Multifluid Eulerian modeling of dense gas–solids fluidized bed hydrodynamics: Influence of the dissipation parameters

Computational fluid dynamic (CFD) models must be thoroughly validated before they can be used with confidence for designing fluidized bed reactors. In this study, validation data were collected from a fluidized bed of (Geldart's group B) alumina particles operated at different gas velocities involving two fluidization hydrodynamic regimes (bubbling and slugging). The bed expansion, height of bed fluctuations and frequency of fluctuations were measured from videos of the fluidized bed. The Eulerian–Eulerian two fluid model MFIX was used to simulate the experiments. Two different models for the particle stresses—Schaeffer [Syamlal, M., Rogers, W., O’Brien, T.J., 1993. MFIX documentation: theory guide. Technical Report DOE/METC-94/1004 (DE9400087), Morgantown Energy Technology Centre, Morgantown, West Virginia (can be downloaded from Multiphase Flow with Interphase eXchanges (MFIX) website left angle brackethttp://www.mfix.orgright-pointing angle bracket); Schaeffer, D.G., 1987. Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations 66, 61–74.] and Princeton [Srivastava, A., Sundaresan, S., 2003. Analysis of a frictional–kinetic model for gas–particle flow. Powder Technology 129(1–3), 72–85.] models—and different values of the restitution coefficient and internal angle of friction were evaluated. 3-D simulations are required for getting quantitative and qualitative agreement with experimental data. The results from the Princeton model are in better agreement with data than that from the Schaeffer model. Both free slip and Johnson–Jackson boundary conditions give nearly identical results. An increase in coefficient of restitution (e) from 0.8 to 1 leads to larger bed expansions and lower heights of fluctuations in the bubbling regime, whereas it leads to unchanged bed expansion and to a massive reduction in the height of fluctuations in the slugging regime. The angle of internal friction (φ) in the range 10–40ring operator does not affect the bed expansion, but its reduction significantly reduces the height of fluctuations

Silicon CVD on powders in fluidized bed: Experimental and multifluid Eulerian modelling study

The Computational Fluid Dynamics code MFIX was used for transient simulations of silicon Fluidized Bed Chemical Vapor Deposition (FBCVD) from silane (SiH4) on coarse alumina powders. FBCVD experiments were first performed to obtain a reference database for modelling. Experimental thermal profiles existing along the bed were considered in the model. 3D simulations provide better results than 2D ones and predict silane conversion rate with a mean deviation of 9% compared to experimental values. The model can predict the temporal and spatial evolutions of local void fractions, gas and particle velocities, species gas fractions and silicon deposition rate. We aim at mid term to model FBCVD treatments of submicronic powders in a vibrated reactor since we have performed experiments proving the efficacy of the process to treat submicronic particles

Process Modeling Phase I Summary Report for the Advanced Gas Reactor Fuel Development and Qualification Program

This report summarizes the results of preliminary work at Oak Ridge National Laboratory (ORNL) to demonstrate application of computational fluid dynamics modeling to the scale-up of a Fluidized Bed Chemical Vapor Deposition (FBCVD) process for nuclear fuels coating. Specifically, this work, referred to as Modeling Scale-Up Phase I, was conducted between January 1, 2006 and March 31, 2006 in support of the Advanced Gas Reactor (AGR) Program. The objective was to develop, demonstrate and "freeze" a version of ORNL's computational model of the TRI ISOtropic (TRISO) fuel-particle coating process that can be specifically used to assist coater scale-up activities as part of the production of AGR-2 fuel. The results in this report are intended to serve as input for making decisions about initiating additional FBCVD modeling work (referred to as Modeling Scale-Up Phase II) in support of AGR-2. The main computational tool used to implement the model is the general-purpose multiphase fluid-dynamics computer code known as MFIX (Multiphase Flow with Interphase eXchanges), which is documented in detail on the DOE-sponsored website http://www.mfix.org. Additional computational tools are also being developed by ORNL for post-processing MFIX output to efficiently summarize the important information generated by the coater simulations. The summarized information includes quantitative spatial and temporal measures (referred to as discriminating characteristics, or DCs) by which different coater designs and operating conditions can be compared and correlated with trends in product quality. The ORNL FBCVD modeling work is being conducted in conjunction with experimental coater studies at ORNL with natural uranium CO (NUCO) and surrogate fuel kernels. Data are also being obtained from ambient-temperature, spouted-bed characterization experiments at the University of Tennessee and theoretical studies of carbon and silicon carbide chemical vapor deposition kinetics at Iowa State University. Prior to the current scale-up activity, considerable effort has gone in to adapting the MFIX code to incorporate the unique features of fuel coating reactors and also in validating the resulting simulation features with experimental observations. Much of this work is documented in previous AGR reports and publications (Pannala et al., 2004, Pannala et al., 2005, Boyalakuntla et al., 2005a, Boyalakuntla et al., 2005b and Finney et al., 2005). As a result of the previous work described above, the ORNL coater model now has the capability for simulating full spatio-temporal details of the gas-particle hydrodynamics and gas-particle heat and mass transfer in the TRISO coater. This capability provides a great deal of information about many of the processes believed to control quality, but the model is not yet sufficiently developed to fully predict coating quality for any given coater design and/or set of operating conditions because the detailed chemical reaction kinetics needed to make the model fully predictive are not yet available. Nevertheless, the model at its current stage of development already provides the most comprehensive and detailed quantitative information available about gas flows, solid flows, temperatures, and species inside the coater during operation. This level of information ought to be highly useful in expediting the scale-up process (e.g., in correlating observations and minimizing the number of pilot-scale tests required). However, previous work had not yet demonstrated that the typical design and/or operating changes known to affect product quality at the lab scale could be clearly discriminated by the existing model. The Modeling Scale-Up Phase I work was initiated to produce such a demonstration, and two detailed examples are discussed in this report

