倾斜气流作用下酒精池火燃烧特性及传热机制研究

发布时间：2018-05-24 09:00

本文选题：倾斜气流 + 池火　；参考：《中国科学技术大学》2013年博士论文

【摘要】：纵向气流作用下的液体池火研究是火灾科学中的一个重要领域。前人针对纵向气流作用下的火灾特性研究,已经开展了大量的工作,并且积累了宝贵经验,然而这些工作主要都是针对水平气流作用下进行的。在实际环境中,通风状况极为复杂,可能存在不同风向的通风气流,研究表明,通风特性的微小变化都会对火灾产生较大的影响。池火作为一种重要的火灾现象,具有很好的代表性。液体池火的燃烧通常包含了较为复杂的过程,其中包括空气卷吸、对流、燃料蒸发、沸腾、燃烧以及传热等诸多过程,燃烧过程较为复杂,因此成为火灾科学研究中一个重要的研究课题。前人已经对液体池火做了大量而且卓有成效的研究工作,并总结出液体池火在无风条件与纵向气流作用下燃烧特性的变化规律,如质量损失速率、火焰高度、火焰频率、火焰长度以及火焰辐射特性等。液体池火的燃烧动力学特性与燃料自身所能收到的热量密切相关,不论是在无风还是纵向气流作用下,对于小尺度池火而言,燃料接收热量的主要途径包括：热对流以及热传导,热辐射所起到的作用相对较小。本文的工作主要是研究和分析处于倾斜气流作用下小尺度池火的燃烧动力学特征和传热机理。希望通过本文的工作可以拓展人们对纵向气流作用下液体池火燃烧特性及传热机理的认识,丰富相应的理论模型,更希望能够应用于实际,以保护人员和财产的安全。本文的研究目标是：研究液体池火随着油盘尺寸、风速大小、风向角以及液位深度等参数的变化所导致的燃烧动力学特性的变化规律；研究风向角的变化对液体池火传热机制的影响,建立相关的无量纲参数模型；研究不同形状的油盘对质量损失速率、火焰长度的影响,归纳总结两者的动力学特征,建立或发展相应的理论模型；探讨无风条件下,不同液位深度对燃烧动力学特性的影响,发展相应的传热机制模型；研究不同风速、不同风向角条件下,燃料液位深度的变化对燃烧动力学特性的影响,比较揭示影响其特性的主导因素,发展相应的物理模型。本文的具体工作包括：搭建可倾斜的风洞平台,通过对气流进行整流,提供0～3.0ms-1的稳定气流；通过调节风洞一端的高度,同时始终保持油盘水平,提供0°～30°的风向角范围；通过搭建火源与供油盘之间的连通装置,对燃料液面进行稳定,用于稳定小尺度液体池火的燃料表面的深度。建立了倾斜气流作用下液体池火传热及燃烧速率模型。本文细致分析了液体池火在倾斜气流作用下传热的物理机制。根据所测得的实验结果,得出酒精池火在不同风速与不同风向角作用下的质量损失速率,结合油盘壁面温度的变化,研究了水平气流与倾斜气流作用下,质量损失速率增量与壁面温度增量之间的关系,并将两者进行耦合。结果表明,两者之间存在一定的线性关系,而相关系数与油盘尺寸的乘积为一常数。同时,通过对倾斜气流作用下的质量损失增量和壁面温度增量进行分析,发现随着风速的增大,燃料表面所受到的风压逐渐增强,间接导致了可燃蒸汽扩散速率的增大,因此质量损失速率逐渐增大。此外,通过对不同形状酒精池火的质量损失速率进行分析,发展了不同形状液体池火的传热机制模型。发展了酒精和正庚烷池火在水平纵向气流作用下的火焰长度模型,本文研究了小尺度液体池火在纵向气流作用下火焰长度的变化规律,建立了火焰长度与理查森数之间的物理模型,并通过对比实验结果发现,不同燃料种类液体池火的火焰长度变化规律存在差异。其次,研究了在倾斜气流作用下的火焰长度与风向角之间的变化规律,实验发现,当Ri值相同时,风向角越大,火焰长度的最大值越小。研究了小尺度酒精池火在无风且液位深度不同时的燃烧动力学特征,分析了影响小尺度液体池火传热特性的主导因素,并通过与实验结果对比发现,质量损失速率和火焰高度均会随着液位深度的逐渐增大,先增大,后减小。发生此现象的主要原因是,液位深度的增大首先会导致燃料所能接收到的热反馈总量增大,逐渐降低的原因是油盘内部可燃蒸汽燃烧的供氧总量降低。同时,实验发现,火焰的脉动频率基本保持不变,不会随着液位深度的变化而变化。通过结合前几章的工作,研究了倾斜气流作用下,不同液位深度的变化对质量损失速率的影响。初步建立了影响其燃烧特性的传热机制模型。实验发现水平气流作用下,质量损失速率随着液位深度的增大,首先增大,而后减小；而在倾斜气流作用下,在相同的风速作用下,质量损失速率会随着倾角的增大而逐渐增大。
[Abstract]:The study of liquid pool fire under the action of longitudinal airflow is an important field in fire science. A lot of work has been carried out and valuable experience has been carried out in the study of fire characteristics under the action of longitudinal airflow. However, these work are mainly carried out for horizontal airflow. In the actual environment, the condition of ventilation is very important. For complex reasons, there may be ventilation flow with different wind directions. The study shows that slight changes in ventilation characteristics will have a greater impact on fire.
As a kind of important fire phenomenon, pool fire is very representative. The combustion of liquid pool fire usually contains more complicated processes, including air entrainment, convection, fuel evaporation, boiling, combustion and heat transfer. The combustion process is more complicated, because this has become an important research topic in the fire science research. A lot of research work has been done on the liquid pool fire, and the combustion characteristics of the liquid pool fire under no wind condition and longitudinal air flow are summarized, such as the mass loss rate, the flame height, the flame frequency, the flame length and the flame radiation characteristics. The heat that the body receives is closely related, whether under the action of no wind or longitudinal air, for small scale pool fire, the main way for fuel to receive heat includes thermal convection and heat conduction, and the effect of heat radiation is relatively small.
The main work of this paper is to study and analyze the dynamic characteristics and heat transfer mechanism of small scale pool fire under the action of inclined airflow. It is hoped that the work can expand people's understanding of the combustion characteristics and heat transfer mechanism of liquid pool fire under the action of longitudinal air flow, enrich the corresponding theoretical model, and hope to apply it to practice more. To protect the safety of personnel and property.
