Contributions of homogeneous and heterogeneous reactions to the catalytically supported thermal combustion of methane-air mixtures in microchannel reactors
Description
The homogeneous and heterogeneous contributions directed to the catalytically supported thermal combustion of methane-air mixtures in microchannel reactors. The microchannel reactor comprises a concentric annular channel, wherein the concentric annular channel further comprises an inner annular channel and an outer annular channel. A platinum catalyst is deposited only upon the interior surface of the inner channel, and the wall of the outer channel is chemically inert and catalytically inactive. The reactant stream flows through the catalytically-coated inner channel and the product stream flows out of the outer non-catalytic channel. Fuel is present for combustion in both the catalytic and non-catalytic channels. The concentrically arranged annular channel is 5.0 millimeters in inner channel length, 5.6 millimeters in outer channel length, 0.8 millimeters in innermost diameter, 2.6 millimeters in outermost diameter, 0.1 millimeters in catalyst layer thickness, and 0.2 millimeters in wall thickness. The spacing between the inner channel and the outer channel is 0.4 millimeters and remains constant. The system can have any dimension unless restricted by design requirements. All the walls have the same thickness. One of the potential problems associated with the system, as with all micro-scale combustion systems, continues to be combustion stability. The maximum Reynolds number is less than 360 at the flow inlet and 960 when the velocity of the flow of the fluid is highest in the channels. The model is implemented in commercially available software FLUENT to obtain the solution of the problem. Detailed chemistry is included in the model. Detailed chemical mechanisms are playing an increasingly important role in developing chemical kinetics models for combustion. Detailed chemical mechanisms are incorporated into the reacting flow for the system. The homogeneous combustion is modeled with the detailed chemical mechanism for methane oxidation in CHEMKIN format. Detailed heterogeneous chemistry in SURFACE-CHEMKIN format is included in the model. The rates of the elementary reactions involved in the combustion process are determined by Arrhenius kinetic expressions. Numerical simulations with the detailed chemical mechanism are typically computationally expensive. The detailed chemical mechanism is invariably stiff and therefore its numerical integration is computationally costly. 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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To solve the conservation equations, a segregated solution solver with an under-relaxation method is used. The segregated solver first solves the momentum equations, then solves the continuity equation, and updates the pressure and mass flow rate. The energy and species equations are subsequently solved and convergence is checked. Natural parameter continuation is performed by moving from one stationary solution to another. A critical point is denoted as the solution to the problem when a turning point is reached.