Browsing by Subject "Flame"
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Item A quantitative analysis of the flame produced by a gas-fueled propellant simulating burner including: soot field characterization, temperature diagnostic techniques, spectral analysis, heat flux, and aluminum particle combustion(Texas Tech University, 2007-05) Jackson, Matthew N.; Pantoya, Michelle; Berg, Jordan M.; Seshaiyer, Padmanabhan; Parameswaran, Siva; Levitas, ValeryThis study details the characterization and implementation of a burner devised to simulate solid propellant fires. The burner is designed with the ability to introduce particles (particularly aluminum) to a gas reactant flame. This work encompasses four different studies that both evaluate the performance of the burner as well as display its ability as a versatile test platform. First, the burner is used to create a high temperature, heavily sooting flame as the basis of the development of a virtual thermocouple model in a fire code at Sandia National Laboratories (VULCAN). Secondly, similar conditions are created to evaluate the effectiveness of dual-pump coherent anti-Stokes Raman scattering (CARS) measurements in heavily sooting flames. These thermometry measurements indicate the temperature profiles that exist in fuel rich conditions. Laser induced incandescence (LII) measurements map soot volume fractions and give insight into the reactant gas mixing in the flame structure. The third project evaluates the aluminized flame conditions produced by this burner based on temperature, heat flux, spectral emission, product species, and particle velocity. Using these results, flame performance is quantified in comparison to other known flames including hydrocarbon and propellant fires. Lastly, an aluminized flame is used to measure the burning rate of the particles. This work indicates the capability of the burner as test platform for Sandia’s ongoing effort to develop a comprehensive particulate combustion model, particularly in propellant fires. These studies accomplish two primary objectives: (1) characterization of a flame produced by a new and unique burner; and, (2) verification that the burner fulfills its design purpose of recreating small scale propellant flame conditions.Item A study of the spectra of hydrocarbon flames supported with oxygen-nitrous oxide(Texas Tech University, 1957-08) Garrett, Bob LeeNot availableItem Burn rates in nano-composite energetic materials(Texas Tech University, 2003-05) Bockman, Bryan SBurn rates were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum tri-oxide (M0O3) oxidizer under wellconfined conditions. Confined pressures were also measured to provide detailed information about the reaction. Samples of three different fuel particle sizes (44, 80, and 121 nm) were analyzed to determine the influence of particle size on bum rate. Bulk powder density was varied from approximately 5 to 10 percent of the theoretical maximum density (TMD). The bum rates ranged from approximately 600 to 1000 m/s. Results indicate that bum rate increased with decreasing particle size. Pressure measurements indicate the strong convective and possibly acoustic shock mechanisms are integral in flame propagation.Item Characterization of strongly forced non-premixed methane jet flames(2006) Lakshminarasimhan, Krishna; Ezekoye, Ofodike A.; Clemens, Noel T.Item A computational fluid dynamics simulation model for flare analysis and control(2006) Castiñeira Areas, David; Edgar, Thomas F.Industrial flares are units designed to safely dispose of waste hydrocarbon gases from chemical and petrochemical plants by burning gases to carbon dioxide and steam, which are then released to the atmosphere. There is still great uncertainty about flare efficiency and the resultant gas emissions under different operating conditions. For this reason, environmental agencies have encouraged the development of predictive models for flare gas combustion systems, so effective control and mitigation strategies can be implemented. The principal focus of this dissertation is to develop mathematical models of industrial flares that predict the efficiency of these industrial combustion systems. For this purpose, a computational fluid dynamics (CFD) simulation model is implemented to analyze the effects of variables such as ambient wind velocity, gas heating value, and steam injection on flare combustion efficiency. Some advanced chemistry and turbulence submodels are also implemented to describe the complex flare flow phenomena. Simulation results show that flares may represent an important source of gas emissions due to inefficient operation at high crosswinds and large steam/fuel ratios. The predictive models presented in this work will allow for better estimation of the resulting gas emissions from industrial plants. Use of these simulation models will also yield economic savings for environmental studies compared to setting up expensive flare experiments. In addition, these predictive models allow for a detailed analysis of species concentration profiles and turbulent flow patterns within the flames, data which is not available experimentally. Furthermore, several instrumentation and control strategies for industrial flares are analyzed in this dissertation. A new approach for flare monitoring based on multivariate image analysis is proposed so that flare combustion efficiency can be measured in real-time.Item Computations of strongly forced laminar cold-flow jet and methane-air diffusion flames(2006) Barve, Vinayak Vidyadhar; Ezekoye, Ofodike A.Previous work has shown that for sufficiently high periodic forcing amplitudes, laminar diffusion flames can burn in an effectively partially premixed mode. Experimental observations show that the luminosity and sooting properties of the forced flames are significantly modified by the presence of strong forcing. In this work, simulations are performed to study the effects of strong forcing on flow field development in strongly forced laminar isothermal jets and methane air diffusion flames. Unforced and strongly forced cold-flow jets are simulated using a higher order finite volume CFD code. The jet was forced by varying the jet exit velocity over a range of forcing amplitudes and frequencies and it was found that the jet Strouhal number (St) was the important