导线绝缘层在弱浮力环境下着火早期演变特性的研究

发布时间：2017-12-27 02:32

  本文关键词：导线绝缘层在弱浮力环境下着火早期演变特性的研究　出处：《中国科学院研究生院(工程热物理研究所)》2016年博士论文　论文类型：学位论文

  更多相关文章： 微重力 弱浮力 导线绝缘层 着火早期演变特性 火灾监测

【摘要】：为保障载人航天器的防火安全,应探索微重力下火灾发生的早期演变机理。但地面微重力实验时间短,同时空间搭载实验费用昂贵,所以非常需要在地面开展微重力实验模拟研究。基于弱浮力环境模拟微重力效应的思路,本文开展了弱浮力下载人航天器中典型非金属材料导线绝缘层着火早期演变特性的研究。基于各种微重力燃烧的地面实验模拟方法,系统研究了弱浮力下过载电流时导线绝缘层的着火早期演变特性,具体包括温升特性、烟气输运特性以及产物烟黑的分布特性,并相应地预测了微重力下导线绝缘层着火早期的演变机理。全文主要研究内容如下：首先,在第2章系统总结了微重力燃烧的地面实验模拟方法,详细介绍了低压法和窄通道法的模拟原理、有效性及其不足；并提出改进,尤其在窄通道法基础上提出了低压窄通道法,给出其具体原理,并指出了该方法在研究热厚材料着火早期演变特性方面的优势。此后,分三章逐步介绍过载电流下绝缘层的着火早期演变特性。第3章,首先建立了绝缘层着火早期温升特性的简化物理模型,并基于模型得到绝缘层温升曲线的理论解,进而分析了弱浮力对其影响机理。此后,利用低压法研究了压力、氧气浓度、环境组分、电流大小、绝缘层种类和厚度等因素对绝缘层着火早期温升特性的影响。结果表明,随着压力的降低,绝缘层的温升率、平衡温度逐步增大,达到平衡温度的时间逐步减小,从而证明低压法有效地抑制了浮力对流,使得自然对流散热被明显削弱。接着利用窄通道法研究了通道高度、壁面种类等因素对绝缘层着火早期温升特性的影响。结果表明,随着通道高度的降低,绝缘层的温升率、平衡温度逐步增大,达到平衡温度的时间逐步减小,从而证明窄通道法也可有效地抑制浮力对流,使得自然对流散热被明显削弱。另外,结果表明,应选择壁面蓄热能力弱、壁面导热系数小的材料来减少窄通道的壁面热损失；并且水平放置的窄通道抑制浮力对流的效果要优于垂直放置的。最后,验证了低压窄通道法模拟微重力下绝缘层着火早期温升特性的有效性,并指出其适用范围。第4章,首先建立了绝缘层烟气微团析出的简化物理模型,并基于模型揭示了烟气微团运动轨迹和烟气喷射角的变化规律,指出压力对烟气微团输运特性的影响机理,并预测了微重力下的结果。然后,利用低压法研究了压力、环境组分、氧气浓度、电流大小、绝缘层种类和厚度等因素对绝缘层着火早期烟气输运特性的影响。结果表明,在纯氮气环境下,压力越低,绝缘层破损模式依次为热膨胀模式、烟气喷射模式、鼓泡模式,其热降解程度越来越剧烈,绝缘层相应的析出烟气时间或起泡时间减小,烟气喷射角增大,表明压力有效削弱了浮力对流作用。而在空气组分和纯氧气环境下,随着压力的降低,由于氧气含量的减少,绝缘层氧化分解程度降低,绝缘层析出烟气的时间增大,此外烟气喷射角随着压力降低逐步增大,这再次表明压力有效削弱了浮力对流作用。此外,降低氮气稀释剂含量可以增加绝缘层的氧化分解速度,表明只降低氮气含量的低压环境可以克服低压法抑制化学反应速率的不足。随着过载电流的增加,绝缘层析出烟气的时间缩短,烟气量明显增加,所以为了预防火灾需要有效监视用电设备的工作电流大小。最后,研究表明绝缘层种类对于绝缘层的烟气输运特性影响大,应优先选用热稳定性良好的材料作为绝缘层。接着利用窄通道法研究了通道高度、通道放置方式对绝缘层着火早期烟气输运特性的影响。结果表明,随着窄通道高度的降低,通道内部绝缘层烟气的输运特性明显不同,依次呈现：发散型、聚散型和聚附型；且当窄通道通道高度在10mm-15mm时,烟气的自然对流流动过程被有效地抑制,与微重力下绝缘层烟气输运过程相似。进一步,相比垂直放置方式,水平放置的窄通道可更有效地抑制浮力对流,得到类似微重力下的烟气输运特性。最后,采用低压窄通道法研究了绝缘层的烟气输运特性。结果表明,低压窄通道法在10mm-21.4mm通道高度内,能够获得近似微重力下的烟气输运特性。第5章,首先阐述激光衰减法测量烟黑浓度的原理,并阐述了烟黑浓度数据反演算法和降噪原理,并基于此编写了一套烟黑浓度Matlab计算程序。此后,搭建了全场烟黑浓度测量的实验系统,并验证了该实验系统和数据处理方法的有效性。接着,研究了环境组分、压力、氮气稀释剂对绝缘层着火早期烟黑分布特性的影响。结果表明,在空气组分下,随着压力降低,绝缘层着火早期的烟黑浓度先降低,此后又逐渐增大。而在相同压力时,纯氧环境工况,绝缘层着火早期生成的烟黑最多,说明氧气含量增加会促进绝缘层的分解,释放出更多烟黑,这表明可用低压富氧环境来预测微重力下的结果。另外,若在氧气含量一定时,随着氮气稀释剂含量的降低,绝缘层析出的烟黑浓度逐步增加,因此只降低稀释剂含量建立的弱浮力环境,可更好地预测微重力下的结果。此外,无论何种环境组分,随着压力降低,由于浮力对流被逐步抑制,使得水平方向上绝缘层的烟黑扩散更远,而垂直方向上绝缘层的烟黑分布更加均匀,逐步接近微重力下的烟黑分布状况。最后,利用场发射扫描电镜分析了典型工况下绝缘层生成的烟黑颗粒形态和粒径。结果表明,随着压力的降低,绝缘层的烟黑颗粒等效直径逐渐增大,该趋势与微重力下的结果一致。总之,通过本文的研究,获得了弱浮力环境下过载电流时导线绝缘层着火早期的演变特性,预测了微重力下的变化趋势,并基于着火早期演变特性的结果对微重力模拟方法提出了有效改进。本文工作将为今后微重力下材料防火性能的检验和着火早期的监测,提供了坚实的理论依据和大量的基础数据。
[Abstract]:In order to protect the fire safety of manned spacecraft, the early evolution mechanism of the fire in microgravity should be explored. However, the experiment time of ground microgravity is short and the space loading experiment is expensive, so it is very necessary to carry out the research of microgravity experiment on the ground. Based on the idea of simulating the microgravity effect in the weak buoyancy environment, the early evolution characteristics of the insulation layer of typical non-metallic conductor insulation in the buoyancy force download spacecraft are studied in this paper. The ground simulation method based on various experimental microgravity combustion, weak buoyancy under overload current when the ignition wire insulation layer of the early evolution characteristics of system were studied, including the temperature rise characteristics of flue gas, transport properties and distribution characteristics of the products and the corresponding soot, predicted under