【作者】 李佳玉；

【导师】 谈和平； 董士奎；

【作者基本信息】 哈尔滨工业大学 ， 工程热物理， 2009， 博士

【摘要】 相变过程中高温粒子的热辐射行为是目标探测与识别、火焰温度测量、森林火灾遥感和监控、等离子喷涂等很多工程技术中所面临的问题。外界辐照条件下粒子的相变行为,燃料液滴燃烧过程中对热辐射的吸收和散射,相变过程中粒子内部的辐射吸收等都是目前很多研究者所关心的问题。本文主要以固体燃料发动机尾喷焰中的氧化铝粒子（ Al₂O₃）为例,分析不同相态粒子辐射特性和相变动力学过程,建立高温条件下粒子相变辐射模型。主要研究内容包括以下五个方面。（1）以尾喷焰中氧化铝粒子凝固过程中最易出现的三种相态（液态、γ相、α相）为研究对象,分析氧化铝粒子分别处于以上三种相态的光学常数及辐射特性。在紫外到近红外光谱范围内,考虑了氧化铝粒子的不同辐射机制,分析了其光学常数随相态的变化关系,以氧化铝粒子不同相态吸收指数模型的计算结果为基础,建立了描述不同相态的等温氧化铝粒子辐射特性的数学模型,发现由此计算出的不同相态氧化铝粒子光谱辐射强度的数值与实验值接近。（2）基于有效介质理论,建立掺有炭黑杂质的氧化铝粒子等效光学常数模型,考虑了粒子在熔点附近相态的变化。分析和比较了采用Maxwell-Garnett混合规则、Bruggeman混合规则、包覆层粒子球等效光学常数模型和复折射率体积平均这四种混合规则所计算的含炭黑杂质的氧化铝粒子等效光学常数数值,同时研究了四种混合规则的计算结果随波长的变化关系。考查了炭黑杂质的含量和炭黑在氧化铝粒子内的混合形态对整个粒子辐射特性的影响。通过计算发现炭黑杂质是尾喷焰中氧化铝粒子的吸收指数在熔点附近不连续性减小的原因之一。（3）熔融态氧化铝粒子凝固过程中动态辐射特性建模。首先,根据熔融氧化铝粒子凝固过程中的动力学方程,推导出了粒子凝固过程中各相态体积份额随时间的变化关系。其次,分别采用介电常数的体积平均、复折射率的体积平均、Bruggeman混合规则以及Maxwell-Garnett混合规则来表征氧化铝粒子相变过程中的等效光学常数的动态演变规律,发现采用以上四种混合规则计算的结果都比较接近。再次,根据熔融氧化铝粒子由液态到固态转变过程中可能出现的两种凝固方式:逐层凝固和容积凝固,分别建立了多层粒子球动态辐射模型和“等效介质”粒子球动态辐射模型。最后采用这两类模型计算氧化铝粒子相变过程中的动态光谱辐射特性,发现两种模型的计算结果都与实验数值呈现类似的变化趋势,而与实验过程比较接近的“等效介质”粒子球模型计算结果与实验结果符合较好。（4）径向非等温多种相态分层共存的氧化铝粒子内部和外表面热辐射特性的电磁理论研究。通过内部电磁场系数ci n和d in的反向递推公式求得多层同心球粒子内部各层电磁场系数a_in, b_in, c_in和d_in的数值,由此计算出的粒子内部吸收因子径向分布与Mackowski D.W.的计算结果非常接近。以液态、γ和α三相共存的氧化铝粒子和含炭黑的γ和α相共存氧化铝粒子为对象,分别采用多层同心球电磁理论模型与等效介质球Mie氏理论模型计算其吸收、衰减因子,发现只有当多层同心球粒子内各组份所在层的厚度比波长小很多时,有效介质理论对这种多层同心球的结构才适用。还采用多层同心球电磁理论模型对单相态和多相态共存的氧化铝粒子内部以及表面的辐射特性进行了计算和分析,考虑了粒子内部相态含量、各相态的排列顺序和径向温度梯度的影响。（5）考虑氧化铝粒子相变过程及粒子中的炭黑杂质对高温粒子流光辐射特性研究。采用反向蒙特卡罗法计算轴对称高温氧化铝粒子流在轴线正侧向辐射强度分布,以粒子的等效光学常数为基础,考察氧化铝粒子相变过程以及粒子中炭黑杂质对粒子流场轴线上辐射特性的影响。模拟结果发现:高温氧化铝粒子中的炭黑对粒子流辐射特性的影响显著,相变过程中的多相共存状态对粒子流的光谱辐射强度的影响在紫外短波处不可忽略。更多还原