parameter in characterizing flowfield development. Further, the forced jets showed increased entrainment and increased entrainment rates as compared to the non-forced jets. The computations are extended to laminar methane–air diffusion flames. The combustion reactions were modeled using detailed gas-phase chemistry and complex thermo-physical properties. The radiation heat transfer was modeled using the S-6 Discrete Ordinates Method. A 2 equation soot chemistry model for soot nucleation, surface growth and oxidation was used. First an unforced flickering methane–air diffusion flame was modeled and then the flame was forced by varying the amplitude and frequency of the fuel velocity in the nozzle. Cases where the peak velocity in the fuel stream reached 6 times the mean velocity are examined. The internal nozzle flow was also simulated since the near-nozzle region was of particular interest due to the strong mixing processes occurring there and the subsequent effect on the flame properties. Lifted forced flames were also examined, and it was found that the partial premixing in the near nozzle region and modified gas phase chemistry in the forced flames can explain the reduction in soot production for the strongly forced flames.Item Development, performance measurement, and modelling of a packed-bed, fire-tube heater(Texas Tech University, 1984-12) Fang, Hang-yenFire-tubes are good candidates for indirect heating of pyrolysis and gasification reactors because of their simplicity and low cost. Typical fire-tube designs use empty tubes filled with hot combustion gases. The open-tube design suffers from a low overall thermal efficiency, typically on the order of 30 to 70 percent. In this study, a new type of fire-tube was designed and evaluated. In the new design a multi-tube burner vas used to obtain a more symmetrical flame. A packed bed was used in the fire-tube to obtain a higher overall thermal efficiency. The packed bed not only confined the flame to the combustion zone, but also increased the radial thermal conductivity between the hot combustion gases and the fire-tube wall. The thermal performance of the new fire-tube design was determined by measuring temperature profiles along the tube wall, radiant heat flux profiles from the tube, and overall heat balances. The overall thermal efficiency was found to vary between 7 5 and 95 percent, depending on the gas flow rate, packing position, fuel-air ratio, and temperature of the surroundings. A fire-tube with the same burner design, but without packing, exhibited thermal efficiencies ranging between 40 and 75 percent. A mathematical model was developed to predict the fire-tube performance at pyrolysis and gasification reactor conditions. The model was tested by comparing computed and experimental temperature profiles for different operating conditions at much lower external temperatures than will be experienced in an actual application. The overall thermal efficiencies computed from the temperature profiles agreed with the experimental thermal efficiencies to within 3 percent.Item The effects of buoyancy on turbulent nonpremixed jet flames in crossflow(2005) Boxx, Isaac G.; Clemens, Noel T.Item Investigation of buoyancy effects on turbulant nonpremixed jet flames by using normal and low-gravity conditions(2003-12) Idicheria, Cherian Alex, 1977-; Clemens, Noel T.Item Two-point high repetition rate measurement of temperature and thermal dissipation in a turbulent non-premixed jet flame(2004) Wang, Guanghua; Clemens, Noel T.; Varghese, Philip L.A high-repetition rate (10 kHz) laser Rayleigh scattering facility was developed and used to study the temperature fluctuations, power spectra, gradients and thermal dissipation rate characteristics of a nonpremixed turbulent jet flame at a Reynolds number of 15,200. The flame studied here is similar to the Turbulent Nonpremixed Flame Workshop simple jet flame (DLR_A flame). The radial temperature gradient was measured by a two-point technique, whereas the axial gradient was inferred from temperature time-series measurements combined with Taylor’s hypothesis. Resolution and noise can greatly affect such measurements, and thus a model is proposed to account for the effects of resolution, noise, filtering and data processing on the measured dissipation. The model clearly shows the interplay between resolution and noise, and that noise will create an apparent dissipation (or bias), which will be more significant at high spatial resolution. Techniques to correct the measured mean dissipation for this bias are discussed for the two-point time-series thermal dissipation measurements reported here. A general technique to estimate the noise level for scalar dissipation measurements is also proposed. The resulting two-point time-resolved measurements in a turbulent flame show that the temperature power spectra along the jet centerline exhibit only a small inertial subrange due to the low local Reynolds number of the flow (Reδ ∼ 2,500), although a larger inertial subrange is present in the spectra at off- centerline locations. Furthermore, the power spectra collapse in the dissipation range when the frequencies are normalized by the Batchelor frequency. Probability density functions of the thermal dissipation are shown to deviate from lognormal in the low-dissipation portion of the distribution when only one component of the gradient is used; however, nearly lognormal distributions are obtained along the centerline when both axial and radial components are included. A procedure is developed for correcting the thermal dissipation for the apparent dissipation introduced by noise. This procedure uses redundant measurements, either temporally or spatially, to quantify the noise contribution on the mean dissipation. This analysis shows that noise has a dominating effect on the dissipation as the apparent dissipation can be as large as five times the actual dissipation on centerline. The corrected dissipation measurements show that the radial profile of the mean thermal dissipation exhibits a peak off centerline at all downstream locations. These results indicate that the underlying turbulence, as inferred from the temperature fluctuations, is in large part similar to that of nonreacting jet flows, provided the Reynolds number is properly modified to account for heat release.