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Energy transfer in reactive and non-reactive H/sub 2/ + OH collisions

Description: We have used the methods of quasi-classical dynamics to compute energy transfer properties of non-reactive and reactive H/sub 2/ + OH collisions. Energy transfer has been investigated as function of translational temperature, reagent rotational energy, and reagent vibrational energy. The energy transfer mechanism is complex with ten types of energy transfer possible, and evidence was found for all types. There is much more exchange between the translational degree of freedom and the H/sub 2/ vibrational degree of freedom than there is between translation and OH vibration. Translational energy is transferred to the rotational degrees of freedom of each molecule. There is a greater propensity for the transfer of translation to OH rotation than H/sub 2/ rotation. In reactive collisions, increases in reagent translational temperature predominantly appear as vibrational energy in the water molecule. Energy transfer in non-reactive and reactive collisions does not depend strongly on the initial angular momentum in either molecule. In non-reactive collisions, vibrational energy is transferred to translation, to the rotational degree of freedom of the same molecule, and to the rotational and vibrational degrees of freedom of the other molecule. In reactive collisions, the major effect of increasing the vibrational energy in reagent molecules is that, on the average, the vibrational energy of the reagents appears as product vibrational energy. 18 refs., 16 figs., 6 tabs.
Date: April 1, 1985
Creator: Rashed, O. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Influence of fuel sulfur on the selective reduction of NO by NH/sub 3/

Description: The selective reduction of NO by NH/sub 3/ addition has been studied in a lean-burning oil fired laboratory combustion tunnel with pyridine and thiophene added to the fuel oil. Two distinct, but interrelated effects were observed. The conversion of a fixed amount of fuel nitrogen to NO in the flame increased as the fuel sulfur concentration increased. In the post-combustion gases, there was a shift in the temperature dependence of the reduction process when the sulfur combustion products were present. The extent of the NO reduction was not significantly altered, but the optimum temperature for reduction shifted to higher values as the sulfur concentration increased.
Date: October 1, 1981
Creator: Lucas, D. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Characterization of the selective reduction of NO by NH/sub 3/

Description: The selective reduction of NO by NH/sub 3/ addition has been studied in a lean-burning oil-fired laboratory combustion tunnel as a function of equivalence ratio, NH/sub 3/ injection temperature, concentration of NH/sub 3/ added, and the source of NO. Ammonia breakthrough was found to depend strongly on the NH/sub 3/ addition temperature. The total concentration of nitrogen containing species other N/sub 2/, NO, and NH/sub 3/ was measured with a variety of techniques and was found to be less than 5 ppM over the range of conditions studied.
Date: April 1, 1981
Creator: Lucas, D. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Influence of fuel sulfur on the selective reduction of NO by NH/sub 3/

Description: More intensive regulations of the emissions of nitrogen oxides from stationary combustion sources have prompted the innovation and characterization of new control technologies suitable for applications in utilities. One of the more recent and attractive abatement technologies is the Thermal DeNO/sub x/ process which has been described by Lyon and Longwell. This process removes NO by selectively reducing it with NH/sub 3/ added to the post-combustion gases containing excess oxygen. This process is thus independent of the NO formation mechanism and makes no distinction between thermal and fuel NO. The present study is concerned with characterizing the selective reduction process for light distillate oil fuel admixed with variable amounts of pyridene and thiophene in a laboratory scale combustion tunnel under a variety of experimental conditions. This paper reports on those aspects of the study concerned with the investigation of possible synergistic effects between the sulfur and selective reduction chemistry.
Date: January 1, 1981
Creator: Lucas, D. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Development of polishing methods for Chemical Vapor Deposited Silicon Carbide mirrors for synchrotron radiation

