ACERC
Abstracts - 1992 |
ACERC
Abstracts - 1992 |
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Thrust Area 5: Comprehensive Model Development |
Hobbs, M.L.; Radulovic,
P.T. and Smoot, L.D.
AIChE Journal, 38(5):681-702, 1992. Funded by US Department of Energy,
Morgantown Energy Technology Center and ACERC.
A one-dimensional model of countercurrent fixed-bed coal gasification has been developed, and results have been compared to experimental data from commercial-scale gasifiers. The steady-state model considers separate gas and solid temperatures, axially variable solid and gas flow rates, variable bed void fraction, coal drying, devolatilization based on chemical functional group composition, oxidation and gasification of char, and partial equilibrium in the gas phase. Generalized treatment of gas-phase chemistry and accounting for variable bed void fraction were necessary to predict realistic axial temperature and pressure profiles in an atmospheric fixed-bed gasifier. Model evaluation includes sensitivity of axial temperature profiles to model options, model parameters and operational parameters. Model predictions agree reasonably well with experimental temperature and pressure profile data for gasification of eight coal types ranging from lignite to bituminous. The relative importance of char oxidation resistances to bulk film diffusion, ash diffusion, and chemical reaction is identified.
Sikorski, K.; Tsay, C.W.
and Wozniakowski, H.
Journal of Complexity, 1992 (in press). Funded by University of Utah
and ACERC.
We consider the problem of approximating fixed points of contractive functions with using the absolute error criterion. It was proven in [17] that it is impossible to essentially improve the efficiency of the simple iteration whenever the dimension of the domain of contractive functions is large. However, for a moderate dimension we exhibit a fixed-point ellipsoid algorithm which is much more efficient than the simple iteration for mildly contractive functions. This algorithm is based on Khachiyan's construction of minimal ellipsoids used for solving linear programming.
Boardman, R.D.; Brewster,
B.S.; Huque, Z.; Smoot, L.D. and Silcox, G.D.
Air Toxic Reduction and Combustion Modeling, 15:1-9, 1992. (Also presented
at the ASME International Joint Power Generation Conference, Atlanta,
GA, October 1992). Funded by Advanced Fuel Research and ACERC.
A computer model has been developed for predicting mixing and reactions of injected sorbent particles in pulverized coal combustors and gasifiers. A shrinking-core, grain model was used for sulfation. The model accounts for the effects of surface area, pore diffusion, diffusion through the product layer, chemical reaction, and reduction of the pore volume due to grain swelling. The submodel was evaluated for a fuel-lean case and for a fuel-rich case. Predictions were compared with limited experimental data (for the fuel-rich case). The results illustrate the model's capability for predicting the effectiveness of sulfur capture. The importance of sorbent particle properties was also investigated parametrically, and model limitations were identified.
Hobbs, M.L.; Radulovic,
P.T. and Smoot, L.D.
Fuel, 71(10):1177-1194, 1992. Funded by US Department of Energy, Morgantown
Energy Technology Center and ACERC.
Ma, K.-L. and Painter, J.S.
The International Journal of Computers and Graphics, 1992 (in press).
Funded by International Business Machines and ACERC.
This paper discusses the use of general-purpose graphics workstations for interactive high-resolution volume visualization. We survey previous research results in parallel volume rendering as well as commercial products that take advantage of parallel processing to make volume rendering a practical visualization method. Our focus is on developing distributed computation methods that can distribute the memory and computational demands of volume visualization across a network of general-purpose workstations. We describe three distributed computation strategies based on ray-casting volume rendering which can be implemented on either shared-memory multiprocessor workstations or on a network of ordinary workstations. Multiple views of real-time feature extraction give tremendous insight to the volume data. Multiple variable visualization helps scientists to capture the interaction between important variables in a simulation. Divide-and-conquer rendering allows interactive high-resolution volume visualization of large data sets on a network of midrange workstations, even when the data set is too large for available memory on any single workstation. Several examples in medical imaging and computational fluid dynamics are shown illustrating the practicality of these methods.
Fife, P.
Theoretical and Computational Fluid Dynamics, 4:51-70. Funded by National
Science Foundation and ACERC.
Fully developed turbulent flow through straight ducts is considered. An analysis in a Reynolds stress principal-axis coordinate frame is performed with the aim of clarifying the main mechanisms responsible for turbulence-driven secondary (transverse) mean flow in noncircular ducts. Together with this, some basic properties of that flow are deduced.
Ma, K.-L. and Smith, P.J.
Visualization Conference, Boston, MA, October 1992. Funded by International
Business Machines and ACERC.
