Radiative Property Of Inhomogeneous Particle And Its Aggregate

Research on the radiative properties of inhomogeneous particle and soot aggregate is wide and deep in many engineering applications, especial in the aerospace and atmosphere. However, the radiative properties of coal ash in the furnace are hard to determine from the experimental. The multilayer code of electromagnetism theory always appears overflow when the size parameter becomes larger. The radiative properties of the inhomogeneous coal ash, phase-changing droplets and multilayer particle are also hard to determine in practice. Furthermore, the estimation of the radiative properties of soot aggregate coated with water and adulterated with dust in atmosphere. Approximation methods also need further investigated. Therefore, it is necessary to employ the theoretical model to these inhomogeneous particles for calculating their radiative properties.In the present thesis, the radiative properties of inhomogeneous particles, including coal ash, phase-change particles for water, silica, and alumina, as well as multilayer particles, are investigated by effective medium theory in combination with Mie theory. On the other hands, the radiative property of soot aggregate in atmosphere is studied by effective medium theory in combination with T-matrix method. In summary, the scope covered in this dissertation consists of the following five parts:1. The radiative properties of multi-component synthetic ash and crude ash were investigated by effective medium theory (EMT) in combination with Mie theory, and the applicability of this approach is subsequently analyzed. In principle, the effective medium theory based on industrial analytical species can not be applied to coal ash produced in combustion. While it can be used to analyze synthetic ash slag.2. Monte-Carlo ray-tracing method (MCRTM) is developed for calculating the radiative properties of multilayer sphere. The applicability of effective medium theory for phase-change particle and multilayer sphere were analyzed in comparison with the BHCOAT code and the MCRTM. And the applicable range of EMT is subsequently analyzed. The results reveal that it is capable of calculating the effective radiative properties of water and alumina by EMT in combination of Mie theory. For the multilayer spherical particle, where each layer has different optical constant, the MCRTM is approximately applicable to calculate the radiative property of multilayer spherical particle by combining EMT with Mie theory, in the case of the deviation between refractive index and extinction coefficient is small.3. For phase-change particle, phase-change models for droplet and droplet layer are constructed. The corresponding phase process for droplet and droplet layer is then analyzed, respectively. The results reveal that the method of combined effective medium theory and Mie theory is applicable for calculating the radiative properties of phase-change particles. In radiation phase-change process of heat transfer, the evaporation of water droplet in amount and energy irradiated by sun can not be ignored. On the other hand, phase zone and temperature distribution in droplet layer show that the effect of phase-change of droplet on the heat transfer process can not be ignored.4. Radiative properties of soot aggregate with different morphologies are studied. The applicability of spherical approximation method for computing radiative properties of soot aggregate is estimated and compared with that of T-matrix method, where the spherical approximation method is based on equal volume, equal project area, the radius of gyration, and volume and volume-to-projected area ratio. The computation results show that the radiative properties of soot aggregates vary only slightly with morphologies. For absorption cross section, the values of approximation method based on the volume-to-projected area ratio have the smallest deviation in comparison with that of T-matrix method. Meanwhile, for the scattering phase function, the values from approximation method have the smallest deviation in comparison with that of T-matrix method.5. By combining effective medium theory with T-matrix method, the effects of two typically morphological structures, water coating, dust mixing and primary particle size distribution on the radiative properties of soot fractal aggregates in atmosphere are investigated using T-matrix method. The results show that the effect of morphological changes on the radiative properties of soot aggregates can not be neglected in wet air, and the largest relative deviation of their scattering cross section is found to be 48.8%. Furthermore, the radiative properties of soot aggregates coated with water increase notably with an increase in the thickness of water shell. On the other hand, the mixing structures of dust are found to have slightly effect on radiative properties of aggregates.