Description: Material properties of Chemical Vapor Deposited Silicon Carbide (CVD SiC) make it ideal for use in mirrors for synchrotron radiation experiments. We developed methods to grind and polish flat samples of CVD SiC down to measured surface roughness values as low as 1.1 Angstroms rms. We describe the processing details, including observations we made during trial runs with alternative processing recipes. We conclude that pitch polishing using progressively finer diamond abrasive, augmented with specific water based lubricants and additives, produces superior results. Using methods based on these results, a cylindrical and a toroidal mirror, each about 100 x 300mm, were respectively finished by Continental Optical and Frank Cooke, Incorporated. WYCO Interferometry shows these mirrors have surface roughness less than 5.7 Angstroms rms. These mirrors have been installed on the LLNL/UC X-ray Calibration and Standards Facility at the Stanford Synthrotron Radiation Laboratory.
Date: January 1, 1987
Creator: Fuchs, B.A. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Computational study of physical and chemical flame inhibition. [Ar, N/sub 2/, and HBr as inhibitors]

Description: This paper reports a set of modelling studies that were undertaken to acquire a more detailed knowledge of combustion inhibition mechanisms. H/sub 2//O/sub 2//Ar mixtures reacting in the idealized perfectly stirred reactor were investigated. Three H/sub 2//O/sub 2/ kinetic mechanisms were considered, differing from one another by the number of HO/sub 2/ reactions included. Two physical inhibitors, Ar and N/sub 2/, and one chemical inhibitor, HBr, were investigated. Additional parameters considered were pressure, equivalence ratio, inhibitor concentration and rate coefficient variation. HBr was the most effective inhibitor and acted chemically in that it caused substantial reduction in radical concentrations in the mixtures considered. Ar and N/sub 2/ acted as physical diluents with N/sub 2/ the more effective of the two due to its larger heat capacity.
Date: April 1, 1978
Creator: Brown, N.J. & Schefer, R.W.
Partner: UNT Libraries Government Documents Department

Laser startup optics for Baseball II and future mirror machines

Description: The laser startup system for Baseball II-T uses a 300-J CO$sub 2$ laser to hit a 100-$mu$ diameter pellet with a laser power density on the order of 10$sup 13$ W/cm$sup 2$. The laser is a 20-cm diameter unstable resonator transversely excited (TEA) oscillator. The beam is split and then focused using off-axis parabolas. The symmetric configuration and central obscuration of the CO$sub 2$ beam allow coaxial alignment and pellet detection optics. This experiment primarily uses commercially available systems and components. Optical elements were fabricated both by direct machining and standard polishing techniques. The laser and optical systems are directly scalable to reactor requirements using demonstrated technologies. (auth)
Date: October 31, 1975
Creator: Frank, A. M.; Chargin, A. K. & Brown, N. J.
Partner: UNT Libraries Government Documents Department

Environmental research program. 1995 Annual report

Description: The objective of the Environmental Research Program is to enhance the understanding of, and mitigate the effects of pollutants on health, ecological systems, global and regional climate, and air quality. The program is multidisciplinary and includes fundamental research and development in efficient and environmentally benign combustion, pollutant abatement and destruction, and novel methods of detection and analysis of criteria and noncriteria pollutants. This diverse group conducts investigations in combustion, atmospheric and marine processes, flue-gas chemistry, and ecological systems. Combustion chemistry research emphasizes modeling at microscopic and macroscopic scales. At the microscopic scale, functional sensitivity analysis is used to explore the nature of the potential-to-dynamics relationships for reacting systems. Rate coefficients are estimated using quantum dynamics and path integral approaches. At the macroscopic level, combustion processes are modelled using chemical mechanisms at the appropriate level of detail dictated by the requirements of predicting particular aspects of combustion behavior. Parallel computing has facilitated the efforts to use detailed chemistry in models of turbulent reacting flow to predict minor species concentrations.
Date: June 1, 1996
Creator: Brown, N.J.
Partner: UNT Libraries Government Documents Department

Optical components for the Nova laser

Description: In addition to its other characteristics, the Nova Laser Fusion facility may well be the largest precision optical project ever undertaken. Moreover, during the course of construction, concurrent research and development has been successfully conducted, and has resulted in significant advances in various technical areas, including manufacturing efficiency. Although assembly of the first two beams of Nova is just commencing, the optical production, including construction of the special facilities required for many of the components, has been underway for over three years, and many phases of the optical manufacturing program for the first 10 beams will be completed within the next two years. On the other hand, new requirements for second and third harmonic generation have created the need to initiate new research and development. This work has been accomplished through the enormous cooperation DOE/LLNL has received from commercial industry on this project. In many cases, industry, where much of the optical component research and development and virtually all of the manufacturing is being done, has made substantial investment of its own funds in facilities, equipment, and research and development, in addition to those supplied by DOE/LLNL.
Date: May 17, 1982
Creator: Wallerstein, E.P.; Baker, P.C. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

