Thermal performance of mixed electroosmotic-pressure driven flows in microtubes with constant wall temperature

A numerical analysis is performed to explore the heat transfer characteristics of mixed electroosmotic and pressure-driven flows in a microtube with constant wall temperature. Thermally fully-developed flow with Joule heating is considered. The Joule heating is generated by imposed voltage gradient and can be regarded as volumetric heat source. The analysis combines energy equation with overall energy balance equation for a control element to generate a nondimensional governing equation. Of interest are the effects of the relative duct radius a (ratio of the duct radius to Debye length), the pressure gradient parameter P (ratio of pressure gradient to electroosmotic forces) and the Joule number S (ratio of heat generation due to Joule heating to heat transfer at the wall) on the temperature distribution and the local heat transfer rate. The results indicate that the Nusselt number increases with an increase in the relative duct radius and the Joule number or a decrease in the pressure gradient parameter. The resulting solution due to the conditions of energy unbalance in the flow is also discussed.