Fire Safety Journal最新文献_第4页

Modeling study on the pyrolysis kinetics of wood composite in the thermally thin regime: The role of heating rates and thermal gradients

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-12 DOI: 10.1016/j.firesaf.2024.104326

Xiaowen Qin , Franck Richard , Benjamin Batiot , Thomas Rogaume

Pyrolysis of wood composites is a complex process involving reactions with its primary condensed components: cellulose, hemicellulose, and lignin. Thermogravimetric Analysis, within the thermally thin regime, is extensively employed to deduce the kinetics of wood pyrolysis. However, the correlation between heating rates and the pyrolysis kinetics of each component remains unclear, raising concerns about the applicability of these rates in estimating kinetics under varying heating conditions. This paper focuses on examining the influence of heating rate and thermal gradients on the pyrolysis kinetics of wood composite components through a modeling study. The impact on kinetic parameters is analyzed using various chemical mechanisms. These parameters are determined using a model fitting method, which extracts a unique set of kinetics for each heating condition. The study reveals that the heating process interacts significantly with the overall pyrolysis process, and each thermal decomposition reaction of the condensed components is differently influenced by this process. The pyrolysis reaction rate and final mass fraction of the different components vary under distinct heating rates. Notably, higher heating rates tend to shift reactions to higher temperatures, and the interaction between thermal processes and pyrolysis reactions intensifies at increased global heating rates. This paper offers significant insights and considerations for simulating the thermal decomposition of wood on a larger scale.

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引用次数: 0

AFFF foam fire extinguishing by gas-permeated spreading and flame barrier with different foaming gases

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-11 DOI: 10.1016/j.firesaf.2024.104330

Haolan Tan , Yan Zhang , Lei Jiang , Jiaqing Zhang , Fengju Shang , Kaiyuan Li , Yunpeng Yang

Currently, there is a lack of delicate research on flame suppression by foam spreading on the fuel surface. In this study, we propose a new method of varying the foaming gases to control the foam spreading rate on oil surfaces. The kinetic process of foam extinguishing with various gas-liquid ratios is investigated. In addition, the synergistic effect of gas-permeated spreading and flame barrier on the extinguishing efficiency was examined. The results indicate a positive correlation between the extinguishing efficiency and the flame-free spreading rate of CO₂ > He > Ar > N₂ > Air. The extinguishing efficiency decreases with increasing gas-liquid ratio, while the 6:1 ratio leads to a 59% increase in extinguishing time compared to 4:1, and a 90 % increase compared to 1:1. The consumption of foam by the flame enhances as the flame-free spreading rate decreases. The flame consumes over 80% flame-free spreading rates of Air and N₂ foams, leading to fast foam front consumptions by the flame and poor extinguishing performances. Gas permeation in the foam film exacerbates the bubble coalescence and foam drainage, enhancing the foam spreading performance while reducing the foam stability. The foam spreading induced by gas permeation plays a decisive role in spreading rates and extinguishing efficiency, whereas the effect of foam stability on extinguishing efficiency is less influential. Increasing the gas permeability and reducing the gas-liquid ratio enhance the overall foam mobility. Hence, the spreading rate and extinguishing efficiency increase with gas permeability. An empirical model expresses the relationship between extinguishing time and flame-free spreading rate, underscoring the decisive role of foam spreading in the fire extinguishing process.

