考虑开口与火源位置影响的船舶封闭空间火灾动力学特性模拟研究

发布时间：2018-05-24 23:42

本文选题：船舶舱室火灾 + 顶部开口　；参考：《中国科学技术大学》2014年博士论文

【摘要】：火灾是船舶灾难性事故之一,可能导致严重的船舶损伤和人员伤亡。认识开口与火源位置对船舶舱室火灾的影响是船舶安全工程的重要内容,可为船舶安全设计、火灾预防和扑救等提供基础数据和理论支撑。为了研究开口与火源位置对船舶舱室火灾的影响,本文针对不同火源和开口位置下的顶部开口腔室火灾,以及无竖直开口腔室中的火源抬升行为开展了实验研究和理论分析。提出了一系列船舶舱室火灾参数预测模型并对其影响因素进行了表征。本文实验条件下得到的主要结论如下：分析了顶部开口腔室中火源水平位置(火源XY因素)对火灾行为的影响。在顶部中央开口腔室中,将火源移离地板中央会增长稳定燃烧时间并降低火源平均质量损失速率,燃烧全过程的舱内氧气浓度空间平均值和火源平均燃烧效率均会降低。不同火源位置下顶部开口临界尺寸存在显著差异。火源燃烧效率随火源区氧气浓度的时平均值的升高而线性增大。建立了可用于比较不同热释放速率池火的无量纲火焰高度。顶部开口腔室池火存在火焰拉伸现象；以中央火为基准参考,其他位置火焰存在“拉伸”行为和卷吸受限。建立了反应腔室蓄热能力、可用于比较不同位置火源下腔室温升的无量纲温升参数。当火源位于开口正下方时,无量纲温升最小。对于水平位置不同的火源,不同的卷吸率和离顶部开口的距离是影响其火灾行为的两大因素。腔室内平均烟气密度随顶部开口尺寸的增大而减小,中央火的下降趋势较墙壁火和墙角火更为明显。由于具有更大的热释放速率,中央火的腔室烟气填充速率更快。影响中央火的主导因素为热反馈增强,墙角火占主导地位的因素为氧气受限,而墙壁火受“热反馈增强和氧气受限”共同作用。研究了顶部开口腔室的开口位置(开口XY因素)对火灾行为的影响。顶部中央开口腔室火源质量损失速率略大于顶部拐角开口腔室火源质量损失速率,其火源燃烧效率和热释放速率均高于顶部拐角开口腔室火源对应值。不同开口位置情况下的火焰拉伸特性无明显差异。由于蓄热性较顶部拐角开口腔室差,顶部中央开口腔室无量纲温升低于顶部拐角开口腔室无量纲温升。当顶部开口远离火源上方,其室内的氧气受限作用和热反馈效应将增强。顶部开口腔室中的平均温升速率随火源面积指数增大,对应的顶部中央开口腔室的指数大于顶部拐角开口腔室的指数。顶部中央开口腔室平均烟密度随顶部开口尺寸的增大而降低,而顶部拐角开口腔室的平均烟密度则基本保持不变。顶部拐角开口腔室中的烟气填充速度比顶部中央开口腔室烟气填充速度慢。采用恒定火源功率对开口位置的影响进行了数值模拟研究,数值模拟结果与对实验结果进行无量纲分析得出的结论一致。揭示了顶部开口或无开口腔室中抬升火源(Z因素)的行为规律。(1)揭示了顶部开口腔室中抬升火源的行为特性。当火源抬升高度较高时,其质量损失速率变小且稳定燃烧时间变长。抬升火源情况下顶部开口腔室中的烟气消光系数、氧气浓度和气体温度等火灾环境参数具有明显的分层特性。对于较高位置的火源,其烟气沉降速率较慢。(2)揭示了抬升火源情况下无开口封闭腔室典型烟气填充过程。烟气消光系数、氧气浓度和气体温度分布均呈现明显分层,且分层界面为火源高度平面。在抬升火源情况下的无开口封闭腔室中,烟气层沉降并滞止于火源高度平面,进而通过墙壁射流继续烟气填充过程。(3)可视化实验显示墙壁射流穿透分层平面沿着墙壁向下沉降；之后,烟气在地板平面累积并从地板中央上升。(4)发现对于火源位置较高的情况,腔室内不同高度处氧气浓度差异较大,充分混合假设不成立。当火焰触顶时燃料在点燃后迅速沸腾,其燃料平均质量损失速率远大于开放空间自由燃烧值。基于观测到的分层现象建立了氧气消耗率的计算方法。无开口封闭腔室中抬升火源平均燃烧效率和碳转化率随其抬升高度线性降低。火焰触顶情况下的抬升火源在燃烧早期危害性较大。火焰触顶情况下火源平均热释放速率并无明显升高。建立了船舶A60舱室综合传热系数模型、顶部开口腔室火灾温度模型、全舱平均氧气浓度和烟气密度关系式等船舶舱室火灾参数预测模型,并对相关模型的影响因素进行了表征。对于船舶A60结构舱室,其平均综合传热系数与火源热释放速率的三分之一次方成正比。讨论了对现有计算顶部开口传热方法的使用和误用：当火源位于开口正下方时,羽流诱导的顶部开口传热占主导地位。需谨慎应用Cooper模型计算顶部开口传热。提出了当火源位于开口正下方时的开口传热的处理方法。基于能量守恒和顶部开口流动经验关系式,推导建立了顶部开口腔室火灾的温度预测模型。对于水平位置因素,其影响反映在所建立的反映“总热释放量与开口散失热量比"以及“墙壁热损失与开口散热热量比"的两个无量纲量的指数上。对于移离开口正下方的火源,其温升与火源热释放速率的三分之二次方成正比；对于位于开口正下方的火源,其温升与火源热释放速率的三分之四次方程正比,与开口面积的六分之一次方成反比。无论是使用单区模型假设还是双区模型假设,竖直位置因素对所建立模型无显著影响。建立了综合腔室体积、顶部开口尺寸、开口与火源相对位置、火源热释放速率等因素的顶部开口腔室池火无量纲开口因子。基于无量纲开口因子,建立了全舱平均氧气浓度关系式和全舱平均烟气质量密度关系式。
