Meshes and flow fields for the optimum design of autothermal reactors with different flow channel shapes
Description
The meshes and flow fields are illustrated from an autothermal reactors with different flow channel shapes, which can simultaneously carry out exothermic and endothermic reactions in separate flow channels and simultaneously adjust feed composition and flow rates. The state-of-the-art approach for optimizing the heat balance in endothermic processes requires a complex network of reactors and heat ex-changers for heating up the feed, for supplying the heat to the endothermic reaction at the required temperatures and for utilizing the sensible heat of the hot reactor effluents. The flow channels form a variety of cross-sectional shapes ranging from square to ellipse. Corners of the flow channels can be rounded off. Specifically, the cross-sectional shape of the flow channels is defined as follows: an ellipse within a circle, a circle within a larger circle, fillets formed in the corners of a square, a circle within a square, and a square within a larger square. The cross-sectional shape of the flow channels can be defined by means of a number of geometric parameters. A methanol-steam mixture is supplied to the reforming channels to be reformed, and a methanol-air mixture is supplied to the combustion channels to be combusted. The temperatures and pressures of the two streams entering the combustion channels and the reforming channels, respectively, are the same. The temperature of the two streams is 373 degrees Kelvin at the flow inlets. The system operates at a pressure of up to 1.5 megapascals. Typically, high pressure combustion is widely practiced. Although a stoichiometric ratio of fuel to air is sufficient, an equivalence ratio of 0.8 is employed. A steam-to-carbon molar ratio of 1.4 is employed. The fluids flow essentially parallel to the axes of the channels. The velocity of the fluid flowing into the reforming channels is 2.0 meters per second at the flow inlets. In contrast, the velocity of the fluid flowing into the combustion channels varies depending on the desired design requirements. To obtain the solution of the problem, numerical simulations are performed using fluid mechanics. Contributor: Junjie Chen, E-mail address: koncjj@gmail.com, ORCID: 0000-0002-5022-6863, Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China
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Two types of species are defined: gas-phase and surface. The Reynolds numbers are very small so that the gases flow through the channels in a laminar flow regime. ANSYS FLUENT handles thermodynamic properties, transport properties, and chemical kinetics. The mass fluxes of gas-phase species at the phase boundaries are balanced by the production rates of gas-phase species by surface reactions. Heat fluxes in the solid phase are balanced by chemical heat release at the surface. The endothermic process is modeled in such a way as to take into account methanol steam reforming and decomposition and the water-gas shift reaction. The contribution of homogeneous chemical reactions involving gas-phase species is insignificant under the conditions of interest.