in this study, a two-phase mathematical model is adapted to study void fraction distribution, flow field and characteristics of electrolysis process. The model involves transport equations for both liquid and gaseous phases. An experimental set-up is established to collect data to validate and improve the mathematical model. The void fraction is determined from measurement of resistivity changes in the system due to the presence of bubbles. it is observed that there is a good agreement between the numerical results and the experimental data. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.