Thermal and electrochemical model of internal reforming solid oxide fuel cells with tubular geometry

A two-dimensional axisymmetric model of a tubular solid oxide fuel cell (SOFC) is presented. The model analyzes electrochemistry and heat transfer inside the cell with new approaches to thermal and chemical simulations being introduced. For the reforming process a new approach based on traditional hypotheses, equilibrium and kinetic theory, is proposed. Thus, there is not a single assumption for the reaction but both situations are taken as possible depending on composition and temperature; results show that equilibrium is reached near the entry zone of the cell and the reaction is kinetically controlled later. Thermally, a rigorous study of radiative heat exchange between the anodic gas and the anode surface is included in order to evaluate its effect on global performance. Results show that this effect can be neglected in most cases but, under certain operating conditions, deviations of up to 1% may appear.Additionally, other improvements have been done with respect to previous works: viscosity and electrical conductivity of gases depend on concentrations; evaluation of concentration losses includes a new description of binary diffusion coefficients; calculation of convective heat transfer coefficients includes thermal entry length and laminar/turbulent flow; heat generation in the inner part of the cell accounts for the heat release due to Joule effect.