Numerical Modeling Of Flame Spread Over Spherical Solid Fuel Under Low Speed Flow In Microgravity

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Numerical Modeling of Flame Spread Over Spherical Solid Fuel Under Low Speed Flow in Microgravity

Author : Makoto Endo
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (958 download)

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Book Synopsis Numerical Modeling of Flame Spread Over Spherical Solid Fuel Under Low Speed Flow in Microgravity by : Makoto Endo

Download or read book Numerical Modeling of Flame Spread Over Spherical Solid Fuel Under Low Speed Flow in Microgravity written by Makoto Endo and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flame spread over solid fuel presents distinctive characteristics in reduced gravity, especially when the forced flow velocity is low. The lack of buoyancy allows a blue, dim flame to sustain where the induced velocity would otherwise blow it off. At such low velocities, a quenching limit exists where the soot content is low and the effect of radiative heat loss becomes important. The objective of this study is to establish a high fidelity numerical model to simulate the growth and extinction of flame on solid fuels in a reduced gravity environment. The great importance of the spectral dependency of the gas phase absorption and emission were discovered through the model development and therefore, Statistical Narrow-Band Correlated-k (SNB-CK) spectral model was implemented. The model is applied to an experimental configuration from the recent space experiment, Burning And Suppression of Solids (BASS) project conducted aboard the International Space Station. A poly(methyl methacrylate) (PMMA) sphere (initial diameter of 2cm) was placed in a small wind tunnel (7.6cm x 7.6cm x 17cm) within the Microgravity Science Glovebox where flow speed and oxygen concentration were varied. Data analysis of the BASS experiment is also an important aspect of this research, especially because this is the first space experiment that used thermally thick spherical samples. In addition to the parameters influencing the flammability of thin solids, the degree of interior heat-up becomes an important parameter for thick solids. For spherical samples, not only is the degree of internal heating constantly changing, but also the existence of stagnation point, shoulder, and wake regions resulting in a different local flow pattern, hence a different flame-solid interaction. Parametric studies using the numerical model were performed against (1) chemical reaction parameters, (2) forced flow velocity, (3) oxygen concentration and (4) amount of preheating (bulk temperature of the solid fuel). Flame Spread Rate (FSR) was used to evaluate the transient effect and maximum flame temperature, standoff distance and radiative loss ratio were used to evaluate the spontaneous response of the gas phase to understand the overall response of the burning solid fuel. After evaluating the individual effect of each parameter, the efficacy of each parameter was compared. Selected results of this research are:[1]Experimental data from BASS and numerical simulation both showed that within the time periodbetween ignition until the flame tip reaches the shoulder of the sample, the flame length and timehave almost a linear relation.[2]Decreasing forced flow velocity increases the radiative loss ratio whereas decreasing oxygen molefraction decreases the radiative loss ratio. This finding must be considered in the effort to replicatethe behavior of flame spread over thick solid fuels in microgravity on earth.[3]Although the standoff distance will increase when the forced flow velocity is decreased as well aswhen the oxygen mole fraction is decreased, the forced flow velocity has a much stronger effect onthe standoff distance than the oxygen mole fraction.[4]Unlike the previous two comparisons, the effect of forced flow velocity and oxygen mole fraction onthe maximum flame temperature was at similar level, reduction of either parameter would result inlowering the maximum flame temperature.[5]The effect of preheating on the flame spread rate becomes stronger when either the oxygen flowrate or forced flow velocity becomes larger. Depending on which element is more important, we candistinguish oxygen flow rate driven flame spread from preheating driven flame spread. Findings of this research are being utilized in the design of the upcoming space experiment, Growth and Extinction Limits of solid fuel (GEL) project. This research is supported by the National Aeronautics and Space Administration (NASA). This work made use of the High Performance Computing Resource in the Core Facility for Advanced Research Computing at Case Western Reserve University and the Ohio Supercomputer Center.

A Numerical Study of Flame Spread Over Thin Cellulosic Fuels in Microgravity

Author : Yang Long
Publisher :
ISBN 13 :
Total Pages : 348 pages
Book Rating : 4.3/5 (129 download)

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Book Synopsis A Numerical Study of Flame Spread Over Thin Cellulosic Fuels in Microgravity by : Yang Long

Download or read book A Numerical Study of Flame Spread Over Thin Cellulosic Fuels in Microgravity written by Yang Long and published by . This book was released on 2007 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt:

A Gallery of Combustion and Fire

Author : Charles E. Baukal, Jr.
Publisher : Cambridge University Press
ISBN 13 : 1107154979
Total Pages : 193 pages
Book Rating : 4.1/5 (71 download)

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Book Synopsis A Gallery of Combustion and Fire by : Charles E. Baukal, Jr.

