scholarly journals A Comparison of Flame Spread Characteristics over Solids in Concurrent Flow Using Two Different Pyrolysis Models

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Ya-Ting Tseng ◽  
James S. T'ien
Keyword(s):  
Flame Spread ◽  
Flame Structure ◽  
Flame Length ◽  
Spread Rate ◽  
Constant Length ◽  
Concurrent Flow ◽  
First Order ◽  
Spread Model ◽  
Pyrolysis Model ◽  
Order Surface

Two solid pyrolysis models are employed in a concurrent-flow flame spread model to compare the flame structure and spreading characteristics. The first is a zeroth-order surface pyrolysis, and the second is a first-order in-depth pyrolysis. Comparisons are made for samples when the spread rate reaches a steady value and the flame reaches a constant length. The computed results show (1) the mass burning rate distributions at the solid surface are qualitatively different near the flame (pyrolysis base region), (2) the first-order pyrolysis model shows that the propagating flame leaves unburnt solid fuel, and (3) the flame length and spread rate dependence on sample thickness are different for the two cases.

Experimental study of the width effects on self-induced buoyant blow off in upward flame spread over thin fabric fuels

2019 ◽  
Vol 90 (11-12) ◽  
pp. 1404-1413 ◽  
Author(s):  
Guoqing Zhu ◽  
Yunji Gao ◽  
Guoqiang Chai ◽  
Jinju Zhou ◽  
Shuai Gao
Keyword(s):  
Flame Spread ◽  
Flame Length ◽  
Flame Height ◽  
Spread Rate ◽  
Fire Control ◽  
Constant Length ◽  
Flame Spreading ◽  
Upward Flame Spread ◽  
Flame Thickness ◽  
Induced Velocity

In this paper, a series of upward flame spreading experiments were conducted on thin flax fabric with various widths ranging from 3.0 to 8.0 cm and length of 1.6 m. Symmetric ignition at the entire bottom edge of samples led to two-sided upward flame growth initially. A very interesting behavior of flame blown off was observed in upward flame spreading and an explanation was provided based on the increased buoyancy-induced velocity at the flame base. When the sample width is 6 cm or less, the flame length increases to a critical value and, correspondingly, the buoyancy-induced velocity reaches the blow off velocity, which results in a flame being blown off on one side. The remaining flame on the other side would shrink in length and propagate to the end of the sample with an asymptotically constant length and steady spread rate. For samples wider than 6 cm, the two-sided flame continues to spread to the end of samples and the self-induced blow off phenomenon is not observed. Moreover, the width effects on the flame height, flame thickness and flame spread rate are analyzed and explained in this paper. The results of this study may help advance better understanding of flame blow off behaviors over solid surfaces and have implications concerning fire control of flame spread over solid fuels.

Numerical Study of the Effects of Confinement on Concurrent-Flow Flame Spread in Microgravity

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Yanjun Li ◽  
Ya-Ting T. Liao ◽  
Paul Ferkul
Keyword(s):  
Flame Spread ◽  
Numerical Study ◽  
Flame Temperature ◽  
Combustion Model ◽  
Conductive Heat ◽  
Spread Rate ◽  
Transient Model ◽  
Concurrent Flow ◽  
Flame Spread Rate ◽  
Flow Duct

Abstract The objective of this work is to investigate the aerodynamics and thermal interactions between a spreading flame and the surrounding walls as well as their effects on fire behaviors. A three-dimensional transient computational fluid dynamics (CFD) combustion model is used to simulate concurrent-flow flame spread over a thin solid sample in a narrow flow duct. The height of the flow duct is the main parameter. The numerical results predict a quenching height for the flow duct below which the flame fails to spread. For duct heights sufficiently larger than the quenching height, the flame reaches a steady spreading state before the sample is fully consumed. The flame spread rate and the pyrolysis length at steady-state first increase and then decrease when the flow duct height decreases. The detailed gas and solid profiles show that flow confinement has multiple effects on the flame spread process. On one hand, it accelerates flow during thermal expansion from combustion, intensifying the flame. On the other hand, increasing flow confinement reduces the oxygen supply to the flame and increases conductive heat loss to the walls, both of which weaken the flame. These competing effects result in the aforementioned nonmonotonic trend of flame spread rate as duct height varies. Near the quenching duct height, the transient model reveals that the flame exhibits oscillation in length, flame temperature, and flame structure. This phenomenon is suspected to be due to thermodiffusive instability.

