Three-dimensional Two-phase CFD Simulation of Alkaline Electrolyzers
The structural and operation parameters of the electrolyzer play important roles in the efficiency of alkaline water electrolysis. In this article, a 3D numerical model coupled with the electric field and the Euler-Eulerian k-ε turbulence flow field was first established to simulate accurately the performance of alkaline electrolyzers, based on a compact assembly structure of the industrial alkaline water electrolyzers, especially at current density higher than 5000 A·m-2. The simulation results were compared with the experimental data to verify the accuracy of the model. Suitable operating conditions for concentration, flow rates and the optimal design method of the flow channel structure are obtained from the feedback of the electric and flow field characteristics inside the electrolyzers. Properly increasing the electrolyte concentration and flow rate facilitates the reduction of cell voltage. The optimum concentration and flow rate of KOH aqueous solution is 6.0-8.0 mol·L-1 and 30.0-45.0 mL·min-1 respectively. With the increase of the gap between electrode and membrane, the ohmic overpotential increases significantly. The triangular arrangement of conductive columns on the bipolar plate and the increase of the channel height are beneficial to improve the distribution uniformity of the fluid, while the channel height and the arrangement of the conductive columns have little effect on the voltage. Appropriately increasing the spacing between the conductive columns facilitates to reduce the voltage. Multiple outlets and inlets structure is conducive to produce a more uniform fluid distribution. The channel height has little effect on the multiple outlets and inlets electrolyzer. The multiple outlets and inlets electrolyzer G-2.5-T-0-5-3 with wide spacing of conductive columns combined with high flow rate can reduce the cell voltage but also enhance the normal flow rate of the electrolyte on the electrode surface, allowing the best performance of the electrolyzer. This work provides useful guidance on the scale-up design and optimization of highly efficient electrolyzer for alkaline water electrolysis.