Micro-bubbles generated on electrolytic arrays and matrices and released in a water channel

Abstract

The feasibility of generating mono-disperse micro-bubbles by electrolysis in tap water using micro-fabricated devices was investigated towards the development of a high-density bubbler matrix. The effect of electrode geometry and size, as well as artificial nucleation sites, was tested using single and arrays of electrode pairs. The results indicated that circular electrode node shapes (as opposed to triangular or square nodes) nucleated bubbles from the node center and exhibited fewer instances of bubble coalescence and a higher bubble detachment frequency when operated with small anode–anode and cathode–cathode spacings. Artificial nucleation sites, produced by etching the surface of the electrodes, were shown to be able to limit nucleation to one site (though in some cases, bubbles formed underneath the dielectric layer), as well as to increase current efficiency. A device with thousands of electrode pairs (a matrix of nodes) was also fabricated in order to generate a bubble cloud close to the channel wall. At a flow speed of 14 cm/s, this device demonstrated the ability to generate a bubble cloud reasonably close to the wall 20 mm from the trailing edge of the matrix of nodes, with the void fraction peaking at 1 mm from the channel wall and returning to zero at 3 mm. It yielded efficiencies greater than similar thin-wire devices, but spurious bubbles formed on the device, indicating that additional work is needed to develop this technology in a matrix format.