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Journal ArticleDOI

Buoyancy Effects on Concurrent Flame Spread Over Thick PMMA

TL;DR: In this paper, the effect of pressure and microgravity on upward/concurrent flame spread over 10 mm thick polymethyl methacrylate (PMMA) slabs was investigated and correlated in terms of a non-dimensional mixed convection analysis that describes the convective heat transferred from the flame to the solid.
About: This article is published in Combustion and Flame.The article was published on 2019-01-01 and is currently open access. It has received 30 citations till now. The article focuses on the topics: Flame spread & Buoyancy.
Citations
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Journal ArticleDOI
TL;DR: In this article, a microgravity combustion experiment conducted aboard the SJ-10 satellite of China, focusing on the structure and dynamics of diffusion flames spreading over a thick PMMA in low-velocity opposed flows, is reported.

16 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of pressure, and consequently buoyancy and indirectly gravity, on downward flame spread rate over cylindrical samples of polymethyl-methacrylate (PMMA) was studied.
Abstract: Understanding material flammability at different gravity levels is important for fire safety applications in space facilities where the environments may include microgravity, low velocity flows, low pressure and elevated oxygen concentration. One possible approach to simulate on-earth the burning behavior inside spacecraft environments, and facilitate testing, is to reduce buoyancy effects by decreasing ambient pressure. The objective of this work is to study the effect of pressure, and consequently buoyancy and indirectly gravity, on downward flame spread rate over cylindrical samples of polymethyl-methacrylate (PMMA), and by comparison with reduced gravity data, observe up to what point low-pressure can be used to replicate flame spread in space facilities. Experiments in normal gravity are conducted using pressures ranging between 100 kPa and 30 kPa and oxygen concentrations between 19% and 23%, with a forced flow velocity of 100 mm/s. The low-pressure data is compared with microgravity data obtained aboard the International Space Station during the BASS-II experiments. Results show that reductions of ambient pressure slow down the flame spread process approaching that expected at low gravity. The normal gravity and microgravity data are correlated in terms of a mixed convection parameter that describes the main controlling mechanisms of heat transferred. Although the correlation works well for the normal gravity data it does not work as well for the microgravity data. However, it provides information about what is to be expected in environments of variable ambient pressure, oxygen concentration, and reduced gravity, providing an insight for future designs when considering fire safety in spacecrafts.

10 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the opposed flame spread over polyethylene (PE) in microgravity with varying flow velocity and oxygen concentration, and found that LDPE is more flammable than HDPE.
Abstract: Thermoplastics are melted and often dripped down during the flame spread over them in normal gravity. The flame spread behaviors, therefore, could be quite different from those in microgravity because they involve the dripping. However, no studies have addressed the flame spread over thermoplastics to be dripped in microgravity. This work then studied the opposed flame spread over polyethylene (PE) in microgravity with varying flow velocity and oxygen concentration. Two different PEs, a semi-transparent low-density polyethylene (LDPE) and an opaque high-density polyethylene (HDPE), were tested. Microgravity experiments were conducted in parabolic flights which provided a microgravity environment of 10−2 g for 20 s. Experimental results showed that the limiting oxygen concentration (LOC) of LDPE was 20% and 1% lower than that of HDPE. The flame spread of LDPE was faster than that of HDPE too. These indicate that LDPE is more flammable than HDPE, which well agrees with the literatures on the flame spread over PE-insulated wires. Flame spread rates of both LDPE and HDPE increased with flow velocity and oxygen concentration. The flame length also increased with flow velocity, but the preheating length showed an opposite dependence. The effects of flow velocity and oxygen concentration on flame spread rate, flame length, and preheating length are discussed via a simplified flame-spread model. This study’s findings help ensure fire safety in spacecraft because a flame spreads without melted materials being dripped in a spacecraft environment.

10 citations

Journal ArticleDOI
TL;DR: In this article, a thermally thin slab of PMMA that could be inclined from a horizontal (0°) to a vertical (90°) angle is used to investigate flame spread behavior under the condition of the concurrent ambient airflow.

10 citations

References
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Book
01 Jan 2008

11,281 citations

01 Jan 2011

6,700 citations


"Buoyancy Effects on Concurrent Flam..." refers background in this paper

  • ...Selecting as characteristic pyrolysis length half of the sample length results in a heat flux at the solid surface that would correspond to that in the middle of the sample which is a small varying zone of its value [50], thus the impact of the approximation is relatively small....

