Experimental and theoretical study on downward flame spread over uninhibited PMMA slabs under different pressure environments
25 May 2018-Applied Thermal Engineering (Pergamon)-Vol. 136, pp 1-8
TL;DR: In this article, side-edge effects on downward flame spread over two parallel polymethyl methacrylate (PMMA) slabs under different pressure environments were investigated. But the results showed that the flame spread rate is controlled by ignition along the side-Edge, rather than at the center of the samples, for experiments with both single and two parallel slabs.
About: This article is published in Applied Thermal Engineering.The article was published on 2018-05-25. It has received 26 citations till now. The article focuses on the topics: Flame spread & Diffusion flame.
TL;DR: In this paper, flame spread behavior over high-conductivity copper (Cu) core electrical wire in sub-atmospheric pressures, and compares those with relative low-conductive nickel-chrome (NiCr) core Electrical wire, to quantify the evolutions of wire-driven and flame-driven heat transfer mechanisms in supporting flame spread with pressure decreasing.
TL;DR: In this paper, the authors investigated the combined effects of orientation and environmental pressure on flame characteristics, steady burning experiments of inclined polymethyl methacrylate (PMMA) slabs were conducted at reduced environmental pressures ranging from 0.5 to 1 atm.
••01 Jan 2019
TL;DR: In this paper, the effect of flame propagation along vertical edges on the overall downward spread of flames using polymethyl methacrylate (PMMA) was measured and a MATLAB-based tool was used to calculate instantaneous spread rate for central and edge flames.
Abstract: This systematic experimental study measures the effect of flame propagation along vertical edges on the overall downward spread of flames using Polymethyl Methacrylate (PMMA). Samples with a wide range of regular cross-sections – from triangular through octagonal – as well as irregular ones, have been used to test a large variation of internal angles. A MATLAB-based tool was used to calculate instantaneous spread rate for central and edge flames. The edge flame is shown to significantly enhance the spread rate, as much as five times, in respect to samples with no edges. This amplification is shown to depend primarily on the internal angle at the edge (the smaller the angle, the faster the flame) and fuel thickness, and not on other factors such as aspect ratio or cross-sectional area. Using a phenomenological argument, the edge propagation rate is correlated to the spread rate over an equivalent cylindrical fuel (the limiting shape with infinite edges) with an effective radius obtained from the geometry of the edges and the diffusion length scale of the solid phase. A formula for flame spread over cylindrical fuel from the literature is used to link the new results to existing models. Both thick and thin limits are shown to encompass the wide range of three-dimensional spread rate data within the effective radius (the independent variable), which can be determined from the known parameters. Based on these results, different types of cross-sectional areas can be sorted in the order of their inherent fire safety characteristics.
01 Jan 2021
TL;DR: In this paper, the downward flame spread over polymethyl methacrylate (PMMA) with and without addition of triphenyl phosphate (TPP) was measured using the micro-thermocouple technique and molecular beam spectrometry.
Abstract: Experimental and numerical studies of downward flame spread over polymethyl methacrylate (PMMA) with and without addition of triphenyl phosphate (TPP) are reported. Using the micro-thermocouple technique and molecular beam spectrometry, detailed flame structures of PMMA and PMMA+10%TPP were measured. From the experiments and quantum chemistry calculations, the retardancy capability of TPP on gas-phase reaction is proposed. Addition of flame retardant (10%, 20% TPP) results in reduction of the flame spread rate, the mass burning rate and conductive heat flux from the flame to the polymer surface. Numerical calculation was carried out to simulate the downward flame spread over PMMA and PMMA-TPP slabs. Based on the assumption of the TPP gas phase retardancy performance, a modified one-step reaction rate constant with pre-exponent dependent on the TPP mass content in the polymer and TPP retardancy effectivity is proposed. The predicted results have been compared with the data from sophisticated experimental measurement on thermal and chemical structures of both PMMA and PMMA+TPP flames.
••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.
TL;DR: In this paper, heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation.
Abstract: Recent advances in the experimental study of the mechanisms controlling the spread of flames over the surface of combustible solids are summarized in this work. The heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation. The realization that, in most practical situations, the spread of fire in opposed gas flows occurs at near extinction or non-propagating conditions is particularly significant. Under these circumstances, gas phase chemical kinetics plays a critical role and it must be considered if realistic descriptions of the flame spread process are attempted. In the concurrent mode of flame spread, heat transfer from the flame to the unburnt fuel appears to be the primary controlling mechanism. Although gas phase chemcial kinetics is unimportant in the flame spreading process, it is important in the establishment and extension of the diffusion ...
••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.
01 Jan 1979
TL;DR: In this article, the authors reviewed non-luminous radiation theories and compared them to Hottel's emmissivity charts for typical homogeneous combustion situations and concluded that the presence of luminous soot must be locally supported by chemical heat release in normal fire situations.
Abstract: Non-luminous radiation theories are reviewed and compared to Hottel's emmissivity charts for typical homogeneous combustion situations. Both narrow-band statistical and exponential wide-band models are considered. The results are then extended to luminous flames and the issue of whether flames can be regarded as gray is discussed quantitatively for various flame gases. Experimental investigations of the heat transfer components to burning fuel surfaces show that radiation is dominant at scales of 0.2–0.3 m and above. Comparative measurements of various non-charring plastic fuels show that the flame absorption-emission coefficient is the principal fuel property controlling the fuel's burning rate at hazardous scales. The measurements also indicate that the actual volumetric heat release rate is the same for different fuels burning as buoyant turbulent diffusion flames at similar scales. Concerning flame structure it is shown that the presence of luminous soot must be locally supported by chemical heat release in normal fire situations. It is also suggested that the observed proportionality of radiant heat output to fuel supply rate for geometrically similar buoyant diffusion flames is due to the insensitivity of the characteristic Kolmogorov microscale to changes in fuel flow rate. The review also discusses numerous important unresolved fire research topics.
••01 Jan 1981
TL;DR: In this article, the velocity of flame propagation over the surface of thick PMMA and thin paper sheets has been measured as a function of the velocity and oxygen concentration of a forced gas flow opposing the direction of the flame propagation.
Abstract: The velocity of flame propagation over the surface of thick PMMA and thin paper sheets has been measured as a function of the velocity and oxygen concentration of a forced gas flow opposing the direction of flame propagation. It is shown that although for thin fuels the flame spread rate always decreases as the opposed flow velocity increases, for thick fuels the dependence of the spread rate on the gas velocity is also a function of the ambient oxygen concentration. For low oxygen concentrations the flame spread rate decreases as the velocity of the gas flow increases. For high oxygen concentrations, however, the spread rate increases with the flow velocity, reaches a maximum and then decreases as the gas velocity increases. The velocity of the opposed flow at which the maximum occurs is a function of the oxygen concentration, decreasing as the concentration decreases. Following phenomenological considerations and simplified descriptions of the primary mechanisms occurring during the flame spread process, the experimental results are correlated by two non-dimensional parameters, one describing the gas phase kinetic effects and the other describing the process of heat transfer from the flame to the fuel. Such a correlation provides a powerful means of predicting the flame spread prcess as well as physical insight into the mechanisms controlling the propagation of the flame.