Modelling and simulation of H2-H2O bubbly flow through a stack of three cells in a pre-pilot filter press electrocoagulation reactor

Computational fluid dynamics simulations were carried out to describe the hydrodynamic characteristics of a two-phase bubbly flow in a filter-press flow reactor stack of three cells, which is typically used in electrocoagulation (EC). The hydrogen evolution reaction (HER) took place at the cathode; dissolution of aluminium occurred at the anode. The fundamental transport equations of momentum and electrical potential were simultaneously solved to simulate the H-2-H2O flow. Continuous (H2O) and dispersed phase (H-2) velocity fields were modelled via the Euler-Eulerian approach, using the biphasic Reynolds Averaged Navier-Stokes (RANS) equations and the standard k - epsilon turbulence model. The influence of volumetric flow rate (1.7 <= Q <= 15 cm(3) s(-1)) and applied current density (-28 <= j <= -5 mA cm(-2)) was systematically addressed to calculate the fraction of dispersed phase and current distribution along the electrodes. The evolved H-2 bubbles were transported away from the electrode by the liquid flow. The dispersion of H-2 through the electrode gap showed a modest bubble curtain profile due to the liquid flow rate. A homogeneous current distribution along the electrode length was experienced due to the geometrical design of the electrochemical cell and the low degree of H-2 dispersion. The velocity profiles of the H-2-H2O mixture were different in each cell due to the change of flow direction. H-2 bubbles increased the velocity of the liquid phase but the gas fraction of such bubbles resulted in a higher pressure drop. Good agreement between theoretical and experimental residence time distribution curves was achieved; the experimental aluminium dose released by the anode agreed well with the simulations.