{"title":"AFFF foam fire extinguishing by gas-permeated spreading and flame barrier with different foaming gases","authors":"Haolan Tan , Yan Zhang , Lei Jiang , Jiaqing Zhang , Fengju Shang , Kaiyuan Li , Yunpeng Yang","doi":"10.1016/j.firesaf.2024.104330","DOIUrl":"10.1016/j.firesaf.2024.104330","url":null,"abstract":"<div><div>Currently, there is a lack of delicate research on flame suppression by foam spreading on the fuel surface. In this study, we propose a new method of varying the foaming gases to control the foam spreading rate on oil surfaces. The kinetic process of foam extinguishing with various gas-liquid ratios is investigated. In addition, the synergistic effect of gas-permeated spreading and flame barrier on the extinguishing efficiency was examined. The results indicate a positive correlation between the extinguishing efficiency and the flame-free spreading rate of CO<sub>2</sub> > He > Ar > N<sub>2</sub> > Air. The extinguishing efficiency decreases with increasing gas-liquid ratio, while the 6:1 ratio leads to a 59% increase in extinguishing time compared to 4:1, and a 90 % increase compared to 1:1. The consumption of foam by the flame enhances as the flame-free spreading rate decreases. The flame consumes over 80% flame-free spreading rates of Air and N<sub>2</sub> foams, leading to fast foam front consumptions by the flame and poor extinguishing performances. Gas permeation in the foam film exacerbates the bubble coalescence and foam drainage, enhancing the foam spreading performance while reducing the foam stability. The foam spreading induced by gas permeation plays a decisive role in spreading rates and extinguishing efficiency, whereas the effect of foam stability on extinguishing efficiency is less influential. Increasing the gas permeability and reducing the gas-liquid ratio enhance the overall foam mobility. Hence, the spreading rate and extinguishing efficiency increase with gas permeability. An empirical model expresses the relationship between extinguishing time and flame-free spreading rate, underscoring the decisive role of foam spreading in the fire extinguishing process.</div></div>","PeriodicalId":50445,"journal":{"name":"Fire Safety Journal","volume":"152 ","pages":"Article 104330"},"PeriodicalIF":3.4,"publicationDate":"2024-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143143065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evaluating backdraft phenomenon generated from a wood fuel through a holistic approach

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-09 DOI: 10.1016/j.firesaf.2024.104324

Ryan Falkenstein-Smith, Thomas Cleary

This work examines backdraft phenomenon generated from a wood fuel assembled into a crib structure. Twenty-six backdraft experiments were conducted in a reduced-scale enclosure to determine components that influence the ignition and deflagration required for backdraft phenomenon. A wide range of heat release rates before the enclosure’s isolation time was implemented in the experimental campaign, spanning from 88 kW

\pm

8 kW to 216 kW

\pm

19 kW. The duration of the isolation time, at which the compartment remains closed before an anticipated backdraft event, was also modified between 120 s, 210 s, and 300 s to determine their effect on critical parameters. To account for the complexity of the produced pyrolyzate, a second-generation phi meter was utilized to measure equivalence ratios in the upper and lower regions of the compartment. Temperature and oxygen, carbon dioxide, and carbon monoxide concentration measurements were also obtained at various locations within the reduced-scale enclosure. Time-averaged temperature and oxygen concentration measurements were compared to similar measurements in other works, highlighting limitations in identifying universal conditions conducive to backdraft. Time-averaged equivalence ratio measurements greater than 5 in the upper region of the enclosure were found to signify the occurrence of backdraft, suggesting that its likelihood is associated with the distribution of vapor fuel and oxygen. A logistic regression model was implemented to examine how parameter differences in the compartment’s upper and lower regions contribute to backdraft occurrence. A probability threshold for the backdraft phenomenon between the temperature and vapor fuel ratios in the upper and lower regions of the compartment is established. Spatial ratios of temperature and vapor fuel fraction are compared against each other using the logistic regression model to comment on the incoming flow of the gravity current and residing fuel concentration within the compartment prior to an anticipated backdraft event. A further evaluation of the probability threshold using the backdraft ignition time suggests that the distribution of temperature and fuel affects the gravity current velocity, mixing time, and eventual combustion of incoming air.

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引用次数: 0

Progressive collapse behavior of geometrically similar RC frames at ambient and elevated temperatures

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-05 DOI: 10.1016/j.firesaf.2024.104325

Dongqiu Lan , Liu Jin , Yaowen Yang , Kai Qian , Renbo Zhang , Jian Li

Due to limitations in laboratory capacity, investigations of the resistance of reinforced concrete (RC) frames against progressive collapse often rely on scaled specimens. However, the ability of scaled specimens to accurately reflect the collapse-resistant behavior of real structures is uncertain. Particularly in fire scenarios, the fire resistance of specimens of varying scales fails to maintain a similar relationship in terms of fire resistance. To shed light on this issue, a series of scaled models of RC beam-column assemblies were established to investigate the similarity relationship in progressive collapse resistance of RC frames under both ambient temperature and fire conditions. Numerical findings indicate that the failure of RC frames experiencing minor fire-induced damage is governed by rebar fracture at the beam ends near the side columns, whereas RC frames suffering significant fire-induced damage fail because of rebar fracture at the top rebar cut-off point. Increased fire duration results in a notable reduction in load capacity due to changes in failure modes. While the structural behaviors of scaled RC frames under ambient temperature comply with theoretical geometric similarity criteria, this is not the case under fire conditions. Therefore, a time scale was proposed to build the similarity relationship for fire-exposed RC frames.

