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Author: Chengyao Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 189
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Book Description
Material flammability and burning behaviors of thin solids in concurrent flows in normal and microgravity are studied using a previously-developed transient numerical model. The model consists of an unsteady gas phase and an unsteady solid phase. The gas phase solves full Navier-Stokes equations including mass, momentum, energy and species equations, using Direct Numerical Simulation. A one-step, second-order overall Arrhenius reaction is adopted. Gas phase radiation is considered by solving the radiation transfer equation with a discrete ordinates SN approximation. In the solid phase, conservation equations of the energy and mass are solved. A cotton-fiberglass-blend fabric is considered as the solid material in this research. Test-based two-step decomposition reactions are implemented for the solid pyrolysis. In this work, the following efforts are made: (1) enhancement to the Adaptive Mesh Refinement (AMR) scheme and (2) development of a two-dimensional version of the program (based on the original three-dimensional program). The first effort allows the program to simulate and resolve multiple flames spreading along the surface of the solid combustible. The second effort dramatically reduces the computational cost when simulating flame spread over wide samples. The model is applied to simulate three scenarios: (1) upward flame spread in normal gravity, (2) purely-forced concurrent flow flame spread over a large and wide sample (41 cm wide 94 cm long), and (3) purely-forced concurrent flow flame spread over a moderate size (5 cm wide, 30 cm long) sample. In the first scenario, upward flame spread in normal gravity, the simulations follow the dimension/configuration of a standard test, NASA-STD-6001 Test #1. This test is the current ground-based screening test for materials that are intended for use in space exploration. The tested sample is 5 cm wide and 30 cm long. In the simulation, ambient pressure is the main parameter. At low pressures, the conventional upward flame spread process is observed. As the pressure increases, a special flame splitting phenomenon is observed. The splitting process is presented in details using the solid and gas profiles. It is concluded that the two-step solid pyrolysis is the cause of this special phenomenon. For the second and third scenarios, simulations are performed to support an on-going NASA project Saffire, which consists of a series of large-scale microgravity burning experiments. Concurrent flow speeds at 20 and 25 cm/s are simulated for both large and moderate sized samples. The results of both Saffire experiments and the simulations are presented and compared in detail. The numerical results are also used to interpret the phenomena observed in the experiments. For the wide sample (scenario 2), a parametric study on the sample width (5-41 cm) is conducted, and additional simulations (using the two-dimensional version of the program) at various flow conditions (different flow speeds, ambient pressures, and oxygen percentages) are performed. Based on the simulation results, analytical analysis is conducted and formulations are proposed for flame spread rate and flame length. The proposed formulation for flame spread rate is evaluated using literature data of microgravity experiments and shows seasonable performance.
Author: Chengyao Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 189
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Book Description
Material flammability and burning behaviors of thin solids in concurrent flows in normal and microgravity are studied using a previously-developed transient numerical model. The model consists of an unsteady gas phase and an unsteady solid phase. The gas phase solves full Navier-Stokes equations including mass, momentum, energy and species equations, using Direct Numerical Simulation. A one-step, second-order overall Arrhenius reaction is adopted. Gas phase radiation is considered by solving the radiation transfer equation with a discrete ordinates SN approximation. In the solid phase, conservation equations of the energy and mass are solved. A cotton-fiberglass-blend fabric is considered as the solid material in this research. Test-based two-step decomposition reactions are implemented for the solid pyrolysis. In this work, the following efforts are made: (1) enhancement to the Adaptive Mesh Refinement (AMR) scheme and (2) development of a two-dimensional version of the program (based on the original three-dimensional program). The first effort allows the program to simulate and resolve multiple flames spreading along the surface of the solid combustible. The second effort dramatically reduces the computational cost when simulating flame spread over wide samples. The model is applied to simulate three scenarios: (1) upward flame spread in normal gravity, (2) purely-forced concurrent flow flame spread over a large and wide sample (41 cm wide 94 cm long), and (3) purely-forced concurrent flow flame spread over a moderate size (5 cm wide, 30 cm long) sample. In the first scenario, upward flame spread in normal gravity, the simulations follow the dimension/configuration of a standard test, NASA-STD-6001 Test #1. This test is the current ground-based screening test for materials that are intended for use in space exploration. The tested sample is 5 cm wide and 30 cm long. In the simulation, ambient pressure is the main parameter. At low pressures, the conventional upward flame spread process is observed. As the pressure increases, a special flame splitting phenomenon is observed. The splitting process is presented in details using the solid and gas profiles. It is concluded that the two-step solid pyrolysis is the cause of this special phenomenon. For the second and third scenarios, simulations are performed to support an on-going NASA project Saffire, which consists of a series of large-scale microgravity burning experiments. Concurrent flow speeds at 20 and 25 cm/s are simulated for both large and moderate sized samples. The results of both Saffire experiments and the simulations are presented and compared in detail. The numerical results are also used to interpret the phenomena observed in the experiments. For the wide sample (scenario 2), a parametric study on the sample width (5-41 cm) is conducted, and additional simulations (using the two-dimensional version of the program) at various flow conditions (different flow speeds, ambient pressures, and oxygen percentages) are performed. Based on the simulation results, analytical analysis is conducted and formulations are proposed for flame spread rate and flame length. The proposed formulation for flame spread rate is evaluated using literature data of microgravity experiments and shows seasonable performance.
