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Author: Elmahadi A. Abulbaida
Publisher:
ISBN:
Category :
Languages : en
Pages : 170
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Book Description
ABSTRACT: The purpose of this thesis is to experimentally study the downward flame spread rate and the angle of pyrolysis with different shapes of PMMA at different oxygen concentrations. The effect of sample shape is considered. The effect of oxygen concentration on flame spread rate and the angle of pyrolysis were studied. A modified Critical Oxygen Index Apparatus was used to perform these experiments. The samples of PMMA were burned at different oxygen concentrations. A camera was used to capture the images of the burning and ImageJ software was also used to analyze the images. The result of this work shows that the shape of the sample plays an important role in burning time, where the fuel with a large surface area takes a longer time to burn. It also showed that the velocity increases as the oxygen concentration increases, while the angle of pyrolysis decreases as the oxygen concentration increases for all of the sample shapes tested.
Author: Elmahadi A. Abulbaida
Publisher:
ISBN:
Category :
Languages : en
Pages : 170
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Book Description
ABSTRACT: The purpose of this thesis is to experimentally study the downward flame spread rate and the angle of pyrolysis with different shapes of PMMA at different oxygen concentrations. The effect of sample shape is considered. The effect of oxygen concentration on flame spread rate and the angle of pyrolysis were studied. A modified Critical Oxygen Index Apparatus was used to perform these experiments. The samples of PMMA were burned at different oxygen concentrations. A camera was used to capture the images of the burning and ImageJ software was also used to analyze the images. The result of this work shows that the shape of the sample plays an important role in burning time, where the fuel with a large surface area takes a longer time to burn. It also showed that the velocity increases as the oxygen concentration increases, while the angle of pyrolysis decreases as the oxygen concentration increases for all of the sample shapes tested.
Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 69
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Book Description
The research presented below intends to investigate the role of Poly methyl methacrylate (PMMA) fuel thickness on the spread rate of a downward spreading flame, the thermal radiation being emitted by the flame, and to compare results for both microgravity and normal gravity. To simplify the complex problem of flame spread over solid fuels, the concept of the thermal regime is used to find a constant spread rate for a given fuel thickness. In the thermal regime the opposed flow velocity is high enough to neglect losses due to radiation from the flame but still small enough to not affect the flame through finite rate kinetics. The microgravity results were performed on the International Space Station in the Bass-II Microgravity Science Glove box. This 7.62 cm square duct allows the variation of opposed flow velocity while holding pressure, oxygen and nitrogen constant during each run. The runs are recorded using a digital video camera for spread rate analysis and thermal radiation is read using a radiometer. For normal gravity, SDSU's Flame Stabilizer was used to acquire the downward spread rate from video analysis and thermal radiation is read by a radiometer developed here at SDSU. With the use of a Matlab image analysis code, the videos are analyzed to obtain the spread rate for each fuel thickness. When compared, these results show good experimental agreement for spread rate and thermal radiation. These results, along with known thermodynamic properties and scaling analysis are used to refine the de Ris-Delichatsios formula for the thermal regime. With very few examples of the de Ris-Delichatsios formula being matched to experimental results it is hard to define where the thin regime ends and where the thick regime starts. The refined formula is applied to both the thin and thick regimes to show approximately where the transition lies between the two and compared to experimental results. This transition zone in both microgravity and normal gravity is of great interest for researchers trying to predict the behavior of flame spread both here on earth and in space aboard the International Space Station.
