Reactive shock and detonation propagation in U-bend tubes

The objective of the research outlined in this paper was to provide new experimental and computational data on initiation, propagation, and stability of gaseous stoichiometric propane–air detonations in tubes with U-bends. Extensive experimental and computational studies with the tube 51 mm in diameter with U-bends of two curvatures and two different shock-wave generators were performed. Numerical simulations of the process were used to reveal the salient features of the accompanying phenomena.     

三氯杀螨醇生产过程中的DDT环境排放研究

三氯杀螨醇生产工艺流程主要包括缩合、碱解、氯化和水解等步骤。对工作场所中空气样品、生产过程排放的废酸及废水样品进行采集和分析。工作场所空气中DDT总质量浓度均值为6.69×10-3mg/m3。其中,碱解反应工序中质量浓度水平较低,为1.10×10-3mg/m3;包装车间质量浓度水平较高,为16.72×10-3mg/m3。所有空气样品中p,p’-DDE均是主要贡献物质,占DDT杂质总量的80.2%;p,p’-DDT的质量浓度范围为0.053×10-3~1.66×10-3mg/m3,平均为0.49×10-3mg/m3,低于国家标准限值。缩合废酸与水解废酸中DDT杂质总质量比分别为4.84μg/kg和334.83μg/kg;碱解废水与水解废水中的DDT杂质总质量比分别为456.48μg/kg和75.65μg/kg。废水及废酸样品中各种DDT杂质的质量比水平存在差异;生产工艺阶段不同,杂质组成也各具特点。水解废酸的p,p’-DDT的质量比最高,为146.82μg/kg;缩合废酸与水解废水处质量比水平较低,分别为0.33μg/kg和1.41μg/kg。该企业随废水及废酸排放的DDT杂质总量为1234.08 g/a,其中随碱解废水的排放量高达912.95 g/a。p,p’-DDT的年排放总量为163.37 g/a,随碱解废水和水解废酸的排放量分别为86.98 g/a和73.41 g/a。     

Effect of ignition position on the run-up distance to DDT for hydrogen-air explosions

The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.     

Flame acceleration and transition to detonation in an array of square obstacles

We study flame acceleration and DDT in a two-dimensional staggered array of square obstacles by solving the compressible multidimensional reactive Navier–Stokes equations. The energy release rate for a stoichiometric H₂-air mixture is modeled by a one-step Arrhenius kinetics. The space between obstacles is filled with a stoichiometric H₂-air mixture at 1 atm and 298 K. Initially, the flow is at rest, and a flame is ignited at the center of the array. Computations show effects of the obstacles as a series of events leading to DDT. During the initial flame acceleration, the speed of the flame depends on the direction of flame propagation since some directions are more obstructed than others. This affects the macroscopic shape of the expanding burned region, which forms concave boundaries in more obstructed directions. As the flame accelerates, shocks form ahead of the flame, reflect from obstacles, and interact with the flame. There are more shock–flame interactions in more obstructed directions, and this leads to a greater flame acceleration and stronger leading shocks. When the shocks become strong enough, their collisions with obstacles ignite the gas mixture, and detonations form. The simulation shows four independent DDT events within a 90-degree sector, all in more obstructed directions. Resulting detonations spread in all directions. Some parts of detonation fronts are quenched by diffractions around obstacles, but they are reignited by collisions of decoupled shocks, or overtaken by other detonations. Thus detonations continue to spread and quickly burn all the material between the obstacles.     

The acceleration of flames in tube explosions with two obstacles as a function of the obstacle separation distance

The separation distance (or pitch) between two successive obstacles or rows of obstacles is an important parameter in the acceleration of flame propagation and increase in explosion severity. Whilst this is generally recognised, it has received little specific attention by investigators. In this work a vented cylindrical vessel 162 mm in diameter 4.5 m long was used to study the effect of separation distance of two low blockage (30%) obstacles. The set up was demonstrated to produce overpressure through the fast flame speeds generated (i.e. in a similar mechanism to vapour cloud explosions). A worst case separation distance was found to be 1.75 m which produced close to 3 bar overpressure and a flame speed of about 500 m/s. These values were of the order of twice the overpressure and flame speed with a double obstacle separated 2.75 m (83 characteristic obstacle length scales) apart. The profile of effects with separation distance was shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced further downstream than the position of maximum turbulence determined in the cold flow studies. It is suggested that this may be due to the convection of the turbulence profile by the propagating flame. The present results would suggest that in many previous studies of repeated obstacles the separation distance investigated might not have included the worst case set up, and therefore existing explosion protection guidelines may not be derived from worst case scenarios.     

