Computational Modeling of Radiative, Thermal, and Kinetic Regimes of Flame Spread PDF Download
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ISBN:
Category : Electronic books
Languages : en
Pages : 86
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Book Description
The purpose of this thesis presented is to analyze flame spread over thermally thin solid fuels in three regimes of flame spread process; radiative, thermal, and kinetic regimes. The analyses have been performed using a comprehensive two dimensional computational fluid dynamics (CFD) model written in Fortran language developed by Bhattacharjee. Flame spread over thermally thin fuels in quiescent and opposing flow microgravity environments is investigated. An extinction study is performed with different computational domain sizes for a set of fuel thicknesses to understand the effect of domain size on the extinction velocities in the radiative and kinetic regimes. The effect of development length boundary layer is studied in both radiative and kinetic regimes. It is found that flame spread rate, flame size, flame temperature, blow-off and radiative extinction velocities depend on the development length and the boundary layer created by the opposing flow. A correlation between the extinction development length and opposed flow velocity is established. Flame spread over open cell phenolic foam is investigated in detail in a quiescent microgravity environment. The critical fuel thickness is found at different oxygen concentrations and compared to those for PMMA. Pressure, oxygen concentration, and radiation studies are also performed to analyze the flame spread over foam. To understand the effect of radiation on flame spread, the CFD model is coupled with two different radiation models in a microgravity environment. The first radiation model includes gas to surface conduction, gas to environment radiation loss, gas to surface feedback radiation, and surface to environment radiation loss. The second model only excludes gas to surface radiation feedback. The results obtained using these two models are compared with the CFD results; one with radiation completely neglected, and one with only gas to surface radiation feedback neglected. Flame spread in downward configuration is also studied using the radiation models in a quiescent normal gravity environment. The radiation effects, fuel width effect, and kinetic effects are analyzed for different fuel thicknesses.
Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 86
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Book Description
The purpose of this thesis presented is to analyze flame spread over thermally thin solid fuels in three regimes of flame spread process; radiative, thermal, and kinetic regimes. The analyses have been performed using a comprehensive two dimensional computational fluid dynamics (CFD) model written in Fortran language developed by Bhattacharjee. Flame spread over thermally thin fuels in quiescent and opposing flow microgravity environments is investigated. An extinction study is performed with different computational domain sizes for a set of fuel thicknesses to understand the effect of domain size on the extinction velocities in the radiative and kinetic regimes. The effect of development length boundary layer is studied in both radiative and kinetic regimes. It is found that flame spread rate, flame size, flame temperature, blow-off and radiative extinction velocities depend on the development length and the boundary layer created by the opposing flow. A correlation between the extinction development length and opposed flow velocity is established. Flame spread over open cell phenolic foam is investigated in detail in a quiescent microgravity environment. The critical fuel thickness is found at different oxygen concentrations and compared to those for PMMA. Pressure, oxygen concentration, and radiation studies are also performed to analyze the flame spread over foam. To understand the effect of radiation on flame spread, the CFD model is coupled with two different radiation models in a microgravity environment. The first radiation model includes gas to surface conduction, gas to environment radiation loss, gas to surface feedback radiation, and surface to environment radiation loss. The second model only excludes gas to surface radiation feedback. The results obtained using these two models are compared with the CFD results; one with radiation completely neglected, and one with only gas to surface radiation feedback neglected. Flame spread in downward configuration is also studied using the radiation models in a quiescent normal gravity environment. The radiation effects, fuel width effect, and kinetic effects are analyzed for different fuel thicknesses.
Author: Jeffrey S. West
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 842
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Book Description
A detailed numerical model of opposed-flow flame spread over solid fuels is developed. The model is used to study flame spread in three regimes of flame spread; the Thermal, Chemical Kinetic and Near Quiescent Regimes. Simplifying assumptions that have been historically applied to this problem are investigated and their effect on the flame spread rate and flame structure are quantified in each regime. A semi-empirical flame spread formula for thermally thick fuels is developed from knowledge of the dominant simplifying assumptions in this regime. Spread rate predictions compare well to experimental and computed results. This semi-empirical model provides field variables which previous theories are unable to predict. Mechanisms of heat transfer ahead of the flame are studied in each regime. Forward heat transfer though the solid fuel becomes more important in the Chemical Kinetic and Near Quiescent Regimes, a previously unknown result. The rate and path of forward heat transfer is found to depend strongly on simplifying assumptions and the flame anchor location. These results explain the relationship between previous analytical and experimental forward heat transfer results. A dimensionless criterion predicting the fuel thickness at which transition from thermally thick to thermally thin is developed which compares well with experimental and computed results. Finite-rate gas-phase chemical kinetics are found to be the cause of the super-thin regime of flame spread. A formula for the limiting flame spread rate in this regime is developed. Correlation of computed spread rates with the Damkohler number is revisited. Uncertainty in residence time due to uncertainties in characteristic velocity and gas-phase properties is found to be the cause of spread in the correlation. The Damkohler number alone explains variations in many parameters although it alone cannot explain changes in gas-phase activation energy. The boundary between the Near Quiescent and Thermal Regime is quantified using a dimensionless radiation number. A new extinction limit for thick fuels in the Near Quiescent Regime is discovered. Radiative losses cause the flame to grow small and spread so slowly that sufficient oxygen is not available to sustain the flame. Recent experimental results confirm this conclusion.
