High-Frequency Monitoring of Residual and Bound Water in Nonconductive Fluids

This paper presents a novel application of open-ended microwave cavities for monitoring residual water content or bound water content in nonconductive fluids transported in circular pipes. The sensor consists of a section of a circular waveguide lined with a solid dielectric inserted in series with the piping system transporting the test fluid. At the selected frequency of operation, the end waveguides formed by the piping system operate below cutoff, while the sensor forms a resonant cavity. The resonant frequency of the cavity, which is a measure of the water content in the test fluid, is monitored automatically by an electronic system.