[Abstract]:Fire is one of the disaster accidents of a ship, which may cause serious damage and casualties. Understanding the impact of the opening and fire location on the cabin fire is an important part of the ship safety engineering. It can provide basic data and theoretical support for ship safety design, fire prevention and rescue, in order to study the location of the opening and fire source. In this paper, an experimental study and theoretical analysis are carried out on the fire in the top opening chamber under different fire sources and opening positions, as well as the uplifting behavior in the non vertical open mouth chamber. A series of prediction models for the fire parameters of the ship cabin are presented and the influencing factors are characterized. This paper is under the experimental conditions. The main conclusions are as follows:
The effect of fire source level position (fire source XY factor) on fire behavior in the top opening chamber is analyzed. In the top central open mouth chamber, moving the fire source from the center of the floor will increase the steady combustion time and reduce the average mass loss rate of the fire source. The average oxygen concentration space average in the cabin and the average combustion efficiency of the fire source will be all in the whole process of combustion. There is a significant difference in the critical size of the top opening at the top of different fire sources. The combustion efficiency of the fire source increases linearly with the increase of the time average of the oxygen concentration in the fire source area. The regenerative capacity of the reaction chamber is established, which can be used to compare the dimensionless temperature rise parameters of the chamber temperature rise under the different positions of the fire source. When the fire is located under the opening, the dimensionless temperature rise is minimal. For different fire sources with different horizontal positions, the different coiling rates and off top open. The distance of the mouth is the two factor affecting the fire behavior. The average flue gas density in the chamber decreases with the increase of the opening size of the top, and the downward trend of the central fire is more obvious than that of the wall fire and the wall angle. Feed enhancement, the main factor of corner fire is oxygen limitation, and wall fire is affected by "thermal feedback enhancement and oxygen limitation".