Structure of a poly(ethylene) opposed flow diffusion flame

Description: Structural measurements were obtained and compared with other investigations of diffusion flames. Departures from the commonly assumed collapsed flame model of laminar diffusion flames were observed in terms of excessive CO concentrations and oxygen penetration into the fuel side of the flame. An upper bound on the importance of oxygen diffusion to the fuel surface and subsequent surface oxidation was placed at 20% of the energy required for fuel pyrolysis, with the remainder of the energy being delivered to the surface from the flame through heat transfer processes. As the oxygen concentration in the oxidizer flow was decreased and extinction conditions approached, the CO/CO/sub 2/ ratio at the flame increased slightly, the oxygen concentration at the luminous flame zone decreased, the flame stand-off distance decreased, and the flame temperature decreased. Radial similarity in the composition and temperature profiles was established experimentally which confirms predictions and greatly simplifies the modeling of the opposed flow diffusion flame.
Date: August 1, 1980
Creator: Pitz, W.J.; Brown, N.J. & Sawyer, R.F.
Partner: UNT Libraries Government Documents Department

Transport Properties for Combustion Modeling

Description: This review examines current approximations and approaches that underlie the evaluation of transport properties for combustion modeling applications. Discussed in the review are: the intermolecular potential and its descriptive molecular parameters; various approaches to evaluating collision integrals; supporting data required for the evaluation of transport properties; commonly used computer programs for predicting transport properties; the quality of experimental measurements and their importance for validating or rejecting approximations to property estimation; the interpretation of corresponding states; combination rules that yield pair molecular potential parameters for unlike species from like species parameters; and mixture approximations. The insensitivity of transport properties to intermolecular forces is noted, especially the non-uniqueness of the supporting potential parameters. Viscosity experiments of pure substances and binary mixtures measured post 1970 are used to evaluate a number of approximations; the intermediate temperature range 1 < T* < 10, where T* is kT/{var_epsilon}, is emphasized since this is where rich data sets are available. When suitable potential parameters are used, errors in transport property predictions for pure substances and binary mixtures are less than 5 %, when they are calculated using the approaches of Kee et al.; Mason, Kestin, and Uribe; Paul and Warnatz; or Ern and Giovangigli. Recommendations stemming from the review include (1) revisiting the supporting data required by the various computational approaches, and updating the data sets with accurate potential parameters, dipole moments, and polarizabilities; (2) characterizing the range of parameter space over which the fit to experimental data is good, rather than the current practice of reporting only the parameter set that best fits the data; (3) looking for improved combining rules, since existing rules were found to under-predict the viscosity in most cases; (4) performing more transport property measurements for mixtures that include radical species, an important but neglected area; (5) using the TRANLIB approach ...
Date: February 19, 2010
Creator: Brown, N.J.; Bastein, L. & Price, P.N.
Partner: UNT Libraries Government Documents Department

Framework for assessing key variable dependencies in loose-abrasive grinding and polishing

Description: This memo describes a framework for identifying all key variables that determine the figuring performance of loose-abrasive lapping and polishing machines. This framework is intended as a tool for prioritizing R&D issues, assessing the completeness of process models and experimental data, and for providing a mechanism to identify any assumptions in analytical models or experimental procedures. Future plans for preparing analytical models or performing experiments can refer to this framework in establishing the context of the work.
Date: December 1, 1995
Creator: Taylor, J.S.; Aikens, D.M. & Brown, N.J.
Partner: UNT Libraries Government Documents Department

The reduction of NO[sub x] by HNCO. [RAPRENOx process]

