Wind-aided flame spread over an unsteadily vaporizing solid
01 Jan 1992-Vol. 24, Iss: 1, pp 1685-1693
TL;DR: In this paper, a simple but realistic model for the flame length and the flame front speed during wind-aided flame spread on a thick vaporizing solid like PMMA is presented.
Abstract: A simple but realistic model for the flame length and the flame front speed during windaided flame spread on a thick vaporizing solid like PMMA is presented. The model predictions compare favorably with the experiments conducted in the ceiling configuration. This model is based on the following experimental observations: (i) During wind-aided flame spread, the solid-phase undergoes transient pyrolysis while the gas-phase remains quasi-steady, (ii) In the ceiling configuration, the flame stand-off distance is much smaller than the thermal boundary layer thickness. To incorporate the first observation into the model, an expression was derived for the transient mass flux as a function of the net incident heat flux. This expression was verified by transient pyrolysis experiments conducted on PMMA for heat fluxes ranging from 1.6 to 5 W/cm2 in N2 atmosphere. The second observation was exploited to obtain considerable simplification in the gas-phase enabling an explicit expression for the convective heat flux from the flame to the solid. This heat flux was corrected for shielding due to blowing of fuel mass from the solid surface. A comparison of the model with the experimental results show that shielding of heat transfer due to blowing and the radiative heat loss from the sample surface have a large effect on the flame length and the flame front speed. It was also found that for cases where the flow is laminar and flame radiation is small, surface heat loss causes the pyrolysis front speed to eventually become zero for a thick sample. This may occur even before the pyrolyzing zone achieves steady state as assumed by previous theoretical models. Once the pyrolysis front speed becomes zero, the flame spread rate is controlled by the speed of the burnout front which propagates behind the pyrolysis front for thin or charring materials.
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TL;DR: In this article, the thermal degradation of a black poly(methyl)methacrylate (PMMA) in a cone calorimeter (CC) in air with a piloted ignition has been studied.
104 citations
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15 Dec 1998-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: The mechanisms that lead to ignition of fires and the reasons behind the experimental correlations available in the literature are discussed and it is concluded that within the approximation of constant surface temperature at ignition, the ignition delay data may be correlated by a simple thermal model based on inert heating of the solid.
Abstract: This paper discusses the mechanisms that lead to ignition of fires and the reasons behind the experimental correlations available in the literature. The objective is to understand and quantify the ...
92 citations
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...1990; Agrawal & Atreya 1992)....
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TL;DR: In this article, a mathematical model that describes transient thermal energy transport, chemical reactions, and transport of gases through the condensed phase is proposed to predict the behavior of materials exposed to fire.
Abstract: One of the main obstacles to development of more effective passive fire protection for transportation is the lack of a quantitative understanding of the relations between the results of various materials fire tests used in this field. The need for multiple testing techniques arises from the complexity of fire phenomena and their sensitivity to environmental conditions. This work addresses this problem by developing a computational tool that predicts the behavior of materials exposed to fire. While it is not expected that this tool will eliminate the need for fire testing, the goal is to considerably reduce the number and complexity of the tests necessary for a comprehensive characterization of the materials of interest. The foundation of this tool is a mathematical model that describes transient thermal energy transport, chemical reactions, and transport of gases through the condensed phase. The model also captures such important aspects of material’s behavior as charring and intumescence. This paper provides a detailed description of the onedimensional version of this model and summarizes results of its verification.
83 citations
Cites background from "Wind-aided flame spread over an uns..."
...Such models are frequently used to simulate the spread of flame [5,6] (flame spread models are usually two-dimensional)....
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TL;DR: In this article, a numerical model was developed to examine steady, laminar flame spread and extinction over a thin solid fuel in low-speed concurrent flow, incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point, and a parabolic treatment of downstream flame, which has a higher flow Reynolds number.
