Numerical Analysis of EDL Effect on Heat Transfer Characteristic of 3-D Developing Flow in a Microchannel

Abstract

It has been suggested that microchannels are very effective heat transfer devices. However, the electrical double layer (EDL) effect in microchannels is suspected to be significant. In this article, two EDL models together with Navier-Stokes equations are used to compute 3-D developing microchannel flow. The Poisson-Boltzmann model (PBM) has been shown to be a promising tool in studying the EDL effect for developed microchannel flow, with acceptable accuracy and efficiency. However, it has been reported that the assumption of Boltzmann distribution in the PBM for electric ion concentration distribution is questionable in the developing flow. The Nernst-Planck model (NPM), with its two extra partial differential equations (PDEs), to predict the ion concentration distribution has been suggested to be a more appropriate model for developing microchannel flow, but more RAM and CPU are needed as compared to the PBM. The governing equations for both models are discretized for developing rectangular microchannel flows in Cartesian coordinates. An additional source term, which is related to the electric potential resulting from the EDL effect is introduced in the conventional z-axis momentum equation as a body force, thereby modifying the flow characteristics. A finite-volume scheme is used to solve the PDEs. The results predicted by both EDL models with and without EDL effects are shown. It is concluded that the differences in heat transfer performance of a microchannel predicted using the two models are insignificant. However, the performance of the microchannel is significantly affected by the EDL effect.