Download or read book A Gallery of Combustion and Fire written by Charles E. Baukal, Jr. and published by Cambridge University Press. This book was released on 2020-09-03 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book to present a full-color visual panorama of combustion images along with explanatory and tutorial overviews.

A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel

Author : National Aeronautics and Space Administration (NASA)
Publisher : Createspace Independent Publishing Platform
ISBN 13 : 9781722903831
Total Pages : 158 pages
Book Rating : 4.9/5 (38 download)

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Book Synopsis A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel by : National Aeronautics and Space Administration (NASA)

Download or read book A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: A numerical model is developed to examine laminar flame spread and extinction over a thin solid fuel in lowspeed concurrent flows. The model provides a more precise fluid-mechanical description of the flame by incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point. Parabolic equations are used to treat the downstream flame, which has a higher flow Reynolds number. The parabolic and elliptic regions are coupled smoothly by an appropriate matching of boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Steady spread with constant flame and pyrolysis lengths is found possible for thin fuels and this facilitates the adoption of a moving coordinate system attached to the flame with the flame spread rate being an eigen value. Calculations are performed in purely forced flow in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Both quenching and blowoff extinction are observed. The results show that as flow velocity or oxygen percentage is reduced, the flame spread rate, the pyrolysis length, and the flame length all decrease, as expected. The flame standoff distance from the solid and the reaction zone thickness, however, first increase with decreasing flow velocity, but eventually decrease very near the quenching extinction limit. The short, diffuse flames observed at low flow velocities and oxygen levels are consistent with available experimental data. The maximum flame temperature decreases slowly at first as flow velocity is reduced, then falls more steeply close to the quenching extinction limit. Low velocity quenching occurs as a result of heat loss. At low velocities, surface radiative loss becomes a significant fraction of the total combustion heat release. In addition, the shorter flame length causes an increase in the fraction of conduction downstream compared to conduction to the fuel. The...

Flame Spread in Confined Spaces

Author : Yanjun Li
Publisher :
ISBN 13 :
Total Pages : 170 pages
Book Rating : 4.:/5 (13 download)

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Book Synopsis Flame Spread in Confined Spaces by : Yanjun Li

Download or read book Flame Spread in Confined Spaces written by Yanjun Li and published by . This book was released on 2021 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

A Gallery of Combustion and Fire

Author : Charles E. Baukal, Jr.
Publisher : Cambridge University Press
ISBN 13 : 1108660886
Total Pages : 193 pages
Book Rating : 4.1/5 (86 download)

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Book Synopsis A Gallery of Combustion and Fire by : Charles E. Baukal, Jr.

Download or read book A Gallery of Combustion and Fire written by Charles E. Baukal, Jr. and published by Cambridge University Press. This book was released on 2020-09-03 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Opposed-Flow Flame Spread Over Solid Fuels in Different Burning Regimes

Author : Luca Carmignani
Publisher :
ISBN 13 :
Total Pages : 130 pages
Book Rating : 4.:/5 (113 download)

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Book Synopsis Opposed-Flow Flame Spread Over Solid Fuels in Different Burning Regimes by : Luca Carmignani

Download or read book Opposed-Flow Flame Spread Over Solid Fuels in Different Burning Regimes written by Luca Carmignani and published by . This book was released on 2019 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several aspects of opposed-flow flame spread are experimentally investigated because of their relevance in fire safety studies. Different burning regimes based on the intensity of the opposed flow velocity are identified for acrylic fuels. In downward flame spread, where the flow around a flame is only naturally induced by gravity, the spread rate is highly dependent on fuel size and geometry. The fuel cross-sectional shape is experimentally varied, and a formula which takes into account geometrical effects is proposed by extending previous solutions for two-dimensional flames. The burning region of a solid fuel shows a consistent slope due to the competition between flame spread and surface regression. The angle at the vertex of the pyrolysis region, called burn angle, can be used to indirectly calculate the fuel burning rate. The burn angle depends on fuel thickness; a numerical model and a scale analysis are used to explore the reasons for this behavior. Next, the effect of a forced flow is investigated. The extreme case of blow-off extinction over thin fuels is considered, with flames extinguishing at locations determined by the flow velocity. Results suggest that the interaction between fuel and flow field is more important than the dependence on fuel thickness. The evolution of flame structure and pyrolysis also appear to be driven by flow interactions. A scale analysis is used to explore these dependencies. Finally, previous microgravity experiments are used to explore differences and similarities with ground-based results. By suppressing the buoyant flow, flame radiation becomes essential for the flame spread process. The experimental conditions are simulated numerically to describe the importance of a developing boundary layer in this regime. A numerical parametric study of the radiative emission of flames in microgravity, inspired by the experimental data, shows its dependence on flame area, mass burning rate and flame temperature by changing the burning conditions. For these small flames, soot does not seem to dominate flame radiation, although its generation increases with fuel thickness, oxygen concentration and flow velocity. The experiments in microgravity considered in this work showed flame extinction in a quiescent environment. However, two acrylic cylinders at higher oxygen concentrations from a previous investigation can burn vigorously. To clarify whether these flames are stable, a scale analysis is used to study the influence of surface curvature on radiation losses.