Author: Hai-Tien Loh
Publisher:
ISBN:
Category : Combustion
Languages : en
Pages : 147
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Book Description
An experimental study has been performed of the spread of flames over the surface of thick PMMA and thin filter paper sheets in a forced gaseous flow of varied oxygen concentration moving in the direction of flame spread. It is found that the rate of spread of the PMMA pyrolysis front is time independent, linearly dependent on the gas flow velocity and approximately square power dependent on the oxygen concentration of the gas . The experimental data with thin filter paper sheets shows that the flame spread rate is independent of the flow velocity for forced flow conditions and linearly dependent on the oxygen concentration of the flow. In both experiments, it was found that the flame spread rate data can be correlated in terms of parameter deduced from heat transfer considerations only. This indicates that heat transfer from the flame to the condensed fuel is the primary mechanism controlling the spread of flame. Finite rate chemical kinetic effects have apparently a small influence on the flame spread process itself. Analytical and numerical methods were also employed to study theoretically the name spread process over thermally thick fuel and the influence on the flow field behavior in the presence of a flame. It is found that an analytical model based on a quasi-steady analysis and the flame sheet approximation predicts a square power law dependence of the flame spread rate on the flow oxygen concentration and a linear dependence on the flow velocity. The correct and encouraging qualitative descriptions of the flow structure and surface fluxes in the region downstream from the pyrolysis front.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 968
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Author: Shmuel Link
Publisher:
ISBN:
Category :
Languages : en
Pages : 112
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Book Description
The ignition of and flame spread over solid fuels is of fundamental importance to the field of fire safety. Knowing how, why, and when a material will ignite informs how dangerous a materials use may be. Luckily, there have been no fatal spacecraft based fires beyond the tragedy of the Apollo 1 mission in January 1967. And baring the February 1997 fire aboard the Russian Mir Space Station, there have been very few spacecraft fires in the decades since. This fact can be primarily attributed to the extraordinary caution exercised in design, planning, use of materials, and rigorous fire safety testing. To that end, the effects of environmental variables and material properties on the time to ignition of and opposed flow flame-spread rate over cast cylindrical thermoplastic rods has been investigated. The stated goal of this work being to assess the importance of environmental variables and experimental parameters on the time to ignition or flame spread of a common laboratory thermoplastic, and to gain a better understanding of the lower bounds of material flammability in both 1g and micro-gravity environments. In the case of time to ignition over cast PMMA rods it is found that clear PMMA rods exhibit longer times to ignition than do black PMMA rods for similar experimental conditions. Additionally, mass flux at ignition, as determined during time to ignition experiments, does not exhibit a discernible trend as a function of external radiant heat flux given the available experimental data and corresponds very well to the theoretically predicted range of mass fluxes. As a part of the BASS-II campaign of micro-gravity combustion experiments conducted aboard the ISS, it is seen that increasing oxygen concentration or opposed flow velocity acts to increase the flame-spread rate for all three rod diameters within the range of environmental variable values tested. In conjunction with the BASS-II experiments, ground based experiments were conducted to investigate the effects of oxygen concentration, external radiant heating, and sample diameter on flame spread over cast black and clear PMMA rods under earth standard gravity. Similar to the micro-gravity BASS-II experiments, it was found that flame-spread rate increases with increasing oxygen concentration or eternal radiant heat flux, but increased with decreasing sample diameter. It was also found that with the use of external radiant heating, the effective LOI, or oxygen concentration at which sustained flame-spread was possible, could be reduced. In comparing the BASS-II micro-gravity flame-spread results to those obtained in 1g, it is clear that flame-spread in micro-gravity is faster if one accounts for the fact that the flow velocities tested in both cases are near the lower bound of what are feasible or relevant flow velocities in each case. Similar trends in flame-spread rate with sample diameter, oxygen concentration, and flow velocity (beyond the natural convection break-point in 1g) were observed, but for the tested conditions, flame-spread in micro-gravity is categorically faster than in 1g. Lastly, numerical modeling of flame-spread over cast PMMA rods as a function of ambient oxygen concentration, external radiant heating, and gravitational acceleration was undertaken with NIST's FDS. FDS does effectively model increases in flame-spread rate with increasing externally applied radiant heating (at 21 percent oxygen by volume), as well as an increase in flame-spread rate with an increase in ambient oxygen concentration, both for 1g and micro-gravity conditions. Yet, the magnitude of the flame-spread rates calculated from these simulations is approximately an order of magnitude greater than the experimental results for both 1g or micro-gravity conditions. The exact cause of this difference is hypothesized to be attributable to a combination of the numerical mesh resolution and the solid and gas phase kinetic parameters employed. Additionally, in all cases investigated the numerical simulations correctly predicted the fact that micro-gravity flame-spread was faster than flame-spread under earth standard gravity.