【Abstract】 The radiation of high temperature particle with phase transformation is encountered in numerous technologically important applications such as target diagnostics and investigation, temperature measurements of flame, remote sensing and suppression of forest fires, plasma spraying and many others. The corresponding problems, such as phase transformation of an irradiated particle, absorption and scattering of thermal radiation in combustion of fuel droplet, the local volumetric absorption of radiation in the particle with phase transformation and others, are of obvious interest to researchers in several fields. In this research, the alumina （ Al 2 O 3） particles in Solid Propellant Motor exhaust plume are taken as the primary research objects, and the radiative mechanisms of different phases and phase transformation kinetics are investigated, the models for simulating the thermal radiation of high temperature particles with phase transformation are established. The scope of present research contains five parts:（1） Three kinds of phases （liquid,γandαstates） that melted alumina particle in the exhaust is most likely to evolve into during its solidification are taken as research objects. The effect of different phase states of alumina particles on their optical constants and radiative properties is analyzed. Different mechanisms which are responsible for the alumina particles radiation are considered in the spectral range from ultraviolet to near infrared region. Based on the model for calculating absorption coefficient of alumina particles in different phases, the model for calculating radiative properties of isothermal particles is built up. Calculated results show satisfactory agreement with experimental data.（2） The optical constant of an alumina particle containing carbon impurity is simulated based on the effective medium theory, and phase transformation is considered when particle temperature goes through the melting point. The effective optical constants calculated by Maxwell-Garnett and Bruggeman mixing rules, volume-averaged complex refractive index and the concentric shell model for the particle are compared with each other, and the wave-dependence of effective optical constants calculated by the four mixing rules is studied. The effects of carbon content and mixing morphology on the particle’s radiative properties are investigated. It is indicated that carbon impurity is an important factor that can reduce the discontinuity in the absorption index of pure alumina through the melting point.（3） Modeling for the transient radiative properties of alumina particles with phase transformation. First, the time dependence of the volume fraction of different phases is calculated based on the kinetic equation of alumina particles’crystallization process. Second, the transient effective optical constants of alumina particles with phase transformation are calculated by different mixing rules. It is indicated that results calculated by these mixing rules are very close. Third, two kinds of models are built up based on two possible solidification modes, including the multilayered sphere model and the effective-medium sphere model, and then the spectral radiance of alumina particle is calculated in the phase transformation. It can be summarized that the present results show a trend similar to the experimental results, and the results of the effective-medium sphere model which is more in accord with the experimental process shows better agreement with the experimental data.（4） The electromagnetic model is constructed to determine thermal radiation inside and outside the radially nonisothermal multiphase alumina particle. The downward recurrence relations for c i n and d in are developed to determine the values for coefficients a_in , b_in , c_in, d_in . Then the internal absorption factors are calculated, and the results of this paper are close to Mackowski D.W.’s results. Take two kinds of particles, which are multiphase alumina particle containing liquid,γ,αphases and particle containingγ,αphases, carbon soot impurity, as research objects, and the absorption and extinction factors are calculated by multilayered sphere model based on electromagnetic theory and effective-medium sphere model with Mie theory for these two kinds of particle. It is indicated that these two models’results show satisfactory agreement when the thickness of each layer is much less than the wavelength. The thermal radiation inside and outside the single phase and multiphase alumina particle is investigated by multilayered sphere model based on electromagnetic theory. The effects of constituent materials contents, the arrangement of constituent materials and radially temperature difference are also considered.（5） The influences of phase transformation and carbon soot impurity on the radiative properties of alumina particles flow are studied. The distribution of spectral radiance along the axis at 90o angle is calculated with backward Monte-Carlo method for axisymmetric high temperature alumina particles flow. Based on effective optical constant of the particle, the effect of alumina particle’s phase transformation and carbon soot impurity on the spectral radiance along the particles flow axis is analyzed. The calculated results indicate that the spectral radiance along the particles flow axis is obviously changed when carbon soot impurity mixed into the high temperature alumina particle. The influence of multiphase state on the ultraviolet radiation of high temperature particles flow can not be neglected.更多还原