Description: A chemical mechanism for the reduction of NO[sub x] by HNCO has been constructed to model NO[sub x] reduction in exhausts typical of natural gas combustion with the addition of radical boosters (fuel). Variables considered were the initial concentrations of NO, NO[sub 2], CO, O[sub 2], CH[sub 4], H[sub 2], and HNCO as well as initial temperatures. The chemical model was validated by comparing results with earlier model calculations of Miller and Bowman and with the experiments of Caton and Siebers and Lyon and Cole. Agreement with experiments was satisfactory. The reduction chemistry must be preceded by thermal ignition chemistry which generates radicals. The lowest temperature for which ignition occurs is the optimum temperature for reduction and defines the beginning of the temperature window. Reduction was not achieved for the natural gas exhaust'' for a reasonable residence time. Additional H[sub 2] added to the exhaust mixture enhanced reduction, but the addition of CO and CH[sub 4] did not. Under some conditions the computed sensitivity coefficient for nitrogen species and temperature exhibited self-similarity. Four reaction paths were identified which controlled the fate of the NO: the conversion of NO to NO[sub 2] via HO[sub 2], the conversion of NO[sub 2] to NO via reaction with H or O, the reduction of NO via NCO, and the reduction of NO from reactions with NH[sub i] species. The relative importance of the four was determined by the initial conditions.
Date: October 1, 1992
Creator: Brown, N.J. & Garay, J.
Partner: UNT Libraries Government Documents Department

The reduction of NO{sub x} by HNCO

Description: A chemical mechanism for the reduction of NO{sub x} by HNCO has been constructed to model NO{sub x} reduction in exhausts typical of natural gas combustion with the addition of radical boosters (fuel). Variables considered were the initial concentrations of NO, NO{sub 2}, CO, O{sub 2}, CH{sub 4}, H{sub 2}, and HNCO as well as initial temperatures. The chemical model was validated by comparing results with earlier model calculations of Miller and Bowman and with the experiments of Caton and Siebers and Lyon and Cole. Agreement with experiments was satisfactory. The reduction chemistry must be preceded by thermal ignition chemistry which generates radicals. The lowest temperature for which ignition occurs is the optimum temperature for reduction and defines the beginning of the temperature window. Reduction was not achieved for the ``natural gas exhaust`` for a reasonable residence time. Additional H{sub 2} added to the exhaust mixture enhanced reduction, but the addition of CO and CH{sub 4} did not. Under some conditions the computed sensitivity coefficient for nitrogen species and temperature exhibited self-similarity. Four reaction paths were identified which controlled the fate of the NO: the conversion of NO to NO{sub 2} via HO{sub 2}, the conversion of NO{sub 2} to NO via reaction with H or O, the reduction of NO via NCO, and the reduction of NO from reactions with NH{sub i} species. The relative importance of the four was determined by the initial conditions.
Date: October 1, 1992
Creator: Brown, N. J. & Garay, J.
Partner: UNT Libraries Government Documents Department

Scaling and efficiency of PRISM in adaptive simulations of turbulent premixed flames

Description: The dominant computational cost in modeling turbulent combustion phenomena numerically with high fidelity chemical mechanisms is the time required to solve the ordinary differential equations associated with chemical kinetics. One approach to reducing that computational cost is to develop an inexpensive surrogate model that accurately represents evolution of chemical kinetics. One such approach, PRISM, develops a polynomial representation of the chemistry evolution in a local region of chemical composition space. This representation is then stored for later use. As the computation proceeds, the chemistry evolution for other points within the same region are computed by evaluating these polynomials instead of calling an ordinary differential equation solver. If initial data for advancing the chemistry is encountered that is not in any region for which a polynomial is defined, the methodology dynamically samples that region and constructs a new representation for that region. The utility of this approach is determined by the size of the regions over which the representation provides a good approximation to the kinetics and the number of these regions that are necessary to model the subset of composition space that is active during a simulation. In this paper, we assess the PRISM methodology in the context of a turbulent premixed flame in two dimensions. We consider a range of turbulent intensities ranging from weak turbulence that has little effect on the flame to strong turbulence that tears pockets of burning fluid from the main flame. For each case, we explore a range of sizes for the local regions and determine the scaling behavior as a function of region size and turbulent intensity.
Date: December 1, 1999
Creator: Tonse, Shaheen R.; Bell, J.B.; Brown, N.J.; Day, M.S.; Frenklach, M.; Grcar, J.F. et al.
Partner: UNT Libraries Government Documents Department

