【作者】 丁以斌；

【导师】 孙金华； 徐耀；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2010， 博士

【摘要】 建立了一套适合于研究粉尘云火焰传播特性的实验系统,利用该实验系统,结合粒子图像测速(PIV)技术、高速显微和高速纹影技术等,研究了锆粉云中传播火焰的特性、火焰的微观结构及其传播机理,以及粒径、浓度等因素对火焰传播的影响规律。利用PIV技术测量了喷粉结束后管道中扬尘湍流强度随时间的变化过程,得到湍流强度随时间的衰减规律。应用管法测量了粉尘云的湍流燃烧速度,同时使用微细热电偶测量了火焰传播过程中温度变化特征,得到了初始湍流强度、粉尘云浓度和粉尘粒径对湍流燃烧速度和火焰温度的影响规律。研究结果表明,火焰湍流燃烧速度和火焰温度之间成线性关系,锆粉云火焰传播过程中,燃烧区主要是通过热传导的方式向预热区传递热量,而热辐射在热量传递过程中占次要地位。分别实验研究了点火端开口和封闭时火焰的传播特性,得到了不同粒径和粉尘云浓度下的火焰形态、火焰温度和火焰传播速度等表征火焰传播特性的参数,分析了粉尘粒径和浓度对锆粉云中传播火焰的影响规律。研究结果表明,火焰温度和传播速度均先随粉尘云浓度的增加而增加,在某个浓度时达到最大值,而后均随粉尘云浓度的增加缓慢减小；对于不同平均粒径的锆粉,其最大火焰传播速度和最高火焰温度所对应的粉尘云浓度却不同；获得了四种平均粒径下锆粉云的最低爆炸浓度,得到了随锆粉平均粒径的增加其最低爆炸浓度升高的规律,并在理论上进行了论证。利用高速纹影、高速显微摄像技术,研究了锆粉云火焰传播的精细结构,以及火焰阵面前粒子的运动速度,构建了火焰的结构模型,分析了火焰的传播机理。研究结果表明,根据锆粉粒径和浓度的不同,火焰前面的预热区厚度也不同,最大厚度可达2cm左右,预热区后为燃烧区,其厚度为数毫米量级,在燃烧区最前沿约1mm范围内主要是小的锆粒子在燃烧,其后的1-4mm范围内为大的锆粒子在燃烧；锆粒子和氧气在粒子的表面发生化学反应,形成气-固表面燃烧体系。根据实验结果和理论分析推测锆粒子的燃烧过程为：锆粒子在预热区内不断升温,当其温度达到某一值时,由于热应力的作用导致锆粒子表面的金属氧化膜破裂,空气中氧气可以和纯锆接触,从而发生燃烧反应。火焰在锆粉云中传播时,相对于大粒径锆粉,小粒径锆粉对火焰传播具有更重要的作用。更多还原

【Abstract】 A set of experimental system was established which is suitable for studying dust flame propagation characteristic. Combining with PIV technology, microscopic lens and high-speed schlieren, flame propagation characteristic and flame microstructure as well as its propagation mechanism of zirconium particle cloud were investigated. At the same time particle size and dust concentration effect on flame propagation regularity were also studied.At first, the PIV measurement technique was used to measure turbulent intensity change with time after the end of dispersion,thus decay regularity of turbulent intensity was obtained. Turbulent burning speed was gained by Application of tube methods and at the same times superfine thermocouple was used to measure temperature change during the flame propagation. The initial turbulent intensity, the concentrations of dust cloud and dust particle size effect on the turbulent burning speed and flame temperature were gained. Flame propagation characteristics impacted by these three factors were further analyzed. The results demonstrate that the turbulent burning speed and flame temperature have a linear relationship, so the main heat transfer way was revealed in zirconium dust cloud flame propagation process. Combustion zone is mainly driven by thermal conductivity to transfer heat to preheated zone, while heat transfer by thermal radiation accounts for the secondary position in the process.Flame propagation characteristic with ignition end open or close was investigated. The flame shape, flame temperature and flame propagation speed which represent flame propagation characteristic parameters were obtained and at the same time change regularity in flame propagation was also further analyzed. The results show that the flame temperature and flame propagation speed increase remarkably with the concentration of zirconium particle cloud at lower concentrations, reach the maximum value, and then decrease slightly at higher concentrations. For four different average particle sizes, the dust concentrations are different when flame temperature and flame propagation speed reach the maximum value. The minimum dust explosion concentration of four particle sizes was tested. The results reveal the particle sizes effect on the minimum dust explosion concentration and a theoretical qualitative analysis is also given.High-speed schlieren and microscopic lens were used to study flame microstructure and particle velocity before flame front.Flame structure model and propagation mechanism were reconstructed. The results demonstrate that the flame preheated zone thickness is different depending on particle size and dust concentration. Maximum thickness of preheated zone is up to 2cm or so. The combustion zone lays behind the preheated zone. The combustion zone thickness is mm order of magnitude. Smaller particles mainly exist in the width 1.0mm in the leading edge of the combustion zone, while the larger particles mainly appear 1-4mm behind the leading edge of the combustion zone. Zirconium particles and oxygen take chemical reaction on the zirconium particle surface and form gas-solid surface combustion system. According to the experimental results and theoretical analysis, the combustion process of zirconium particle was speculated. With the preheated zone temperature rise, when the preheated zone temperature reaches a certain value, the surface of zirconium particles causes the breakdown of the oxide film due to thermal stress. After the breakdown of the oxide film, pure zirconium can contact with the oxygen, no longer hindered by the surface oxide film. When temperature of the preheated zone reaches 220℃, Zirconium particles start to ignite. In the zirconium dust cloud flame propagation process, the smaller particles have the relatively more important role than the larger particles.更多还原