3D modeling of the electrolyte bubble flow in the distance between two electrodes of a flow battery by considering different spacers

In Zn-Ag2O flow batteries, the electrolyte as one of active substances in electrochemical reactions flows circulatory in the narrow distance between electrodes, and in order to avoid of short circuit inside the battery cells, the spacers are used between their electrodes. In these batteries, the hydrogen gas bubble due to electrochemical reactions is produced on the cathode and then released within the electrolyte flow and a two-phase current is formed. Especially at high-rate discharge processes, this event can reduce the electrochemical active surface of the electrodes, increase the ohmic resistance, and thereby, reduce in the battery capacity. In this paper in order to solve this problem, the behavior of gas bubbles on the electrodes and within the electrolyte flow and their effect on the electrochemical active surface by considering two types of cross-sectional surfaces for spacers, is studied numerically. The results shown that the gas bubbles within the two-phase electrolyte flow spent more time behind the spacers with square cross-section compared to the case of spacers with a circular cross-section at the narrow distance between the electrodes. Therefore, this delay has led to other gas bubbles reaching each other in the electrolyte flow and as a result, they are combined. This event is investigated with two positive and negative approaches in this article.