The effect of penetration factor, deposition, and environmental factors on the indoor concentration of PM2.5 sulfate, nitrate, and carbon

Description: Indoor exposure to particles of outdoor origin constitutes an important exposure pathway. We conducted an intensive set of indoor particle measurements in an unoccupied house under differing operating conditions. Real-time measurements were conducted both indoors and outdoors, including PM2.5 nitrate, sulfate, and carbon. Because the time-scale of the fluctuations in outdoor particle concentrations and meteorological conditions are often similar to the time constant for building air exchange, a steady state concentration may never be reached. The time-series experimental data were used to determine the effect of changes in air exchange rate and indoor/outdoor temperature and relative humidity differences on indoor particle concentrations. A multivariate regression was performed to investigate the difference between measured indoor concentrations and results from a simple time-dependent physical model. Environmental conditions had a significant effect on indoor concentrations of all three PM2.5 species, but did not explain all of the model variation.
Date: April 15, 2002
Creator: Thatcher, T. L.; Lunden, M. M.; Sextro, R. G.; Hering, S. & Brown, N. J.
Partner: UNT Libraries Government Documents Department

Sorption of organic gases in residential bedrooms andbathrooms

Description: Experiments were conducted to characterize organic gas sorption in residential bedrooms (n=4), bathrooms (n=2), and a furnished test chamber. Rooms were studied ''as-is'' with material surfaces and furnishings unaltered. Surface materials were characterized and areas quantified. Experiments included rapid volatilization of a volatile organic compound (VOC) mixture with the room closed and sealed for a 5-h Adsorb phase, followed by 30-min Flush and 2-h closed-room Desorb phases. The mixture included n-alkanes, aromatics, glycol ethers, 2-ethyl-1-hexanol, dichlorobenzene, and organophosphorus compounds. Measured gas-phase concentrations were fit to three variations of a mathematical model that considers sorption occurring at one surface sink and one potential embedded sink. The 2-parameter sink model tracked measurements for most compounds, but improved fits were obtained for some VOCs with a 3-parameter sink-diffusion or a 4-parameter two-sink model. Sorptive partitioning and initial adsorption rates increased with decreasing vapor pressure within each chemical class.
Date: January 5, 2005
Creator: Singer, B.C.; Hodgson, A.T.; Hotchi, T.; Ming, K.Y.; Sextro,R.G.; Wood, E.E. et al.
Partner: UNT Libraries Government Documents Department

Indoor, outdoor and regional profiles of PM2.5 sulfate, nitrateand carbon

Description: Fine particle concentrations were measured simultaneously at three locations: a regional monitoring site in Fresno, California, a backyard of an unoccupied residence in Clovis, California located 6 km northeast of the regional site; and indoors at the same residence. Measurements included 10-min determination of PM{sub 2.5} nitrate, sulfate and carbon using an automated collection and vaporization system, and black carbon measured by light attenuation through a filter deposit. Specific outdoor PM{sub 2.5} constituents were compared to assess the appropriateness of using regional data to model indoor concentrations from outdoor sources. The outdoor data show that, in general, the regional results provide a good representation of the concentrations seen at the building exterior. The indoor concentrations showed considerable attenuation as well as a broadening and time-lag for the concentration peaks. The concentration reduction was the largest for PM{sub 2.5} nitrate, which appears to undergo phase changes in addition to indoor deposition and penetration losses.
Date: January 31, 2002
Creator: Hering, S. V.; Lunden, M. M.; Kirchstetter, T. W.; Thatcher, T. L.; Revzan, K. L.; Sextro, R. G. et al.
Partner: UNT Libraries Government Documents Department

Environmental Research Program. 1994 annual report

Description: The objective of the Environmental Research Program is to enhance the understanding of, and mitigate the effects of pollutants on health, ecological systems, global and regional climate, and air quality. The program is multi-disciplinary and includes fundamental research and development in efficient and environmentally-benign combustion, pollutant abatement and destruction, and novel methods of detection and analysis of criteria and non-criteria pollutants. This diverse group conducts investigations in combustion, atmospheric and marine processes, flue-gas chemistry, and ecological systems.
Date: April 1, 1995
Creator: Brown, N. J.
Partner: UNT Libraries Government Documents Department