谐振腔微扰技术测量湿蒸汽两相流的理论分析

Theoretical Analysis of Cavity Perturbation Techniques for Measuring Wet Steam Tow-phase Flow

蒸汽湿度的准确测量对汽轮机的安全、经济运行和优化设计具有重要意义。根据湿蒸汽混合物的介电性质，采用微波谐振腔介质微扰理论，建立圆柱形谐振腔在TE011模式下测量蒸汽湿度的关系式。测量湿度与湿蒸汽的热物性、温度（压力）、谐振腔的谐振频率和相对频偏有关。湿蒸汽的温度（压力）降低、谐振腔的谐振频率升高、相对频偏升高，湿度测量结果会增大，反之减小。谐振频率降低、温度升高，湿度的测量精度提高。蒸汽湿度测量谐振腔的谐振频率建议在5～10GHz。对某200MW凝汽式汽轮机进行排汽湿度测量实验，湿度测量结果与理论计算值吻合，验证了微波谐振腔微扰法测量蒸汽湿度理论的正确性。

The accurate measurement of wet steam humidity is important to safe, economic operation and optimization design for turbine. According to the dielectric properties of wet steam mixture, using microwave cavity dielectric perturbation theory, a relationship of cylindrical cavity for humidity measurement in TE011 mode was established. Thermal properties of wet steam, temperature （pressure）, resonance frequency and relative frequency offset of the cavity affect the humidity measurement. Humidity measurement increases with temperature （pressure） decreasing, cavity resonant frequency and relative frequency offset increasing, otherwise decreases. The humidity measurement accuracy increases with resonance frequency decreasing and temperature increasing. It suggests that the cavity resonance frequency is between 5～10 GHz for steam humidity measurements. The experiment for measuring exhaust humidity in a 200 MW steam turbine was carried out. The humidity measurement results agree well with the theoretical calculation results. The correctness of the microwave cavity perturbation theory for measuring wet steam humidity was verified.