Mathematical and chemical kinetic models for microchannel steam reforming reactor systems for the production of hydrogen
Description
To develop the mathematical and chemical kinetic models for microchannel steam reforming reactor systems for the production of hydrogen, fluid mechanics is used. To facilitate computational modeling of transport phenomena and chemical kinetics in the flowing system of complex chemical reactions involving gas-phase and surface species, steady-state analyses are performed. The problem is solved using structured meshes. The mesh is refined in the computational domains of the catalytically active layers. A mesh independence study is carried out. The solution is independent of the mesh resolution. Numerical simulations are performed within ANSYS FLUENT using computational fluid dynamics. Boundary conditions are specified and physical properties are defined for the fluids, solids, and mixtures. Physical properties depend on temperature and composition. A piecewise-polynomial function is specified for the temperature dependence. To define composition-dependent properties for the mixtures, the mass-weighted-mixing-law is applied. The mathematical formalism developed to describe transport phenomena and chemical kinetics is implemented into ANSYS FLUENT. The computer code and its usage are fully documented. More specifically, ANSYS FLUENT is applied to define the terms in the equations relating to conservation, thermodynamics, chemical production rates, and equation of state, and then combine the results to define the problem involving surface chemistry. To describe the surface reaction mechanisms in symbolic form, the following information is required, including the thermochemical properties of surface species in the surface phases, names of the surface species, site densities, names of all surface phases, Arrhenius rate coefficients, reaction descriptions, and any optional coverage parameters. 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
Each porous medium is modeled by the modification of a heat conduction flux term to the standard gas phase energy balance equation. 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 pressure-based segregated algorithm is used with SIMPLE-type pressure-velocity coupling. The under-relaxation factors are reduced for all variables. The residuals decrease by at least six orders of magnitude. 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 and overall property conservation is satisfied. A general and flexible framework is provided for describing the model involving complex transport phenomena and chemical kinetics. Predetermined boundary conditions may be necessary in order to exactly matches the specifications or requirements.