依赖于壁面电荷的壁面滑移对微通道内电渗流和传热特性的影响

Microscale fluid flow is fluid flow problem in microchannel and has a wide range of applications in many fields such as physics, biology, medicine and chemistry. The decrease of length scale leads to the emergence of new phenomena different from those in macroflow, such as electrokinetic effect and boundary slip. The interaction between ions of electrolyte and wall surface leads to the formation of the electric double layer. Under the action of external electric field, the free ions can move, dragging the nearby fluid by the viscous force, and thus creating electroosmotic flow. Although electroosmotic flow and boundary slip effect have been widely studied, a few studies have considered the effect of surface charge on boundary slip. In this project, the effects of surface charge-dependent boundary slip on electroosmotic flows and heat transfers of Newtonian and non-Newtonian fluids in microchannels will be studied theoretically using integral transform method，variable separation method and finite difference method. The variations of electric, velocity and temperature fields with the relevant parameters will be given and the results will reveal that the mechanisms of the effect of surface charge-dependent boundary slip on electroosmotic flows and heat transfers in microchannels, and will provide a foundational basis for the design, optimization and development of the microfluidic devices.

微流体流动是指在微尺度通道内流体的流动问题，近年来在物理、生物、医学和化学等多学科领域有着广泛的应用。由于流动特征尺度的减少，微通道间流体流动中会出现不同于常规尺度流动的新现象，如电动效应和滑移效应等。通常电解质溶液中的离子与微通道壁面的相互作用会产生双电层，在外电场的作用下，由于流体的黏性，移动的自由离子将会带动附近流体微团运动，最终形成了电渗流。目前有很多有关电渗流和滑移效应的研究，但考虑壁面电荷对壁面滑移的影响的研究少之又少。本项目将用积分变换法，分离变量法和有限差分数值模拟，通过理论分析，研究依赖于壁面电荷的壁面滑移对微通道内牛顿和非牛顿流体的电渗流和传热特性的影响。给出电场、流场和温度场随相关参数的变化规律，揭示依赖于壁面电荷的壁面滑移对电渗流和传热特性的影响机理，为微流控设备的设计、优化、发展奠定理论基础。

微纳流控技术是微纳米尺度通道内驱动和操控流体流动的科学和技术，近年来在物理、生物、医学和化学等多学科领域有着广泛的应用。由于流动特征尺度的减少，微通道间流体流动中会出现不同于常规尺度流动的新现象，如电动效应、热质传输效应和滑移效应等。通常电解质溶液中的离子与微通道壁面的相互作用会产生双电层，在外电场的作用下，由于流体的黏性，移动的自由离子将会带动附近流体微团运动，最终形成了电渗流。本项目研究了依赖于壁面电荷的壁面滑移对微纳米通道间热完全发展的牛顿/非牛顿流体的电渗流动的影响及pH调节平行板纳米通道中的时间周期电渗流动。结果包括：对于牛顿流体，无量纲速度和温度分布随着zeta势的增加而增加；努塞尔数随着外加电场强度和zeta电势的增大而减小；在壁面电荷相关滑移流中，努塞尔数小于壁面电荷无关滑移流中的努塞尔数。对于非牛顿幂律流体，也有类此的结果。即，假塑性流体(n<1)，速度和温度分布随着壁面zeta势和滑移长度的增大而变大；对于膨胀性流体(n>1)，速度分布在双电层附近随着壁面zeta势增大而变大，远离狭窄的双电层区域趋势相反；温度的大小随着壁面zeta势增大而变大；无论牛顿/非牛顿流体，当滑移长度依赖于壁面电荷时，流动速度显著降低。