Contour plots of species mole fractions for micro-structured steam reforming reactors with thermally insulating walls
Description
The contour plots of species mole fractions are presented from a micro-structured heterogeneous reaction system, which can simultaneously carry out exothermic and endothermic reactions in separate micro-channels and simultaneously adjust feed composition and flow rates. Specifically, the contour plots of species mole fractions relate to a catalytic process of steam-methanol reforming for the production of hydrogen in a micro-channel reactor with thermally insulating walls. To obtain the solution of the problem, numerical simulations are performed using fluid mechanics. The thermal conductivity of the wall material is 0.02 watts per meter-kelvin at room temperature. To assure that adequate temperatures are provided for endothermic reforming, operating flow conditions are specified for the reactor by giving the gas velocity. The gas velocity is 2.0 meters per second at the reforming channel inlets and 0.6 meters per second at the oxidation channel inlets, thereby assuring sufficient heat in the reactor to carry out endothermic reforming of methanol. The effective thermal conductivity of the catalyst layers is 16 watts per meter-kelvin at room temperature. The porosity of the catalyst layers is 0.5. The cross-sectional configuration of the channels is square. The channels are 0.7 millimeters in height and in width and 30.0 millimeters in length. Channel height refers to the inside height of a channel. To ensure the mechanical strength at elevated pressures, the thickness of the uncoated walls is 0.7 millimeters. The oxidation catalyst consists essentially of oxides of copper, zinc and aluminum. The reforming catalyst consists essentially of copper and oxides of zinc and aluminum. The exothermic and endothermic processes are conducted at a pressure of 0.8 megapascals, with a methanol-air equivalence ratio of 0.8 and a steam-to-methanol molar ratio of 1.17. The inlet temperature of the mixtures is 373 degrees Kelvin. The temperature of the reactor can be regulated by the balance of the flow rates so that the catalyst is not overheated by the exothermic process and thus damaged. 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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Steps to reproduce
The governing equations are solved numerically for the conservation of mass and momentum and for energy and species. The governing equations are discretized in space, and the second-order upwind discretization scheme is used. The under-relaxation factors are reduced for all variables. Overall heat and mass balances are achieved and the net imbalance is less than one percent of smallest flux through the domain boundaries. The solution converges when the residuals reach the specified tolerance. Computational fluid dynamics simulations are performed with respect to various factors pertaining to the catalytic reactor. Steady-state analyses are carried out to investigate the effects of various key parameters on processes such as chemical reactions or heat and mass transfer in the reactor system.