Transient Joule Heating and Its Effects on Electroosmotic Flow in a Microcapillary Packed Wth Microspheres

The Joule heating induced temperature development and its effects on the electroosmotic flow in a capillary packed with microspheres is analyzed in this paper using finite-difference based numerical method. The model incorporates the coupled momentum equation for the electroosmotic velocity, the energy equations for temperature distributions, and the mass and electric current continuity equations. The temperature-dependent physical properties of the electrolyte solution are taken into consideration. The simulation predicts that, in the presence of Joule heating, there exists a significant axial temperature gradient in the thermal entrance region. This high temperature gradient strongly enhances the local electric field at the entrance, resulting in a non-uniform distribution along the flow direction. The temperature shows a parabolic radial profile but the gradient is very small due to the small system Biot number. The non-uniform temperature distribution in turn greatly affects the EOF velocity by means of changing the local viscosity and the dielectric constant of the fluid phase, and the local electric field strength. The results by this model are found to be in a good agreement with published analytical and experimental works in the literature.