微纳复合结构高效毛细吸液机制及其对沸腾换热的强化机理研究

The enhancement in boiling heat transfer on surfaces by micro/nano hybrid structures is the result of coupling and synergistic effects of micro/nano-meter structures. Due to the complexity of coupling, it is difficult to analyze the enhancing mechanism in boiling heat transfer quantitatively. In this project a multiscale research idea of “solve hierarchically and transfer by scale” is adopted. The capillary wickability is studied as a bridge to connect the micro/nano-meter structures and the critical heat flux (CHF). Firstly, a microscopic system of infiltration process of liquid into the nano-pillar structure is constructed at the nanometer scale, the influence rule of nano-pillar structure parameters on infiltration depth, curvature of meniscus and velocity boundary condition at the top of nano-pillars is found out by using molecular dynamics (MD) method. Secondly, combining with the simulation results at the nanometer scale, the flow field in the micro-pillar structure is solved by using finite volume method (FVM) at the micrometer scale to reveal the influence rule of micro/nano-meter structure parameters on capillary pressure and flow resistance, then a unidirectional capillary flow model is built. Finally, the wetting path in actual boiling heat transfer is found out, and the distribution pattern of liquid leading edge is obtained, then a radial capillary flow model is built. Ultimately, a CHF prediction model is developed to unravel the synergistic enhancing mechanism in boiling heat transfer by micro/nano-meter structures. This project aims to supplement and complete the theory of boiling heat transfer enhancement by micro/nano hybrid structures, and to provide theoretical guidance for developing novel enhanced surface structures.

微纳复合结构对换热表面的沸腾换热强化是微/纳米结构相互耦合、协同作用的结果，耦合方式的复杂性导致对沸腾换热强化机理的定量描述极为困难。本项目拟采用“分层求解，逐级递进”的多尺度研究思路，以毛细吸液能力为桥梁，构建微/纳米结构与临界热流密度的本质联系。首先，从纳米尺度出发构建液体浸润纳米柱状结构的微观体系，采用分子动力学方法查明结构参数对浸润深度、弯月面曲率和纳米柱顶端速度边界条件的影响规律；然后，结合纳米尺度研究结果，在微米尺度采用有限容积法求解微米柱状结构内部流场，查明微/纳米结构参数对毛细压力和流动阻力的影响规律，建立单向毛细流动模型；最后，探明实际沸腾换热中液体浸润路径，获得液体前缘分布规律，发展径向毛细流动模型，构建临界热流密度预测模型，揭示微/纳米结构协同强化沸腾换热机理。本项目研究可进一步补充和完善微纳复合结构强化沸腾换热理论，为开发新型强化表面结构提供理论指导。

随着集成化和高频化程度的不断提高，现代电子设备单位容积的发热量不断增加。微小空间高热通量的散热技术是信息、电子、航空航天以及国防军事技术发展的重要保障。微纳复合结构表面沸腾传热是解决微小空间高热通量散热难题的有效手段。本项目首先研究了纳米孔内部水的浸润过程，获得了相变条件下的浸润规律；然后开展了二维纳米柱状结构表面沸腾成核规律研究，得到了表面柱状结构和润湿性对气泡成核的综合影响规律，并提出了一种新型混合润湿性柱状结构表面，能够同时促进成核和传热；最后开展了三维纳米柱状结构表面沸腾成核规律研究，总结了纳米柱结构及其润湿性对气泡成核位置和固液传热效率的影响规律，揭示了三维纳米柱状结构表面的气泡形成机制。本项目对于理解纳米结构表面的沸腾成核机制和传热规律具有重要的意义，并且为在实际应用中利用纳米结构表面提高沸腾传热性能提供了重要的参考。