燃烧管中烟煤粉粉尘云传播参数的试验研究

利用自行设计的长29.6 m,内径199 mm,配有特殊扬尘装置的大犁卧式燃烧爆炸管道试验系统,对弱点火条件下烟煤粉与空气两相悬浮流中的爆炸过程进行了试验研究,用压电传感器测量了管内各测点的压力信号,观测到快速爆燃的状态稳定,分析了爆燃波稳定传播机理.结果表明:在煤粉浓度为300g/m~3及弱点火条件下,悬浮烟煤粉粉尘云中爆燃波能够稳定传播,且稳态传播距离持续20 m以上,峰值超压和波速平均值分别约为70 kPa和430m/s.     

Fires, explosions and related incidents at work in Great Britain in 1996/97 and 1997/98

Incidents in Great Britain reported to the Health and Safety Executive during 1996/97 and 1997/98 involving fires, explosions, runaway chemical reactions and unignited releases of flammable materials are reviewed. Statistical comparisons are made against previous years based on the materials involved, and a number of common themes and causes are identified.     

氢氧爆轰电离模型研究

提出了利用氢能的脉冲爆轰波磁流体发电的设想,发电系统可以解决一般磁流体发电中的高温耐热材料问题和排渣问题.对脉冲爆轰磁流体发电中的核心参数——爆轰产物的电导率进行了理论研究.应用稳态爆轰的ZND理论和局部热力学平衡的热电离理论建立了爆轰产物电导率的计算模型,计算了不同初始压力下当量氢氧混合气体的爆轰电导率.模型计算结果与实验数据基本吻合.同时利用该模型预测了爆轰温度与氢气和氧气的混合比对爆轰产物电导率的影响.研究发现,爆轰产物的平衡电导率主要由爆轰温度决定,氢气与氧气的混合比在接近当量比的时候可以取得最大爆轰电导率,混合气体初始压力对爆轰电导率影响不大,当量氢氧混合气体的爆轰电导率在10-3～10-1 S/m范围内.     

Numerical simulation of propane detonation in medium and large scale geometries

A modelling strategy has been developed for consequence analysis of medium and large scale gaseous detonation. The model is based on the solution of Euler equations with one-step chemistry. The Van Leer flux limited method which is a total variation diminishing scheme is used for shock capturing. Preliminary calculations were firstly conducted for small domains with fine grids which resolve the wave, relatively coarse grids which have less than 10 grids across the wave and coarse grids in which the minimum grid size is larger than the wave thickness to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure, temperature and velocity in the resolutions used in the different cases. The model was firstly tested against a medium scale detonation test in a shock tube with U-bends. Reasonably good agreement is achieved on detonation pressure and mean shock wave velocities at different measuring segments of the tube. Following the validation, the detonation of a hypothetical planar propane-air cloud is simulated. The predictions uncovered some interesting features of such large scale detonation phenomena which are of significance in the safety context, especially for accidental investigations. The findings from the present analysis are in line with the forensic evidence on damages in some historic accidents and challenges previous analysis of a major accident in which forensic evidence suggested localised detonation but was considered as the consequence of fire storms by the investigation team.     