Author:
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 546
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Book Description
Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 53
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Book Description
The purpose of the thesis is to numerically evaluate the effect varying the solid fuel thermal conductivity has on the flame spread rate in an opposed flow microgravity environment. The computational fluid dynamics model written in Fortran language was developed by Dr. Bhattacharjee. The work encompasses understanding the effect of varying the solid fuel conductivity in all three regimes, i.e. radiative, thermal and kinetic regime. Specific opposed flow velocity was chosen for the three regimes. Additionally, domain and grid studies were executed to adequately capture the flame structure as well as the heat fluxes into the solid fuel prior to investigating the effect of the solid fuel conductivity. Polymethyl Methacrylate hereby denoted PMMA, was the fuel source evaluated. Parameters such as the flame spread rate, vapor temperature, flame temperature, solid fuel temperature and contribution of the forward solid conduction were used to evaluate the effect of varying the solid fuel conductivity. Results collected were compared back to the baseline case established by using the solid phase thermal properties of PMMA for all three regimes. The solid fuel conductivity was incrementally increased by a factor of five, till 15x the baseline conductivity case. Outcome from the studied, highlighted both the thermal and radiative regime didn’t exhibit an influence when varying the solid fuel conductivity. However, at a very low near flame extinction opposed flow velocity in the radiative regime, a noticeable response was observed for varying the solid fuel conductivity. In the kinetic regime varying the solid fuel conductivity resulted in the flame spread rate increase. A length scaling was introduced to formulate non-dimensional representation explaining the result collected. It should be noted, in the kinetic regime at very high opposed flow velocity the data collected near flame extinction deviated from the trend observed at lower kinetic regime opposed flow velocity. This anomaly was repeated for other fuel thicknesses to eliminate potential computational errors.
Author: Jennifer L. Rhatigan
Publisher:
ISBN:
Category : Dynamics
Languages : en
Pages : 158
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Book Description
This is the first attempt to analyze both radiation and detailed kinetics on the burning and extinction of a solid fuel in a stagnation-point diffusion flame. We present a detailed and comparatively accurate computational model of a solid fuel flame along with a quantitative study of the kinetics mechanism, radiation interactions, and the extinction limits of the flame. A detailed kinetics model for the burning of solid trioxane (a trimer of formaldehyde) is coupled with a narrowband radiation model, with carbon dioxide, carbon monoxide, and water vapor as the gas-phase participating media. The solution of the solid trioxane diffusion flame over the flammable regime is presented in some detail, as this is the first solution of a heterogeneous trioxane flame. We identify high-temperature and low-temperature reaction paths for the heterogeneous trioxane flame. We then compare the adiabatic solution to solutions that include surface radiation only and gas-phase and surface radiation using surface model.
Author: Paul R DeCicco
Publisher: Routledge
ISBN: 135185495X
Category : Psychology
Languages : en
Pages : 166
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Book Description
A collection of papers that address such issues as model limits and reliability, emerging expert systems and integrated gas and solid phase combustion simulation models.
Author: Raymond Viskanta
Publisher:
ISBN: 9781567003185
Category : Combustion engineering
Languages : en
Pages : 454
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Book Description
Destined to clarify the research, development, and design requirements in modern and computational terms needed for sustainable technological advances. Written for the combustion scientist/engineer to understand radiative effects on the pollution of the environment. Interrelates the process of thermodynamics, chemical kinetics, fluid mechanics, heat and mass transfer and turbulence. Includes computational design tools. Lays the foundation for modeling and prediction of chemically reacting combustion systems; collects data for operation of combustion devices. Analyzes the construction, use, and numerical results of combustion systems simulation.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 492
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Book Description
Author: Ralph A. Nelson
Publisher:
ISBN:
Category :
Languages : en
Pages : 163
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Book Description
Author: Michael F. Modest
Publisher: Springer
ISBN: 3319272918
Category : Science
Languages : en
Pages : 167
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Book Description
This introduction reviews why combustion and radiation are important, as well as the technical challenges posed by radiation. Emphasis is on interactions among turbulence, chemistry and radiation (turbulence-chemistry-radiation interactions – TCRI) in Reynolds-averaged and large-eddy simulations. Subsequent chapters cover: chemically reacting turbulent flows; radiation properties, Reynolds transport equation (RTE) solution methods, and TCRI; radiation effects in laminar flames; TCRI in turbulent flames; and high-pressure combustion systems. This Brief presents integrated approach that includes radiation at the outset, rather than as an afterthought. It stands as the most recent developments in physical modeling, numerical algorithms, and applications collected in one monograph.