The aim of this paper is to study the variation of the dynamic characteristics of the combustion of liquid pool fire with the change of the parameters such as the size of the oil plate, the wind speed, the angle of the wind and the depth of the liquid level, and the influence of the change of the wind direction on the heat transfer mechanism of the liquid pool fire. The effect of the disk on the rate of mass loss and the length of the flame, summarize the dynamic characteristics of the two, establish or develop the corresponding theoretical model, explore the influence of the depth of the liquid level on the dynamic characteristics of the combustion and develop the corresponding heat transfer mechanism model under the condition of no wind, and study the depth of the fuel level under the different wind speed and the different wind direction angle. The influence of variation on combustion kinetics is compared, and the dominant factors affecting its characteristics are revealed, and the corresponding physical models are developed.
The specific work of this article includes:
To set up an inclined wind tunnel platform, by rectifying the air flow, providing 0 ~ 3.0ms-1 of the stable air flow; by adjusting the height of the end of the wind tunnel, and maintaining the oil disk level at the same time, providing the air direction angle range from 0 to 30 degrees, and stabilizing the fuel level by building the connecting device between the fire source and the oil supply plate to stabilize the small scale. The depth of the fuel surface of a liquid pool fire.
The heat transfer and combustion rate model of liquid pool fire under the action of inclined airflow is established. In this paper, the physical mechanism of heat transfer in the liquid pool fire under the action of inclined airflow is carefully analyzed. The relationship between the increment of the mass loss rate and the wall temperature increment under the action of the horizontal and inclined airflow is investigated and the two are coupled. The results show that there is a linear relationship between the two, and the product of the correlation coefficient and the size of the oil disk is a constant. With the increase of surface temperature, it is found that with the increase of wind speed, the wind pressure on the fuel surface increases gradually, which indirectly leads to the increase of the diffusion rate of combustible steam, so the rate of mass loss increases gradually. In addition, through the analysis of the rate of mass loss of different shapes of alcohol pool fire, the transmission of different shape liquid pool fires is developed. Heat mechanism model.
The flame length model of alcohol and n-heptane pool fire under the horizontal longitudinal air flow is developed. The change law of flame length in the small scale liquid pool fire under the action of longitudinal air flow is studied. A physical model between the flame length and the Richardson number is established. The variation of flame length is different. Secondly, the change law between the flame length and the wind direction angle is studied. The experiment shows that when the Ri value is the same, the larger the wind direction is, the smaller the maximum value of the flame length is.
The characteristics of the combustion dynamics of small scale alcohol pool fire in the non wind and liquid level depth are studied. The leading factors affecting the heat transfer characteristics of the small scale liquid pool fire are analyzed. By comparing with the experimental results, it is found that the mass loss rate and the flame height will increase first and then decrease with the gradual increase of the liquid level depth. This phenomenon occurs. The main reason is that the increase of the depth of the liquid level first results in the increase of the total amount of thermal feedback that the fuel can receive. The reason is that the total amount of oxygen supply in the flammable steam combustion in the oil tray is reduced. At the same time, the experimental results show that the frequency of the flame pulsation is basically unchanged and does not change with the change of the depth of the liquid level.
By combining the work of the previous chapters, the influence of the change of the depth of the liquid level on the mass loss rate is studied under the action of the inclined air flow. The heat transfer mechanism model which affects the combustion characteristics is initially established. The experimental results show that the mass loss rate increases with the increase of the level depth and decreases with the increase of the level of the liquid level. Under the same wind speed, the mass loss rate increases with the increase of the inclination angle.
【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】：2013
【分类号】：X932

【参考文献】