液滴冲击流动液膜时多液滴交错区流体迁移与换热机理

Droplet impact on liquid film is witnessed in horizontal-tube falling film evaporation, spray cooling and many other technologies. In practical view, the liquid film is in motion and impinged by multiple droplets, lacking understanding of which has become a bottleneck for the development of relevant technologies. This project is directed to multi-droplet impact on a liquid film flowing through a heated wall. With the aid of transient measurement of high-speed visualization, theoretical analysis and high-accuracy three-dimensional numerical simulation, dynamic characteristics and heat transfer process during horizontally-aligned simultaneous droplets, vertically-aligned successive droplets, and droplet arrays impact on the flowing liquid film are studied. This project will identify the major driving factors for internal transfer process and external interface evolution, and clarify the nonlinear coupling mechanisms between them, under the complex interplay of multi-droplet superposition, interference, and fluid migration caused by the flowing film. And, it will also reveal the interfacial feature and micro flow regularity in the multi-droplet overlap region, and ascertain the asymmetric and uneven migration characteristics and corresponding regulatory mechanisms during impact on the flowing liquid films with different directions, and will further resolve the fluid migration and heat transfer in the overlap region both physically and mathematically. In addition, this project will propose an optimized match for multi-droplet distribution and parameters of the flowing film, and build up an optimum design criteria for heat transfer of droplets impact on a liquid film, facilitating theoretical exploration and technological development of the thin liquid film high-efficiency heat transfer.

液滴冲击液膜在水平管降膜蒸发、喷雾冷却等技术中广泛存在。实际工程技术中液膜多处运动状态且冲击过程体现为多液滴连续冲击，对其认识不足已成为制约相关技术发展的一个主要瓶颈。本项目针对多液滴冲击热表面流动液膜过程，通过高速可视化瞬态实验测试、理论分析结合高精度三维数值模拟，开展水平同步液滴、竖直连续液滴基本单元和阵列连续多液滴冲击热表面流动液膜动力学特征与换热过程。甄别多液滴叠加、干涉及液膜流动引起的流体迁移复杂作用下液体内部传递现象和外部界面演变的主要动力因素，阐明二者间非线性耦合作用机理。揭示多液滴交错区界面特征及微细流动规律，阐明冲击不同流向液膜时非对称、非均匀传递过程的迁移特性与调控机制，作出液滴交错区流体迁移与换热的物理数学描述。获得多液滴分布与流动液膜参数的最佳匹配，以期初步建立液滴冲击液膜换热的优化设计准则，推动薄液膜高效换热理论探索和技术发展。

液滴冲击液膜在水平管降膜蒸发、喷雾冷却等技术中广泛存在。实际工程技术中液膜多处运动状态且冲击过程体现为多液滴冲击，对其认识不足已成为制约相关技术发展的一个主要瓶颈。本项目采用实验测试、数值模拟和理论分析的手段，对同步、连续、异步多液滴冲击静止液膜和流动液膜的动力学与传热过程开展了系统研究。阐释界面加速重要作用，提出流体失稳溅射高斯分布扰动模型，可精确预测液滴冲击溅射过程。发现了多液滴冲击过程中出现的传热盲区，揭示了残余液膜内流场与温度场耦合效应对对流传热的增强作用。揭示了液膜内部气泡在同步、连续冲击过程中的一系列运动与变形现象，总结出局部传热量的相关变化规律，最大传热系数出现在三相接触线处。观测到了冲击流动液膜时出现的非对称溅射现象和界面演变特征，并确定了溅射临界参数的预测方法。通过三维数值模拟揭示了流动液膜剪切作用力引发的界面特征滑移机理，并分析了不同特征参数作用下界面滑移的变化规律。本项目的完成，对推动薄液膜高效传热的理论探索和技术发展具有重要意义。