Theoretical And Experimental Study On The Inverse Radiation Problem Of Disperse Particles

Particles have been found in many fields such as chemical industry, metallurgy, power, architecture, medicine, biology, food, aerospace, military and atmospheric science, etc. Typical particulate media include: the flame containing carbon black or fly ash, the jet stream and plume of solid propellant rockets. The plume of solid propellant rocket engine contains many kinds of high temperature metal oxide particles. For detecting the plume of solid rockets, the spectral radiative properties of high temperature particles must be calculated accurately. The complex refractive index (optical constant) is a fundamental radiative property of particles which is related to the composition, temperature and surface condition. Since the surface ratio of the particle material is much bigger than that of the bulk material and the high temperature particles are easy to accumulate into an aggregate mass, the structure of high temperature particle is very complicated and the complex refractive indices of particles are not equal to the bulk material which must be studied individually. The complex refractive indices of particles can not be directly measured through experiment, which must be retrieved from other experimental physical parameters by the corresponding inverse model.In this thesis, the radiative properties of particles are studied comprehensively and systematically, and main attention has been paid to the following four aspects of investigations:1. The particle radiative direction problems are analyzed systematically. From the viewpoint of the electromagnetic theory, the radiative property of non-spherical particles and aggregate particles is studied by the Discrete Dipole Approximation (DDA), T-Matrix method and Generalized Multi-particle Mie solution (GMM). By comparison with the equivalent sphere, the difference and variation principle of absorption factor, scattering factor, extinction factor and scattering phase function of non-spherical particles with different size parameter, shape ratio and complex refractive indices are investigated. Meanwhile, the influence of interaction of element sphere in the aggregate particles on the radiative property and the comparison of the influence on the temperature distribution of different shape aggregate particles with the equivalent sphere are also studied. Finally, the computational method for particle system is introduced.2. The inverse radiative problem of the particle media by using the Particle Swarm Optimization (PSO) algorithm is investigated. The standard PSO, Stochastic PSO (SPSO) and the Mutli-Phase PSO (MPPSO) are used to retrieve the radiative properties (such as the absorption coefficient, scattering coefficient, phase function, optical thickness and albedo etc.) and the geometrical parameter (such as the particle size distribution). Meanwhile, the converge velocity and computational accuracy for retrieving of different PSO algorithms are analyzed.3. Two theoretical models for retrieving the complex refractive index of high temperature spherical particle and non-spherical particle have been developed based on the Equivalent Spectral Transmittance Ratio (ESTR). In these two models, the forward simulation is based on the complete radiative transfer equation considering the particle's self-radiation and scattering enhancement. Meanwhile, the monodromic characteristics of these two models are analyzed thoroughly. The monodromic range of size parameter and complex refractive index is also determined. By retrieving the known complex refractive indices of particles, the present models are validated. The influence of measurement errors on the inverse results is also analyzed. The sensitivity analysis of the radiation inverse problem is studied systematically, which provide the theoretical basis.4. The design proposal of the high temperature particle spectral radiation property measurement system is proposed and the experimental platform is built. It is the first time to retrieve the spectral complex refractive index of high temperature particles in China. The experimental platform concludes both particulate and bulk material measurement. The spectral measurement range is from 1μm to 25μm and the maximum temperature is 1500K. The sparse particle system is suspended and heated successfully. The pseudo-stabilized space distribution of particles at different temperature is obtained. Combined with the inverse model, the complex refractive indices of Al2O3 particle at different temperature has been obtained by the experimental investigation.