不同环境条件下扩散射流火焰形态特征与推举、吹熄行为研究

发布时间：2018-03-04 03:24

本文选题：扩散射流火焰　切入点：高原低氧低压环境　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：扩散射流火焰因易于控制而在工业燃烧设备中应用十分广泛,但是一些不受控制的扩散射流火焰也能给人们带来巨大伤害。近年来,因燃气管道破裂形成的扩散射流火灾事故频繁发生,造成了极大的人员伤亡和财产损失。因此,研究扩散射流火焰燃烧行为特征对工业燃烧设备的设计和安全高效运行以及相关的火灾安全问题都具有重要的意义。前人对常规条件下的扩散射流火焰燃烧行为已开展了大量的研究,且形成了较为成熟的理论。但是,对一些特殊环境条件(例如,高原低氧低压环境,低压与环境风耦合环境以及微重力环境等)下的扩散射流火焰燃烧行为,人们却研究得相对较少。随着经济的发展和科技的进步,人们在这种特殊环境下的生产活动却越来越频繁。因此,十分有必要开展针对性的研究,以揭示扩散射流火焰在这种特殊环境下的燃烧行为特性,完善相关的火灾动力学理论,并为火灾防治技术的开发和改进提供理论和数据支持。本文采用理论分析和实验研究相结合的方法,对不同环境条件下的扩散射流火焰行为特征开展了研究。为此,我们分别设计了：(1)合肥和拉萨自由扩散射流火焰行为特性实验研究装置；(2)合肥和拉萨水平环境风作用下扩散射流火焰行为特性实验研究装置；和(3)微重力和常重力伴流扩散射流火焰行为实验研究装置。通过对典型特征参数(火焰形态、火焰中心线温度、火焰辐射、火焰推举和吹熄行为)的分析,结合火灾和燃烧动力学经典理论,揭示了三种不同特殊环境条件下扩散射流火焰行为演化机制,并建立了相应的无量纲数学表征模型。具体的研究工作包括：研究了高原低氧低压环境和平原常压常氧环境下自由扩散射流火焰高度、火焰中心线温度、火焰辐射和推举行为。通过研究合肥和拉萨两地火焰高度的差别,发现低压下的平均火焰高度要显著高于常压环境下的平均火焰高度。通过分析火羽流基本物理模型,建立了量化两地空气卷吸差别的方法,对经典火焰高度物理模型进行了修正。引入了虚点源理论,考虑其与火焰火源功率、火焰尺寸和大气环境等因素之间的耦合关系,得到了两种气压环境下虚点源无量纲模型。并通过虚点源模型修正了自由扩散射流火焰中心线温度分布三段模型。另外,通过实验还发现了气压越低推举高度越大的现象。通过分析经典火焰推举模型及其中受到压力影响的关键性因素,发现了不同气压下火焰推举产生差异的根本原因,修正了Kalghatgi经典火焰推举模型。研究了合肥和拉萨两种气压条件水平环境风作用下的扩散射流火焰演化过程,发现：1)在常压环境中,随着风速的增加,火焰形态和颜色都会发生显著的变化。火焰迹线长度先随着风速的增加而逐步减小,而后会达到一个最小值,最后将保持相对稳定或者被拉长。而在低压环境中,随着风速的增加,火焰长度则保持单调减小的趋势。另外,通过分析经典的理论模型,得到了两种气压环境下火焰长度的预测模型；2)还研究了高原低压和平原常压水平环境风作用下火焰的吹熄极限,发现两种环境下吹熄临界风速都先随着燃料喷出速度的增加而逐步增加,到达一个最大值之后又随着燃料喷出速度的增加而减小。同时,发现低氧低压环境(64kPa)下的吹熄临界风速显著低于常压环境(100kPa)(约为1/3)。研究了环境风作用下的火焰吹熄机制,建立了基于Damkohler数、耦合压力影响的扩散射流火焰吹熄极限数学表征模型。最后,通过开展落塔微重力环境下的扩散射流火焰行为实验,观察到微重力条件下扩散射流火焰高度更高,火焰更明亮,碳黑生成更多的现象。同时,还研究了受伴流作用的扩散射流火焰吹熄过程,发现微重力下火焰吹熄临界伴流空气速度要显著大于常重力下的结果。
[Abstract]:Jet diffusion flame is easy to control in industrial combustion equipment is widely used, but some uncontrolled jet diffusion flame can also bring great harm to the people. In recent years, due to gas pipeline rupture diffusion jet fire accident formation occurred frequently, caused great casualties and property losses. Therefore, all have the important significance of jet diffusion flame combustion behaviors of industrial combustion equipment design and the safe and efficient operation and related fire safety problems.
The predecessors have carried out a lot of research on jet diffusion flame combustion behavior under conventional conditions, and formed a relatively mature theory. But, for some special environmental conditions (e.g., low altitude hypoxia environment, low pressure and environmental wind coupling environment and microgravity environment etc.) the combustion behavior of jet diffusion flame is studied under the people relatively small. With the development of economy and the progress of science and technology, in the special environment of production activities of people is more and more frequent. Therefore, it is necessary to study the combustion behavior in order to reveal the jet diffusion flame in the special environment, improve the fire dynamics theory, and for the development of fire prevention and control the improvement of technology and provide theoretical and data support.
This paper uses the method of theoretical analysis combined with experimental study, the jet diffusion flame behavior under different environmental conditions to carry out the research. Therefore, we design: (1) Hefei and Lhasa free diffusion behavior experimental study of flame jet device; (2) diffusion device experimental research on flame behavior of jet fan in Hefei and the level of Lhasa environment; and (3) microgravity and normal gravity coflow diffusion flame behavior experimental study of jet device. Through the parameters of the typical features (flame shape, flame temperature and flame radiation center line, and blow out the flame press behavior) analysis, combined with the fire and combustion kinetics of the classical theory, reveals the evolution mechanism of diffusion the jet flame behavior of three kinds of special conditions, and established the dimensionless mathematical characterization of the corresponding model. The research work includes:
