The DiaCell® electrochemical reactor has been used in several processes such as disinfection without chorine addition, advanced oxidation processes and residual water treatment. The reactor design allows a modification of the configuration from 1 to 4 compartments, changing the effective reactor volume with separators of different sizes that are internal and parallel feed. A computational fluid dynamics (CFD) study of a DiaCell® reactor is needed to describe the detailed flow field and the velocity profiles at each step of the compartments. The CFD analysis is an important tool to scale up the process in a swift and efficient way. The theoretical analysis presented in this paper shows changes in the velocity profiles and flow distribution as a function of the width of the selected separators and the residence time of the cell for four different geometry configurations. The reactor configuration with two separators of 0.3 cm present the most even flow distribution. Furthermore, the analysis shows that it is possible to evaluate for each of the four different geometries where the flow is even and the section of the flow close to the electrode that it is not uniform.
CFD has been used as a useful tool for the description of the phenomena occurring in electrochemical reactors. The present research studies the electrodeionization process from a 3D perspective, coupling the convection, diffusion and migration phenomena involved in the electrodeionization process using COMSOL Multiphysics and a validation of the simulation process is obtained using Digital Image Analysis and Electrodeionization experiments.
The used reactor is a parallel plate reactor, previously used for an electrodialysis process with good results, the total volume of each of the 4 compartments ( one for diluted-treated solution, one for the concentrated-waste solution and two electrodic rinses to close the electrical circuit) is of about 19.2 mL. The diluted compartment is filled with IRA-67 ion exchange resin ( 0.5-0.75 mm of diameter) previously conditioned and hydrated. The treated solution is a 20 ppm fluoride solution from NaF and was pumped into de diluted and concentrated compartments at a velocity that allowed a one minute Time of Residence.
The simulation was carried out with a 3D model of the reactor using its real measures, only the diluted and concentrated compartments were modelled. The flow of the solution in the concentrated compartment was considered as laminar and in the diluted compartment ( filled with ion exchange resin) a Brinkman-Darcy condition was applied. Nerst-Planck equations were used to describe the transport of the ionic species in the compartments and the flow through a ion exchange membrane.
The results show a good flow distribution,as well as a good ion transport. The simulations, confirmed the experimental results. The analized data is very similar in flow distribution and mass transport in the compartments. The results were analized in a quantitative and qualitative form. The validation of this simulated results will allow the improvement of some problematic zones in the reactor and the methodology developed can be useful to other electrochemical reactors.
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