Electrohydrodynamic mixing in microchannels



Electrohydrodynamic flow generated by the motion of charge carriers in an electric field was investigated for rapid mixing in microchannel devices. A “tee” geometry of channels ranging from 40 to 110 μm in width and 30 to 60 μm in depth was used to contact two miscible fluids, such as alcohols. A fluorescent dye (Rhodamine B) was used to quantify mixing. A potential difference ranging from 0 to 900 V was applied between two electrodes separated by a distance of 450 μm, resulting in field strengths ranging from 0 to 2 × 106 V/m. Results show that when no electric field is applied, mixing of the two streams is driven by diffusion and is, therefore, slow. The mixing length, at which the concentration across the channel becomes essentially uniform, decrease significantly as the applied voltage was increased. There seems to be a threshold of applied voltage below which mixing is not enhanced by the electric field under the conditions studied. In strong electric fields, the mixing length was less than 150 μm, while in the absence of an electric field, the mixing length was greater than 5,000 μm.