Study on a method of steam wetness measurement based on microwave resonant cavity

A method of wetness measurement based on microwave resonant cavity perturbation for wet steam is presented. The dielectric characteristic of wet steam in turbine was analyzed. The dielectric constant of wet steam only depends on the humidity of the steam at a certain temperature. The humidity of the wet steam can be attained by measuring the frequency deflection of the resonant cavity when the wet steam flows through the cavity. A system of steam wetness measurement based on this method and a resonant cavity with special structure were designed. The resonant cavity which has a three-ring network separator at each end is the most suitable cavity. The deposition film on the cavity interior wall is very thin when wet steam flows through the resonant cavity, and it is only a few microns. The influence of water film on measurement result can be neglected. Comparing with the thermodynamic methods and optic methods, the system of this method is simple and can be achieved online for measuring the humidity of flowing wet steam. This method has a high precision.