Downward flame spread over extruded polystyrene: Effects of sample thickness, pressure, and sidewalls
01 Feb 2015-Journal of Thermal Analysis and Calorimetry (Springer Netherlands)-Vol. 119, Iss: 2, pp 1091-1103
TL;DR: In this article, the effects of sample thickness (d), sidewalls and atmospheric pressure (p) on the flame spread of extruded polystyrene (XPS) are studied.
Abstract: An experimental study on the characteristics of downward flame spread of extruded polystyrene (XPS) is presented. The parameters investigated include average mass loss rate per unit of thickness (
$$ \dot{m}^{'} $$
), average flame height (H
f), average flame spread rate (v
f), and mass growth rate (
$$ \dot{m}_{1} $$
) of molten XPS. The effects of sample thickness (d), sidewalls and atmospheric pressure (p), and the combined effects of these factors on the flame spread are studied. The larger sample thickness corresponds to larger $$ \dot{m}^{'} $$
and higher flame upon most occasions. As d rises, v
f and $$ \dot{m}_{1} $$
increase under all conditions; v
f and d follow the equation: $$ {\text{v}}_{\text f} = A ( 1- {\text{exp(}} - {\text{Cd))}} $$
. The dimensionless heat release rate: $$ \dot{Q}^{*} \propto { \exp }( - 0. 3d) $$
. $$ \dot{m}^{'} $$
, v
f , and $$ \dot{m}_{1} $$
obtained without sidewalls are higher than those with sidewalls. $$ \dot{m}^{'} $$
, v
f, and H
f obtained on the plain (p = 100.8 kPa) are larger than those obtained on the plateau (p = 65.5 kPa). $$ \dot{m}_{1} $$
obtained on the plain is lower than that on the plateau. In most cases without sidewalls, $$ \dot{m} \propto p^{{\text n_{0}} } $$
, where 1.9 < n
0 < 2, and $$ H_{\text f} = a + \mu p^{{\text n_{0} }} $$
. H
f obtained in the cases without sidewalls is larger than that with sidewalls when the sample thickness is small, while the opposite is true for thicker samples. When sidewalls are absent, on the plain, with a rise in thickness, the increase of v
f is significant for thin samples while the variation is not considerable for thick samples; on the plateau, this increase is significant for all thicknesses tested. The experimental results agree well with the theoretical analysis.
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TL;DR: In this article, the effects of altitude and sample orientation on flame spread behavior were quantitatively analyzed, and the results showed that extinction and secondary ignition occur for XPS on plateau, as the oxygen concentration in air entrainment is influenced by the generated smoke in the pool fire zone.
Abstract: Experiments were carried out on insulation foams of EPS and XPS in a small-scale flame spread experimental bench in the Tibetan plateau area of Lhasa and the plain area of Hefei both in China, respectively. The effects of altitude and sample orientation on flame spread behavior were quantitatively analyzed. The results show that extinction and secondary ignition occur for XPS on plateau, as the oxygen concentration in air entrainment is influenced by the generated smoke in the pool fire zone. The flame spread speed of EPS increases with the incline angle both in Lhasa and in Hefei, but for XPS (downward flame spread), the flame spread speed increases with the decrease in incline angle, especially in Lhasa. It is found that the heat transfer process is different for EPS and XPS. The transition fire zone plays an important role in heat transfer over XPS for downward flame spread resulting in total heat transfer including the flame convective and radiative heat $$ q_{\text{f}}^{\prime \prime } \delta_{\text{f}} $$
and the conductive heat $$ q_{\text{c}}^{\prime \prime } L $$
increase with the decrease in incline angle, while for EPS, the surface flame zone dominates the heat transfer in two places.
18 citations
TL;DR: In this paper, a series of experiments were conducted to study the flame spread and radiation characteristics for diesel tray fires against a sidewall, where the tray width and the height of the sidewall were varied.