Author: Yanjun Li
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 170
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Book Description
Fire behaviors can be significantly different in confined spaces compared with in an open space. Evidence has shown that when subjected to flow confinement, flame can be stronger and spread faster over solid materials. This raises fire safety concern in confined spaces both on earth (e.g., tunnels, building structures) and in space (e.g., space vehicle). To address this concern and to advance understanding of the fire dynamics in confined environments, concurrent-flow flame spread over solid combustibles are investigated in microgravity aboard the International Space Station (ISS). Two types of solid fuel, thin cotton blend fabric (SIABL) and 1 mm thick PMMA slabs are burned in a small flow duct. To effectively reduce the space for flame growth, flow baffles are mounted parallel to the sample. Three different types of baffles are used to alter the radiative boundary conditions of the space that the flame resides: transparent, black, and reflective. By configurating sample/baffles in different ways, three burning scenarios are achieved and examined: double-sided, single-sided, and parallel burning samples. For each burning scenario, confinement levels (i.e., sample-baffle distance) are varied. In addition, the imposed flow speed is also varied to investigate its interplay with the confinement level. Through this, a rich dataset of flame spread is obtained. Different natures of flame spread (i.e., steady state, accelerating flame growth, and flame quenching) are observed when confined conditions vary. Flame characteristics (e.g., spread rate, flame length, flame shape) are also compared between different confined environments. To fully understand the experiment results, an inhouse three-dimensional transient Computational Fluid Dynamics (CFD) combustion model is utilized to conduct the numerical study. The model is first used to simulate the exact geometry of the ISS experiment. The effects of the confinement on solid burning behaviors observed in the experiments are successfully replicated by the numerical model. The model is then used to conduct parametric studies on the confinement levels and radiative reflection from surrounding walls. Through this, detailed profiles of the gas and solid phases are obtained. These include gas temperature, reaction rate contour, and heat fluxes on the sample surface. These profiles are compared between different cases and are used to help explain the burning behaviors observed in the ISS experiments.
Author: Ama R. Carney
Publisher:
ISBN:
Category : Aerospace engineering
Languages : en
Pages : 125
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Book Description
Microgravity experiments are performed to study wind-assisted flame spread over discrete fuel elements. Ultra-thin cellulose-based fuel segments are distributed uniformly in a low-speed flow and flame spread is initiated by igniting the most upstream fuel segment. Similar to continuous fuels, flame spread over discrete fuels is a continual process of ignition. Flame propagation across a gap only occurs when a burning fuel segment, before it burns out, ignites the subsequent segment. During this process, gaps between samples reduce the fuel load, increasing the apparent flame spread rate and decreasing the heat transfer between adjacent segments. The reduction in heat transfer decreases the solid burning rate. In this study, sample segment length, gap size, and imposed flow velocity are varied to study the impacts on burning characteristics, including propensity of flame spread, flame spread rate, and solid burning rate. Detailed profiles of the transient flame spread process are also presented.
Author: Sheng-Yen Hsu
Publisher:
ISBN:
Category : Chemical kinetics
Languages : en
Pages : 250
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Book Description
A detailed three-dimensional model for steady flame spread over thin solids in concurrent flows is used to compare with existing experiments in both buoyant and forced flows. This work includes (1) several improvements in the quantitatively predictive capability of the model, (2) a sensitivity study of flame spread rate on input parameters, (3) introduction of flame radiation into the buoyant-flow computations and (4) quantitative comparisons with two sets of buoyant upward spread experiments using cellulosic samples and a comparison with forced downwind spread tests using wider cellulosic samples. In additional to sample width and thickness, the model computation and experimental comparison cover a substantial range of environmental parameters such as oxygen percentage, pressure, velocity and gravity that are of interest to the applications to space exploration. In the buoyant-flow comparison, the computed upward spread rates quite favorably agree with the experimental data. The computed extinction limits are somewhat wider than the experimental limits based on only one set of older test data (the only one available). Comparison of the flame thermal structure (also with this set of older data) shows that the computed flame is longer and there is structure difference in the flame base zone. This is attributed to the sample cracking phenomenon near the fuel burnout, a mechanism not treated in the model. Comparison in forced concurrent flows shows that the predicted spread rates are lower than the experimental ones if the flames are short but higher than the experimental ones if the flames are long. It is believed that the experimental flames may have not fully reached the steady states at the end of 5-second drop. The effect of gas-phase kinetic rate on concurrent flame spread rates is investigated through the variation of the pre-exponential factor. It is found that flames in forced flow are less sensitive to the change of kinetics than flames in buoyant flow; and narrow samples are more sensitive to the change of kinetics compared with wide samples. The rate of chemical kinetics affects the flame spread rates primarily through two mechanisms: the amount of un-burnt fuel vapors escaping the reaction zone and the induced velocity variation through flame temperature change in the case of the buoyant flames.