对一起热水锅炉爆管事故的分析

通过对一起锅炉爆管事故的现场检查 ,详细地分析了爆管的原因 ,并提出了处理意见     

约束空间可燃气体燃烧爆轰特性的数值研究

在可燃气体的输送、贮存、加工和使用过程中,容易发生可燃气体的燃烧和爆炸事故。文中基于有限体积方法,采用五阶WENO格式进行左右状态量的重构后,利用ROE格式进行空间离散,自行开发程序对甲烷氧气的气相爆轰波传播过程进行了数值研究。计算结果表明:在CH4质量分数为10%的混合气体中,高温高压气团可诱导气相发生爆轰,爆轰波以2133.3 m/s的速度传播。在带有障碍物的约束空间内,文中分析了障碍物不同高度、不同间距条件下爆轰波传播时波的绕射、马赫反射等现象,给出障碍物表面压力随时间变化历程和冲量值,揭示波与障碍物的相互作用机理以及由此引发流场的变化规律,为有效地控制可燃气体的燃烧速率、防治爆炸灾害的发生提供理论依据。     

Flame propagation in hybrid mixture of coal dust and methane

To investigate the flame propagation through hybrid mixture of coal dust and methane in a combustion chamber, a high-speed video camera with a microscopic lens and a Schlieren optical system were used to record the flame propagation process and to obtain the direct light emission photographs. Flame temperature was detected by a fine thermocouple. The suspended coal dust in the mixture of methane and air was ignited by an electric spark. The flame propagation speeds and maximum flame temperatures of the mixture were analyzed. The results show that the co-presence of coal dust and methane improves the flame propagation speed and maximum flame temperature notably, which become much higher than that of the single-coal dust flame. The flame front temperature varies with the coal dust concentration.     

瓦斯爆炸过程中火焰传播的实验与数值模拟研究

为了研究矿井瓦斯爆炸火焰发展过程中结构与参数的动态变化特征,建立小尺寸管道气体爆炸实验平台,结合高速纹影摄影技术,探测了不同浓度的甲烷-空气预混气体火焰在管道内传播的结构变化特性,并得出速度变化特征曲线。同时建立相应的数学模型和物理模型,通过模拟实验研究管道内气体爆炸反应过程中火焰传播速度变化过程,计算图像和实验图像走向趋向一致。     

Uncertainty representation and propagation in quantified risk assessment using fuzzy sets

It is generally acknowledged that there are substantial uncertainties present in any analysis of risk. This paper provides a brief overview of the current techniques used for uncertainty analyses, and highlights their inappropriateness for practical use in the complete risk assessment process. The concept of fuzzy sets as a means for quantifying uncertainty is introduced and a case study demonstrates the application of this method to a simple consequence analysis where parameter uncertainty is considered. The results of this fuzzy analysis are compared with those of a more traditional probabilistic approach using a Monte Carlo simulation. This comparison demonstrates that the novel approach of fuzzy sets is a more appropriate technique due to its non-statistical nature and that the amount of computation required is substantially reduced compared to the traditional probabilistic approach. The versatility of fuzzy set theory suggests that this approach could also be used to quantify other types of uncertainty present in the risk assessment process, including model uncertainty and expert opinion.     

基于两相流模型数值研究可燃颗粒燃烧爆轰的特性

粉尘爆炸是工业爆炸灾害的重要形式。建立可燃颗粒非均相系统的燃烧爆轰模型,基于Eulerian-Eulerian数值描述方法,采取有限差分方法编制非均相系统燃烧和爆轰发展的数值模拟程序,对封闭空间内两相非定常爆轰过程进行研究。数值分析可燃颗粒尺度、颗粒浓度对非均相系统燃烧、爆轰特性的影响。结果表明:在一定的范围内,当可燃颗粒的体积分数为10%,粒径0.5mm时,流场的燃烧爆轰效应最强。即10.6ms时刻,流场压力值达到28MPa,温度高达2600K,颗粒燃烧效率最高。     

General and public opinion about the general speed limits in Finland in 1973–1974

This article analyzes the general opinion (of the population) and the public opinion (of the press) about the general speed limits in Finland during the speed limit experiment of 1973–1976, as well as background and changes of opinions. The results showed: (1) The public opinion on speed limits has been more negative than the general opinion. (2) Negative attitudes toward speed limits are connected to at least three side issues — right-wing ideology, motoring as sport, and speed limits as a threat to one's own traffic behavior. (3) The significant decrease in traffic accidents during the speed limit experiment acted as a pressure of facts that rapidly increased the number of supporters of speed limits. (4) Comparison with other studies showed no great differences in support of speed limits among the countries of Europe. In West Germany, however, the public opinion about speed limits was more negative than in Finland.     