Study on low altitude hypoxia environment and plain atmospheric oxygen environment free jet diffusion flame height, flame temperature and flame radiation center line, press behavior. Through the study of Hefei and Lhasa found that the average flame height difference, flame height, average flame height to low pressure higher than atmospheric environment. Through the analysis of fire plume the basic physical model, establishes a quantitative difference between the two air entrainment method, the classical physics flame height model was modified. The virtual point source theory, considering the fire and fire power, the coupling relationship between flame size and atmospheric environment and other factors, we obtain two kinds of pressure under the environment of virtual point source dimensionless model and fixed free jet diffusion flame center line three temperature distribution model through the virtual point source model. In addition, it was also found that the lower the air pressure is more highly recommended Phenomenon. By analyzing the classical flame lift model and the key factors which are affected by pressure, we find the root cause of the difference in the flame lift under different barometric pressure, and modify the classical Kalghatgi flame lift model.
Study on the jet diffusion flame in Hefei and Lhasa two pressure level under the action of wind environment evolution process, it is found that: 1) in the atmospheric environment, with the increase of wind speed, flame shape and color will change significantly. The flame trace length first increases as wind speed decreases gradually, and will reach a minimum the final value will remain relatively stable or elongated. While in low pressure environment, with the increase of wind speed, the flame length is monotonically decreasing. In addition, through the analysis of classical theory model, and obtained two kinds of pressure environment prediction model of flame length; 2) of Plateau and plain low blow out limit the level of atmospheric environment under the action of wind fire, found that two kinds of environment are first with the increase of blow out the critical wind speed of the fuel spray and gradually increased to a maximum and then with fuel injection Speed increases. At the same time, found that the low pressure environment (64kPa) blew out under the critical wind speed was significantly lower than that of atmospheric environment (100kPa) (about 1/3). The mechanism of environmental wind blew out the flame, is established based on the Damkohler number, expanding the scattering coupling pressure effect flow flame blowoff limit mathematical representation model.
Finally, through the development of diffusion jet flame behavior experiment tower under microgravity environment, the observed jet diffusion flame in microgravity flame height higher, more bright, more soot formation phenomenon. At the same time, has also been studied by diffusion jet flame wake effect blew out the process, found that microgravity flame blow out air flow with critical the speed is bigger than that under normal gravity results.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TK16

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