Simulation Numérique Couplée des Phénomènes Thermo- fluide,Electrochimique et Mécanique dans une Pile à Combustible type PEMFC

Abstract : The study and performance analysis of a PEMFC fuel cell (Polymer Exchange Membrane Fuel Cell) requires coupled modeling of phenomena that takes place during its operation: Transport and transfer of reagents, reactions electrochemical, heat transfer, and mechanical stresses. In this thesis we have developed a coupled model that takes into account all physicochemical phenomena that occur in the heart of the pile. For this we have developed a global model that includes the three sub-models: the Thermo-Fluid submodel, the submodel Electrochemical and mechanical sub-model. Indeed, the first sub-model represents the mass transport and heat transfer in different parts of the cell (channels, diffusion layers of gases, and membrane). The second represents the process of the redox reactions of the reagents in the electrodes and materializes the different voltage drops. The third concerns the mechanical behavior of the membrane due to elasto-plastic and hygrothermal deformations. The phenomena we have studied are represented by a formulation theoretical and our resolution was carried out by COMSOL MULTIPHYSIC software. We have been able to couple the three mathematical sub-models by an algorithm the interaction of physical, electrochemical and mechanical parameters within the cell. The results of our simulation, which represents coupled modeling, have been validated by experimental results from the literature and showed an improvement solutions to the results of the sequential modeling. The results showed that with a current density set at 3000A / m 2 the voltage Electrical was improved by 3% when the temperature was increased from 60 ° C to 120 ° C. Also, for the same current density, the voltage has improved by 10% when the pressure has been increased from 1 to 3 atm. This is due to the easy diffusion of gases at the interface electrode / electrolyte when increasing the pressure which leads a concentration of the reactants to the chemical reaction. The results also showed that the reduction of the membrane thickness from 175 to 75 μm allowed an increase of voltage of 11% for a current density 3000A / m2. Also, we found that the better stack performance is achieved when Relative Humidity (RH) is located between 60% and 80%, indeed, the results showed that for a voltage of 0.7V, a significant increase in current density from 2800 A / m2 to 3200 A / m2 is obtained when the HR has been increased from 40% to 80%. We also found that the increase tightening torque increases the mechanical stresses in the cell which causes a reduction in the porosity of the porous media and consequently the difficulty of diffusion gases. Simulations carried out allowed us to identify the optimal parameters of operation of the battery studied and which are: an operating temperature of 80 ° C, a gas pressure of 2 atm, a membrane thickness of 75 μm, a conductivity of 15m / s, diffusion layer porosity 0.6 and relative humidity between 60% and80%.
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Mohammed Jourdani. Simulation Numérique Couplée des Phénomènes Thermo- fluide,Electrochimique et Mécanique dans une Pile à Combustible type PEMFC. Mécanique des fluides [physics.class-ph]. Université Mohammed V - Rabat, 2019. Français. ⟨tel-02194893⟩

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