微细通道内液滴运动行为的调控及混合与吸收过程强化机理的研究

Droplet-based technology has received considerable attention due to its broad potential applications, such as micro reactor, micro mixer, micro absorber and micro heat exchanger. For fluid flow in miniochannel, the surface tension turns to be the dominating force rather than the regular body forces, such as gravity and buoyancy. Fluidic actuation driven by surface tension has, therefore, drawn much attention recently. Various mechanisms for droplet manipulation are based on electro wetting, thermocapillary, dielectrophoresis, and so on. However, the study of droplet evolution and movement in confined hydrophobic space, especially in minichannels, is limited. In order to explore a more detailed insight in the transport phenomena and droplet movement in micro systems, this project will experimentally and theoretically investigate the droplet evolution in minichannels with surface treatment techniques to optimize droplet formation and manipulations in mini device platforms. The dominant factors and the mechanism of the droplet spreading and movement in the minichannel will be studied, such as the physical picture of the droplet deformation, triple phase line evolution, and contact angle hysteresis. Mathematics models will be established to describe the influence mechanism to the internal flow field. To achieve the internal optimization and regulation of the droplet mixing and absorption processes, the innovative strategies of the regulate droplet dynamic process and strengthen the mass transfer process will be put forward on the base of the droplet regulation mechanism influenced by the minichannel characteristics. The rusults will obviously provide a baseline for the novel techniques development in micro- chemical engineering processes.

液滴技术在微流控、微反应器、微混合器、微吸收器和微换热器等高新技术的性能操控中具有重要的作用。流体微流动过程中，惯性力和浮力影响很小，表面张力起主导作用，流体各质点平行于通道内部有规则流动，呈层流状态。传统的微液滴调控的策略多采用机械驱动或介电电泳法等手段，关于界面润湿性能对液滴尺度及运动规律调控方面的研究报道较少。本项目基于微细通道内液滴运动和演化过程，研究界面润湿特性、微细通道结构对液滴尺寸及分布以及液滴运动、弹跳的影响，揭示微细通道内液滴铺展和运动的主导因素及其调控机制；刻画微细通道内液滴形变、三相线演化、接触角滞后的物理图景。建立数学物理模型研究表面形貌和界面性能对微细通道内液滴内部流场的影响机制。进而，基于微细通道内液滴的运动和弹跳特性，实现液滴混合、吸收过程强化，提出调控液滴动态过程和强化传质过程的新型策略，为微化工过程的新技术研发提供支撑。

液滴技术在微反应器、微混合器、微吸收器和微换热器等微流控系统的过程控制中具有重要价值。微流体过程的惯性力和浮力影响很小，粘性力和表面张力起主导作用，流体流动呈有序层流状态，边界层效应显著。. 本项目针对气泡/液塞生成过程及水动力学特征，分别研究了微通道内冷凝相变、传质吸收等过程的两相流流型和输运。揭示了混合蒸汽浓度、通道构型及壁面润湿性对流型转换的内在影响；重点研究了Taylor流内液相物性（表面张力和粘度）变化条件下的气泡输运过程，拓宽了气泡/液塞长度的预测模型适应性；基于上述输运特征，提出了利用空气微腔结构调控输运的定量调控技术，实现了微通道内多气泡形态的快速输运。.系统地研究了超疏水表面上液滴弹跳现象及其影响因素，揭示了液滴尺寸效应和初始液滴排布对液滴弹跳的影响规律。进一步，明晰了液滴合并过程液桥撞击壁面与弹跳有效动能转化率的内在关联，并提出利用界面几何结构调控弹跳高度方法，列举了利用凸起和凹陷纹理对液滴弹跳速度的定性作用效果和定量调控技术。基于上述对液滴合并动力学和空间运行规律的认识，设计并搭建了“EHD-超疏水表面”液滴弹跳强化吸收系统，实现了液滴在超疏水表面多次弹跳的流动形式，揭示了单液滴多次弹跳的运动轨迹和液滴合并碰撞动态规律。. 测得了微通道泰勒流的不同气液相体系在CO2吸收过程的液相体积传质系数，针对物理吸收和化学吸收的不同机制，结合微流动过程中液塞内循环、二次流强度和泄露流对传质模型进行修正。在明晰微通道内气液分散体系的吸收性能基本调控参数及其影响的基础上，进一步研究基于超疏水板间液滴弹跳运动的吸收强化过程。一方面液滴的弹跳使气相发生扰动，另一方面撞击弹跳液滴内部发生流动，使内部流体和表面流体发生更新。实验初步测量了开放的超疏水表面和限制的超疏水通道内收集水中CO2的浓度。小液滴在超疏水通道内发生了多次弹跳有利于CO2的吸收，与开放超疏水表面相比，超疏水通道内收集水中的CO2的浓度增加了30%-50%。