Importance of flow velocity to the temperature distribution in catalytically supported thermal combustion systems with high exterior heat losses
Description
The temperature data at different flow velocities are presented for catalytically supported thermal combustion systems with high exterior heat losses. Catalytically supported thermal combustion surmounts the mass transfer limitation. Sustained catalytically-supported thermal combustion occurs at a substantially lower temperature than conventional adiabatic thermal combustion. Combustion is no longer limited by mass transfer. The catalytically supported thermal 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 and remains constant. The catalytically supported thermal combustion 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 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 ANSYS FLUENT to obtain the solution of the problem. Detailed chemistry is included in the model. Detailed chemical mechanisms are incorporated into the reacting flow for the catalytically supported thermal combustion 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. Natural parameter continuation is performed by moving from one stationary solution to another. Two types of species are defined: gas-phase and surface. The contribution of homogeneous chemical reactions involving gas-phase species is significant under the conditions of interest. 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. The problem is solved using structured meshes. The mesh is refined in the computational domains of the catalytically active layers.