Simulation studies on electrothermal fluid flow induced in a dielectrophoretic microelectrode system

The inhomogeneous ac electric fields used for particle manipulation in dielectrophoresis(DEP)-based microdevices not only produce forces on the particle, but also generate volume forces in the liquid by producing gradients in conductivity and permittivity due to local heating. The forces on the liquid give rise to fluid motion, which is referred to as electrothermal flow. This paper presents a numerical study on the electrothermally induced fluid flow on the dielectrophoretic microelectrode array. The fluid movement is numerically solved by coupling electrical, thermal and mechanical equations. A number of parameters including frequency, electrode structure, conductivity of the fluid and external heating that influence the fluid flow patterns are investigated. Particle behavior under the effects of electrothermal flow is studied. The viscous drag force on the particles arising from the electrothermal fluid flow becomes apparent as the particle size is reduced to the sub-micrometer scale. In certain circumstances, the drag force may be of the same order as or much greater than the DEP force. Under the effect of the electrothermal fluid flow, small particles may exhibit movements differing from that in the common DEP environment. These results provide significant suggestions for the manipulation of nanoparticles using ac electric fields under the normal DEP conditions.