Mixing enhancement by utilizing electrokinetic instability in different Y-shaped microchannels

An experimental study was conducted to assess the effectiveness of manipulating convective electrokinetic instability (EKI) waves to control/enhance fluid mixing inside three Y-shaped microchannels, which includes a conventional straight channel, a channel with micro-cavities, and a channel with microsteps. Epi-fluoresence imaging technique was used to conduct qualitative flow visualization and quantitative scalar concentration field measurements inside the microchannels. The effects of the applied static and alternating electric fields on the evolution of the convective EKI waves and the resultant fluid mixing process were quantified in terms of scalar concentration distributions, shedding frequency of the EKI waves, fluid mixing efficiency and mixing augmentation factor. While the fluid mixing efficiency was found to increase monotonically with the increasing strength of the applied static electric fields for all the studied microchannels, the channel with micro-cavities was found to have the best overall mixing enhancement performance among the three studied microchannels. It was found that fluid mixing processes in the microchannels would be further enhanced by adding alternating electric perturbations to the applied static electric fields, regardless the frequency and magnitude of the alternating electric perturbations. The fluid mixing process would be most enhanced when the frequency of the alternating electric perturbations is close to the ‘‘natural frequency’’ of the EKI waves (i.e., the shedding frequency of the EKI waves with the applied static electric fields only).