微纳液滴核化生长和合并弹跳协同强化高不凝气含量蒸汽冷凝机理

Heat and mass transfer enhancement of steam condensation in the presence of high fraction non-condensable gas is significant in the temperature/humidity management of aeronautical and space and the waste heat recovery from effluent gases and tail gases of steamer. Efficient micro/nano droplets centralized nucleation, rapid nucleated droplet growth rate and effective coalescence-induced self-propelled jumping provide important techniques to the improvement of condensation heat and mass transfer in the presence of high fraction non-condensable gas through eliminating the constraints of the slow nucleation and growth rate, isolated arrangement and difficult drainage of micro/nano droplets. This project will focus on the automatic adjustment of micro/nano structured multi-functional byphilic surfaces to the micro/nano droplets dynamic properties consisting of the nucleation and growth rate, directional motion and coalescence-induced self-removal. The mechanism of the centralized droplets nucleation and rapid growth enhanced by the properties of nanostructures will be revealed clearly by experimental, theoretical model analysis and numerical investigations thus a principle for optimizing the nanostructures properties can be obtained. Moreover, the project will also investigate the influence of microstructures properties and the wetting modes of micro/nano droplets on the minimum critical radius that can achieve effective coalescence-induced self-propelled jumping. Therefore, the mechanism of reducing the critical self-removal radius by adjusting the dimensions (diameter and spacing) of nanostructures region with hydrophilic apexes and the microstructures properties will be demonstrated subsequently. A novel synergistic enhancement strategy for condensation heat and mass transfer in the presence of high fraction non-condensable gas will be proposed and the new-type condensation heat and mass transfer enhancement techniques will be developed finally through studying the intrinsic relationship between local optimization and global enhancement by combining the theoretical model analysis and experimental visualization.

高不凝气含量蒸汽冷凝过程传热传质的强化在航空航天温湿控制、烟道气和轮船尾气余热回收等方面具有重要的意义。通过驱动微纳液滴在冷凝表面集中快速核化生长和高效合并弹跳自排离，消除微纳液滴核化生长缓慢、孤立分散和移除困难的制约是强化高不凝气含量蒸汽冷凝传热传质的重要手段和有效策略。本项目拟采用微纳结构多功能组合表面自主调控微纳液滴的核化生长、定向迁移及合并弹跳自排离。通过实验研究、数值模拟和模型分析，揭示纳米结构特性驱动微纳液滴集中快速核化生长的物理机制，获得纳米结构特性的优化策略。考察微米结构特性和微纳液滴润湿模式对合并弹跳微纳液滴最小临界尺寸的影响规律，阐明顶端亲水纳米结构区域直径和间距及微结构特性参数减小微纳液滴合并弹跳自排离尺寸的驱动机制。结合模型分析和实验观测阐明局部优化和整体强化之间的内在关系，提出高不凝气含量蒸汽冷凝传热传质协同强化的新策略和指导新型冷凝传热传质强化技术的开发。

高不凝气含量蒸汽冷凝过程传热传质的强化在航空航天温湿控制、烟道气和轮船尾气余热回收等方面具有重要的意义。通过驱动微纳液滴在冷凝表面集中快速核化生长和高效合并弹跳自排离，消除微纳液滴核化生长缓慢、孤立分散和移除困难的制约是强化高不凝气含量蒸汽冷凝传热传质的重要手段和有效策略。本项目采用微纳结构多功能组合表面自主调控微纳液滴的核化生长、定向迁移及合并弹跳自排离。. 在理论分析中，将不凝气作为传热过程中的独立热阻，建立了含不凝气蒸汽滴状冷凝传热模型，获得了超疏水表面液滴脱落半径与表面柱间距之间的关系,分析了不同过冷度、不同不凝气含量下，超疏水表面结构参数对于滴状冷凝传热性能的影响。发现在不凝气浓度低于20%时，增大柱间距以减小表面结构热阻有利于传热性能的提高；当不凝气浓度高于20%时，减小柱间距使液滴脱落半径增大更能强化换热。. 在数值模拟中，采用ANSYS Fluent软件分别对30°、60°和90°接触角表面及相应组合表面上的冷凝进行了模拟。研究了25%不凝气含量下液滴的成核、合并机制及不同润湿性表面液滴生长周期内的液滴动力学特征和冷凝传热性能。发现90°接触角的均匀润湿性表面对高不凝气下滴状冷凝换热性能的强化更为显著；液滴在不同润湿性表面间存在定向输运，而60°&90°组合表面相较于30°&90°组合表面传热性能提升了2%。. 在实验探究中，设计并搭建了可实现水平管与竖壁蒸汽冷凝交替进行的试验台，构建了高精度热电偶检测系统以及接触角测量系统。旨在结合模型分析和实验观测阐明局部优化和整体强化之间的内在关系，提出高不凝气含量蒸汽冷凝传热传质协同强化的新策略和指导新型冷凝传热传质强化技术的开发。. 此外，依托本项目对相变储能系统充/放热性能进行了优化研究，通过调控功能翅片参数和储能材料物性参数优化整体充/放热性能，消除自然对流换热控制区域和导热控制区域不协调和不匹配矛盾的影响，获得了最优功能结构翅片的选择准则，为驱动组合相变材料充热性能强化的翅片系统的选择提供参考。