Validation of an accurate vibrating-wire densimeter : Density and viscosity of liquids over wide ranges of temperature and pressure

A new vibrating-wire instrument for the measurement of the density of fluids at high pressures was described in a previous paper. The technique makes use of the buoyancy force on a solid sinker and detects this force with a vibrating wire placed inside the measuring cell. Owing to the simple geometry of the oscillating element there exists a complete theoretical description of its resonance characteristics, enabling the calculation of the density of the fluid from their measurement. In the present paper a new method for the determination of the cell constants is outlined which permits the operation of the densimeter essentially as an absolute instrument. Furthermore, it is shown that the viscosity of the fluid can be measured simultaneously with the density. New results for three fluids are presented: for cyclohexane at temperatures from 298 to 348 K and pressures up to 40 MPa, for 2,2,4-trimethylpentane between 197 and 348 K at 0.1 MPa, and for 1,1,1,2-tetrafluoroethane from 197 to 298 K close to saturation. The sets of measurements were chosen with the intention of testing the performance of the apparatus, complementing previous work at higher pressures. The densities and viscosities measured exhibit the same accuracy for all of the three fluids over the entire temperature and pressure ranges and were obtained using the same set of cell parameters. The precision of the densities is plus or minus 0.03% and their estimated accuracy is plus or minus 0.05%. The viscosities have a precision of plus or minus 0.6% and an estimated accuracy of plus or minus 2%.