    [...]

  • ...transfer coefficient along a solid surface is not uncommon in heat transfer [50]....

    [...]

  • ...The boundary layer thickness is determined through the Reynolds number (Re) in pure forced flow, or through the Grashof number (Gr) in pure natural convection (free) flow [50]....

    [...]

  • ...This approximation is somewhat reasonable because the growth of the boundary layer, and in turn the flame stand-off distance, is moderate since the boundary layer thickness grows with a 1/2 to 1/4 power of the distance from the sample leading edge [50]....

    [...]

Book
29 Dec 1998
TL;DR: In this paper, the authors describe the physical chemistry of combustion in fire and discuss the physical properties of fire and its application in a wide range of applications in fire science and combustion.
Abstract: Machine generated contents note: About the AuthorPreface to the Second EditionPreface to the Third EditionList of Symbols and Abbreviations1 Fire science and combustion 1.1 Fuels and the Combustion Process 1.2 The Physical Chemistry of Combustion in Fires Problems2 Heat transfer 2.1 Summary of the heat transfer equations 2.2 Conduction 2.3 Convection 2.4 Radiation Problems3 Limits of flammability and premixed flames 3.1 Limits of flammability 3.2 The structure of a premixed flame 3.3 Heat losses from premixed flames 3.4 Measurement of burning velocities 3.5 Variation of burning velocity with experimental parameters 3.6 The effect of turbulence Problems4 Diffusion flames and fire plumes 4.1 Laminar jet flames 4.2 Turbulent jet flames 4.3 Flames from natural fires 4.4 Some practical applications Problems5 Steady burning of liquids and solids 5.1 Burning of liquids 5.2 Burning of solids Problems6 Ignition: The initiation of flaming combustion 6.1 Ignition of^

1,984 citations

Journal ArticleDOI
01 Jan 1969
TL;DR: In this article, a theoretical description of a laminar diffusion flame spreading against an air stream over a solid- or liquid-fuel bed is presented, where both a thin sheet and a semi-infinite fuel bed are considered.
Abstract: A theoretical description is presented for a laminar diffusion flame spreading against an air stream over a solid- or liquid-fuel bed. Both a thin sheet and a semi-infinite fuel bed are considered. The burning process is described as follows: The hot flame heats the unburned fuel bed, which subsequently vaporizes. The resulting fuel vapor reacts with the oxygen supplied by the incoming air, thereby producing the heat that maintains the flame-spread process. The formulated model treats the combustion as a diffusion flame, for which the details of the reaction kinetics can be ignored by assuming infinite reaction rates. The model includes the chemical stoichiometry, heat of combustion, gas-phase conductive heat transfer, radiation, mass transfer, fuel vaporization, and fuel-bed thermal properties. The radiation is mathematically treated as a heat loss at the flame sheet and a heat gain at the fuel-bed surface. The calculated flame-spread formulas are not inconsistent with available experimental data. These results reveal much of the physics involved in a spreading, flame. For instance, the flame-spread rate is strongly influenced by (1) the adiabatic stoichiometric flame temperature, and (2) the fuel-bed thermal properties, except for the fuel-bed conductivity parallel to the propagation direction.

356 citations


"Buoyancy Effects on Concurrent Flam..." refers background in this paper

  • ...[53] as the sample size increases and the flames become more turbulent the radiant flux becomes more important eventually dominating the heat transfer from the flame to the solid....

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  • ...(diffusive transport and radiation losses) [51-54]....

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Journal ArticleDOI
01 Jan 1977
TL;DR: In this paper, the authors provide a framework within which various studies can be placed, focusing on the underlying heat-transfer, fluid-flow and chemical-kinetic phenomena of fire spread.
Abstract: Mechanisms involved in many types of fire spread are described in a manner that sacrifices accuracy for the purpose of emphasizing general aspects of the underlying heat-transfer, fluid-flow and chemical-kinetic phenomena. Consideration is given to conditions for transition from one mode of propagation to another. Research on fire spread has been pursued intensively in recent years, and in the present contribution at attempt is made to provide a framework within which various studies can be placed. Entries to current literature are provided. Areas of apparent importance that do not seem to have been emphasized are suggested.

241 citations