Open-Source Software in Computational Research: A Case Study

A case study of open-source (OS) development of the computational research software MFIX, used for multiphase computational fluid dynamics simulations, is presented here. The verification and validation steps required for constructing modern computational software and the advantages of OS development in those steps are discussed. The infrastructure used for enabling the OS development of MFIX is described. The impact of OS development on computational research and education in gas-solids flow, as well as the dissemination of information to other areas such as geophysical and volcanology research, is demonstrated. This study shows that the advantages of OS development were realized in the case of MFIX: verification by many users, which enhances software quality; the use of software as a means for accumulating and exchanging information; the facilitation of peer review of the results of computational research

On large eddy simulations of reacting two-phase flows

Ph.D.Suresh Meno

Multiscale modeling approaches for multiphase flows

Talk: Regular Abstract: Developing new and efficient commercial scale chemical reactors is extremely difficult as one needs to consider the complex interactions over a wide range of both temporal and spatial scales encountered in these systems (from molecules to macroscale). Therefore, it is important to codify and automate the knowledge collectively acquired so far, reserving human resources for the creative solutions that build upon codifying past learnings. Computational science (algorithms, theory and modeling, computer science, etc.) combined with exponential growth in computing hardware has great potential to revolutionize the way science and engineering has been performed. For this reason, computational science is often called the third pillar of modern science, complementing observations and theory. The complexity of the problem is introduced using biomass gasifier/pyrolyser, nuclear fuel coater, and fluidized bed polymerization reactors as examples and I will provide an overview of the various models currently used at the different scales. The coupling across the scales will be introduced through few different approaches: a) Discrete-Continuum Coupling using Discrete Element Method for particles b) A wavelet based technique for coupling multiple modeling approaches at different scales c) Upscaling data from Discrete Element Modeling results to continuumNon UBCUnreviewedAuthor affiliation: SABICOthe

Hybrid (OpenMP and MPI) Parallelization of MFIX: A Multiphase CFD Code for Modeling Fluidized Beds

We describe the effort and experience in generating a hybrid parallel version of MFIX (Multiphase Flow with Interphase eXchanges), a code for modeling reactive multiphase flow in fluidized beds. The code uses portable OpenMP and MPI in a unified source code. The resulting parallel code has been ported to Beowulf Linux clusters, SGI shared memory multiprocessors, Compaq SC clusters, and an IBM SP. We present hybrid parallel performance results specifically on the 32-way node of IBM SP. This experience is relevant, as most modern high-performance computing (HPC) systems are clusters of SMP nodes. 1. BACKGROUND Fluidized bed reactors have a long history of application in many industrial processes, e.g., in the chemical, petroleum, pharmaceutical, mineral and fossil fuel processing industries

Numeric Modified Adomian Decomposition Method for Power System Simulations

This paper investigates the applicability of numeric Wazwaz El Sayed modified Adomian Decomposition Method (WES-ADM) for time domain simulation of power systems. WES-ADM is a numerical method based on a modified Adomian decomposition (ADM) technique. WES-ADM is a numerical approximation method for the solution of nonlinear ordinary differential equations. The non-linear terms in the differential equations are approximated using Adomian polynomials. In this paper WES-ADM is applied to time domain simulations of multi-machine power systems. WECC 3-generator, 9-bus system and IEEE 10-generator, 39-bus system have been used to test the applicability of the approach. Several fault scenarios have been tested. It has been found that the proposed approach is faster than the trapezoidal method with comparable accuracy