梯度温度壁面上液滴蒸发过程Marangoni对流及传热传质机理研究

Marangoni convection and heat and mass transfer during droplet evaporation is the key thermophysical problem of evaporation self-assembly. Furthermore, droplet evaporation on gradient temperature surface provides a good opportunity to achieve ordered nonuniform self-assembly. Therefore, it is necessary to lucubrate the Marangoni convection and heat and mass transfer mechanism of droplet evaporation on gradient temperature surface. In the project, experiments will be carried out to synchronously investigate the characteristic of Marangoni convection as well as heat and mass transfer during the evaporation of droplet on gradient temperature surface. Moreover, the project will develop a three dimensional unsteady theory model on coupling processes of Marangoni convection and heat and mass transfer during droplet on the gradient temperature surface and conduct the numerical simulation. The effect of surface temperature gradient, contact angle and fluid property on the coupling processes of Marangoni convection and heat and mass transfer during droplet evaporation is explored to reveal the generation and evolution mechanism of Marangoni convection and surface motions, and influence of Marangoni convection on heat and mass transfer during droplet evaporation on gradient temperature surface. Based on the research, a mean to adjust the Marangoni convection and heat and mass transfer of droplet evaporation is proposed. This project is not only of significant academic value in the development of evaporation phase change heat and mass transfer theory, but also will provide theoretical bases and key technical supports for the regulation of droplet evaporation in the real application.

液滴蒸发Marangoni对流及传热传质过程是蒸发自组装技术的关键热物理问题，梯度温度壁面上液滴蒸发为实现有序非均匀自组装提供了良好契机。因此深入研究梯度温度壁面上液滴蒸发Marangoni对流及传热传质机理十分必要。项目将同步实验观测梯度温度壁面上蒸发液滴内Marangoni对流及表面传热传质特性；建立梯度温度壁面液滴蒸发Marangoni对流与传热传质耦合过程三维非稳态理论模型并数值模拟；揭示梯度温度壁面液滴蒸发Marangoni对流及界面运动的产生与演化机理；探析壁面温度梯度、接触角、工质物性等对液滴蒸发Marangoni对流及传热传质耦合过程影响规律；掌握Marangoni对流影响液滴表面蒸发传热传质机制；基于研究结论发展液滴蒸发Marangoni对流与传热传质调控方法。项目研究不仅有助于完善蒸发相变传热传质理论，还将为工程实际中液滴蒸发过程调控提供重要理论基础和关键技术支撑。

两相传质过程中的传热传质及流动是蒸发自组装、微反应器、芯片实验室等实际工程应用中的关键过程。为此，项目组围绕两相传质过程中传质及流动特性，尤其是蒸发过程中工质内Marangoni对流与传热传质的耦合机理，设计并搭建了基于红外测温技术、纹影观测技术及数字粒子测速技术（DPIV）的传质过程的非接触式可视化实验平台，建立了定接触角模式下，考虑气液界面演化、蒸发传热传质及流动过程的梯度温度壁面上液滴蒸发的三维理论模型，以及基于Level set方法的浓度差驱动下液滴两相传质过程的二维理论模型，分析了蒸发过程中传热传质与Marangoni对流的过程及耦合机理，揭示了液-液两相传质过程中RBM对流演化特征及受浓度、界面张力等的影响机理。.研究结果表明：（1）液层蒸发过程中随着液层厚度降低，内部Marangoni对流影响相对于自然对流逐渐增强；液层表面温度不均匀性先增大后逐渐减小，表面温度离散系数先逐渐增加后又逐渐减小；壁面温度越高，内部自然对流影响越明显，表面温度离散系数越小；（2）传热及表面蒸发不均匀使液滴表面形成三相接触线处高、顶端低的温度分布，在液滴内部形成Marangoni对流；梯度温度壁面上液滴蒸发过程的前期，壁面温度斜率为负条件下Marangoni对流更剧烈，而后期当斜率为正时Marangoni对流更剧烈；工质界面张力温度系数越大，Marangoni对流越剧烈，此外增大液滴粘度有利于抑制Marangoni对流；（3）液层液-液两相传质过程中沿界面处可以观察到丘状流，并逐渐演化为羽状流，传质过程中羽状流相互合并或逐渐消失；液层/液滴液-液两相传质过程中，两相浓度差及尺寸越大，传质诱发的RBM对流越强烈；向外相添加溶质，有利于抑制相间传质的RBM对流；（4）液滴液-液两相传质初期主要依靠扩散传质，不均匀传质诱发的界面张力不均匀分布在液滴内部引起Marangoni对流，形成涡胞状对流结构并相互合并，且数量受界面张力分布波动影响。.本项目研究不仅有助于完善蒸发相变传热传质及液-液两相传质与流动的相关理论，还将为工程实际中液滴蒸发及扩散传质过程调控提供重要理论基础和关键技术支撑。基于项目研究成果，在国内外权威刊上或会议上发表论文10篇，其中SCI 收录8篇，会议论文2篇，申请专利4件；依托项目培养博士生2人，硕士生3人，其中毕业博士生及硕士生各1名。