【作者】 付强；

【导师】 张和平；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2012， 博士

【摘要】 当今社会飞速发展,电缆在各个行业应用越来越广泛。但是,电缆的应用给社会带来了极大的利益的同时也造成了很多的火灾安全隐患,一旦发生火灾,其不单加大火势而且火势容易沿着电缆的敷设方向快速蔓延,此外,由于电缆材料多为聚合物,燃烧过后产生大量的烟气,其中大部分还为对人体有害的有毒气体和腐蚀性气体,不仅对火场中人员造成极大的威胁,还会妨碍消防人员的救援工作。目前电缆行业当中所使用最为广泛的电缆材料为聚氯乙烯(PVC)、聚乙烯(PE)以及天然橡胶,另外,随着核电等行业的发展对于电缆的阻燃性能要求的不断提高,交联聚烯烃、添加无机阻燃剂电缆材料应用越来越广泛,本文针对这几种常用的电缆材料从微观层面出发,结合宏观实验,对其火灾特性及其影响进行了全面的探讨。本文首先从微观的角度对这几种常用电缆可燃的护套材料进行了实验研究,利用热重-差热(TG-DSC)分析设备对几种典型电缆护套材料的热解及反应动力学进行了研究,分析了电缆护套结构和成分在受热过程中的变化,升温速率以及空气、氮气气氛对于电缆护套材料热分解过程的影响,并结合质谱分析仪对燃烧各阶段尾气进行分析,研究每个阶段发生的反应。并通过热解动力学理论推导出了无机阻燃聚烯烃电缆材料的活化能E与指前因子A。由于传统的热分析方法并不能很好的反映真实条件下材料的火灾特性,且单一材料的燃烧性能跟完整电缆材料的燃烧特性有所区别,因此本文利用锥形量热计(CONE)对成品电缆的点燃时间、热释放速率、CO及CO2生成速率等火灾特性参数进行了研究,着重考察了电缆的结构及外加热辐射强度对这些火灾特性参数的影响,此外还利用微型燃烧仪(MCC)对电缆材料的点燃温度、热释放速率等特性进行了研究,并联合锥形量热计实验结果进行了对比分析,研究其测试结果相关性。建立了多层材料带线芯的简化电缆点燃模型,对电缆点燃性能的影响因素进行了分析,同时采用积分方法对电缆表面的温度进行了推导,反映了各有关参量对解的影响,最终建立了二维电缆点燃模型,讨论了电缆点燃时间的影响因素,并结合试验数据证明所建模型可以根据MCC所测点燃温度预测CONE所得点燃时间。随着流体计算方法的进步以及电子计算机运行速度的飞速发展,CFD(Computational Fluid Dynamics)软件越来越多的应用于火灾分析研究当中,在电缆燃烧特性方面开展计算机数值模拟研究工作十分有必要。锥形量热计作为当今小尺寸实验中使用较广泛的燃烧性能测试方法,其数值模拟工作非常值得开展。本文对PVC电缆的锥形量热计实验进行了数值模拟,就点燃时间、热释放速率、CO及CO2等参数跟实际实验进行对比分析,模拟结果与实验结果吻合很好,误差在可接受范围。目前火灾计算机数值模拟研究当中开展最为广泛的为较大规模的火灾场景模拟,电缆垂直成束燃烧试验(IEC60662-3)模拟电缆在垂直空间中的燃烧行为,实验结果与真实火灾相关性较好,对电缆燃烧性能进行测试有着十分重要的意义。本文采用数值模拟的方法对PVC电缆在IEC60332-3成束电缆垂直燃烧试验台中进行燃烧及火焰传播进行计算,对电缆内燃烧过程、火焰辐射及烟气气体成分、试验台各点温度变化进行了精确的数值计算。传统电缆火灾危险性能评定标准大多单纯以电缆延燃性能作为评价指标(如IEC60332系列标准),评价结果不能真实反映电缆阻燃性能。其它燃烧性能参数一般很少作为评价指标,或者燃烧性能参数在不同燃烧条件下用不同试验方法来获得,各参数之间相关性较差。本文基于层次分析法计算指标权重,建立了多指标体系的评价方法能够有效评价不同种类电缆火灾危险性能。更多还原

【Abstract】 The cable is widely used in various fields with the rapid development of modern society. The application of cable causes a lot of fire safety problems although it does bring a great deal of convenience. Cable is a combustible material not only enhancing the fire but also paving the way for the spread of fire along the direction it lays as soon as a fire occurs. What makes the situation worse is the cable made of polymer produces plentiful smoke during the combustion including toxic gas and corrosive one which threatens to people in a fire and impedes the rescue work.Polyvinyl chlorides (PVC), polyethylene (PE) as well as natural rubber are widely used cable materials in cable industry nowadays. Along the development of the nuclear power cable with flame retardant properties is increasingly demanded and the flame retardant cable materials like cross-linked polyolefin, inorganic applications are commonly put into use. In this paper, several types of commonly used cable materials are comprehensively studied for their combustion characteristic and impact in a fire by analyzing their chemical composition and conducting experiment.This paper begins with testifying several commonly used cable’s combustible sheath and insulative chemical composition through experiments and then studies their pyrolysis behavior by using thermo gravimetric-differential thermal (TG-DSC).The changes in the structure and composition of the heated material are analyzed, which takes into account the influence of heating rate and heating atmosphere on the pyrolysis of cable material.Because fire characteristics of materials in real conditions are not accurately revealed in traditional thermal analysis and the combustibility of homogenous material differs from the combustibility of cable with composite material, in this paper a cone calorimeter (CONE) is used to study the ignition time, heat release rate, formation rate of CO and CO2and other combustion characteristic with emphasis on the influence of cable structure and the external heating radiation intensity. Moreover, a micro-combustion analyzer (MCC) is utilized to study ignition temperature, heat release rate and other combustion characteristic of those cable materials and experimental results from cone calorimeter were compared. A simplified model of cable with multilayer materials and core is built to analyze influences on cable combustibility and explicit formulation of cable surface temperature is derived by using integral and reveals each relevant parameter on the solution.With the progress of the fluid calculation methods, as well as the rapid development of computer, CFD (Computational Fluid Dynamics) is commonly used in studies of fire and computer numerical simulation studies carried out in studying the cable combustion characteristics is necessary. Utilizing the cone calorimeter is considered as the common approach to test combustion characteristics in Small Scales Experiment and its numerical simulation is worth carrying out. Cone calorimeter of PVC cable is simulated in this paper and ignition time, heat release rate, CO and CO2and other data were compared with the experiment to test its feasibility. The simulation of large-scale fire scenario is widely carried out in present numerical simulation for fire. Experimented cable burned in a vertical bundle (IEC60662-3) simulates cable’s firing behavior in vertical space and the results have a good correlations with the real fire, which has a great significance in this filed. The numerical simulation used in this paper simulates the burring of PVC cable in a vertical bundle and the spread of flame and numerical calculation is carried out for combustion process, flame radiation, component of gas in smoke and different temperature of point set in the test-bed.Traditional cable fire hazard performance assessment standards are mostly simple cable retardant performance evaluation indicators (such as IEC60332series of standards); the evaluation results cannot be a true reflection of the cable flame retardant properties. Combustion characteristics are seldom used as evaluation index or combustion characteristics under different combustion conditions with different test methods to get the poor correlation between the parameters. The analytic hierarchy process was used to calculate the index weight, establish the index system of evaluation methods, which can effectively evaluate different types of cables flame retardant performance.更多还原