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

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.