microgravity insulation fire early evolution mechanism. The main research contents are as follows: firstly, the second chapter summarizes the simulation method of ground microgravity combustion experiment, introduces the simulation principle, low voltage method and narrow channel approach is effective and its shortcomings; and put forward the improvement, particularly in the narrow channel law put forward low pressure narrow channel method, gives the specific principle. And pointed out that the method of fire early evolution characteristics of the advantages in the study of thick material. Since then, the characteristics of the early ignition evolution of the insulation layer under overload current are introduced in three chapters. The third chapter first establishes a simplified physical model of the temperature rise characteristics of the insulation layer at the early stage, and obtains the theoretical solution of the temperature rise curve of the insulation layer based on the model, and further analyzes the influence mechanism of the weak buoyancy on it. Since then, the influence of pressure, oxygen concentration, environmental components, current size, insulation layer type and thickness on the temperature rise characteristics of insulation layer has been studied by low pressure method. The results show that with the decrease of pressure, the temperature rise rate and equilibrium temperature of insulation layer gradually increase, and the time to reach equilibrium temperature decreases. This proves that the low pressure method effectively suppresses buoyancy convection and makes the natural convection heat dissipation obviously weakened. Then the narrow channel method was used to study the influence of the height of the channel and the type of the wall on the temperature rise of the insulating layer at the early stage of ignition. The results show that with the decrease of the height of the channel, the temperature rise rate and the equilibrium temperature of the insulation layer gradually increase, and the time to reach the equilibrium temperature decreases. This proves that the narrow channel method can also effectively restrain buoyancy convection, and the natural convection heat dissipation is obviously weakened. In addition, the results show that the wall heat loss of narrow channel should be chosen to reduce the wall heat loss of narrow channel, and the effect of buoyant convection is better than that of vertical placement. Finally, the validity of the low pressure narrow channel method to simulate the early temperature rise characteristics of the insulating layer under the microgravity is verified, and the scope of its application is pointed out. In the fourth chapter, first, a simplified physical model for the separation of flue gas microcluster in insulation layer is established. Based on the model, the variation rule of flue gas microcluster trajectory and flue gas injection angle is revealed, and the influence mechanism of pressure on the characteristics of flue gas microtransport is pointed out, and the results under microgravity are predicted. Then, the influence of pressure, environmental components, oxygen concentration, current size, type and thickness of insulation layer on the transport characteristics of flue gas at the early stage of ignition were studied by low pressure method. The results show that in pure nitrogen environment, the