International audienceA fluid dynamics simulation was used to study the effect of the internal movement of hydrogen bubbles on current efficiency in a pilot scale fluorine electrolyser. Two dimensional modelling of the gasliquid free convection was carried out using the Estet-Astrid (EA) finite volume code. The effect of hydrodynamics is well highlighted and calculations show that a significant fraction of the hydrogen bubbles can migrate, under certain conditions, into the fluorine compartment. This fraction of hydrogen recombines with fluorine and thus decreases the Faradaic current efficiency of the electrolyser. The numerical results confirm the experimental trends observed on the pilot. The model also clarifies the effect of hydrogen bubble diameter on Faradaic current efficiency
Fluorine electrolysis is characterized by very large overpotentials and bubble effects that are not yet fully understood. The two-phase free flows appearing in the fluorine reactor are complex and attributable mainly to hydrogen bubbles evolving at the cathode. However, large fluorine bubbles gliding along the anode help to drag the electrolyte up along the anode and in doing so also take part to the two-phase movement. The fluorine electrolyser has been modelled in the past but there has been no means of comparing hydraulic computations with measurements in such an aggressive environment. A hydraulic model is presented here to test the ability of the Estet-Astrid finite volume code to model the fluorine reactor. The two-phase free flow was modelled using an Euler-Euler scheme assuming bubbles of uniform diameter. Laser Particle Image Velocimetry was used to measure both gas and liquid velocities. This paper presents the experimental study and the model made to obtain the plume shape. Numerical and experimental results are compared and some discrepancies are explained. Improvements are suggested for future modelling
Two dimensional modelling of the gas-liquid free convection in a fluorine electrolyser was made with use of the Estet-Astrid finite volume code. The model takes into account the specific behaviour of hydrogen and fluorine bubbles evolving at electrodes in free convection in a KF-2HF electrolyte. The numerical results give a satisfactory representation of the velocity field which could not be visualized or measured in such an aggressive medium.
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