Author: Charles E. Baukal, Jr.
Publisher: Cambridge University Press
ISBN: 1108660886
Category : Technology & Engineering
Languages : en
Pages : 193
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Book Description
A Gallery of Combustion and Fire is the first book to provide a graphical perspective of the extremely visual phenomenon of combustion in full color. It is designed primarily to be used in parallel with, and supplement existing combustion textbooks that are usually in black and white, making it a challenge to visualize such a graphic phenomenon. Each image includes a description of how it was generated, which is detailed enough for the expert but simple enough for the novice. Processes range from small scale academic flames up to full scale industrial flames under a wide range of conditions such as low and normal gravity, atmospheric to high pressures, actual and simulated flames, and controlled and uncontrolled flames. Containing over 500 color images, with over 230 contributors from over 75 organizations, this volume is a valuable asset for experts and novices alike.
Author: Howard D. Ross
Publisher: Elsevier
ISBN: 0080549977
Category : Technology & Engineering
Languages : en
Pages : 601
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Book Description
This book provides an introduction to understanding combustion, the burning of a substance that produces heat and often light, in microgravity environments-i.e., environments with very low gravity such as outer space. Readers are presented with a compilation of worldwide findings from fifteen years of research and experimental tests in various low-gravity environments, including drop towers, aircraft, and space.Microgravity Combustion is unique in that no other book reviews low- gravity combustion research in such a comprehensive manner. It provides an excellent introduction for those researching in the fields of combustion, aerospace, and fluid and thermal sciences. * An introduction to the progress made in understanding combustion in a microgravity environment* Experimental, theoretical and computational findings of current combustion research* Tutorial concepts, such as scaling analysis* Worldwide microgravity research findings
Author: Combustion Institute (U.S.). Eastern States Section. Fall Technical Meeting
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 594
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Book Description
Author: United Nations
Publisher:
ISBN: 9789211303940
Category : Political Science
Languages : en
Pages : 0
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Book Description
The Manual of Tests and Criteria contains criteria, test methods and procedures to be used for classification of dangerous goods according to the provisions of Parts 2 and 3 of the United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations, as well as of chemicals presenting physical hazards according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). As a consequence, it supplements also national or international regulations which are derived from the United Nations Recommendations on the Transport of Dangerous Goods or the GHS. At its ninth session (7 December 2018), the Committee adopted a set of amendments to the sixth revised edition of the Manual as amended by Amendment 1. This seventh revised edition takes account of these amendments. In addition, noting that the work to facilitate the use of the Manual in the context of the GHS had been completed, the Committee considered that the reference to the "Recommendations on the Transport of Dangerous Goods" in the title of the Manual was no longer appropriate, and decided that from now on, the Manual should be entitled "Manual of Tests and Criteria".
Author: Eli Pearce
Publisher: Springer Science & Business Media
ISBN: 1468421484
Category : Technology & Engineering
Languages : en
Pages : 463
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Book Description
Flammability has been recognized as an increasingly important social and scientific problem. Fire statistics in the United States (Report of the National Commission on Fire Prevention and Control. "America Burning:' 1973) emphasized the vast devastation to life and property--12.000 lives lost annually due to fire. and these deaths are usually caused by inhaling smoke or toxic gases: 300.000 fire injuries: 11.4 billion dollars in fire cost at which 2.7 billion dollars is related to property loss: a billion dollars to burn injury treatment: and 3.3 billion dollars in productivity loss. It is obvious that much human and economic misery can be attributed to fire situations. In relation to this. polymer flammability has been recognized as an in creasingly important social and scientific problem. The development of flame-retardant polymeric materials is a current example where the initia tive for major scientific and technological developments is motivated by sociological pressure and legislation. This is part of the important trend toward a safer environment and sets a pattern for future example. Flame retardancy deals with our basic everyday life situations-housing. work areas. transportation. clothing and so forth-the "macroenvironment" capsule within which "homosapiens" live. As a result. flame-retardant polymers are now emerging as a specific class of materials leading to new and diversified scientific and technological ventures.
Author: Charles A. Harper
Publisher: McGraw Hill Professional
ISBN: 0071433309
Category : Technology & Engineering
Languages : en
Pages : 562
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Book Description
The first handbook devoted to the coverage of materials in the field of fire engineering. Fire Protection Building Materials Handbook walks you through the challenging maze of choosing form the hundreds of commercially available materials used in buildings today and tells you which burn and /or are weakened during exposure to fire. It is the burning characteristics of materials, which usually allow fires to begin and propagate, and the degradation of materials that cause the most damage. Providing expert guidance every step of the way, Fire Protection Building Materials Handbook helps the architect, designers and fire protection engineers to design and maintain safer buildings while complying with international codes.