Author: Sarzina Hossain
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 203
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Book Description
The opposed flow flame spread over flat solid fuels is of fundamental importance to the field of fire safety. Several features of opposed flow flame spread are experimentally, numerically and analytically investigated.Thermally thick slab of PolyMethylMethAcrylate (PMMA) was used to study the effects of opposed flow velocity (8-58 cm/s) and fuel thickness (6.6, 12.1 and 24.5 mm). The experiments were conducted with a Narrow Channel Apparatus (NCA) at Michigan State University (MSU). The flame spread rate results show that the maximum flame spread occurs at a lower flow velocity for relatively thicker fuel. The peak flame spread rate for 6.6 mm, 12.1 mm and 24.5 mm occurs at 18.5 cm/s, 12.1 cm/s and 10.3 cm/s, respectively. Several flame spread regimes: thermal, chemical and regressive burning are identified from the results. Flame spread regimes are usually depend on the opposed flow velocity. However, the flame spread rate for newly found regressive burning regime is independent of flow velocities. Visual observation of the flame indicates that the flame intensity augments with flow velocity for all thicknesses of PMMA. The comparison between NCA data and legacy data for similar material (PMMA) and thickness (12.1 mm) demonstrated excellent agreement, subject to the extension of the numerical and theoretical analysis to include relevant features of the flame spread stretch rate theory. The results also demonstrated the effectiveness of the stretch rate theory for markedly different experimental configurations. Although thick slab is used to perform tests, complete burn out of the samples for thickness 6.6 and 12.1 mm are observed at high opposed flow velocities (30 ℗ł 5 cm/s and higher). On contrary, the thickest sample (24.5 mm) did not go through complete burning. This indicates the nature of surface regression and its impact on flame spread rate.Based on the results, it can be emphasized that the factors controlling the flame front advancement involves both flame spread and surface regression. So, the burnt samples at different opposed flow velocities of 24.5 mm thickness from flame spread study is measured for surface regression depth experimentally. A semi-empirical correlation is developed to relate the flame spread and regression and to determine the mass loss rate from the burnt fuel surface. Mass loss rate is also a key aspect of characterizing the flammability of materials. Results show that the power law dependency of mass loss rate changes with opposed flow velocity. A comparison of power law exponents of current results and results from literature are made. Results demonstrate that the power law dependency at flow velocity 8.2, 10.3 and 12 cm/s is -0.5 which show excellent agreement with legacy work.Next, another study is conducted on the post-flame-spread 24.5 mm PMMA sample, burnt at opposed flow velocity 15 cm/s. Visual observation of post-burn sample shows the formation of significant number of internal bubbles. Three samples of similar thickness burnt at similar condition were investigated for bubble count and size. Results indicate higher and smaller bubble presence near the leading edge of the flame compared to the trailing edge side. Comparison of bubble size distribution with several distribution function demonstrates that the bubble size shows good agreement with Log-normal distribution function.Finally, the transient regression rate has been investigated analytically and numerically. The effect of external heat flux simulating flame heat flux is analyzed for PMMA considering it as an ideal-vaporizing solid. Results indicate a strong dependency of heat flux on material regression for a time duration. After a certain time period, the regression rate became insensitive to heat flux change. A scale analysis is performed to compare the analytical-numerical regression rate results with experimental surface regression depth. The predicted regression followed a similar pattern as the experimental surface regression.
Author:
Publisher: ScholarlyEditions
ISBN: 1481689843
Category : Science
Languages : en
Pages : 81
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Book Description
Methylmethacrylates—Advances in Research and Application: 2013 Edition is a ScholarlyPaper™ that delivers timely, authoritative, and intensively focused information about ZZZAdditional Research in a compact format. The editors have built Methylmethacrylates—Advances in Research and Application: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about ZZZAdditional Research in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Methylmethacrylates—Advances in Research and Application: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 62
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Book Description
The purpose of this thesis is to simulate the downward flame spread over thin fuel (Cellulose and Polymethylmethacrylate) in a natural convection environment. Flame spread over thermally thin fuels in quiescent and opposed-flow environment condition is studied. The study of the flame geometry, size of domain, grid points in x and y directions and boundary conditions are considered. For PMMA fuel comparison of the computational and experimental result for quiescent environment is performed. Effect of fuel half thickness, opposed flow velocity, ambient oxygen concentration and ambient pressure level on the flame spread rate was studied. Comparison of flame spread rate of complete combustion model, equilibrium model and experiments with different half thicknesses for PMMA and cellulose was performed. For cellulose fuel velocity fields and pressure field plots are plotted to understand the flow behavior near the leading edge of the flame. Two dimensional Navier-Stokes equations were implemented in a FORTRAN code which was used for numerical simulation and later on the code is modified. A Matlab code is implemented for plotting the pressure field, temperature field, reaction rate contours, fuel mass fraction and other kind of plots.
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:
Publisher:
ISBN:
Category : Fire extinction
Languages : en
Pages : 112
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Book Description
