2005 Volume 30 Issue 2 Pages 66-71
There is an optimum condition on water electrolysis efficiency due to effects of generated bubbles between electrodes. In this paper, in order to explain the existence of the optimum condition, a revised two-phase flow model of alkaline water electrolysis was explained. Bubble rising velocity between electrodes was assumed to be constant in the whole area. The model can express void fraction and current density profiles along electrodes, and show the existence of the optimum condition. In addition, the model exhibits the existence of water electrolysis limit where void fraction becomes almost 100% and water electrolysis can not be conducted. A non-dimensional parameter, Vn, was newly proposed that shows the degree of bubble packing between electrodes. For verification of this model, the optimum condition and the water electrolysis limit were measured during water electrolysis of KOH solution. The model predictions show good agreements with the experimental results.
The experimental parameter in the presented model was only bubble rising velocity between electrodes, which is strongly affected by bubble diameter distribution. Therefore, in order to obtain basic information for modeling bubble departure criterion in the future, diameter distribution of departure bubbles on electrodes was measured using micro fiberscope. The obtained results show that mean diameter of departure bubbles increases as current density increases.
