Thermal end effects on electroosmotic flow in a capillary

Thermal end effects on electroosmotic flow in a capillary are numerically investigated in this paper. The model accounts for the dynamic coupling effects of Joule heating on the temperature field, the electrical double layer field, the applied electric potential field and the flow field in the full capillary from reservoir to reservoir. These fields are strongly coupled via temperature dependent liquid properties. We find the electric field intensity is non-uniform due to reservoir-based thermal end effects. The resulting cross-stream velocity profile is concave near the inlet and outlet regions, and convex through the central portion of the capillary. These deviations from ideal electroosmotic flow are induced by axial temperature gradients. The calculated liquid temperature lies between the values predicted by previous “solid” solution models with constant and the models with variable electric conductivities, and is in qualitative agreement with experimental observations. The influence of various working parameters (including applied electric field, ionic concentration, zeta potential) and also the capillary size (including diameter and length) is investigated.