电渗流通过外加电场来驱动液体通过微小通道,同时由于焦耳热效应的存在,也会在流体及通道表面形成热传导现象。应用计算流体力学方法,对矩形发散形微通道内电渗流流动所产生的流场、温度场进行了数值模拟和研究。由于流体的介电常数、电导率、粘性、热导率等属性依赖于温度的变化,焦耳热效应产生的温度场会改变流体的多种属性,并进而影响到流动速度、压力分布等。计算结果表明，焦耳效应在微管道芯片上产生了一个非均匀的热梯度场,并同时影响液体流动。热梯度场的存在在均匀截面通道内可以提高液体的流动速度,但在发散形通道内却不能产生相似的效果,此时的出口速度和体积流速都明显下降,分别达到约16%和60μl/min.焦耳热效应同时通过降低流速和流动压力减弱了发散形管道的电渗流泵送性能。

The electroosmotic flow drives a fluid passing through microchannels by an applied electric field,which also induces heat transfers both in the fluid and channel walls because of a Joule-heating. Using the Computing Flow Dynamics(CFD) technique,a flow field and a temperature field in diverging channels are numerically investigated with a 3-D microchip model. Due to the temperature-dependent physical properties of the fluid including viscosity,relative dielectric constants,electric conductivity,and thermal conductivity,the induced temperature gradient imposes great influence on flow behaviors of channels. The results suggest that a nonuniform gradient thermal field is formed in a microchip by the Joule heating and it affects the flow field severely. This gradient thermal field has increased the flow velocity in uniform cross-section channels but can not do it similarly in diverging channels,so that the outlet velocity and volume flow rate have decreased by 16 % and 60 μl/min,respectively.Moreover,the Joule heating also weakens the pumping performance of diverging channels by decreasing the flow velocity and pressure.