The dimensionless local Sherwood number data pertaining to the catalytic oxidation assisted methanol steam reforming in microchannel reactors
Description
The dimensionless local Sherwood number data are obtained for the catalytic oxidation assisted methanol steam reforming in microchannel reactors. The reactor system offers relatively simple designs and operation. The reactor system is in the form of a catalytic coating on a substrate composed of ceramic or metal walls defining straight reforming or oxidation channels which are parallel to each other and to the axis of the reactor. Relatively high mass transfer is provided by using high cell density channels, namely low hydraulic diameter channels. The design increases the number of boundary layers between a fluid and a reactor wall by a factor of one hundred or more, and boundary layers are known to impede heat transfer. However, relatively high heat transfer is provided. Only two half oxidation and reforming channels as well as the surrounding walls are modeled due to the symmetry of the structurally integral system. The ratio of the height of the channels to the width of the channels may vary. Heterogeneous reactions at a catalytically active surface affect the heat and mass balance at the surface. In addition, surface reactions create sources and sinks of chemical species on the surface and in the gas phase. The mathematical formalism developed to describe transport phenomena and chemical kinetics is implemented into ANSYS FLUENT. 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. 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 and overall property conservation is satisfied. 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. The latter is monitored through both the values of the residuals of the conservation equations and the difference between subsequent iterations of the solution.