Coupling K convection-diffusion and Laplace equations in an open-source CFD model for tertiary current distribution calculations

A mathematical model to calculate tertiary current distributions in electrochemical reactors is presented taking into account the potential and concentration fields together with the hydrodynamics under laminar or turbulent conditions. Multiple reactions with different kinetic controls are considered at both electrodes. The computational algorithm solving the model was implemented in OpenFOAM. It allows the calculations for a given local potential at the working electrode, potentiostatic control, or for a fixed cell potential difference and also for a current flowing through the cell, galvanostatic operation. The model was validated by using the reduction of ferricyanide and the oxidation of ferrocyanide from dilute solutions as main test reactions and hydrogen and oxygen evolution as secondary ones, in a modified hydrocyclone. A close agreement between experimental and predicted current distributions was obtained. The hydrocyclone presents a promising electrochemical performance being the mass-transfer conditions in its cylindrical part better than in the conical region. The computational tool developed in this paper can be employed to optimize both cells stack design and system operation conditions. Likewise, the algorithm can also be used to check, when limiting current studies are needed, whether the desired reaction is under mass-transfer or charge-transfer control for a given geometric configuration.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Non-Precious Electrodes for Practical Alkaline Water Electrolysis

Water electrolysis is a promising approach to hydrogen production from renewable energy sources. Alkaline water electrolyzers allow using non-noble and low cost materials. An analysis of common assumptions and experimental conditions (low concentrations, low temperature, low current densities and short-term experiments) found in the literature is reported. The steps to estimate the reaction overpotentials for hydrogen and oxygen reaction are reported and discussed. The results of some of the most investigated electrocatalysts, namely from the iron group elements (iron, nickel and cobalt) and chromium are reported. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The experimental work is done involving the direct-current electrolysis of highly concentrated potassium hydroxide solutions at temperatures between 30 and 100°C which are closer to industrial applications than what usually found in literature. Stable cell components and a good performance was achieved using as a cathode Raney nickel and stainless steel 316L as an anode by means of a monopolar cell at 75°C which ran for one month at 300 mA cm?2. Finally, the proposed catalysts show a total kinetic overpotential of circa 550 mV at 75 °C and 1 A cm?2.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Girault, Hubert. Ecole Polytechnique Federale de Lausanne; FranciaFil: Battistel, Alberto. Ecole Polytechnique Federale de Lausanne; Franci

Theoretical and experimental study of the non-ideal behaviour of electrochemical reactors

El objetivo de esta tesis es analizar las desviaciones de la idealidad en reactores electroquímicos mediante el método estímulo-respuesta. Esta técnica es complementada con cálculos basados en fluidodinámica computacional. Asimismo, se presentan modelos matemáticos para representar a los reactores, los cuales son comparados con resultados experimentales para establecer la validez de los algoritmos teóricos. Primeramente, se trata el modelo de dispersión axial y las condiciones de contorno, se comparan las diferentes soluciones y se obtienen conclusiones sobre rangos de aplicación. Seguidamente, se analizan las desviaciones de la idealidad de un reactor electroquímico asociado a un tanque de almacenaje. Se informan modelos analíticos y resultados experimentales para esta configuración y se discuten las desviaciones con respecto al comportamiento ideal. Asimismo, se examina este arreglo para la determinación experimental de los coeficientes de transferencia de masa discutiendo el error que se comete al utilizar los modelos simplificados. Posteriormente, se estudian reactores electroquímicos de placas paralelas, para ello se resuelven las ecuaciones de Navier-Stokes y el balance de materia con el objetivo de determinar la influencia de la zona de entrada fluidodinámica sobre el desempeño del equipo vacío o en presencia de diferentes promotores de turbulencia. Finalmente, se plantea la optimización de reactores electroquímicos de placas paralelas mediante: i) una contracción continua en sentido axial para disminuir el espesor de la capa límite y ii) el ingreso del fluido perpendicular al electrodo de trabajo generando un flujo acumulativo que suaviza los altos valores de densidad de corriente.The objective of this thesis is to analyze the non-ideal behavior of electrochemical reactors by means of the stimulus-response method. This technique is complemented with computational fluid dynamics calculations. Also, mathematical models are presented to represent the reactors, which are compared with experimental results to establish the validity of the theoretical algorithms. First, axial dispersion model and the boundary conditions are analyzed, the different solutions are compared and conclusions of application ranges are obtained. Subsequently, the deviations from ideality of an electrochemical reactor associated with a storage tank are analyzed. Analytical models and experimental results for this configuration are reported and deviations from the ideal behavior are discussed. Also, this arrangement for the experimental determination of mass transfer coefficients using rigorous and simplified models is examined. Subsequently, parallel plate electrochemical reactors are discussed. The Navier-Stokes equations and the mass balance are solved in order to determine the influence of the entrance length on the hydrodynamic behavior for an empty reactor or in presence of different turbulence promoters. Finally, optimization of parallel plate electrochemical reactors by means of i) an axially continuous contraction to decrease the thickness of the boundary layer and ii ) the entrance of the fluid perpendicular to the working electrode generating a cumulative flow which softens the high current density values.Consejo Nacional de Investigaciones Científicas y TécnicasAgencia Nacional de Promoción Científica y TecnológicaUniversidad Nacional del Litora

Current and Potential Distribution in Two-Phase (Gas Evolving) Electrochemical Reactors by the Finite Volume Method