Concurrent-Flow Flame Spread Over a Thin Solid in a Narrow Confined Space in Microgravity

2019 ◽  
Author(s):  
Yanjun Li ◽  
Ya-Ting T. Liao ◽  
Paul Ferkul
Keyword(s):  
International Space Station ◽  
Flame Spread ◽  
Numerical Study ◽  
Space Station ◽  
Spread Rate ◽  
International Space ◽  
Concurrent Flow ◽  
Microgravity Experiments ◽  
Flame Spread Rate ◽  
Flow Duct

Abstract A numerical study is pursued to investigate the aerodynamics and thermal interactions between a spreading flame and the surrounding walls as well as their effects on fire behaviors. This is done in support of upcoming microgravity experiments aboard the International Space Station. For the numerical study, a three-dimensional transient Computational Fluid Dynamics combustion model is used to simulate concurrent-flow flame spread over a thin solid sample in a narrow flow duct. The height of the flow duct is the main parameter. The numerical results predict a quenching height for the flow duct below which the flame fails to spread. For duct heights sufficiently larger than the quenching height, the flame reaches a steady spreading state before the sample is fully consumed. The flame spread rate and the pyrolysis length at steady state first increase and then decrease when the flow duct height decreases. The detailed gas and solid profiles show that flow confinement has competing effects on the flame spread process. On one hand, it accelerates flow during thermal expansion from combustion, intensifying the flame. On the other hand, increasing flow confinement reduces the oxygen supply to the flame and increases conductive heat loss to the walls, both of which weaken the flame. These competing effects result in the aforementioned non-monotonic trend of flame spread rate as duct height varies. This work relates to upcoming microgravity experiments, in which flat thin samples will be burned in a low-speed concurrent flow using a small flow duct aboard the International Space Station. Two baffles will be installed parallel to the fuel sample (one on each side of the sample) to create an effective reduction in the height of the flow duct. The concept and setup of the experiments are presented in this work.

Limiting Length, Steady Spread, and Nongrowing Flames in Concurrent Flow Over Solids

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Ya-Ting Tseng ◽  
James S. T’ien
Keyword(s):  
Steady State ◽  
Radiative Heat ◽  
Flame Length ◽  
Two Dimensional ◽  
Spread Rate ◽  
Radiative Heat Loss ◽  
Transient Model ◽  
Concurrent Flow ◽  
Burnout Rate ◽  
Growth Features

A detailed two-dimensional transient model has been formulated and numerically solved for concurrent flames over thick and thin solids in low-speed forced flows. The processes of flame growth leading to steady states are numerically simulated. For a thick solid, the steady state is a nongrowing stationary flame with a limiting length. For a thin solid, the steady state is a spreading flame with a constant spread rate and a constant flame length. The reason for a nongrowing limiting flame for the thick solid is the balance between the flame heat feedback and the surface radiative heat loss at the pyrolysis front, as first suggested by Honda and Ronney. The reason for achieving a steady spread for thin solids is the balance between the solid burnout rate and the flame tip advancing rate. Detailed transient flame and thermal profiles are presented to illustrate the different flame growth features between the thick- and thin-solid fuel samples.

Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

2020 ◽  
pp. 004051752094774
Author(s):  
Yunji Gao ◽  
Hui Zhu ◽  
Yuchun Zhang ◽  
Guoqing Zhu ◽  
Guoqiang Chai
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Flame Spread ◽  
Ignition Time ◽  
Flame Length ◽  
Standoff Distance ◽  
Spread Rate ◽  
Area Density ◽  
Upward Flame Spread ◽  
Flame Spread Rate

Few investigations have systematically addressed the porosity effects of upward flame spread over fabric fuels, although the porosity is a special property for fabric fuels. The present paper studies the porosity and area density effects on upward flame spreading using 160.0 cm tall and 8.0 cm wide flax fabric samples with various porosities and area densities. The flame shape, flame length, flame spread rate, ignition time, standoff distance and surface temperature distribution are obtained and analyzed. The major findings are summarized as follows: as the porosity increases and corresponding area density declines, the flame spread rate and flame length increase, whereas the ignition time decreases, which is because the oxygen can reach the fuel surface in the pyrolysis region more easily and, subsequently, the heat flux received by the virgin fuels increases. The two parameters of flame standoff distance and surface temperature in the preheating region can be applied to characterize the heat flux received by the virgin fuels. Generally, when the porosity increases and the corresponding area density decreases, the flame standoff distance and the surface temperature at the same distance from pyrolysis front increase, which reveals that the heat flux received by the virgin surface increases.

Experimental investigations on two-sided upward flame spreading over thin flax fabric under the influence of restricted distance

2021 ◽  
pp. 004051752110510
Author(s):  
Yunji Gao ◽  
Xiaolong Yang ◽  
Yueyang Luo ◽  
Zhisheng Li ◽  
Liang Gong
Keyword(s):  
Heat Flux ◽  
Flame Spread ◽  
Ignition Time ◽  
Flame Length ◽  
Solid Fuels ◽  
Spread Rate ◽  
Upward Flame Spread ◽  
Opposite Trend ◽  
Distance Effects ◽  
Flame Spread Rate

