Simulations of H2-H2o Flow during the Electrolysis of Water in a Continuous Reactor Equipped with a Six-Cell Stack

Abstract

Nowadays the electrochemical reactors in specific the filter-press type in parallel plates configuration are commonly used in industrial and laboratory applications and as multipurpose flow cells utilized in a widely range of electrochemical processes [1]. The characterization of the reaction environment inside of any filter-press reactor must be considered in the design to obtain effective flow dispersion, plus a uniform current and potential distribution. The hydrodynamics is so important inside the reaction environment, because the uniformity and magnitude of mass transport and therefore the current distribution depend on the flow pattern inside the cell, specifically near the electrodes. In many electrochemical processes such as chlorine production, water electrolysis, alumina reduction, electrocoagulation, and many other electrochemical processes appears gas release on the electrodes, H2 or O2 [2]. The hydrodynamic properties and the gas-flow motion in electrochemical cells is of great interest in practice, because the dispersed phase (gas) modifies the electrical properties of the electrolyte (as well as mass and heat transfers), and therefore the macroscopic cell performance. Therefore, this works deals with the H2O-H2 flow simulations inside of a pre-pilot-scale continuous reactor with a stack of six cells in a serpentine array by solving the Reynolds-averaged Navier-Stokes (RANS) equations with κ-ε turbulence model (Euler-Euler approach). The hydrogen evolution reaction comes from the electrolysis of water. The electrodes were plates of aluminum, typically used in electrocoagulation processes. In order to perform a more complete flow pattern characterization, residence time distribution (RTD) studies were carried out to validate the CFD simulations. The RTD simulations were calculated solving the averaged diffusion-convection equation. Close agreement between experimental and theoretical RTD simulations were attained. Finally, comparisons between H2O-H2 and single-phase flow (H2O) simulations were also performed, highlighting that the dispersed phase improves the dispersion of the continuous phase.