The effect of the opening position of the opening chamber of the top opening (XY factor) on the fire behavior is studied. The mass loss rate of the fire source in the top central open mouth chamber is slightly greater than that in the top corner of the oral chamber. The combustion efficiency and the heat release rate of the fire source are higher than the corresponding value of the open mouth chamber fire source at the top corner. There is no obvious difference in the tensile properties of the flame under the condition of the top corner opening in the mouth chamber, and there is no dimensionless temperature rise at the top of the central open mouth chamber below the top corner in the oral chamber. The average smoke density in the top central open mouth chamber decreased with the increase of the opening size of the top, while the average smoke density in the top corner opening remained unchanged. The top corner opened the smoke in the oral cavity. The velocity of gas filling is slower than that in the central open mouth chamber of the top. The influence of the constant fire power on the opening position is numerically simulated. The numerical simulation results are in agreement with the conclusion of the undimensional analysis of the experimental results.
The behavior characteristics of the elevated fire source (Z factor) in the top open or no opening chamber were revealed. (1) the behavior characteristics of the lifting fire in the top opening chamber were revealed. When the height of the fire was raised, the mass loss rate became smaller and the combustion time became longer. The smoke extinction coefficient in the top opening chamber in the top of the fire source and the concentration of oxygen were strong. The fire environment parameters, such as degree and gas temperature, have obvious stratification characteristics. For the high position fire source, the rate of flue gas settlement is slow. (2) the typical flue gas filling process without open closed chamber is revealed. The smoke extinction coefficient, oxygen concentration and gas temperature distribution are obviously stratified, and the stratified interface is fire. The source height plane. In the open closed chamber of the lift fire source, the smoke layer subsided and stagnant at the height plane of the fire source, and then the fume filling process was continued through the wall jet. (3) the visualization experiment showed that the wall jet penetrated down the wall down the wall; after that, the smoke accumulated on the floor plane and from the center of the floor. (4) (4) it is found that the oxygen concentration varies greatly at the different height of the chamber, and the full mixing assumption is not established. When the flame hits the top, the fuel is boiling quickly after the ignition. The average mass loss rate of the fuel is far greater than the free combustion value in the open space. The average combustion efficiency and carbon conversion rate of the elevated fire source in the open closed chamber are linearly decreased with the elevating height. The rising fire source at the top of the flame is more harmful in the early combustion. The average heat release rate of the fire source is not obviously increased.
The comprehensive heat transfer coefficient model of the ship's A60 cabin, the fire temperature model at the top opening chamber, the average oxygen concentration of the whole cabin and the relation of the smoke density, and so on, are used to predict the fire parameters of the ship cabin, and the influencing factors of the related models are characterized. The average comprehensive heat transfer coefficient and the heat release rate of the fire source in the ship's A60 cabin room The 1/3 time ratio is proportional. The use and misuse of the current heat transfer method at the top opening are discussed. When the fire source is located below the opening, the top opening heat transfer induced by the plume is dominant. It is necessary to use the Cooper model carefully to calculate the heat transfer at the top opening. Based on the energy conservation and the empirical relationship of the top opening flow, a temperature prediction model for the top opening chamber fire is derived. For the horizontal position factor, the effect is reflected by the two quantities that reflect the "total heat release rate and the opening heat loss ratio", and the "wall heat loss and the opening heat dissipation ratio". The temperature rise is proportional to the 2/3 square of the heat release rate of the fire source; for the fire source under the opening, the temperature rise is proportional to the 4/3 equation of the heat release rate of the fire source, and is inversely proportional to the 1/6 square of the open area. It is assumed that the vertical position factor has no significant influence on the established model. The undimensional opening factor of the oral chamber pool fire is established at the top of the chamber volume, the top opening size, the relative position of the opening and the fire source and the heat release rate of the fire source. Based on the dimensionless opening factor, the average oxygen concentration in the whole cabin is established. The relationship between the average gas mass density of the system and the whole cabin.
【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】：2014
【分类号】：U698.4

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