Abstract: A series of experiments were conducted to study the flame spread and radiation characteristics for diesel tray fires against a sidewall. The tray width and the height of the sidewall were varied. The flame spread appearances and rate, subsurface flow and transverse fuel surface temperature were analyzed. Results showed that the sidewall has a great influence on the flame spread behavior due to its restriction on air entrainment. The flame distribution was uneven along the length of the tray, and the front propagating flame inclines to the tray outboard side edge (i.e. the tray's long side that is not attaching to the sidewall) for more oxygen, then more heat transferred from the flame through tray wall to the fuel results in uneven surface temperature profiles. The main flame being one short distance away from the flame spread front is against the sidewall. When the ratio of the sidewall height to the tray width, H/W, is less than 1, both the flame spread rate and subsurface flow increase with the increasing H/W, due to enhanced heat transfer. For H/W > 1, both of these parameters decrease with the increasing H/W, indicating a strong restriction of air entrainment by the sidewall. To estimate the flame radiation to the fuel surface during propagation, a multi-cylinder radiation model was proposed. By dividing the whole flame into several cylindrical sub-flames, the radiation blockage and sidewall effects are considered in the model. The comparison of calculated and measured radiation heat fluxes shows that the proposed model is reliable with a maximum error of 20%. These findings will provide scientific supports to fire monitoring and contribute to estimating radiative heat flux of spreading flame.
17 citations
TL;DR: The results surprisingly showed that about 80% of the generated hot liquid fuel remained in the pool fire during a certain period, and it was suggested that horizontal noncombustible barriers for preventing the accumulation and dripping of liquid fuel are helpful for vertical confining of XPS fire.
Abstract: The objective of this work is to investigate the distinctive mechanisms of downward flame spread for XPS foam. It was physically considered as a moving down of narrow pool fire instead of downward surface flame spread for normal solids. A method was developed to quantitatively analyze the accumulated liquid fuel based on the experimental measurement of locations of flame tips and burning rates. The results surprisingly showed that about 80% of the generated hot liquid fuel remained in the pool fire during a certain period. Most of the consumed solid XPS foam didn't really burn away but transformed as the liquid fuel in the downward moving pool fire, which might be an important promotion for the fast fire development. The results also indicated that the dripping propensity of the hot liquid fuel depends on the total amount of the hot liquid accumulated in the pool fire. The leading point of the flame front curve might be the breach of the accumulated hot liquid fuel if it is enough for dripping. Finally, it is suggested that horizontal noncombustible barriers for preventing the accumulation and dripping of liquid fuel are helpful for vertical confining of XPS fire.
17 citations
TL;DR: In this paper, a series of comparative lab-scale experiments was carried out in plain area of Hefei and plateau area of Lhasa to reveal the altitude and orientation effects on the flammability behaviors of insulation material of polystyrene.
Abstract: In order to reveal the altitude and orientation effects on the flammability behaviors of insulation material of polystyrene, a series of comparative lab-scale experiments was carried out in plain area of Hefei and plateau area of Lhasa The piloted ignition time was identified for EPS and XPS with sample orientations of 0°, 15°, 30° and 90° It was found that the piloted ignition time was shorter in Hefei than that in Lhasa for the same slab at the same inclination Meanwhile, for EPS, due to the greater shrinkage, the ignition time was not influenced by thickness obviously, while for XPS, it was decreased with thickness for the receiving heat flux enhanced The ignition time during flame spread case was longer than that in piloted ignition, attributed to the longer time of shrinking and melting The combustion characteristics including pool fire length, flame length and mass loss rate were also explored With the sample thickness increase, the maximum pool fire length and mass loss rate were both increased, leading to greater fire hazard For the dripping and smoke influence, the slope of flame length against pyrolysis length at 90° would increase from slope1 to slope2
17 citations
Cites background from "Downward flame spread over extruded..."
...[5, 6] experimentally and theoretically studied the downward flame spread behaviors over XPS....
[...]
TL;DR: In this paper, a new experimental setup is used to quantitatively analyze the burning characteristics of pool fires at different steady mass feeding rates, including dripping rate, flowing rate of hot molten liquids, burning rate and radiant flux of flowing pool fires.
