仿生亲疏水异质梯级沟槽表面强化冷凝传热机理研究

Surface wettability and microstructures play an important role in phase change heat transfer of steam condensation. Inspired by the process of fog harvesting in the hierarchical grooved surface of a Sarracenia trichome, a new type of hydrophobic-hydrophilic heterogeneous surface with bionic hierarchical grooves is proposed to enhance condensation heat transfer, which upgrades the striped hydrophilic-hydrophobic heterogeneous surface. The fractal Cantor structure is introduced to characterize and reconstruct the hierarchical grooved surface of a Sarracenia trichome and a new type of enhanced condensation surface is fabricated accordingly. The project will measure the heat transfer performance of condensation on the fabricated surface and conduct visualization experimental investigation on the dynamic evolution of vapor-liquid interface via high speed microscope camera. In addition, a lattice Boltzmann model of condensation heat transfer process is developed and numerically analyzed. In this model, the surface wettability, topography of the hierarchical grooved structure and the dynamic behavior of vapor-liquid interface are considered. Through the visualization experiment and mesoscopic simulation, the project will elucidate the cooperative transport mechanism of droplet growth and coalescence, liquid film flow and suction, droplet and liquid film fusion and oscillation on the present surface during condensation. The effects of surface wettability, morphology of hierarchical grooved structure, and condensation parameters on the characteristics of condensation heat transfer are going to be expounded. The occurrence condition for the dropwise-filmwise condensation will be clarified. The mechanism of condensation heat transfer enhancement on the hydrophobic-hydrophilic heterogeneous surface with bionic hierarchical grooves will be revealed. This project will be of significant scientific value in the theory development for microscale phase change heat transfer and interface dynamics. It will also provide important technical supports for the optimization design of bionic condensation surface.

表面润湿性和微结构在蒸汽冷凝相变传热过程中发挥着主导作用。受瓶子草绒毛表面梯级沟槽结构在雾气中高效集水现象启发，本项目在条纹型亲疏水异质表面基础上，配置梯级沟槽，提出仿生亲疏水异质梯级沟槽表面用于强化冷凝传热。基于Cantor集分形开展瓶子草绒毛表面梯级沟槽的仿生重构并据此研制新型强化冷凝表面，结合高速显微成像技术开展该表面冷凝传热性能测试及可视化实验；基于格子Boltzmann方法建立冷凝相变传热理论模型并数值求解；探析仿生亲疏水异质梯级沟槽冷凝表面液滴生长合并、液膜流动抽吸以及液滴、液膜融合振荡全过程的协同输运机制，阐明表面润湿性、梯级沟槽形貌和冷凝工况参数对冷凝传热特性的影响规律，掌握滴膜共存冷凝模式及发生条件，进而揭示仿生亲疏水异质梯级沟槽表面强化冷凝传热机理。本项目不仅有助于进一步完善微尺度相变传热及多相界面动力学基础理论，也将为仿生表面冷凝调控和优化设计提供关键技术支撑。

亲水区液膜流动可快速吸收输运疏水区冷凝液滴，加快疏水区表面液滴更新频率，因此合理布置亲疏水区域，对强化整体传热有重要意义。受瓶子草绒毛表面梯级沟槽结构对水分连续运输的启发，本项目构建基于Cantor 集分形几何特征仿生梯级沟槽表面用于强化纯蒸汽冷凝。搭建了自相似亲疏水异质梯级沟槽表面冷凝传热特性可视化实验平台，观测了亲疏水异质多级沟槽结构表面上冷凝液滴在不同过冷度下液滴动力学行为，揭示了滴膜共存冷凝模式及发生机制。建立槽道内液膜抽吸脊部液滴模型，探究冷凝过程中疏水梯级沟槽内液滴生长合并、亲疏水区交界处液膜抽吸液滴以及亲水梯级沟槽内冷凝液膜快速输运过程的协同排液机制。.研究结果表明：液滴冷凝生长初始阶段，疏水表面液滴脱除方式主要为液滴合并弹跳以及重力驱动的液滴滚动，过冷度对液滴动力学行为以及冷凝传热影响很大；合理布置多级沟槽结构，能够在高过冷度下第一级沟槽失效后，第二级沟槽仍有效限制大液滴形态，继而维持高效弹跳排液模式，从而实现高过冷度下高效传热；多级沟槽的引入可以显著提高亲水区域对大液滴的容纳，克服了平板表面和沟槽表面亲疏水区域跨区域液膜形成，有效提高了表面刷新率，减少了大液滴的延迟，与纯疏水表面相比传热效果提升明显；槽道内液膜与脊部液滴接触后就会通过毛细作用将液滴输运至液膜中，从而清洁槽道脊部，使之暴露出更多的有效表面以开启新一轮的冷凝循环，在其他条件相同时，不同尺寸的液滴与液膜合并的过程具有自相似性。.研究工作揭示了亲疏水异质梯级沟槽表面上的液滴排液动力学行为、滴膜共存冷凝传热特性、液膜抽吸脊部液滴机理，阐明了自相似亲疏水异质梯级沟槽表面强化纯蒸汽冷凝传热机制，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、Physics of fluids等期刊上发表SCI收录论文8篇，申请发明专利6件，其中授权3件。