Joule Heating Effect of Electroosmosis in a Finite-Length Microchannel Made of Different Materials
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摘要: 采用数值方法，分析有限长PDMS/玻璃微通道电渗流热效应．数值求解双电层的Poisson-Boltzmann方程，液体流动的Navier-Stokes方程和流-固耦合的热输运方程,分析二维微通道电渗流的温度特性．考虑温度变化对流体特性（介电系数、粘度、热和电传导率）的反馈效应．数值结果表明，在通道进口附近有一段热发展长度，这里的流动速度、温度、压强和电场快速变化，然后趋向到一个稳定状态．在高电场和厚芯片的情况下，热发展长度可以占据相当一部分的微通道．电渗流稳定态温度随外加电场和芯片厚度的增加而升高．由于壁面材料的热特性差异，在稳定态时的PDMS壁面温度比玻璃壁面温度高．研究还发现在微通道的纵向和横向截面有温度变化．壁面温升降低双电层电荷密度．微通道纵向温度变化诱发流体压强梯度和改变微通道电场特性．微通道进流温度不改变热稳定态的温度和热发展长度．Abstract: A numerical analysis was presented to study Joule heating effect of electroosmosis in a finite-length microchannel made of glass and PDMS polymer. Poisson-Boltzmann equation of electric double layer, Navier-Stokes equation of liquid flow and liquid-solid coupled heat transfer equation were solved to investigate temperature behavior of electroosmosis in two-dmiensional microchannel. The feedback effect of temperature variation on liquid properties (dielectric constant, viscosity, thermal and electric conductivities) was taken in to account. Numerical results indicate that there exists a heat developing length near channel in let where flow velocity, temperature, pressure, electric field rapidly vary. The flow velocity, electric field and temperature approach to a steady state after heat developing length, which may occupy a considerable portion of the microchannel in cases of thickchip and high electric field. Liquid temperature of steady state increases with increase of applied electric field, channel thickness and chip thickness. The temperature on PDMS wall is higher than that on glass wall due to difference of heat conductivities. Temperature variations are found in both longitudinal and tran sverse derictions of the microchannel. Temperature increase on wall decreases charge density of the electric double layer. Longitudinal temperature variation induces a pressure gradient and changes behavior of electric field in microchannel. In flow liquid temperature does not change liquid temperature of steady state and heat developing length.
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Key words:
- microchannel /
- electric double layer /
- electroosmosis /
- Joule heating effect
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