Experimental and LES investigation of premixed methane/air flame propagating in a chamber for three obstacle BR configurations

The paper aims at revealing the effect of blockage ratio (BR) on the flame acceleration process and the flame-vortex mechanism in an obstructed chamber based essentially on the experimental and numerical methods. In the experiments, high-speed video photography and pressure transducer are used to study the flame shape changes and pressure dynamics. In the numerical simulations, large eddy simulation (LES) with the flame surface density (FSD) model is applied to investigate the interaction between the moving flame and vortices induced by obstacle. The results demonstrate that the flame propagation process can be divided into four stages, namely spherical flame, finger-shaped flame, jet flame and volute flame for three obstacle BR configurations, and a small recirculation zone is observed above the obstacle only for BR = 0.5. The peak of flame tip speed and pressure growth rate increases with the blockage ratio. The generation and evolution of the vortex behind the obstacle can be attributed to the initial flame acceleration, while the subsequent flame deceleration is due to the flame-vortex interaction. In addition, the transition from a “thin reaction zones” to a “broken reaction zones” is also observed in the simulation.     

Reaction zone structures and propagation mechanisms of flames in stearic acid particle clouds

Reaction zone structures and propagation mechanisms of two representative flames established in stearic acid (CH₃(CH₂)₁₆CO₂H) particle clouds have been investigated. The reacting zone structure was examined by using a micro-electrostatic probe and a high-speed schlieren system. A distinct difference was observed in the ion current fluctuations recorded across the two representative flames propagating through the clouds of the same total mass density of particles and different mass densities of the particles smaller than 60 μm in diameter. When the mass density of smaller particles was high, a single peak was recorded in the ion current fluctuation. On the other hand, when the mass density of smaller particles was low, multi-peaks of various heights and widths were recorded. In the former case, the single peak was considered to be attributable to a unitary and a relatively thin flame started burning in vapor generated by the evaporation of smaller particles in the preheat zone. The flame propagation mechanism in this case was inferred to be similar to that of a usual hydrocarbon–air premixed flame, although the reaction zone thickness is much larger than that of the premixed flame. In the latter case, the multi peaks of various shapes were considered to be attributable to strong combustion at blue spots far behind the schlieren front. The flame propagation in this case was inferred to be supported by the heat release due to combustion at the blue spots.     

广州市SARS传播与空气污染相关性研究

探讨SARS传播与空气污染的关系.根据广州市及周边城市自SARS发病以来主要空气污染物的监测统计结果,结合广州市SARS发病例数和气象观测资料等进行相关性研究,并与香港进行对比.结果表明,广州市SARS发病数与发病前5 d的可吸入颗粒物污染浓度密切相关,香港SARS发病数与发病前1～2 d的可吸入颗粒物污染浓度密切相关.研究表明,SARS发病数与发病前空气污染状况有密切关系.     

乙炔-空气预混火焰在狭窄通道中的传播与熄灭

针对预混火焰在狭窄通道中传播过程的研究是进行阻隔防爆技术研发的基础。本文首先通过数值计算模拟了预混乙炔一空气爆燃火焰在狭窄通道中的传播与熄灭过程,然后采用高速数字摄像技术对火焰的传播过程进行捕捉,分析临界火焰传播速度、狭缝高度和熄灭长度之间的关系。研究结果均表明,当狭缝高度一定时,临界火焰传播速度越大,熄灭长度越大,熄灭长度与临界火焰传播速度近似呈正比例关系。在相同的临界火焰传播速度条件下,随着狭缝高度的增加,熄灭长度值迅速增大,说明狭缝高度对预混火焰的传播与熄灭有显著影响。本文研究成果将可为工业阻火防爆装置的设计和实际应用提供参考依据。