Piloted Ignition and Flame Spread Over Clear and Black PMMA Cylinders in Opposed Flows

Author : Shmuel Link
Publisher :
ISBN 13 :
Total Pages : 112 pages
Book Rating : 4.:/5 (957 download)

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Book Synopsis Piloted Ignition and Flame Spread Over Clear and Black PMMA Cylinders in Opposed Flows by : Shmuel Link

Download or read book Piloted Ignition and Flame Spread Over Clear and Black PMMA Cylinders in Opposed Flows written by Shmuel Link and published by . This book was released on 2015 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Flame Spread Over Thermally Thick Solid Fuels Against a Low Velocity Oxidizer Flow in a Microgravity Environment

Author : Jacob Lawrence Deering
Publisher :
ISBN 13 :
Total Pages : 100 pages
Book Rating : 4.:/5 (429 download)

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Book Synopsis Flame Spread Over Thermally Thick Solid Fuels Against a Low Velocity Oxidizer Flow in a Microgravity Environment by : Jacob Lawrence Deering

Download or read book Flame Spread Over Thermally Thick Solid Fuels Against a Low Velocity Oxidizer Flow in a Microgravity Environment written by Jacob Lawrence Deering and published by . This book was released on 1998 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Microgravity Science & Applications

Author :
Publisher :
ISBN 13 :
Total Pages : 390 pages
Book Rating : 4.:/5 (317 download)

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Book Synopsis Microgravity Science & Applications by :

Download or read book Microgravity Science & Applications written by and published by . This book was released on 1993 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

NASA Technical Memorandum

Author :
Publisher :
ISBN 13 :
Total Pages : 492 pages
Book Rating : 4.:/5 (319 download)

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Book Synopsis NASA Technical Memorandum by :

Download or read book NASA Technical Memorandum written by and published by . This book was released on 1994 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:

A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel

Author : Paul Vincent Ferkul
Publisher :
ISBN 13 :
Total Pages : 160 pages
Book Rating : 4.:/5 (317 download)

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Book Synopsis A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel by : Paul Vincent Ferkul

Download or read book A Model of Concurrent Flow Flame Spread Over a Thin Solid Fuel written by Paul Vincent Ferkul and published by . This book was released on 1993 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Concurrent-Flow Flame Spread Over Ultra-Thin Discrete Fuels in Microgravity

Author : Ama R. Carney
Publisher :
ISBN 13 :
Total Pages : 125 pages
Book Rating : 4.:/5 (131 download)

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Book Synopsis Concurrent-Flow Flame Spread Over Ultra-Thin Discrete Fuels in Microgravity by : Ama R. Carney

Download or read book Concurrent-Flow Flame Spread Over Ultra-Thin Discrete Fuels in Microgravity written by Ama R. Carney and published by . This book was released on 2020 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Investigation of Opposed Flow Flame Spread Over Solid Fuels

Author : Sarzina Hossain
Publisher :
ISBN 13 :
Total Pages : 203 pages
Book Rating : 4.5/5 (355 download)

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Book Synopsis Investigation of Opposed Flow Flame Spread Over Solid Fuels by : Sarzina Hossain

Download or read book Investigation of Opposed Flow Flame Spread Over Solid Fuels written by Sarzina Hossain and published by . This book was released on 2021 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Effect of Oxygen Concentration on Flame Spread Over Thin Fuels in Different Regimes

Author :
Publisher :
ISBN 13 :
Total Pages : 70 pages
Book Rating : 4.:/5 (15 download)

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Book Synopsis Effect of Oxygen Concentration on Flame Spread Over Thin Fuels in Different Regimes by :