Abstract: Nowadays, thermoplastic materials, which represent a risk of the high melt flow fire spread, are widely used in construction industry. The flow of thermoplastic’s melt drips will accelerate the downward flame spread and fall into the pool fires which appears at the foot of the wall fires. Fire will develop to larger and larger soon because of the wall fires and pool fires mutual enhancement mechanism. In this paper, a new experimental setup is used to quantitatively analyze the burning characteristics of pool fires at different steady mass feeding rates. PP (polypropylene), PE (polyethylene) and PS (polystyrene) thermoplastic polymers are selected as test materials and were heated to be the molten phase by electric heater. N2 gas is continuously injected into the chamber to avoid a sudden ignition. The characteristics parameters including dripping rate, flowing rate of hot molten liquids, burning rate and radiant flux of flowing pool fires are analyzed. The experiment results preliminarily suggest that the hot molten liquids induced by PP polymers are easier to drop and flow than that by PE and PS. Therefore, PP materials may be more dangerous for their faster pool fires flowing rate on the floor. Meanwhile, the burning rate of pool fires induced by PS is higher than that by PE and PP, although the dripping rate and flowing rate of PS is the slowest for its large viscosity. For larger mass feeding rates, the dripping rate of three hot molten drips becomes faster. It also indicates that the experimental process of surface tension flow and the flame front of pool fires do not coincide with melt flow front for PP and PE at different mass feeding rates. Specifically, the flame front of pool fires induced by molten PP or PE polymers is slower than the forward movement of the hot molten liquids. The reason for these combustion characteristics of molten thermoplastic polymers that mentioned above may be related to viscosity and structures of thermoplastics, as well as the pyrolysis process of different thermoplastics.
13 citations
Cites methods from "Downward flame spread over extruded..."
...[10, 11] conducted an experiment to study the effects of thickness, pressure and sidewalls of the samples on the characteristics of the downward flame spread of thermoplastic material—extruded polystyrene (XPS)—and established the preliminary quantitative model....
[...]
References
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01 Jan 2011
6,700 citations
"Downward flame spread over extruded..." refers methods in this paper
...The Grashof number (Gr) could be applied to represent the instability of buoyancy [15]:...
[...]
01 Jan 2016
TL;DR: This book provides thorough treatment of the current best practices in fire protection engineering and performance-based fire safety, and remains the indispensible source for reliable coverage of fire safety engineering fundamentals, fire dynamics, hazard calculations, fire risk analysis, modeling and more.
Abstract: Revised and significantly expanded, the fifth edition of this classic work offers both new and substantially updated information. As the definitive reference on fire protection engineering, this book provides thorough treatment of the current best practices in fire protection engineering and performance-based fire safety. Over 130 eminent fire engineers andresearchers contributed chapters to the book, representing universities and professional organizations around the world. It remains the indispensible source for reliable coverage of fire safety engineering fundamentals, fire dynamics, hazard calculations, fire risk analysis, modeling and more. With seventeen new chapters and over 1,800 figures, the this new editioncontains: • Step-by-step equations that explain engineering calculations • Comprehensive revision of the coverage of human behavior in fire, including several new chapters on egress system design, occupant evacuation scenarios, combustion toxicity and data for human behavior analysis • Revised fundamental chapters for a stronger sense of context • Added chapters on fire protection system selection and design, including selection of fire safety systems, system activation and controls and CO2 extinguishing systems • Recent advances in fire resistance design • Addition of new chapters on industrial fire protection, including vapor clouds, effects of thermal radiation on people, BLEVEs, dust explosions and gas and vapor explosions • New chapters on fire load density, curtain walls, wildland fires and vehicle tunnels • Essential reference appendices on conversion factors, thermophysical property data, fuel properties and combustion data, configuration factors and piping properties.
1,563 citations
01 Jan 1953
608 citations
"Downward flame spread over extruded..." refers methods in this paper
...Spalding also proposed that [17]: B ¼ ½YO2;1QO2 cpðTs T1Þ _m00= _q00conv: ð5Þ Inserting Eq....
[...]
...The expression of this function was investigated by Spalding [17] and Delichatsios and Delichatsios [18]....
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Book•
21 Apr 2006
TL;DR: In this article, the authors present an overview of the history of fire and its application in the field of fire safety, including a discussion of the role of mass and energy conservation in chemical reactions.