The paper introduces a new technique for computer visualization of simultaneous three-dimensional vector and scalar fields such as velocity and temperature in reaction fluid flow fields. The technique, which we call Virtual Smoke, simulates the use of colored smoke for experimental gaseous fluid flow visualization. However, it is noninvasive and can animate, in particular, the dynamic behaviors of steady state or instantaneous flow fields obtained from numerical simulations. Virtual Smoke is based on Volume Seeds and Volume Seedlings, which are direct volume visualization methods previously developed for highly interactive scalar volume data exploration. We use data from combustion simulations to demonstrate the effectiveness of Virtual Smoke.
Brewster, B.S.
Ninth Annual Pittsburgh Coal Conference, Pittsburgh, PA, October 1992.
Funded by Advanced Fuel Research.
A 2-D combustion model with advanced submodels for coal reactions and pollutants was used to simulate a cyclone combustor. Predicted gas velocity, coal particle trajectories, burnout, and sulfur capture by injected sorbent are presented. Particle trajectories are predicted to be very sensitive to particle size. The predictions give insight into the effects of reactor L/D ratio, coal; and sorbent particle size distribution, and optimal slag tap location. Needed model improvements include accounting for particle rebounding, sorbent calcinations and sintering, and sorbent particle dynamics. A 3-D model is needed to investigate the effects of particle injection geometry.
Hill, S.C.; Cannon, J.N.
and Smoot, L.D.
International Chemical Recovery Conference, Seattle, WA, June 1992. (Also
presented at The Effects of Coal Quality on Power Plants, San Diego,
CA, August 1992, and the Ninth Annual Pittsburgh Coal Conference, Pittsburgh,
PA, August 1992). Funded by ACERC.
A new generalized 3-dimensional combustion model has been developed to simulate large-scale, steady state, particle laden reacting and non-reacting systems. The model, which is based on an earlier 2-dimensional model has been applied to turbulent, pulverized-coal combustion systems. It uses an Eulerian framework for the gas phase and a Lagrangian framework for the particles. The code assumes equilibrium gas-phase chemistry, and couples the turbulent flow field with the chemical reactions by integrating the equations over a probability density function. The model uses advanced numerics and a differencing scheme capable of solving the large computational meshes required to simulate practical furnaces. The model has been evaluated by comparison of predictions with new experimental data from a large-scale, 80 MWe coal-fired utility boiler. The data include furnace profile measurements obtained with intrusive and laser-based optical probes. These comparisons show qualitative agreement of model predictions with observed trends, and indicate that the model can be used to provide insights into boiler operation. The comparisons also indicate the further evaluation, concepts for improvement of some sub models are required, and provide direction for future model development.
Solomon, P.R.; Hamblen,
D.G.; Serio, M.A.; Smoot, L.D. and Brewster, B.S.
21st, 22nd, and 23rd Quarterly Reports for the US Department of Energy,
1992. Funded by US Department of Energy and Morgantown Energy Technology Center.
The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal, a feedstock whose variable and often unexpected behavior presents a significant challenge. This program is merging significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation is being implemented and the technology was expanded to fixed-bed reactors. The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model has been integrated with BYU's comprehensive two-dimensional reactor mode, PCGC-2, which is a widely used reactor simulation for combustion or gasification. The program includes: 1) validation of the submodels by comparison with laboratory data obtained in this program, 2) extensive validation of the modified comprehensive code by comparison of predicted results with data from bench-scale and process scale investigations of gasification, mild gasification and combustion of coal or coal-derived products in heat engines, and 3) development of well documented user friendly software applicable to a "workstation" environment.
Cohen, M.F.; Painter, J.S.;
Mehta, A.K. and Ma, K.-L.
ACM Symposium on Interactive 3-D Graphics, Cambridge, MA, March 1992.
Funded by International Business Machines and ACERC.
Recent advances in software and hardware technology have made direct ray-traced volume rendering of 3-d scalar data a feasible and effective method for imaging of the data's contents. The time costs of these rendering techniques still no not permit full interaction with the data, and all of the parameters affecting the resulting images. This paper presents a set of real-time interaction techniques that have been developed to permit exploration of a volume data set. Within the limitation of a static viewpoint, the user is able to interactively alter the position and shape of an area of interest, and modify local viewing parameters. A run length encoded cache of volume rendering samples provides the means to rerender the volume at interactive rates. The use locates and plants "seeds" in areas of interest through the use of data slicing and isosurface techniques. Image processing techniques applied to volumes (i.e. volume processing), can then automatically form regions of interest that in turn modify the rendering parameters. This "region growing" of "seedlings" incrementally alters the image in real-time providing further visual cues concerning the contents of the data. These tools allow interactive exploration of internal structures in the data that may be obscured by other imaging algorithms. Magnetic Resonance Angiography (MRA) provides a driving application for this technology. Results from preliminary studies of MRA data are included.
Michelsen, P.S.
Optimization of
the Numerically Intensive ACERC Combustion Code for Execution of the New Super-Workstations,
M.S./BYU, April 1992. Advisor: Nelson
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