Research On Measurement Technology Of Particle Size Based On Static Light Scattering

Demand for online measurement of particle size distribution(PSD) is very urgent in the field of environment, agriculture, energy, chemical industry, aerospace and so on. It is important to achieve particle size distribution quickly and accurately for the development of related fields. Light scattering method has become a widely used technique for online measurement of PSD in recent years because it is simple, high precision, good repeatability and easy to realize online measurement. The calculation of particle size distribution is an ill-posed problem so that the inversion algorithm is needed. The accuracy, robustness, speed and noise immunity of inversion algorithm is the key to online measurement. Therefore, Derivation and calculation of mathematical model, inversion algorithms and experimental analysis are studied in this paper.Firstly, the mathematical model based on Mie scattering theory, Fraunhofer diffraction theory and Rayleigh scattering is studied. Scattering coefficient, extinction coefficient, scattering intensity and light energy coefficient matrix based on Mie scattering theory and Fraunhofer diffraction theory are computed and the difference of two matrixs is compared, which provides the basis for inversion algorithm and experimental system.Secondly, in inversion algorithm, the nonparametric data-processing method and the dependent mode algorithm are studied in this paper. In the side of dependent mode algorithm, the instability phenomena that the distribution curve is over fitting and characteristic parameter is easy to overflow by using the conventional objective function in the process of inversion. For this reason, an objective function based on Tikhonov regularization theory is built. Based on this objective function, artificial fish swarm algorithm(AFSA) and quantum behaved particle swarm optimization algorithm(QPSO) are applied to retrieve the PSD respectively. In the side of nonparametric data-processing method, the conventional Chahine algorithm is poor antinoise ability and sensitive to the number of iterations, which leads to the instability phenomena such as burrs, false peaks and concussion etc. in the process of inversion. Therefore, an improved algorithm is proposed that combines regularization theory with Chahine algorithm to improve the stability of inversion algorithm and accuracy of inversion results.Finally, small angle forward scattering measurement system based on Mie scattering theory is built, which uses CCD to receive scattered signal. Then, the actual scattering light distribution can be extracted by image processing technology. At last, the PSD of standardized polystyrene microsphere is retrieved by using proposed algorithms. Results show that proposed algorithms can retrieve the particle size distribution successfully, speedly and accurately. The relative errors for median diameter D50 that gotten by AFSA and QPSO combined with Tikhonov regularization theory are both within 1%. The relative errors for median diameter D50 that gotten by improved Chahine algorithm is within 3%, and D10, D90 are both within 5%.