加工技术制备仿仙人掌刺梯度表面，结合红外热成像技术和高速显微成像技术开展珠状冷凝传热性能测试及可视化实验；研究梯度表面珠状冷凝过程中液滴核化、生长、脱离、自驱动及聚并的热力学和动力学耦合输运机制，阐明珠状冷凝过程中表面效应、多尺度协同效应、热质耦合机理及相界面演化行为。本项目将从本质上揭示梯度表面珠状冷凝的微观传热机理和调控优化机制，获得集成液滴快速生长与高效脱除性能的冷凝功能表面，为冷凝强化技术的进步提供理论支撑。

梯度表面对于促进珠状冷凝液滴快速生长与高效脱除，强化冷凝换热具有重要的作用。受仙人掌刺从雾气中高效收集水分的现象启迪，本项目将仙人掌刺多尺度沟槽结构梯度表面拓展应用于强化优化珠状冷凝传热。从疏水表面珠状冷凝过程单液滴相变传热特性和动力学行为出发，建立了冷凝液滴生长过程理论模型，分析了沟槽内凝结液滴的自发去润湿行为，定量给出了沟槽尺寸和表面润湿性的影响特性，继而探究了梯度功能表面液滴动力学行为及珠状冷凝传热特性。在此基础上，设计搭建了表面冷凝相变传热性能测试实验平台，可视化研究了梯度表面冷凝相变传热行为及表面润湿梯度、沟槽结构的影响特性。.研究结果表明：液滴冷凝生长初始阶段，接触角大则液滴相界面和内部导热热阻大，使得液滴生长越缓慢；疏水沟槽结构中凝结液滴存在部分去润湿和完全去润湿这两种自发去润湿行为，且槽道的高宽比和底部润湿性是液滴是否有残留沟槽的主要影响因素；亲水性粗糙表面上可能形成珠状冷凝，疏水粗糙表面可能出现滴-膜共存冷凝模式；梯度表面湿空气凝结相变出现亲水和疏水表面的膜状和滴状凝结这两种典型特征；多层润湿梯度周期性排列的梯度表面是湿空气冷凝换热大尺度应用的优选；低过冷度下超疏水表面液滴去除以合并驱动弹跳为主；高过冷度下超疏水表面液滴润湿模式发生转变，表面液滴脱除方式由合并弹跳转变为重力扫掠，减弱沟槽表面冷凝传热效果；渐变沟槽表面因独特的多米诺液滴去除方式，提高了表面刷新率，减少了大液滴延迟，在高过冷度下对珠状冷凝相变传热仍然有强化作用。.研究工作揭示了液滴自驱动行为、珠状冷凝微观机理、液滴自发去润湿机制以及冷凝相变强化特性，阐明了多尺度沟槽结构梯度表面冷凝液滴快速生长和高效脱除的协同强化机制，为冷凝强化技术的进步提供理论支撑，在电子器件热管理、空间热控等领域具有重要应用前景。在Int J Heat Mass Transfer、Applied physics letters等期刊上发表SCI收录论文15篇，申请和授权发明专利6项，受邀作主题报告2次；项目负责人获得国家自然科学基金委优秀青年科学基金资助；研究成果获得江苏省工程热物理学会科学技术一等奖。