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Jianxin Wang - One of the best experts on this subject based on the ideXlab platform.

  • unsteady temperature fields of monoliths in Catalytic Converters
    Chemical Engineering Journal, 2004
    Co-Authors: Shijin Shuai, Jianxin Wang
    Abstract:

    This paper measured unsteady temperature fields of uncoated-monolith and Catalytic monolith under real engine operating conditions using thermocouples. A multi-dimensional flow model of the turbulence, heat and mass transfer, and chemical reactions in monoliths was established and numerically solved in the whole flow field of the Catalytic converter. The purpose of this paper is to study unsteady warm-up characteristics of the monoliths and to investigate effects of inlet cone structure on temperature distribution of the Catalytic converter. Experimental results show that the warm-up behaviors between uncoated-monolith and Catalytic monolith are quite different. Simulation results indicate that the established model can qualitatively predict the warm-up characteristics. Increasing the inlet cone angle can improve the light-off characteristics of the catalysts due to high flow velocity and high temperature in the center of the monoliths.

Sandip Mazumder - One of the best experts on this subject based on the ideXlab platform.

  • toward simulation of full scale monolithic Catalytic Converters with complex heterogeneous chemistry
    Computers & Chemical Engineering, 2010
    Co-Authors: Ankan Kumar, Sandip Mazumder
    Abstract:

    Abstract Computational fluid dynamic (CFD) modeling of full-scale Catalytic Converters with realistic chemistry has remained elusive primarily due to the extreme computational requirements. In this work, a new low-memory coupled implicit solver, based on the conservative unstructured finite-volume method, was utilized to simulate laboratory-scale Catalytic Converters with implicit coupling between fluid flow, heat transfer (including conjugate heat transfer), mass transfer, and heterogeneous chemical reactions. Steady-state calculations were performed for a Catalytic methane–air combustion process with 24 reaction steps and 19 species (8 gas-phase species, 11 surface-adsorbed species), and for a three-way Catalytic conversion process with 61 reaction steps and 31 species (8 gas-phase species, 23 surface-adsorbed species). Both calculations were conducted on a single processor for a monolith with 57 channels discretized using 354,300 control volumes. The Catalytic combustion simulation was completed in 19 h and required 900 MB of memory, while the three-way conversion simulation required 6 days and 1 GB of memory, indicating that the complexity of the surface reaction mechanism dominates the overall CPU time requirements. Subsequently, the solver was parallelized, and the same Catalytic combustion case was simulated for a monolith with 293 channels discretized using 1.27 million control volumes. A 4-node cluster was utilized for the parallel computations, and the parallelization efficiency was found to be about 80%.

  • modeling full scale monolithic Catalytic Converters challenges and possible solutions
    Journal of Heat Transfer-transactions of The Asme, 2007
    Co-Authors: Sandip Mazumder
    Abstract:

    Modeling full-scale monolithic Catalytic Converters using state-of-the-art computational fluid dynamics algorithms and techniques encounters a classical multiscale problem: the channels within the monolith have length scales that are ∼1-2 mm, while the converter itself has a length scale that is ∼5-10 cm. This necessitates very fine grids to resolve all the length scales, resulting in few million computational cells. When complex heterogeneous chemistry is included, the computational problem becomes all but intractable unless massively parallel computation is employed. Two approaches to address this difficulty are reviewed, and their effectiveness demonstrated for the computation of full-scale Catalytic Converters with complex chemistry. The first approach is one where only the larger scales are resolved by a grid, while the physics at the smallest scale (channel scale) are modeled using subgrid scale models whose development entails detailed flux balances at the "imaginary" fluid-solid interfaces within each computational cell. The second approach makes use of the in situ adaptive tabulation algorithm, after significant reformulation of the underlying mathematics, to accelerate computation of the surface reaction boundary conditions. Preliminary results shown here for a Catalytic combustion application involving 19 species and 24 reactions indicate that both methods have the potential of improving computational efficiency by several orders of magnitude.

  • sub grid scale modeling of heterogeneous chemical reactions and transport in full scale Catalytic Converters
    Combustion and Flame, 2002
    Co-Authors: Sandip Mazumder, Debasis Sengupta
    Abstract:

    This article presents a novel approach to treat heterogeneous Catalytic reactions occurring in porous or honeycomb monoliths. The approach allows accurate modeling of full-scale Catalytic Converters with low computational cost. In this approach, the entire Catalytic monolith is treated as an anisotropic porous medium, and sub-grid scale models are employed to represent the heterogeneous chemical reactions occurring at the solid-fluid interfaces within the monolith. Full coupling between fluid flow, heat transfer, species transport, and heterogeneous chemical reactions is achieved through flux balance of species and energy at the solid-fluid interfaces. The model allows for unlimited number of finite-rate reaction steps and species, including surface-adsorbed species and site coverage effects. The model was validated for hydrogen-assisted combustion of methane-air mixtures over platinum catalyst clusters in a full-scale Catalytic converter. Validation against experimental data exhibits excellent match for ignition temperature for various methane and/or hydrogen inlet concentrations. Transient calculations show that the time constant for ignition matches well with previously reported results. Because the model is based on a sub-grid scale approach, it is orders of magnitude more efficient for modeling full-scale Catalytic Converters than conventional approaches where each channel within the Catalytic monolith has to be represented by a computational grid.

Grigorios C Koltsakis - One of the best experts on this subject based on the ideXlab platform.

