1,721,262 research outputs found
Efficient Coupling Between Microkinetic Modeling and CFD: Towards a Fully First-Principles Catalytic Chemical Reaction Engineering
No full textCoupling CFD with detailed microkinetic modeling in heterogeneous catalysis
No full textThe atomic-scale understanding of a catalytic process is crucial for the rational development of catalytic technologies. It requires the identification of the dominant reaction mechanism, that is an intrinsic multiscale property of the system. In this respect, it is of utmost importance to obtain a fundamental understanding about the interactions of the catalyst reactivity with the surrounding flow field in the reactor. Here, we propose a new solver (catalyticFOAM), that allows for the solution of Navier–Stokes equations for complex and general geometries for reacting flows at surfaces, based on a detailed microkinetic description of the surface reactivity. The catalyticFOAM solver exploits the operator-splitting technique, based on the separation of transport and reaction terms. The proposed numerical algorithm makes possible the simulation of multidimensional systems with complex and detailed kinetic mechanisms, overcoming the unfeasible computational effort that would be required by fully-coupled algorithms. Examples concerning the H2 fuel rich combustion on Rh are presented as showcases in structured and randomly packed reactors. The proposed approach represents an essential step for the first-principles based multiscale analysis of catalytic processes and paves the way toward the rational understanding and development of new reaction/reactor concepts
In situ adaptive tabulation for the CFD simulation of heterogeneous reactors based on operator-splitting algorithm
No full textIn situ Adaptive Tabulation algorithm is applied to efficiently solve the chemical substep in the context of the simulation of heterogeneous reactors. A numerical strategy—specifically conceived for unsteady simulation of catalytic devices—has been developed and interfaced, in the context of the operator splitting technique, with the solution of the chemical substep, which requires 70–90% of the total computational time. The algorithm performances have been illustrated by considering a single channel of a honeycomb reactor operating the catalytic partial oxidation of methane and a methane steam reforming packed bed reactor. The application of in situ adaptive tabulation resulted in a speed-up of the chemical substep up to ∼500 times with an overall speed-up of ∼5–15 times for the whole simulation. Such reduction of the computation effort is key to make affordable fundamental computational fluid dynamics simulations of chemical reactors at a level of complexity relevant to technological applications. © 2016 American Institute of Chemical Engineers AIChE J, 63: 95–104, 2017
Complete multicomponent versus mixture-averaged calculations of a laminar H2/N2 diffusion flame including heat transfer at the burner and Soret effects
Full text linkThe implementation of full multicomponent treatment of diffusion fluxes in the CFD solver for laminar reacting flows with detailed kinetic mechanisms laminarSMOKE++ is presented. The optimised 1+M multicomponent formulation (including Fick diffusion and Soret effects) derived from the Kinetic Theory of Gases, with a similar computational cost as mixture-averaged, is considered. Results are presented for a H2/N2 laminar coflow diffusion flame, where either heat transfer at the burner wall is included, either the wall is considered adiabatic. We observe that full multicomponent and mixture-averaged results are very similar when Soret effects are neglected. However, differences are observed when including thermodiffusion. In particular with heat transfer at the wall, large differences are observed whether thermodiffusion is neglected or included. In this case, the mixture-averaged approximation used for the thermal diffusion coefficients leads to significant differences in the results compared to the full multicomponent 1+M formulation
Hierarchical analysis of the gas-to-particle heat and mass transfer in micro packed bed reactors
No full textIn this paper we propose and apply a hierarchical approach for an efficient exploitation of fundamental multi-scale modeling for the analysis and design of the kinetic-transport interactions in chemical reactors. In essence, detailed and computationally demanding analyses - based on computational fluid dynamics simulations (CFD) of the reactor - are first used to study in detail a selected and limited number of conditions. Then, the CFD results are interpreted by means of 1D heterogeneous models for the derivation of lumped parameters to be used in classical reactor models. On one side, this approach limits the use of computationally demanding simulations. On the other side, it allows for the rational derivation of parameters, which are related to a detailed and sound description of the governing phenomena. The very good agreement between the predictions of CFD and 1D heterogeneous models at different operating conditions shows that the CFD-based correlation for transport properties fully retains all the main features of the detailed CFD simulation. Moreover, we found that the hierarchical derived correlations to be very similar to the ones experimentally obtained for typical industrial scale packed bed reactors, thus confirming that the conventional correlations may be reliably used in micro-packed bed reactors. On a more general basis, this work clearly demonstrates the potentiality of the hierarchical application of CFD simulation for the derivation of transport parameters in reactor engineering, which can be used for the efficient and fundamental analysis and design of novel reactor technologies
Handling contact points in reactive CFD simulations of heterogeneous catalytic fixed bed reactors
Full text linkThe mesh generation is a crucial step for Computational Fluid Dynamic (CFD) simulations and incorrect numerical descriptions of the geometry may strongly affect the reliability and the accuracy of the results. This is especially true in handling the contact points in random packed bed of spheres. In this respect, we provide a systematic investigation of the treatment of the contact points for reactive CFD simulations of gas-solid packed beds of spheres. In particular, building on previous literature results on radial heat transfer and pressure drop simulations, we extend and assess the bridge method to reaction at surfaces. At this scope, we first analyze a regular bed of spheres in laminar conditions (Re~80). This regular packed bed and the laminar flow regime allow for a direct and feasible meshing of the contact points, thus giving the possibility to perform explicit comparisons between meshes with and without bridges. In doing so, we identify guidelines that are then extended and tested to the meshing of a random packed bed reactor. In this way, we identify a meshing protocol, which can be adopted to properly describe surface reactivity in packed bed reactors along with a concomitant sound description of pressure drops and heat transfer
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