COUPLING COMPLEX REFORMER CHEMICAL KINETICS WITH THREE- DIMENSIONAL COMPUTATIONAL FLUID DYNAMICS Graham Goldin a , Huayang Zhu b , Kyle Kattke b , Anthony M. Dean b , Robert Braun b , Robert J. Kee b , Dan Zhang c , Lubow Maier c and Olaf Deutchmann c a ANSYS/Fluent, Lebanon, NH 03766, USA b Engineering Division, Colorado School of Mines, Golden, CO 80401, USA c University of Karlsruhe, Engesserstrasse 20, 76131 Karlsruhe, Germany A new capability is developed that enables the modeling of certain logistics-fuel reformers. The system described in this paper considers a shell-and-tube configuration for which the catalytic reforming chemistry is confined within the tubes. The models are designed to accommodate detailed gas-phase and catalytic reaction kinetics, possibly including hundreds of species and thousands of reactions. The shell flow can be geometrically complex, but does not involve any complex chemistry. An iterative coupling algorithm is developed with which the geometrically complex flow is modeled with FLUENT and the chemically complex reforming is confined to straight tubes. The paper illustrates the model using propane partial oxidation and reforming as an example. Introduction Logistics-fuel reformers play essential roles in mobile SOFC applications such as auxiliary power units (APU). Modeling practical systems requires the coupling of geometric and fluid-mechanical complexity with chemical-kinetics complexity. The catalytic reforming kinetics of practical fuels (e.g., diesel fuel) depends upon gas-phase and heterogeneous reaction mechanisms that can involve over a thousand elementary reactions. Directly coupling chemistry at this level greatly exceeds the capability of computational fluid dynamics (CFD) models, which can handle geometric complexity. The present paper describes a new capability to couple full chemical kinetics with computational fluid dynamics in FLUENT (www.ansys.com). The approach exploits the structure of reformers in which the combined gas-phase and catalytic chemistry is confined within geometrically simple tubes or channels. Flow over the external surfaces of the catalyst tubes is used to achieve thermal control. For example, hot exhaust products from an SOFC tail-gas combustor may be used to support endothermic steam reforming. Figure 1 illustrates such a configuration. The coupling is accomplished with a User Defined Function (UDF) in FLUENT. Flow within the catalyst tubes is modeled with low-dimensional models that are written to accommodate chemical complexity using CHEMKIN, CANTERA, or DETCHEM interfaces. The outer fluid and thermal transport is modeled in FLUENT, which handles essentially arbitrary geometry. Coupling is via the exchange of temperature and heat-flux profiles at the tube walls. The UDF is written in C and provides the interface between geometrically complex three-dimensional outer mesh and the one-dimensional axial mesh for the catalyst tubes. In addition to outer fluid flow, the FLUENT model also represents solid- body heat transfer in the reactor walls and to the external environment.