Abstract: A numerical model is developed to examine steady, laminar flame spread and extinction over a thin solid fuel in low-speed concurrent flow. The model incorporates an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point, and a parabolic treatment of the downstream flame, which has a higher flow Reynolds number. This provides a more precise fluid-mechanical description of the flame than using parabolic equations throughout, and is the first time such an approach has been used in concurrent flame spread modeling. The parabolic and elliptic regions are coupled smoothly by matching boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Calculations (with the flame spread rate being an eigenvalue) are performed for forced flow without gravitational influences in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Steady spread with constant flame and...
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TL;DR: In this paper, the effect of the design on the fire behaviour of materials and measurement accuracy in the controlled atmosphere cone calorimeter (CACC) was investigated under ambient and non-ambient oxygen conditions.
35 citations
References
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TL;DR: In this article, the authors examined and partially solved the problem of controlling the rate of combustion in large droplets, where the heat transfer and diffusion processes will have removed the chemical reaction zone far enough from the droplet to where it is less sensitive to the effects of the droplets itself.
Abstract: Fur Tropfchen, die groser als, sagen wir, 10−1 Zoll sind, entfernen Warmeleitungs- und Diffusionsprozesse die chemische Reaktionszone weit genug vom Tropfchen dorthin, wo sie fur die Effekte des Tropfchens selbst weniger sensibel ist, und daher die Verbrennungsgeschwindigkeit von den Warmeleitungs- und Massenprozessen selbst gesteuert wird. Dieses Problem wird in dieser Arbeit untersucht und teilweise gelost.
For larger droplets - than say 10−1 inches - the heat transfer and diffusion processes will have removed the chemical reaction zone far enough from the droplet to where it is less sensitive to the effects of the droplet itself and hence the control of the rate of combustion will be the heat and mass transfer processes themselves. It is this problem that will be examined and partially solved in this paper.
257 citations
TL;DR: In this article, a theoretical model for the propagation of flames over a solid fuel in a laminar forced oxidizing gas flow moving in the direction of flame propagation is developed, which makes use of a boundary-layer approximation to describe the flow and of an ignition surface temperature.
53 citations
TL;DR: In this paper, steady-state solutions for the speed of surface recession and internal temperature history of a slab which uniformly absorbs heat on one face at a large caloric rate were obtained.
Abstract: In an attempt to bound the problem, steady‐state solutions are obtained for the speed of surface recession (melting) and the internal temperature history of a slab which uniformly absorbs heat on one face at a large caloric rate. The solutions are found to be sensitive to assumptions that must be made regarding both the thickness attained by the layer of molten matter produced during the heat pulse and the mechanisms (e.g., air drag, evaporation) that control this thickness.
31 citations
TL;DR: The American Society of Testing and Materials test E84 is widely used in North America to characterize the rate of flame spread along samples of material proposed for use in construction of buildings; by this test, materials in part, are qualified with respect to fire safety for classes of application as discussed by the authors.
Abstract: The American Society of Testing and Materials test E84 is widely employed in North America to characterize the rate of flame spread along samples of material proposed for use in construction of buildings; by this test, materials, in part, are qualified with respect to fire safety for classes of application. In this ten-minute-duration test, an 8 meter slab of the material comprises the ceiling of a sealed duct (termed a Steiner tunnel) through which hot vitiated air (up to about 1150 K) flows after time zero at about 1.2 m/s. Materials are rated according to the distance from the leading edge that the wind-aided flame propagates (or, alternatively for samples that become totally involved, by the elapsed time to flameover at the downwind end). An unsteady two-spatial-dimensional model of this test has been undertaken, as a first step toward the goal of anticipating behavior of a sample from knowledge of its chemical and physical properties. In the formulation, at any fixed position along the sampl...
31 citations
TL;DR: In this paper, the authors theoretically analyzes flame spread over thick solid fuels (noncharring) in concurrent oxidizer flows, and they make rationally justifiable physical approximations that produce useful results.
14 citations