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

Abstract

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 l,l,l,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 _+0.03% and their estimated accuracy is +0.05% . The viscosities have a precision of +0.6% and an estimated accuracy of _ 2 %.

Validation of a Vibrating-Wire Viscometer: Measurements in the Range of 0.5 to 135 mPa·s

“…Parameter ∆ 0 is obtained experimentally from the resonance curve of the sensor under vacuum, 7,9 and the density of the wire is taken from the literature. 13 As discussed before, 7,9 the average radius of the wire is advantageously determined in a single experimental run at a temperature and pressure where the viscosity and density of a reference fluid are well known.…”

Tris(2-ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part I: Viscosity measurements at temperatures from (303 to 373) K and pressures up to 65 MPa, using a novel vibrating-wire instrument

“…1). The tungsten wire was tensioned, prior to clamping, using a weight with a mass of about 1.6 kg, acquiring a resonance frequency of about 1 kHz in air at room temperature corresponding to a vertical tension around 50% of the yield strength of tungsten [47][48][49]. The magnets (8 in Fig.…”

“…One particular characteristic of the magnetic circuit assembly is that it can be replaced without changing the tension of the wire, which may be useful if magnets with a higher Curie temperature must be placed in order to enable work at higher temperatures. The distance of the magnets and the spacers to the tungsten wire was set at a minimum of 60 times the wire radius, R s , which is deemed to introduce an error less than 0.2% due to the finite distance from the cell walls [44,[47][48][49][50].…”

“…The wire density was taken from the literature [52] and the internal damping was determined from the frequency response of the sensor under vacuum as described in Ref. [48].…”

Viscosity Measurements of Liquid Toluene at Low Temperatures Using a Dual Vibrating-Wire Technique

“…We have previously described a vibrating-wire instrument, operated in a forced mode, which has been used for the simultaneous measurement of the density and the viscosity of fluids, over wide ranges of temperature and pressure [1][2][3][4]. Recently [5], we have described some preliminary tests of a novel instrument, showing that it is possible to perform mutually consistent viscosity measurements by operating a vibrating-wire sensor both in forced and free decay modes.…”