Download or read book Effect of Oxygen Concentration on Flame Spread Over Thin Fuels in Different Regimes written by and published by . This book was released on 2018 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this research is to investigate how oxygen concentration, opposed flow velocity and thickness of a thin PMMA fuel affect the flame spread rate and flame extinction in microgravity. The flame spread rate increases with an increase in oxygen concentration. The critical oxygen level, which is the minimum concentration for a flame to spread, is inversely related to the fuel thickness. For fuel thickness above and below a critical thickness, the flame spread rate increases and decreases with a decrease in fuel thickness, respectively. Also, an unexpected extinction is discovered. The critical fuel thickness is inversely related to the opposed flow velocity. The flame spread rate decreases when the opposed flow velocity decreases. Unexpected extinction is discovered when oxygen level is low and opposed flow is absent or weak. The simulation results are consistent with the available experimental results obtained by NASA. For a quiescent environment in microgravity, the critical oxygen level increases with the fuel thickness while the critical oxygen level decreases with the fuel thickness for environments with an opposed flow. The research on how a flame extinguishes reveals that the flame temperature in the anomaly region is lower than the flame temperature in the normal region. A flame extinguishes when the percentage surface radiation loss, which is the ratio of the surface radiation loss to heat generated from combustion, is higher than 45% with an opposed flow and 48% in quiescent environment.

Numerical Study of Concurrent Flame Spread Over an Array of Thin Discrete Solid Fuels

Author : Jeanhyuk Park
Publisher :
ISBN 13 :
Total Pages : 131 pages
Book Rating : 4.:/5 (13 download)

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Book Synopsis Numerical Study of Concurrent Flame Spread Over an Array of Thin Discrete Solid Fuels by : Jeanhyuk Park

Download or read book Numerical Study of Concurrent Flame Spread Over an Array of Thin Discrete Solid Fuels written by Jeanhyuk Park and published by . This book was released on 2018 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: Building fire, Forrest fire, and warehouse compartment fire are some of the most frequently occurring practical fire hazards in modern world. Although these types of hazards seem irrelevant from one another, they have some things in common from the perspective of fire protection engineering, in that they all have a very similar fundamental fuel-gap configuration, or discrete fuel configuration. There has been some studies in the past regarding the subject, yet it is not the most popular in the field. Furthermore, there is even fewer, if not any, numerical analysis done to fires in discrete fuel configuration. Discrete fuel arrangements represent some practical fire hazard situations, such as compartment fires in enclosed vehicles. In this study, an unsteady two-dimensional numerical model (Fire Dynamics Simulator) was used to simulate concurrent flame spreadover paper-like thin solid fuels in discrete configurations in microgravity (0g, where a20cm/s flow is imposed) and in normal gravity (1g). An array of ten 1cm-long fuel segments is uniformly distributed in the flow direction (0g) or in the vertical direction (1g).A hot spot ignition source is applied at the upstream leading edge of the first fuel seg-ment. The separation distance between the fuel segments is a parameter in this study, ranging from 0 (corresponding to a continuous fuel) to 3cm. Using this setup, the spread rate of the flame base and the fuel burning rate were studied. The spread rate in 1g and 0g increases with increasing separation distance. This is due to the gaps in the discrete fuel that force the flame base to jump to the subsequent fuel segment when the upstream segment burns out. On the other hand, the fuel burning rate behaves differently in 1g versus 0g. At a flow velocity of 20 cm/s in 0g, the flame reaches a limiting length and the flame length is approximately the same ( 4cm) for all fuel configurations. Therefore, as the separation distance increases, the preheating length (the fuel area exposed to the flame) decreases, resulting in a smaller burning rate. In 1g, the buoyancy driven flow accelerates as it rises, resulting in a longer flame as the separation distance increases. In all simulated configurations, the flame extends to the last fuel segment before the first fuel segment burns out and the flame spans the entire set of fuel segments. However, flame standoff distance reduces at the gaps between fuel segments, and in some con-figurations, the flame breaks into multiple flamelets. The shorter standoff distance and intense burning at each flamelet base result in a larger total burning rate as the separation distance increases.

Material Flammability and Burning Behavior of Thin Solids in Concurrent Forced Flow in Microgravity

Author : Chengyao Li
Publisher :
ISBN 13 :
Total Pages : 189 pages
Book Rating : 4.:/5 (116 download)

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Book Synopsis Material Flammability and Burning Behavior of Thin Solids in Concurrent Forced Flow in Microgravity by : Chengyao Li

Download or read book Material Flammability and Burning Behavior of Thin Solids in Concurrent Forced Flow in Microgravity written by Chengyao Li and published by . This book was released on 2020 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.