Dielectric properties of wet steam based on a double relaxation time model.

Abstract

The last stages of most steam turbines operate in wet steam, resulting in water erosion of the rotor blades and the reduction of turbine efficiency. Accurate measurement of steam wetness is the key to ensure an efficient and stable operation of steam turbines. The equivalent complex permittivity model of wet steam was established by Maxwell-Wagner non-homogeneous dielectric theory, and the complex permittivity distribution of frequency and temperature changes of saturated water, dry saturated steam, and wet steam was derived. The measurement experiments verified the above properties of dry saturated steam and wet steam. The complex permittivity of the wet steam is similar to that for the dry saturated steam. The real part increases with increasing frequency and temperature. When the frequency is large or the temperature is low, the real part approaches 1. The imaginary part increases first and then decreases with the increase of frequency. In addition, with the increase of temperature, the imaginary part becomes larger. When the temperature is low, the imaginary part is close to 0, which is independent of the frequency.