Study Of Inversion Algorithm Of Particle Size Distribution Using Total Light Scattering Method

In total light scattering particle sizing technique, the particle size distribution can be obtained by the measurements of light extinction data at multiwavelengths. The data processing of this technique is actually the solution of Fredholm integral equation of the first kind. At present, there is no analytical solution for the Fredholm integral equation of the first kind, thus it is necessary to apply an appropriate inversion algorithm of particle size distributions. This project is supported by the National Natural Science Foundation of China. Its intention is to study the inversion algorithms of particle size distributions, which makes the total light scattering method especially suitable for in-line particle size measurement.This paper specifically focuses on the inversion algorithms of particle size distributions for spherical and non-spherical particles. The research work could be summarized as follows:1.Since the inversion of particle size distribution is accomplished by solving the Fredholm integral equation of the first kind, the lower and upper integration limits, that is, the particle size range, must be determined beforehand. By analyzing and comparing the inversion results for different monomodal and bimodal R-R spherical particle distributions in the visible and visible-infrared region, the particle size range in the independent model can be determined. Meanwhile, the modified Mie extinction efficiency is applied instead of the original Mie extinction efficiency, which can obtain the particle size range with more accuracy.2.In order to overcome the complexity in calculation extinction efficiency and instability in inversion results, four inversion algorithms are proposed to retrieve the spherical particle size distributions from the light extinction data in the dependent model. Because the calculation of extinction efficiency based on Mie theory for a spherical particle is expensive in both time and resources, the anomalous diffraction approximation method for calculating the extinction efficiency of spherical particles is investigated, and then the particle size distributions are also retrieved. To alleviate the ill-posedness of the inversion equation and to improve the ability of anti-interference, an inversion algorithm based on the moment method of particle size distribution is proposed for the spherical particles. By use of the light extinction data at several wavelengths in combination with the moment relation, the spherical particle size distribution can be retrieved indirectly. In the dependent model, some a prior information about the type of the size distribution must be assumed beforehand, and then the particle size distribution is retrieved by the optimization algorithm. However, the type of the size distribution measured may not be known exactly sometimes. To overcome this difficulty, a classification inversion method based on the genetic algorithm is proposed in dependent model algorithm. The measured particle size distribution is retrieved with different particle distribution functions, and then the ultimate inversion result of particle size distribution is selected according to the inversion errors. In total light scattering particle sizing technique, the extinction spectrum of particle system contains some information about the particle size and its refractive index. So the visible extinction spectrum of particle system is analysed and the selection method of the optimal wavelength is proposed. The computer simulation and experimental data are performed to valid the feasibility and reliability of the four inversion algorithms.3.In retrieving the particle size distribution with the total light scattering technique, the shape of particle system is generally assumed to be spherical, which could decrease the complexity in calculating the non-spherical extinction efficiency. In fact, most particle systems are non-spherical particles. In this paper, the inversion algorithms proposed for the spherical particles is also considered to be applied to the non-spherical particles. Because the higher order polynomial about particle size is fit for the extinction efficiency in the inversion algorithm on the basis of the moment method, which is only suitable for the spherical particles, the other three inversion algorithms are studied for the inversion of non-spherical particles.