Available online at www.sciencedirect.com Chemical Engineering and Processing 47 (2008) 1926–1932 Two-phase electrolysis process: From the bubble to the electrochemical cell properties Ph. Mandin a,∗ , A. Ait Aissa a , H. Roustan b , J. Hamburger c , G. Picard a a Laboratoire d’Electrochimie et de Chimie Analytique, LECA UMR CNRS 7575, ENSCP, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France b Alcan, Centre de Recherche de Voreppe, 725 rue Aristide Berg` es, BP 27, 38341 Voreppe Cedex, France c Transoft International, Fluidyn, 7 Bd de la Lib´ eration, 93200 Saint-Denis, France Received 5 February 2007; received in revised form 15 October 2007; accepted 22 October 2007 Available online 3 December 2007 Abstract During two-phase electrolysis for aluminium, fluorine or hydrogen production there are bubbles which are created at the electrode which imply a great hydrodynamic acceleration but also a quite important electrical field and electrochemical processes disturbance. This disturbance can lead to the modification of the local current density and to anode effects for example. There are also few local experimental measurements in term of chemical composition, temperature or current density because considered media are often very aggressive (high temperature, very strong reactivity). Then, the modelling and numerical simulation appears to be one important tool to understand and optimize associated processes, though the rigorous validation of numerical calculations is difficult. The goal of the present work is the modelling and the numerical simulation of the local gas production at an industrial scale vertical electrode. Because bubbles modify species, heat and electricity transport and are motion sources, there is a strong coupling between all these phenomena and between the bubble scale and the macroscopic one. Because bubbles are at the origin of all macroscopic disturbances, it appears necessary to investigate phenomenological laws at the bubble scale. The finite volume of the Fluidyn ® and Fluent ® software has been used. © 2007 Elsevier B.V. All rights reserved. Keywords: Two-phase electrolysis; Modelling bubbles; Phenomenological laws 1. Introduction Gas release and induced fluid flow over electrodes exist in many electrochemical processes such as aluminium, fluorine production, water electrolysis and many other electrochemi- cal processes. The hydrodynamic properties and the gas-flow motion in electrochemical cells is of great practical interest in electrochemical engineering science since the dispersed phase modifies the electrical properties of the electrolyte (as well as mass and heat transfers), and therefore modifies the macroscopic cell performances. In most cases, this phenomenon has to be avoided, but, in some other processes, the gas flow rate has to be controlled; this is the case namely for gas production (CO 2 ,F 2 , H 2 ,O 2 , Cl 2 , etc.) [1–8] and other special processes such as e.g. ∗ Corresponding author. E-mail address: philippe-mandin@enscp.fr (Ph. Mandin). chemical engraving [2]. In all these different electrochemical processes, a coupling effect is particularly strong (as shown by Hine [3] e.g. for simple gas evolving electrodes) because bubble- dispersed phase acts like an electrical shield, the shielding effect depending on the bubbles number, which is namely the local gas volume fraction of the dispersion, and also on the electrode inter- face screening. Tobias [4] has obtained with a segmented vertical electrode the current density distribution modification due to evolving bubbles. The bubble scale modelling has also been investigated [5–7]: the gaseous bubble is submitted to capillar- ity forces, friction forces and Archimede forces. One important aim of the present paper is to show that macroscopic calcula- tions in term of electricity and mass exchanges distribution along electrodes need the non-available knowledge of phenomenolog- ical correlations due to the two-phase character of the electrode vicinity and interface. This problematic is almost the met for vapour generator heat exchanger due to the thermal phase change [9–11]. 0255-2701/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2007.10.018