lower the pressure, damage to the insulation layer pattern followed by thermal expansion mode, gas injection mode, the bubble model, the thermal degradation degree is increasing, the insulating layer corresponding precipitation time of flue gas or foaming time decreases, flue gas injection angle increases, that pressure can reduce the buoyancy convection. In the composition of air and pure oxygen environment, as the pressure decreased due to the decrease of oxygen, reduce the degree of oxidative decomposition of insulating layer, the insulating layer of the flue gas precipitation time increases, in addition to flue gas injection angle as the pressure decreases gradually increased, it shows once again that the pressure effectively weakened the buoyancy convection. In addition, reducing the content of nitrogen diluent can increase the decomposition rate of insulating layer, indicating that the low pressure environment that only reduces nitrogen content can overcome the shortage of low pressure method to inhibit the chemical reaction rate. With the increase of overload current, the time of flue gas emission from insulation layer is shortened, and the amount of smoke is increased. Therefore, in order to prevent fire, it is necessary to effectively monitor the working current of electrical equipment. Finally, the study shows that the type of insulating layer has great influence on the gas transport characteristics of the insulating layer, and the material with good thermal stability should be chosen as the insulating layer. Then the narrow channel method was used to study the effect of channel height and channel placement on the gas transport characteristics at the early stage of ignition. The results show that with the decrease of the height of the narrow channel, the channel transport properties of internal insulation layer of flue gas is obviously different, which appears divergent, and type of type and poly; and when the narrow channel height in 10mm-15mm, natural convection flow process of flue gas is effectively suppressed, and the insulating layer of flue gas transport under microgravity a similar process. Further, the narrow channel placed horizontally can more effectively suppress the buoyancy convection and obtain the gas transport characteristics under microgravity compared with the vertical placement. Finally, the gas transport characteristics of the insulating layer are studied by the low pressure narrow channel method. The results show that the low pressure narrow channel method can obtain the gas transport characteristics under the approximate microgravity at the height of the 10mm-21.4mm channel. The fifth chapter first describes the principle of laser attenuation measurement of soot concentration, and expounds the soot concentration data inversion algorithm and the denoising principle, and based on this to prepare a set of soot concentration calculation program Matlab. Since then, the experimental system was built to measure the soot concentration field, and verifies the validity of the experimental system and data processing method. Then, the research of environmental components, pressure, nitrogen diluent on the insulation effect of ignition soot distribution characteristics of early
【学位授予单位】：中国科学院研究生院(工程热物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：V445;V416.5
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本文编号：1339911