Análisis en CFD del efecto de la porosidad de los soportes metálicos sobre los gradientes térmicos en una celda de combustible de tipo SOFC.
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Date
2025
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Universidad de Concepción
Abstract
La presente Memoria de Título investiga el comportamiento térmico y electroquímico de celdas de combustible de óxido sólido tipo plana (SOFC) con soporte metálico, analizando el efecto de la porosidad de los soportes sobre los gradientes térmicos. Se analizan problemas relacionados con las tensiones térmicas en materiales cerámicos, las cuales pueden ocasionar problemas como delaminaciones y grietas debido a altos gradientes térmicos. Mediante simulaciones de dinámica de fluidos computacional (CFD) en ANSYS Fluent, se estudian configuraciones con porosidades en los soportes desde 0.2 hasta 0.8, manteniendo constante la porosidad en los electrodos.
Los resultados muestran que la porosidad de los soportes impacta en el rendimiento térmico y electroquímico. Un aumento en la porosidad mejora la difusión de reactantes hacia la zona de reacción en la frontera de triple fase (TPB), aumentando la densidad de corriente y la potencia generada. Sin embargo, para porosidades muy altas en los soportes se generan cuellos de botella en la difusión de especies, limitando el transporte efectivo de reactantes y, por ende, la eficiencia de la celda. Además, el aumento de porosidad reduce la capacidad de los soportes para distribuir el calor producido por las reacciones electroquímicas, lo que provoca un aumento en los gradientes térmicos. A partir de porosidades mayores a 0.5, en ciertas zonas de los electrodos, cercanas a la zona del INLET, estos gradientes pueden superar los 10 [°C/cm], comprometiendo la estabilidad estructural de la celda. Esta concentración de grandes gradientes térmicos es explicada debido a la intensificación de las reacciones electroquímicas por la mayor concentración de reactantes y el salto térmico de los gases al alcanzar la zona de reacción.
Se identifica una porosidad óptima de 0.4 para los soportes metálicos, ya que equilibra la distribución térmica y el transporte de reactantes, optimizando el rendimiento de la celda y manteniendo los gradientes térmicos dentro de límites seguros para su durabilidad. Se destaca además la necesidad de estudios adicionales que incluyan heterogeneidades microestructurales, la difusión de knudsen, propiedades térmicas anisotrópicas y el comportamiento a largo plazo de los materiales bajo.
Los hallazgos en este informe representan un avance significativo en el diseño de SOFC más eficientes y duraderas, especialmente para aplicaciones estacionarias de generación de energía, abriendo la puerta a futuros trabajos e investigaciones que permitan optimizar el desempeño y reducir fallas estructurales en este tipo de celdas.
This study investigates the thermal and electrochemical behavior of planar solid oxide fuel cells (SOFC) with metallic supports, analyzing the effect of the support porosity on thermal gradients. It examines issues related to thermal stresses in ceramic materials, which can lead to problems such as delaminations and cracks due to high thermal gradients. Through computational fluid dynamics (CFD) simulations in ANSYS Fluent, configurations with support porosities ranging from 0.2 to 0.8 are studied, while maintaining constant porosity in the electrodes. The results show that the porosity of the supports significantly impacts thermal and electrochemical performance. An increase in porosity enhances the diffusion of reactants towards the reaction zone at the triple-phase boundary (TPB), increasing current density and power output. However, very high porosity in the supports creates bottlenecks in species diffusion, limiting the effective transport of reactants and thus the cell's efficiency. Additionally, increased porosity reduces the ability of the supports to distribute the heat generated by electrochemical reactions, leading to an increase in thermal gradients. For porosities greater than 0.5, in certain areas of the electrodes near the inlet zone, these gradients can exceed 10 [°C/cm], compromising the cell's structural stability. This concentration of high thermal gradients can be explained by the intensification of electrochemical reactions due to the higher concentration of reactants and the thermal jump of the gases upon reaching the reaction zone. An optimal porosity of 0.4 for metallic supports is identified, as it balances thermal distribution and reactant transport, optimizing cell performance while keeping thermal gradients within safe limits for durability. Furthermore, the need for additional studies is highlighted, which should include microstructural heterogeneities, Knudsen diffusion, anisotropic thermal properties, and the long-term behavior of materials under operating conditions. The findings in this report represent a significant advancement in the design of more efficient and durable SOFCs, particularly for stationary energy generation applications. It opens the door to future work and research aimed at optimizing performance and reducing structural failures in this type of cell.
This study investigates the thermal and electrochemical behavior of planar solid oxide fuel cells (SOFC) with metallic supports, analyzing the effect of the support porosity on thermal gradients. It examines issues related to thermal stresses in ceramic materials, which can lead to problems such as delaminations and cracks due to high thermal gradients. Through computational fluid dynamics (CFD) simulations in ANSYS Fluent, configurations with support porosities ranging from 0.2 to 0.8 are studied, while maintaining constant porosity in the electrodes. The results show that the porosity of the supports significantly impacts thermal and electrochemical performance. An increase in porosity enhances the diffusion of reactants towards the reaction zone at the triple-phase boundary (TPB), increasing current density and power output. However, very high porosity in the supports creates bottlenecks in species diffusion, limiting the effective transport of reactants and thus the cell's efficiency. Additionally, increased porosity reduces the ability of the supports to distribute the heat generated by electrochemical reactions, leading to an increase in thermal gradients. For porosities greater than 0.5, in certain areas of the electrodes near the inlet zone, these gradients can exceed 10 [°C/cm], compromising the cell's structural stability. This concentration of high thermal gradients can be explained by the intensification of electrochemical reactions due to the higher concentration of reactants and the thermal jump of the gases upon reaching the reaction zone. An optimal porosity of 0.4 for metallic supports is identified, as it balances thermal distribution and reactant transport, optimizing cell performance while keeping thermal gradients within safe limits for durability. Furthermore, the need for additional studies is highlighted, which should include microstructural heterogeneities, Knudsen diffusion, anisotropic thermal properties, and the long-term behavior of materials under operating conditions. The findings in this report represent a significant advancement in the design of more efficient and durable SOFCs, particularly for stationary energy generation applications. It opens the door to future work and research aimed at optimizing performance and reducing structural failures in this type of cell.
Description
Tesis presentada para optar al título de Ingeniero Civil Mecánico
Keywords
Materiales porosos, Dinámica de fluidos Métodos de simulación, Eficiencia térmica