A solver was developed and implemented in the OpenFOAM framework in order to predict the current distribution in gas evolving electrochemical reactors. The solver takes into account both liquid and gas flows under turbulent conditions and assumes a bubble population balance with a range of bubble sizes. The possibility of coalescence and breakup of bubbles is also considered. The comparison between experimental results of gas fraction and current distribution, from this research and from previous ones, demonstrates that the solver is able to predict the behavior of this kind of electrochemical systems. The model presented is supplied as a free source code.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Mass-transfer characterization in a parallel-plate electrochemical reactor with convergent flow

A continuous reduction in the cross-section area is analysed as a means of improving mass-transfer in a parallel-plate electrochemical reactor. Experimental local mass-transfer coefficients along the electrode length are reported for different values of the convergent ratio and Reynolds numbers, using the reduction of ferricyanide as a test reaction. The Reynolds numbers evaluated at the reactor inlet range from 85 to 4600 with interelectrode gaps of 2 and 4 mm. The convergent flow improves the mean mass-transfer coefficient by 10-60% and mass-transfer distribution under laminar flow conditions becomes more uniform. The experimental data under laminar flow conditions is compared with theoretical calculations obtained by a computational fluid dynamics software and also with an analytical simplified model. A suitable agreement is observed between both theoretical treatments and with the experimental results. The pressure drop across the reactor is reported and compared with theoretical predictions.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Current and potential distribution in electrochemical reactors with activated or resistive electrodes. A multiregion and open source approach

An open source compact and general tool, implemented in OpenFOAM including a novel solver with a new boundary condition and post-processing utilities, is derived to enable calculations of local current and potential distributions in electrochemical systems with activated or resistive electrodes and also leakage currents in the case of a bipolar connection. The algorithm allows the calculations for a given local potential in any electrode, for a fixed cell potential difference and also for a current flowing through the cell under galvanostatic control. In order to validate the algorithm, a detailed comparison between the suggested strategy with experimental results and some simplified theoretical models is made. It was concluded that the proposed mathematical treatment is reliable for the modelling of these electrochemical systems due to the good agreement between theoretical and experimental values with a mean relative percent error of 8.8 ± 2.1% for the current distribution for the whole set of experiments.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

A multi-region and open-source computational fluid dynamic tool for electrochemical systems with three-dimensional electrodes

In this work, a solver, implemented in OpenFOAM, is developed to investigate the mechanisms of ion transport through activated or resistive three-dimensional (3D) electrodes, and also leakage currents in the case of a bipolar connection. The transport model, which accounts for the balance of mass, momentum, species, and electric charge in the fluid, 3D and solid phases, was solved using a multi-region approach. The algorithm permits calculations for a fixed cell potential difference, and also for a current flowing through the cell under galvanostatic control. Analytical models and experimental results of the current and potential distribution are compared with the present tool, obtaining a close agreement between them. The model presented here is supplied as a free source code and can be employed to optimize both cell stack design and system operation conditions.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Tertiary current and potential distribution including laminar/turbulent convection, diffusion, and migration by the finite volume method using OpenFOAM

A numerical tool is presented under a finite volume framework, implemented in the open-source package OpenFOAM, to calculate concentrations and current and potential distributions in electrochemical systems composed of two-dimensional electrodes with a monopolar connection. The convection, diffusion, and migration of species in electrochemical systems are considered in coupling the potential and concentration fields together with the hydrodynamics under laminar or turbulent conditions. Multiple reactions with any kind of kinetic control (charge-transfer, mass-transfer, mixed, or special cases) are permitted at both electrodes. The algorithm allows calculations for a given local potential at the working electrode (potentiostatic control) or for a fixed cell potential difference and also for a current flowing through the cell (galvanostatic operation). The model was verified by using analytical expressions and simplified numerical implementations. Moreover, a new test reaction is proposed in order to study the effect of ionic migration and validate the model. A good match between experimental results and predicted calculations was obtained. This computational tool can be employed to optimize both cell stack design and system operation conditions. Furthermore, the algorithm can also be used to check, for a given geometrical configuration and reaction environment, the validity of some assumptions such as tertiary current distribution without migration, mass-transfer-controlled reactions, or primary-secondary current distributions.Fil: Colli, Alejandro Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Bisang, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentin

Validation of theory with experiments for local mass transfer at parallel plate electrodes under laminar flow conditions

Theoretical equations are reported to calculate the local Sherwood number for a parallel plate electrochemical reactor with a developing flow region under laminar flow conditions. These equations were deduced from analytical velocity profiles according to different proposals, which are compared with the velocity profiles given by the numerical solution of the Navier-Stokes equations. A comparison between the theoretical mass transfer equations with experimental results is also given.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

A CFD study with analytical and experimental validation of laminar and turbulent mass-transfer in electrochemical reactors

This work presents numerical simulations, with validation considering analytical expressions and experimental results, of masstransfer in electrochemical reactors under laminar and turbulent flows in ducts of rectangular and tubular shape. Sudden expansion at the reactor inlet and segmented electrodes are also analyzed. Computational fluid dynamics (CFD) simulations were performed solving the laminar or RANS equations with the Shear Stress Transport (SST) k-ω turbulence model using the open source code OpenFOAMin steady-state. For mass-transfer simulations, the averaged diffusion-convection equation was implemented and solved. A good agreement between mass-transfer simulations with experimental data and analytical results were attained for both laminar and turbulent flow. Discussions about the segmented electrode technique in order to obtain local mass-transfer data in laminar and turbulent flow are also performed.Fil: Colli, Alejandro Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Bisang, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentin