This paper describes the heat, momentum and mass transfer in a tubular internal reformer for SOFCs (Solid Oxide Fuel Cell). The reforming is one of the fundamental steps of the fuel processing to convert methane into hydrogen in an SOFC system. Since very little fuel slippage through the reformer can be tolerated a detailed analysis of heat, mass and momentum transfer must be conducted to verify the total depletion of the methane. By means of Computational Fluid Dynamic (CFD) simulations these transport phenomena can be quantified. A computational investigation was carried out to estimate the efficiency of a reformer made up of a simple fuel pipe and an internal ceramic support for the catalyst. A mixture of CH4, H2O, CO, CO2 and H2 at 1000 K was fed into the reactor. Methane reforming and CO shift are endothermic reactions, thus to facilitate these reactions, heat has been supplied to the cross-flow type reactor by impinging air at 1300 K against the external walls of the fuel pipe. The temperature-dependent heat capacities, thermal conductivities and viscosities of the chemical species have been calculated by a polynomial function and the mass diffusivities were computed following the Chapman-Enskog theory and Stefan-Maxwell equation. At the inlet to the reactor the fuel mass flow rate, operating pressure and temperature were set experimentally. In the current paper the reactions were treated as volumetric and the main emphasis is placed on the fundamental reaction kinetics. These depend on the amount of active catalyst that has been deposited on the ceramic support.Correlations for Nusselt, Prandtl, Grashof and Graetz numbers were implemented into the CFD software to describe the heat transfer. A Reynolds analogy was applied to the Stanton number to derive Sherwood and Lewis numbers for the mass transport and the Schmidt number for the momentum transfer. The experimental validation of the computational model allowed one to conclude that such a reactor was working in a laminar regime (Re=200-2000) and the reforming reaction was mass transfer limited. Consequently the overall conversion of methane was significantly reduced and the overall efficiency of the reformer