{"title":"Progressive collapse behavior of geometrically similar RC frames at ambient and elevated temperatures","authors":"Dongqiu Lan , Liu Jin , Yaowen Yang , Kai Qian , Renbo Zhang , Jian Li","doi":"10.1016/j.firesaf.2024.104325","DOIUrl":"10.1016/j.firesaf.2024.104325","url":null,"abstract":"<div><div>Due to limitations in laboratory capacity, investigations of the resistance of reinforced concrete (RC) frames against progressive collapse often rely on scaled specimens. However, the ability of scaled specimens to accurately reflect the collapse-resistant behavior of real structures is uncertain. Particularly in fire scenarios, the fire resistance of specimens of varying scales fails to maintain a similar relationship in terms of fire resistance. To shed light on this issue, a series of scaled models of RC beam-column assemblies were established to investigate the similarity relationship in progressive collapse resistance of RC frames under both ambient temperature and fire conditions. Numerical findings indicate that the failure of RC frames experiencing minor fire-induced damage is governed by rebar fracture at the beam ends near the side columns, whereas RC frames suffering significant fire-induced damage fail because of rebar fracture at the top rebar cut-off point. Increased fire duration results in a notable reduction in load capacity due to changes in failure modes. While the structural behaviors of scaled RC frames under ambient temperature comply with theoretical geometric similarity criteria, this is not the case under fire conditions. Therefore, a time scale was proposed to build the similarity relationship for fire-exposed RC frames.</div></div>","PeriodicalId":50445,"journal":{"name":"Fire Safety Journal","volume":"152 ","pages":"Article 104325"},"PeriodicalIF":3.4,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143143024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Smoke movement and stratification of tunnel fires under coupled effects of rainfall and ventilation

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-04 DOI: 10.1016/j.firesaf.2024.104323

Dia Luan , Tianyang Chu , Jakub Bielawski , Chuangang Fan , Wojciech Węgrzyński , Xinyan Huang

This study investigates the smoke movement and stratification characteristics of tunnel fires under coupled effects of rainfall and ventilation through a series of reduced-scale tests. Results show that the smoke movement is affected by both ventilation and rainfall-induced airflow. The smoke tends to move downstream of the dominant airflow. As the increase in ventilation velocity, the height of the downstream smoke layer decreases. Conversely, as the rainfall intensity increases, the height of the upstream smoke layer decreases. Forced shear airflow consistently disrupts the smoke stratification downstream of the flow, whether induced by ventilation or rainfall. Although strong ventilation is capable of controlling smoke downstream, it may destroy the downstream smoke stratification. Compared to critical velocity, the confinement velocity is more suitable for tunnel smoke control as it maintains the stability of downstream smoke and thus can be applied in the early stage of fires. The confinement velocity is found to be 0.73 times the critical velocity. A model of the confinement velocity under the effect of rainfall is established. Findings are helpful in emergency rescue and evacuation of tunnel fires under rainfall conditions.

{"title":"Smoke movement and stratification of tunnel fires under coupled effects of rainfall and ventilation","authors":"Dia Luan , Tianyang Chu , Jakub Bielawski , Chuangang Fan , Wojciech Węgrzyński , Xinyan Huang","doi":"10.1016/j.firesaf.2024.104323","DOIUrl":"10.1016/j.firesaf.2024.104323","url":null,"abstract":"<div><div>This study investigates the smoke movement and stratification characteristics of tunnel fires under coupled effects of rainfall and ventilation through a series of reduced-scale tests. Results show that the smoke movement is affected by both ventilation and rainfall-induced airflow. The smoke tends to move downstream of the dominant airflow. As the increase in ventilation velocity, the height of the downstream smoke layer decreases. Conversely, as the rainfall intensity increases, the height of the upstream smoke layer decreases. Forced shear airflow consistently disrupts the smoke stratification downstream of the flow, whether induced by ventilation or rainfall. Although strong ventilation is capable of controlling smoke downstream, it may destroy the downstream smoke stratification. Compared to critical velocity, the confinement velocity is more suitable for tunnel smoke control as it maintains the stability of downstream smoke and thus can be applied in the early stage of fires. The confinement velocity is found to be 0.73 times the critical velocity. A model of the confinement velocity under the effect of rainfall is established. Findings are helpful in emergency rescue and evacuation of tunnel fires under rainfall conditions.</div></div>","PeriodicalId":50445,"journal":{"name":"Fire Safety Journal","volume":"152 ","pages":"Article 104323"},"PeriodicalIF":3.4,"publicationDate":"2024-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143142495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The impact of initial fuel depth on the combustion efficiency of pool fire in an enclosed compartment: A study based on zone model theory

