Importance of wall thermal conductivity to the flow velocity distribution in catalytically stabilized combustion systems with extremely high exterior heat losses
Description
The flow velocity data at different wall thermal conductivity are presented for catalytically stabilized combustion systems with extremely high exterior heat losses. An improved method is provided for more efficiently operating a catalytically stabilized combustion system, and at the same time provide low emissions of unburned hydrocarbons, carbon monoxide, and nitrogen oxides. In the adiabatic combustion of the fuel and air admixture, at least a portion of the thermal combustion of the fuel takes place in the expansion zone of the combustion system to counteract the cooling effect of the expansion of the gases. Catalytically stabilized combustion surmounts the mass transfer limitation. Sustained catalytically stabilized combustion occurs at a substantially lower temperature than conventional adiabatic thermal combustion. Combustion is no longer limited by mass transfer. The catalytically stabilized combustion system comprises a concentric annular channel, wherein the concentric annular channel further comprises an inner annular channel and an outer annular channel. 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. The catalytically stabilized combustion system can have any dimension unless restricted by design requirements. 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 ANSYS FLUENT to obtain the solution of the problem. Detailed chemistry is included in the model. 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. Chemical species can exist in the gas phase or on surface sites. Surface reactions create sources and sinks of chemical species on the surface and in the gas phase. 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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ANSYS FLUENT is applied to the problem involving surface chemistry. ANSYS FLUENT handles thermodynamic properties, transport properties, gas-phase equation-of-state, and chemical kinetics. Physical properties depend on temperature and composition. The governing equations are solved numerically for the conservation of mass and momentum and for energy and species.