Up to 2021, most previous work focused on upward flame spread over thin solid fuel completely attached to objects or with both sides freely exposed to the air, but did not take the restricted distance (distance between fuel and objects) effects into account. In this paper, the restricted distance effects on upward flame spread over thin solid fuels were investigated using 0.65 mm thick, 120 cm tall and 6.0 cm wide flax fabric sheets under various restricted distances of 1.0–3.5 cm. The essential parameters were monitored and analyzed simultaneously, including flame length, pyrolysis spread rate, surface temperature and ignition time. The main conclusions drawn are as follows: when the restricted distance is no more than 1.5 cm, the flame length on the unrestricted side is larger than that on the restricted side, whereas the variation exhibits the opposite trend when the restricted distance is beyond 1.5 cm. As the restricted distance increases from 1.0 to 3.5 cm, the flame length and flame spread rate first increase and then decrease, reaching a maximum value at 3.0 cm restricted distance, whereas the ignition time shows the opposite trend. The decrease rate of the surface temperature with the distance from the pyrolysis front first drops and then rises as the restricted distance increases, which qualitatively characterizes that the heat flux received by the virgin surface first increases and then decreases with restricted distance. The non-monotonic trends of heat flux received by the virgin surface and consequently the flame spread rate as a function of restricted distance are due to the combined restricted distance effects of the chimney effect, wall radiation and restricting oxygen supply. The results of this paper are not only helpful in better understanding the upward flame spread over a thin flax fabric under restricted distance, but also provide some basic data for fire prevention of thin solid fuels.

Experimental study of welding region effects on upward flame spread over textile membranes

2018 ◽  
Vol 89 (10) ◽  
pp. 2041-2053 ◽  
Author(s):  
Yunji Gao ◽  
Guoqing Zhu ◽  
Mengwei Yu ◽  
Feng Guo ◽  
Yu Xia ◽  
...  
Keyword(s):  
Flame Spread ◽  
Ignition Time ◽  
Flame Temperature ◽  
Air Entrainment ◽  
Flame Length ◽  
Flame Height ◽  
Spread Rate ◽  
Pyrolysis Gas ◽  
Upward Flame Spread ◽  
Pyrolysis Spread Rate

Textile membranes are used widely as a main architectural material in membrane structure buildings. However, very few studies have been conducted to investigate the flame spread characteristics of textile membranes, especially in the case of upward flame spread. In this paper, the effects of welding region on upward flame spread were investigated experimentally using sample sheets of textile membranes 60 cm tall and 6 cm wide with and without welding region. The corresponding observations are as follows: the width of flame with welding region is narrower than that without welding region; flame height, pyrolysis height, preheating length, flame length, and pyrolysis spread rate decrease significantly in the presence of a welding region, while ignition time increases; flame temperature decreases in the presence of a welding region, and temperature along the welding region is higher than that near the edge. The welding region effects are as follows: in presence of a welding region, the thickness of welding region increases and, accordingly, ignition time shows an increase, leading to relatively low pyrolysis gas generated per unit time and relatively less heat released; in addition, a relatively larger pyrolysis gas concentration gradient over the width for welding membranes results in a relatively stronger air entrainment occurring at the sample sides, taking away part of the heat flux and narrowing the flame width. Thus, the presence of a welding region has negative effects of increasing ignition time and reducing preheating length on upward flame spread over textile membranes, eventually decreasing the pyrolysis spread rate.

Biodegradation rates of aromatic contaminants in biofilm reactors

1995 ◽  
Vol 31 (1) ◽  
pp. 117-128 ◽  
Author(s):  
Jean-Pierre Arcangeli ◽  
Erik Arvin
Keyword(s):  
Aromatic Hydrocarbons ◽  
Competitive Inhibition ◽  
Removal Rate ◽  
First Order ◽  
Biofilm Reactors ◽  
First Order Kinetics ◽  
Reducing Conditions ◽  
Low Concentrations ◽  
Degradation Rates ◽  
Order Surface

This study has shown that microorganisms can adapt to degrade mixtures of aromatic pollutants at relatively high rates in the μg/l concentration range. The biodegradation rates of the following compounds were investigated in biofilm systems: aromatic hydrocarbons, phenol, methylphenols, chlorophenols, nitrophenol, chlorobenzenes and aromatic nitrogen-, sulphur- or oxygen-containing heterocyclic compounds (NSO-compounds). Furthermore, a comparison with degradation rates observed for easily degradable organics is also presented. At concentrations below 20-100 μg/l the degradation of the aromatic compounds was typically controlled by first order kinetics. The first-order surface removal rate constants were surprisingly similar, ranging from 2 to 4 m/d. It appears that NSO-compounds inhibit the degradation of aromatic hydrocarbons, even at very low concentrations of NSO-compounds. Under nitrate-reducing conditions, toluene was easily biodegraded. The xylenes and ethylbenzene were degraded cometabolically if toluene was used as a primary carbon source; their removal was influenced by competitive inhibition with toluene. These interaction phenomena are discussed in this paper and a kinetic model taking into account cometabolism and competitive inhibition is proposed.

Sign in / Sign up

Export Citation Format

Share Document