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-12-02 DOI: 10.1016/j.firesaf.2024.104316

Jinbo Wang, Xiao Chen, Yi Zhang, Jun Zhou, Qilin Chen, Shouxiang Lu

In this paper, the effect of initial fuel depth on the combustion efficiency of pool fires in an enclosed compartment was experimentally studied. Three different sizes of pool fires were conducted in the experiments. Several combustion parameters including burning rate, smoke temperature distribution, and oxygen concentration of pool fires under the different initial fuel depths in closed compartments were obtained. Results showed that the pool fire with the different initial fuel depths would appear in two typical extinction modes: fuel burning out and self-extinction due to lack of oxygen. The whole burning process of the pool fire in the enclosed compartment can be divided into the following five stages: rapid rise stage, transition stage, stable combustion stage, boiling combustion stage, and extinguishing decay stage. The maximum and average values of the burning rate presented the power function of the initial fuel depth. The consumption of oxygen concentration in the compartment was mainly affected by the initial fuel depth, the pool size, and the compartment volume. Dimensionless characterization of the oxygen concentration was adopted to characterize the fire extinction behavior in the enclosed compartment. In addition, on the basis of the combustion process and the extinction behavior, a global combustion efficiency of pool fire was proposed to predict the combustion characteristic while considering the initial fuel depth in the enclosed compartment.

{"title":"The impact of initial fuel depth on the combustion efficiency of pool fire in an enclosed compartment: A study based on zone model theory","authors":"Jinbo Wang, Xiao Chen, Yi Zhang, Jun Zhou, Qilin Chen, Shouxiang Lu","doi":"10.1016/j.firesaf.2024.104316","DOIUrl":"10.1016/j.firesaf.2024.104316","url":null,"abstract":"<div><div>In this paper, the effect of initial fuel depth on the combustion efficiency of pool fires in an enclosed compartment was experimentally studied. Three different sizes of pool fires were conducted in the experiments. Several combustion parameters including burning rate, smoke temperature distribution, and oxygen concentration of pool fires under the different initial fuel depths in closed compartments were obtained. Results showed that the pool fire with the different initial fuel depths would appear in two typical extinction modes: fuel burning out and self-extinction due to lack of oxygen. The whole burning process of the pool fire in the enclosed compartment can be divided into the following five stages: rapid rise stage, transition stage, stable combustion stage, boiling combustion stage, and extinguishing decay stage. The maximum and average values of the burning rate presented the power function of the initial fuel depth. The consumption of oxygen concentration in the compartment was mainly affected by the initial fuel depth, the pool size, and the compartment volume. Dimensionless characterization of the oxygen concentration was adopted to characterize the fire extinction behavior in the enclosed compartment. In addition, on the basis of the combustion process and the extinction behavior, a global combustion efficiency of pool fire was proposed to predict the combustion characteristic while considering the initial fuel depth in the enclosed compartment.</div></div>","PeriodicalId":50445,"journal":{"name":"Fire Safety Journal","volume":"152 ","pages":"Article 104316"},"PeriodicalIF":3.4,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143142497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Accelerated piloted ignition on an edge of a PMMA cube 在PMMA立方体的边缘加速引燃

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-11-28 DOI: 10.1016/j.firesaf.2024.104296