  • transient modelling of flow distribution in automotive Catalytic Converters
    Applied Mathematical Modelling, 2004
    Co-Authors: Dimitrios N Tsinoglou, Grigorios C Koltsakis, D Missirlis, K Yakinthos
    Abstract:

    Abstract The transient Catalytic converter performance is governed by complex interactions between exhaust gas flow and the monolithic structure of the Catalytic converter. Therefore, during typical operating conditions of interest, one has to take into account the effect of the inlet diffuser on the flow field at the entrance. Computational fluid dynamics (CFD) is a powerful tool for calculating the flow field inside the Catalytic converter. Radial velocity profiles, obtained by a commercial CFD code, present very good agreement with respective experimental results published in the literature. However the applicability of CFD for transient simulations is limited by the high CPU demands. The present study proposes an alternative computational method for the prediction of transient flow fields in axi-symmetric Converters time-efficiently. The method is based on the use of equivalent flow resistances to simulate the flow paths in the inlet and outlet catalyst sections. The proposed flow resistance modelling (FRM) method is validated against the results of CFD predictions over a wide range of operating conditions. Apart from the apparent CPU advantages, the proposed methodology can be readily coupled with already available transient models for the chemical reactions in the catalyst. A transient model for heat transfer inside the monolith is presented. An example of coupling between FRM and transient heat transfer inside the converter is included. This example illustrates the effect of flow distribution in the thermal response of a Catalytic converter, during the critical phase of Catalytic converter warm-up.

  • oxygen storage modeling in three way Catalytic Converters
    Industrial & Engineering Chemistry Research, 2002
    Co-Authors: Dimitrios N Tsinoglou, Grigorios C Koltsakis, James Peyton C Jones
    Abstract:

    Mathematical modeling of three-way Catalytic converter (3WCC) operation is increasingly employed in automotive catalyst and converter systems optimization. Oxygen storage is known to strongly affect Catalytic converter operation under real world transient operating conditions. This paper presents a modeling approach embodying a comprehensive oxygen storage and release submodel into an existing 3WCC quasi-steady model. The dynamic model developed according to this approach is validated against previously published experimental data. The model sensitivity to each of the oxygen storage parameters is examined. The results of this investigation encourage further application of mathematical modeling in areas such as air-to-fuel (A/F) ratio control strategy optimization, which lie beyond the scope of traditional kinetic 3WCC models.

  • modeling dynamic phenomena in 3 way Catalytic Converters
    Chemical Engineering Science, 1999
    Co-Authors: Grigorios C Koltsakis, Anastasios M. Stamatelos
    Abstract:

    Mathematical modeling of 3-way Catalytic converter (3WCC) operation is increasingly employed in automotive catalyst and converter systems optimization. The majority of the models employed in this direction employ a &quasi-steady’ approach in the reaction kinetics computations. This approach is useful in predicting real-world performance of the catalyst. However, certain improvements, that are produced by the application of specially tuned redox oscillations, can not be predicted. This paper presents an approach embodying certain types of dynamic phenomena into an existing 3-WCC quasi-steady model. The dynamic model developed according to this approach is validated against literature data and results from experimental investigations. It is con"rmed, that the catalyst behavior under dynamic exhaust composition conditions signi"cantly di!ers from what is predicted under the quasi-steady-state assumption. More speci"cally, oxygen storage and the transient character of water gas shift reaction are shown to a!ect dynamic behavior. The results of this investigation encourage further application of mathematical modeling in areas like lambda control strategy optimization, which lied beyond the scope of traditional 3WCC models. ( 1999 Elsevier Science Ltd. All rights reserved.

M Cross - One of the best experts on this subject based on the ideXlab platform.

  • the recovery mechanism of platinum group metals from Catalytic Converters in spent automotive exhaust systems
    Resources Conservation and Recycling, 2000
    Co-Authors: M Benson, C R Bennett, J E Harry, M K Patel, M Cross
    Abstract:

    The recovery of platinum group metals (PGMs) from Catalytic Converters of spent exhaust systems is considered in this paper. To be cost-effective, recovery processes must be well over 90% efficient and so the optimisation of their operation is vital. Effective optimisation requires a sound understanding of the operation and the underlying process mechanisms. This paper focuses on pyrometallurgical recovery operations used and typified by the Johnson–Matthey process. Analysis of this process reveals that it cannot be simply explained by the gravity model that is normally assumed. The analysis reveals that the affinity of PGM particles for the melted collector metal is a key factor in the behaviour of the process. A rational explanation of the key issues that govern the process behaviour is proposed and shown to be consistent with available operational data. The results generated would be applicable to other similar processes.

Patrick Da Costa - One of the best experts on this subject based on the ideXlab platform.

  • multi scale flow simulation of automotive Catalytic Converters
    Chemical Engineering Science, 2014
    Co-Authors: Cansu Ozhan, Daniel Fuster, Patrick Da Costa
    Abstract:

    The flow distribution within the automotive Catalytic converter is an important controlling factor on the overall conversion efficiency. Capturing the flow features minimizing the computational cost is the first important step towards the solution of the complex full engineering problem. In this work we present a novel approach that combines physical and numerical multi-resolution techniques in order to correctly capture the flow features inside an automotive Catalytic converter. While Adaptive Mesh Refinement techniques are optimized in order to minimize the computational effort in the divergent region, a novel subgrid model is developed to describe the flow inside the Catalytic substrate placed between the convergent and divergent regions. The proposed Adaptive Mesh Refinement methods are tested for two test cases representative of the flow features found in the divergent region of a Catalytic converter. The performance of the new subgrid model is validated against the non-uniformity index and the radial velocity profile data obtained by Benjamin et al. (2002). The effective coupling of AMR techniques and the subgrid model significantly reduces the error of the numerical predictions to 5–15% in conditions where the full simulation of the problem is out of current computational capabilities.