MEMS-Based Electrolytic Microbubbler in a Water Channel

This study investigated the development of microbubble injection using a MEMS-based electrolytic device capable of generating small bubbles introduced with nearly zero injection velocity. Three generations of electrolytic microbubblers with gold electrodes and photoresist (PR) as an insulator were fabricated. The objective for the first-generation microbubbler was to understand the influence of voltage and flow speed. The goal of the second-generation microbubbler was to understand the influence of electrode area and spacing, the distance between the cathode and anode. The purpose of the third generation device was to investigate the effect of electrode shape as well as further reduction in the size and spacing of the electrodes. Measurements of the sizes of the bubbles and the bubble generation rates of a first-generation device in a square water channel at different voltages and under different flow conditions were taken. At all but the lowest applied voltage, more than 65% of the observed bubbles were less than 50 μm in diameter. As the applied voltage was increased, the mean bubble diameter and the variation from the mean decreased while bubble generation rates increased. As the flow increased, mean bubble diameter and the deviation from the mean decreased as well. For the second-generation devices, the largest mean bubble diameter and smallest percentage of bubbles smaller than 50 μm occurred at an intermediate value of the ratio between the electrode size and the electrode spacing of approximately 0.7. For the third generation devices, increased detachment frequency occurred with the circular geometries, compared to triangular or square node shapes. The minimum allowable spacing between two electrodes to avoid coalescence was approximately 1.5 times the electrode diameter.