基于激光散射机理及CCD成像的蒸汽湿度测量方法研究

A way of measurement of precision, on - line determine the wetness and the droplet size as well as its distribution in the last stage of a steam turbine to be realized , which is still a worldwide technical problems. Though much work have been done by researchers who come from all over the world, an effective and feasible method of measurement haven't got still. The purpose of steam wetness measurement study was based on the mechanism of laser light scattering and CCD imaging. The main research contents : (1)Based on the internal structure of steam turbine last stage low pressure cylinder, by using two-phase flow theory, similarity theory and jet theory, a wet steam generator test bench could be studied. According to two phase flow theory and steam condensation nucleation as well as water-drop growth theory, steam and humidity distribution of wet steam generator steam was researched with numerical simulation methods. Adopting Mie scattering theory researching on laser wavelength, measurement angle, water-drop particle size, water-drop density parameters how to affect the scattering intensity distribution was studied. A scattering light transmission and measurement model was be established. Because of the Mie scattering theory, the scattering intensity distribution and humidity parameter of the empirical model was set up, real-time processing of experimental data could be realized. By fractal theory, we reconstruct three-dimensional distribution of water particles in the wet steam was reconstructed from wet steam distribution of scattered light images. 　　 The research results will provide new technical support for steam turbo-generator unit safe and economic operation, fault diagnosis.

如何实现汽轮机末级蒸汽湿度与水滴粒径的高精度、在线和实时测量，至今仍是一个世界性的技术难题，国内外诸多研究人员做了大量工作，但目前仍没获得一种高效和可靠的测量方法。本课题研究目标是基于激光散射理论和CCD成像技术实现对蒸汽湿度的实时测量。主要研究内容包括：（1）基于汽轮机末级低压汽缸的内部结构，根据两相流理论、相似理论和射流理论，研制湿蒸汽发生器实验台；（2）采用两相流理论和蒸汽凝结成核以及水滴生长理论，就湿蒸汽发生器中蒸汽湿度分布进行数值模拟研究；（3）基于米散射理论研究激光波长、测量角度、水滴粒径、水滴数密度等参数对散射光强分布的影响，建立散射光传输和测量模型；（4）根据米散射理论，通过建立散射光强分布与湿度参数的经验模型，实现对实验数据的实时处理；采用分形理论从湿蒸汽散射光分布图像中重建湿蒸汽中水滴颗粒的三维分布。 本课题研究成果将为汽轮发安全经济运行、故障诊断提供全新技术支持。

基于激光散射和CCD成像的蒸汽湿度高精度在线测量技术是极具应用前景的含微粒流体工质参数测量技术。开展本项目研究是为了弄清蒸汽水滴的光散射及测量的机理和规律，解决散射光图像高精度获取、湿度参数反演及在线处理和等难题，以便提高CCD散射测量的精度和环境适应性。本项目基于汽轮机末级低压汽缸的内部结构，根据两相流理论、相似理论和射流理论，研制了蒸汽湿度测量实验台，改进和优化了测量系统，构建了蒸汽测量系统模型及硬件结构框架，完成了系统硬件设计和软件设计开发，使模拟的湿蒸汽环境更接近于真实的汽轮机工作环境，提高了系统测量的准确度；基于激光散射原理，设计和优化了散射体模型，建立了基于后向异轴角散射法的蒸汽湿度测量模型；采用两相流理论和蒸汽凝结成核以及水滴生长理论，对蒸汽湿度分布进行了理论分析和数值模拟，获得了蒸汽湿度分布和水滴浓度特征；基于Mie散射理论，研究了入射光光强、激光波长、测量截面、散射光接收角度、水滴粒径分布、水滴数密度等参数对散射光强分布规律的影响，建立了散射光传输、测量模型和散射光强分布参数模型，获得了微粒群散射相函数与散射角关系，以及散射系数、消光系数、吸收系数之间的关系；通过建立散射光强分布与湿度参数的经验模型，实现了实验数据的实时处理，并通过对不同激光波长、水滴粒径和密度分布等条件下的散射相函数分布进行数值模拟反演寻优，获得了蒸汽湿度分布测量过程中尺寸参量、质量中间半径和散射光接收角度等因素对水滴群散射光强分布的影响规律，重建了湿蒸汽中水滴颗粒的三维分布；研究了单波长/双角度测量蒸汽湿度的方法，揭示了各个截面在不同工况下的散透比和水滴质量中间半径的变化规律，并通过实验测量获得了变工况下蒸汽湿度变化曲线，验证了蒸汽测量系统的可行性和有效性，为将激光散射和CCD成像技术运用于蒸汽湿度测量上提供了理论指导和技术支持。