Junhui Gong , Xiaolu Sun , Michael A. Delichatsios

Ignition on solid edges is easier compared to that on flat surfaces, featuring higher fire hazard. To reveal this unique ignition mechanism, an apparatus capable of emitting two horizontal perpendicular heat fluxes, defined as q₁ and q₂, was built to conduct piloted ignition tests on vertical edges of PMMA cubes. Two sets of tests were designed: (1) q₁ = q₂, denoted as SET1; (2) q₁ remained unchanged while q₂ varied, denoted as SET2. For comparison, 1D ignition tests of vertical samples were also performed. Edge and surface temperatures, mass loss rate (MLR), and ignition time (t_ig) were collected. Results showed that ignition on edge was accelerated compared to 1D ignition. The numerical solver neglecting edge regression captured measured surface temperature but overpredicted edge temperature. Attributed by the same reason, experimental MLRs and t_ig of SET1 and SET2 cannot be accurately estimated by the numerical model. Critical MLR in SET1 and SET2 declined with lower heat flux but remained unchanged in 1D ignition. Critical temperature was identified to be 656.4 ± 3.5 K. In SET1, t_ig^-0.5 linearly depended on heat flux, whereas no such linearity existed in SET2. Using measured t_ig and analytical models, thermal inertia of PMMA and critical heat flux were estimated.

在固体边缘上点火比在平面上更容易，具有更高的火灾危险。为了揭示这种独特的点火机制，建立了一个能够发射两个水平垂直热流的装置，定义为q1和q2，在PMMA立方体的垂直边缘进行引燃试验。设计两组检验：(1)q1 = q2，记为SET1；(2) q1不变，q2变化，记为SET2。为了比较，还进行了垂直样品的1D点火试验。收集了边缘和表面温度、质量损失率（MLR）和点火时间（tig）。结果表明：与一维点火相比，边缘点火速度加快；数值求解忽略了边缘回归，得到了实测的表面温度，但高估了边缘温度。由于同样的原因，SET1和SET2的实验mlr和tig无法通过数值模型准确估计。SET1和SET2的临界MLR随热流密度的降低而降低，但在1D点火过程中保持不变。临界温度为656.4±3.5 K。SET1中tig-0.5与热通量呈线性关系，而SET2中tig-0.5不存在线性关系。利用实测模型和解析模型，估算了PMMA的热惯量和临界热流密度。

{"title":"Accelerated piloted ignition on an edge of a PMMA cube","authors":"Junhui Gong , Xiaolu Sun , Michael A. Delichatsios","doi":"10.1016/j.firesaf.2024.104296","DOIUrl":"10.1016/j.firesaf.2024.104296","url":null,"abstract":"<div><div>Ignition on solid edges is easier compared to that on flat surfaces, featuring higher fire hazard. To reveal this unique ignition mechanism, an apparatus capable of emitting two horizontal perpendicular heat fluxes, defined as <em>q</em><sub><em>1</em></sub> and <em>q</em><sub><em>2</em></sub>, was built to conduct piloted ignition tests on vertical edges of PMMA cubes. Two sets of tests were designed: (1) <em>q</em><sub><em>1</em></sub> = <em>q</em><sub><em>2</em></sub>, denoted as SET1; (2) <em>q</em><sub><em>1</em></sub> remained unchanged while <em>q</em><sub><em>2</em></sub> varied, denoted as SET2. For comparison, 1D ignition tests of vertical samples were also performed. Edge and surface temperatures, mass loss rate (MLR), and ignition time (<em>t</em><sub><em>ig</em></sub>) were collected. Results showed that ignition on edge was accelerated compared to 1D ignition. The numerical solver neglecting edge regression captured measured surface temperature but overpredicted edge temperature. Attributed by the same reason, experimental MLRs and <em>t</em><sub><em>ig</em></sub> of SET1 and SET2 cannot be accurately estimated by the numerical model. Critical MLR in SET1 and SET2 declined with lower heat flux but remained unchanged in 1D ignition. Critical temperature was identified to be 656.4 ± 3.5 K. In SET1, <em>t</em><em><sub>ig</sub></em><em><sup>-0.5</sup></em> linearly depended on heat flux, whereas no such linearity existed in SET2. Using measured <em>t</em><sub><em>ig</em></sub> and analytical models, thermal inertia of PMMA and critical heat flux were estimated.</div></div>","PeriodicalId":50445,"journal":{"name":"Fire Safety Journal","volume":"151 ","pages":"Article 104296"},"PeriodicalIF":3.4,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142759293","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Corrigendum to “New approach to estimate temperatures in pre-flashover fires: Lumped heat case” [Fire Safe. J. 72 (2015) 77-86]

