CFD analysis of mass transport mechanism in porous SOFC electrode

Authors:

• Monika Sikora,
• Marcin Błesznowski,
• Wojciech Orciuch,
• Łukasz Makowski

Abstract

As Mahatma Gandhi used to say, constant development is the law of life. Constant development and population growth increase the demand for energy. Finite fossil fuels resources and deteriorating quality of air is the strong motivation to modernize the energy sector which should base on environmentally and energy efficient technologies. Noteworthy are Solid Oxide Cells (SOC), which distinguish high electrical efficiency in Solid Oxide Fuel Cell mode (over 58%), high rate of fuel conversion in the electrochemical reaction and near-zero greenhouse gases emissions. Nowadays, SOFC technology is in pre-commerce phase where a lot of effort is put to increase the generated power and extend the lifetime. This work concerns computational fluid dynamics (CFD) modelling of diffusion transport mechanism in porous anode in order to examine limiting factors of mass transport throughout porous media at high temperature conditions. Various mathematical models of diffusive mass transport were investigated. Finally, Dusty Gas Model was taken into consideration and implemented in Fluent solver. This work presents the numerical analysis validated by laboratory tests. Experiments were performed using SOFC’s electrodes which were produced in the Institute of Power Engineering in Poland. Obtained results indicate that the most appropriate mathematical model of gas diffusion in porous media at high temperature and in the regime of significant concentration gradients of the gaseous components is Dusty Gas Model. Experiments and simulations results demonstrate satisfactory compliance. The maximum relative error of the computational method does not exceed 15%. The numerical analysis reveals the risk of uneven use of catalyst surface due to the rapid loss of hydrogen kinetic energy and further displacement of hydrogen with steam - the product of electrochemical reaction. It was proven that consideration of Knudsen diffusion coefficients emphasises the difference between diffusion rates of hydrogen and steam throughout the porous electrode. It is worth noting that slower steam diffusion to the flow channel in the worst scenario may lead to its adsorption on porous surface and blockage of reaction sites.