微通道中气体-非牛顿流体两相流的运动特性研究

Microfluidic systems involving gas-non Newtonian liquid two-phase flows are widely used in biology, medicine and environment. In this project, we will use reactive etching, laser processing and self-assembly technologies to construct microchannels with different wall wettability. Microchannel and multi-channel array microfluidic components are fabricated on PDMS substrate by soft lithography. Carboxymethylcellulose aqueous and Polyacrylamide aqueous are selected the as the non-Newtonian fluid. An experimental apparatus is built up to study the kinematic characteristics of nitrogen gas-non Newtonian fluid two-phase flow. The flow patterns of the gas-liquid two-phase flow are measured by a high-speed camera system, and the flow field characteristics were observed by μ-PIV. Pressure sensors are adopted to test the pressure at different positions of the channels. The flow field and pressure drop in the microchannel were calculated by computational fluid dynamics and the lattice Boltzmann method, respectively. Afterwards the influences of the wall geometry, wettability, and the rheological properties of non Newtonian fluid on the pressure drop were analyzed. Non-equilibrium molecular dynamics simulation is conducted to analyze the relaxation process and viscosity characteristics of non-Newtonian fluids and its influence on the rheological properties. The dynamic model of the gas-non Newtonian fluid two-phase flow in the micro-channel was established, which provided the theoretical basis and technical support for the future design and manufacturing of the microfluidic system. Also, the microscale interface dynamics and the rheological properties of non Newtonian fluids were further studied.

涉及气体-非牛顿流体两相流的微流体系统在生物、医学和环境检测等领域具有广泛应用。本项目采用反应刻蚀、激光加工和自组装技术构建具有不同壁面润湿性的微通道，采用软光刻技术在PDMS基底上制备微通道和多通道阵列微流控构件，选取羧甲基纤维素和聚丙烯酰胺水溶液作为非牛顿流体，搭建实验台，研究氮气-非牛顿流体两相流的运动特性。采用高速摄像系统测试气液两相流的流型，采用μ-PIV测试流场特性，采用压力传感器测试通道不同位置的压力。采用计算流体动力学计算微通道内的流场，采用格子玻尔兹曼方法计算微通道内的压力降，分析壁面几何、润湿性、非牛顿流体的流变特性对压力降的影响，采用非平衡态分子动力学模拟探讨非牛顿流体的弛豫过程和黏度特性，阐明对其流变特性的影响。建立气体-非牛顿流体两相流在微通道中运动的动力学模型，为微流体系统的设计制造提供理论依据和技术支持。同时，深化微尺度下界面动力学特性和非牛顿流体流变特性。

微通道中气液两相流因具有广泛的工程和生物医学应用而备受关注。几乎所有应用中的液相都是非牛顿流体，并且微通道内液体流动的剪切率比传统尺寸通道高很多，因此，液体的流变特性对微通道中气体/非牛顿流体两相流的运动具有至关重要的影响。.该项目的主要研究内容包括：不同结构壁面微通道的制备、微通道构件壁面特性的表征、非牛顿流体流变特性的测试、试验台搭建与微通道内两相流运动特性测试、微通道构件内两相流运动特性的数值模拟、非牛顿流体分子弛豫过程和粘度特性的分子动力学模拟、微通道构件的设计准则等。.项目的主要结果包括：（1）微通道结构和壁面结构对气体/非牛顿流体两相流运动特性影响的研究，揭示了微通道结构和壁面结构对两相流压力降和流型的影响规律，特别是对漩涡的产生的影响。（2）设计了一种包含流动聚焦和流体输运的微流控芯片，揭示了通道内压力降以及气泡生成长度和气泡长度的变化规律，阐明了液体的非牛顿特性和工况条件对微通道内压力降和气泡长度的影响。（3）微通道内气液两相流压力降模型的研究，拓展了气液两相流压力降预测模型的适用范围和条件，更加合理地考虑了非牛顿流体的剪切稀化特性对微通道内气液两相流压力降的影响，并与流型特征相关联。（4）应用格子玻尔兹曼方法在介观尺度上模拟了非牛顿流体在微通道中旋涡的形成机理，阐明了雷诺数、分支角度及幂律指数对三支路微通道中旋涡的影响。（5）采用分子动力学模拟的方法，揭示了非牛顿流体剪切稀化现象的微观机理。当对溶液施加剪切作用时，溶液中溶质分子上的氢原子与水氧原子之间形成的氢键作用减弱，剪切边界与水分子层的相对速度增大，宏观上表现为体系的粘度降低。.本项目着重分析了气体/非牛顿流体两相流在微通道中的流型和压力降，阐明了微通道壁面表面特性和非牛顿流体流变特性的影响和作用机制，对生物、医学和环境检测等领域微流控系统的设计和制备具有参考价值。