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-11-26 DOI: 10.1016/j.firesaf.2024.104293

Franz Evegren , Ulf Wickström

引用次数: 0

Dynamic mechanisms of high-pressure hydrogen self-ignition and flame evolution in obstructed tubes: Experimental insights and implications 高压氢气在阻塞管内自燃和火焰演化的动力学机制：实验见解和启示

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-11-25 DOI: 10.1016/j.firesaf.2024.104295

Qiangling Duan , Qian Zeng , Jing Tang, Songlin Zhang, Jinhua Sun

Experimental investigations on high-pressure hydrogen release into obstructed tubes with varying obstacle positions are conducted to explore the dynamic mechanisms of shock propagation, self-ignition and flame evolution. High-speed photography, pressure sensor and light detector are used in the experiments. The results reveal that obstacle position significantly affects self-ignition by the multi-dimensional interactions and the turbulence-promoted mixing. The reflected shock results in an overpressure rise of twice that behind the leading shock. In addition, the intensity of reflected shock decreases when it propagates upstream. The critical burst pressure for self-ignition first decreases and then increases with a further obstacle position away from the burst disk. The lowest burst pressure for self-ignition is 2.08 MPa arising in the tube with obstacles located at 200 mm axially, half that of the smooth tube. In obstructed tubes, three possible self-ignition regions exist, including inclined obstacle walls, tube centerline and tube sidewalls. The patterns of self-ignition are determined by burst pressure and obstacle position. Besides, flame acceleration is observed in the obstructed, which is related to turbulence promoted by the shock-obstacle interaction. The farther obstacles from the burst disk results in more marked effects on flame acceleration.

通过对不同障碍物位置的高压氢气向受阻管内释放的实验研究，探讨了激波传播、自燃和火焰演化的动力学机制。实验采用高速摄影、压力传感器和光探测器。结果表明，障碍物位置通过多维相互作用和湍流促进混合对自燃有显著影响。反射冲击导致的超压上升是前置冲击后的两倍。此外，反射激波向上游传播时，其强度减小。随着障碍物位置的增加，自燃临界爆破压力先减小后增大。在轴向200 mm处有障碍物的管中，自燃爆破压力最低为2.08 MPa，为光滑管的一半。在阻塞管内，存在三个可能的自燃区域，包括倾斜的障碍壁、管中心线和管侧壁。自燃模式由爆破压力和障碍物位置决定。此外，在障碍物中观察到火焰加速，这与激波-障碍物相互作用引起的湍流有关。离爆炸盘越远的障碍物对火焰加速的影响越显著。

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引用次数: 0

Bond shear modulus in reinforced concrete at high temperature: General trends from test results

IF 3.4 3区工程技术 Q2 ENGINEERING, CIVIL

Fire Safety Journal

Pub Date : 2024-11-20 DOI: 10.1016/j.firesaf.2024.104291

Francesco Lo Monte, Pietro G. Gambarova

The scanty attention devoted so far to bond shear modulus (secant or tangent slope of the loading branch of the bond-slip curve) limits the ability to numerically model such phenomena as tension stiffening, that controls the stiffness of cracked RC structures even past a fire. To improve the knowledge of bond shear modulus at high temperature, the bond stress-bar slip curves resulting from the tests of eleven selected experimental campaigns spanning a forty-year period are re-examined in this paper. Bond shear modulus is derived as the initial slope of the bond stress-bar slip curves of stressed or unstressed specimens in either hot or residual conditions. The criteria to compare the test results coming from very different experimental campaigns are discussed at length. Bond shear modulus is shown to be a decreasing function of the residual compressive strength of the concrete (at high temperature or past cooling). The envelopes of the test data allow to assess the roles of bar diameter and concrete grade. Trend curves are derived for normal-strength and high-strength/high-performance concretes, as a first necessary step for the formulation of parametric design-oriented laws, that may be useful to model tension stiffening and to describe the distribution of the bond stresses in long anchored bars. A numerical example is also developed and the consistency with EuroCode EC2 is checked.

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引用次数: 0