Abstract: Preface. Nomenclature. 1 Introduction to Fire. 1.1 Fire in History. 1.2 Fire and Science. 1.3 Fire Safety and Research in the Twentieth Century. 1.4 Outlook for the Future. 1.5 Introduction to This Book. 2 Thermochemistry. 2.1 Introduction. 2.2 Chemical Reactions. 2.3 Gas Mixture. 2.4 Conservation Laws for Systems. 2.5 Heat of Formation. 2.6 Application of Mass and Energy Conservation in Chemical Reactions. 2.7 Combustion Products in Fire. 3 Conservation Laws for Control Volumes. 3.1 Introduction. 3.2 The Reynolds Transport Theorem. 3.3 Relationship between a Control Volume and System Volume. 3.4 Conservation of Mass. 3.5 Conservation of Mass for a Reacting Species. 3.6 Conservation of Momentum. 3.7 Conservation of Energy for a Control Volume. 4 Premixed Flames. 4.1 Introduction. 4.2 Reaction Rate. 4.3 Autoignition. 4.4 Piloted Ignition. 4.5 Flame Speed, Su. 4.6 Quenching Diameter. 4.7 Flammability Limits. 4.8 Empirical Relationships for the Lower Flammability Limit. 4.9 A Quantitative Analysis of Ignition, Propagation and Extinction. 5 Spontaneous Ignition. 5.1 Introduction. 5.2 Theory of Spontaneous Ignition. 5.3 Experimental Methods. 5.4 Time for Spontaneous Ignition. 6 Ignition of Liquids. 6.1 Introduction. 6.2 Flashpoint. 6.3 Dynamics of Evaporation. 6.4 Clausius-Clapeyron Equation. 6.5 Evaporation Rates. 7 Ignition of Solids. 7.1 Introduction. 7.2 Estimate of Ignition Time Components. 7.3 Pure Conduction Model for Ignition. 7.4 Heat Flux in Fire. 7.5 Ignition in Thermally Thin Solids. 7.6 Ignition of a Thermally Thick Solid. 7.7 Ignition Properties of Common Materials. 8 Fire Spread on Surfaces and Through Solid Media. 8.1 Introduction. 8.2 Surface Flame Spread - The Thermally Thin Case. 8.3 Transient Effects. 8.4 Surface Flame Spread for a Thermally Thick Solid. 8.5 Experimental Considerations for Solid Surface Spread. 8.6 Some Fundamental Results for Surface Spread. 8.7 Examples of Other Flame Spread Conditions. 9 Burning Rate. 9.1 Introduction. 9.2 Diffusive Burning of Liquid Fuels. 9.3 Diffusion Flame Variables. 9.4 Convective Burning for Specific Flow Conditions. 9.5 Radiation Effects on Burning. 9.6 Property Values for Burning Rate Calculations. 9.7 Suppression and Extinction of Burning. 9.8 The Burning Rate of Complex Materials. 9.9 Control Volume Alternative to the Theory of Diffusive Burning. 9.10 General Considerations for Extinction Based on Kinetics. 9.10.1 A demonstration of the similarity of extinction in premixed and diffusion flames. 9.11 Applications to Extinction for Diffusive Burning. 10 Fire Plumes. 10.1 Introduction. 10.2 Buoyant Plumes. 10.3 Combusting Plumes. 10.4 Finite Real Fire Effects. 10.5 Transient Aspects of Fire Plumes. 10.5.1 Starting plume. 10.5.2 Fireball or thermal. 11 Compartment Fires. 11.1 Introduction. 11.2 Fluid Dynamics. 11.3 Heat Transfer. 11.4 Fuel Behavior. 11.5 Zone Modeling and Conservation Equations. 11.6 Correlations. 11.7 Semenov Diagrams, Flashover and Instabilities. 12 Scaling and Dimensionless Groups. 12.1 Introduction. 12.2 Approaches for Establishing Dimensionless Groups. 12.3 Dimensionless Groups from the Conservation Equations. 12.4 Examples of Specific Correlations. 12.5 Scale Modeling. Appendix. Flammability Properties. Archibald Tewarson. Index.
599 citations