ALKALINE ELECTROLYSIS CFD MODELING AND APPLICATION: A NOVEL EXPRESSION FOR A VOLUME FRACTION-DEPENDENT CURRENT DENSITY

To enhance the design and efficiency of alkaline water electrolyzer cells, the use of Computational Fluid Dynamics (CFD) is imperative, particularly through multiphysics simulations, able to account for electrochemical phenomena and multiphase flows. Despite noteworthy studies in the literature, the validation of CFD results through detailed experimental measurements remains to date limited and the modeling approach uncertain. Furthermore, most of the studies do not consider the effect that gas accumulation on the electrodes has on the cell performance. The first aim of the study is to evaluate the impact of some of the modeling choices for the CFD simulation of the electrochemical cell. In this context, a novel method concerning the use of an electrochemical module is employed. The two-phase model is validated against PIV experimental measurements for a literature case study of a zero-flux electrochemical cell. The results of the validation highlight a major resemblance to the experiments when a mass source term is employed. The use of electrochemistry is however crucial to ensure a more physical accuracy. The second phase of the study involves the application of the developed model on a 2.5D sector of a real-scale cell of a 1 MW electrolyzer to assess the velocity and volume fraction behaviors at the cathode for various current density values, ranging from 1, 000 to 10, 000 A/m2. Sensitivity analyses are conducted to identify which is the impact of different electrolyte mass flow rates and current densities on the cell. Special attention is dedicated to the impact of gas accumulation on the electrode, by introducing a new function for the current density, with dependence on the local volume fraction. In particular, the ratio between the average electrode and outlet gas volume fraction is considered as a key performance indicator, to evaluate the effect of bubble coverage. The main output observed is that gas accumulation is enhanced by lower current densities and higher mass flow rates.