Analysis of fluid flow and heat transfer in microchannels using combined pressure gradient and electroosmotic pumping

A numerical model has been developed for studying the flow and heat transfer characteristics of single phase liquid flow through a microchannel. In this work the heat transfer characteristics of pressure driven and electroosmotic flow through microchannels have been studied. The governing equations are the Poisson-Boltzmann and Navier-Stokes equations which have been solved numerically using the standard Galerkin and the Mixed 4-1 finite element methods, respectively. Finally the energy equation is solved numerically using the Stream-wise Upwind Petrov Galerkin (SUPG) method. Two dimensional Poisson-Boltzmann equation was first solved to find the electric potential field and net charge distribution in the microchannel. Considering the electrokinetic body forces due to interaction of an external electric field on the charged fluid elements, two dimensional Navier-Stokes equations were solved to obtain the flow field in the microchannel for a combined pressure driven-electroosmotic flow. Local and averaged heat transfer coefficients were calculated for constant wall temperature condition. The results were compared to those of pressure driven flow in the same geometry without using electroosmotic pumping. Comparisons revealed significant changes in the velocity profile and heat transfer characteristics through the channel. It was observed that the convective heat transfer rate was increased due to sharp velocity gradients in the vicinity of the microchannel walls. The influence of various effective parameters including external electric field strength and ionic concentration was also studied. It was seen that aforementioned parameters strongly affect the heat transfer rate and flow pattern through the microchannel.