Steady Electroosmotic Flow in Diverging Microchannels

The electroosmotic flow drives a fluid passing through microchannels by an applied electric field, which also induces heat transfers both in the fluid and channel walls because of a Joule-heating. Using the Computing Flow Dynamics (CFD) technique, a flow field and a temperature field in diverging channels are numerically investigated with a 3-D microchip model. Due to the temperature-dependent physical properties of the fluid including viscosity, relative dielectric constants, electric conductivity, and thermal conductivity, the induced temperature gradient imposes great influence on flow behaviors of channels. The results suggest that a nonuniform gradient thermal field is formed in a microchip by the Joule heating and it affects the flow field severely. This gradient thermal field has increased the flow velocity in uniform cross-section channels but can not do it similarly in diverging channels, so that the outlet velocity and volume flow rate have decreased by 16% and 60 μl/min, respectively. Moreover, the Joule heating also weakens the pumping performance of diverging channels by decreasing the flow velocity and pressure.