Static dielectric constants for liquid water from 300 K to 350 K at pressures to 13 MPa using a new radio-frequency resonator

A stainless steel reentrant cavity with primary resonances at three frequencies has been constructed and used to make dielectric constant measurements on liquid water between 300 K and 350 K, at pressures to 13 MPa. At; the frequencies of this study (25 MHz to 250 MHz), there is no evidence of frequency dependence in the water data. Three methods have been used to convert resonant frequencies to dielectric constants. Using a lumped-parameter model recommended recently by NIST investigators, the dielectric constants from the current work agree within 0.1 with the best data available from other recent investigations. Temperature and pressure derivatives of the dielectric constant are nearly identical using all three methods, and they are found to be in reasonable but not perfect agreement with the best available correlation of previous results. A waveguide model approach resulted in dielectric constants about 0.3 higher than accepted values, likely due to uncertainties in geometry and materials properties. A second lumped-parameter approach also failed, likely due to its dependence on measured resonant frequency half widths with water occupying the cavity.