Study Of The Laser Light Scattering Phase Function Of Stream Dryness In Steam Turbine

In the steam turbine of thermal power plant, the existence of wet steam not only reduces the efficiency of steam turbines, but may also cause serious blade corrosion, and thus may bring great harm to the economic and security of steam turbines. In this paper the author based on laser light scattering theory and Mie scattering theory, using a singlet power and singlet wavelength of 650 nm red semiconductor laser online testing, using inverse fitting scattering phase function method to calculate the stem degrees of internal steam turbine, and thus provide direct data for monitoring the harm that the turbine may incur.According to Mie scattering theory, the distribution of spectroscopy has relationships of particle radius after light scattering by particles scattering, and particle radius is not at the same time, the scattering function of the distribution is different. The radius of the wet steam particle could be obtained by the fitting inversion based on the measuring of the spectral signal distribution. Generally in order to reach a certain precision, multi-angle collection at the same time were needed. This will make sufficient data when in the use of matrix inversion with a radius of the scattering particles for mathematical calculations. Therefore, the scattering spectrum distribution which can not consider the characteristic of the particles, will be obtain the relatively full amount of data. One (or several) point of view of the scattered light would gathered by photo detector, when the particles within the steam turbine present in the measurement zone.The theoretical analysis and numerical calculations of wet steam particle light scattering characteristics are carrying out by using Mie scattering theory. Moreover, the relations of the distribution of scattering light and incident wavelength, the radius of wet steam particle and the complex refractive index are presented. This paper presents a numerical algorithm of Mie scattering. Compared with conventional algorithm, the calculating time of this algorithm is short, and the range of the particle sizes, which can be calculated by programme, is able to satisfy conventional measuring requirements. A single particle phase function distribution of different radius was obtained by using VC++ programming language. The radius of scattering particle can be identified by measuring the distribution of scattered light. By analyzing the impact on the phase function of spectrum parameters, the attenuation of large radius particle was faster than small particles when the scattering angle of phase functions increased from zero degrees. The deviation of real part of complex refractive index has the large impact of the phase function, and has different effects on the different scattering angle. When the particle radius decreases, the impact of real part of the complex refractive index is more obvious. When the particle radius increases, the impact of real part of the complex refractive index is smaller. The deviation of imaginary part of complex refractive index has the small impact of the phase function, and the impact on the order of magnitude is less than 1%. Some fragments of the major procedures are given in this paper. The scattering phase function of particles group is composed by spectral distribution and a single particle scattering function integral. The corresponding spectral distribution can be obtained by given the measured values of scattering phase function in a certain angle. The single particle phase function has many rush ups and downs, the phase function of particle group is more smooth. The phase function of the plural large radius of particle has the more quickly attenuation than the small radius of particle when the scattering angle increases from zero degrees. There are much more difference between maximum and minimum. The real part of complex refractive index has larger affects in the phase function, and has larger affects in after item than former item. Different spectral distribution of particle groups corresponding to the phase function has made the distribution of spectral inversion possible.Dry method of measurement in the low-pressure cylinder of the steam turbine is researched by using Mie scattering theory. Based on the derived and calculated curve of phase function, the data processing method of measurement signal inversion fitting is brought forward. Then the influence of the real part and the imaginary part of light refractive index in this method is studied. According to the practical application of the steam turbine, the basic structure of light scattering in dryness sensor and the basic design on hardware circuit were put forward. In the circumstance when the low-pressure cylinder of the steam turbine ejects steam in the state of wet steam, there is no way to measure the enthalpy since the isotherm and the isobar are overlapped, through the photoelectricity exploration technology and the inversion of phase function, the distributing function of concreting water particles and the most probability radius, the average radius and the maximum radius can be fixed, then the content of the liquid water can be calculated by integral. The dryness fraction of the wet steam can be calculated by the measure of the tension and the temperature and by the dryness steam density figured out in the equation of ideal gas state. The author design an experimental device using laser light scattering theory to measure the steam dryness of steam turbine. This device can be online measurement of the diameter distribution of drop of water lever at the end in the steam turbine, and the extraction sampling is not needed as the thermodynamic, therefore it will not affect the normal operation of steam turbine. At the same time it can be measured the radius of the drip and the spatial distribution of steam wetness, measuring speed and to receive real-time measurement results.Finding of this paper for further research and design of integrated smart sensor system has laid a theoretical and design foundation. And the result of this study provides an online measurement method for wet steam content in the gas and wet two-phase flow. And the technical problems of stem measurement of the enthalpy-entropy diagram were resolved.