Density measurement by oscillating tube. Effects of viscosity, temperature, calibration and signal processing

Abstract

A frequency counter and precision thermostat, designed to operate in conjunction with an Anton Paar DMA 602 oscillating tube densitometer, have been built. The apparatus is capable of rapid density determinations. It can detect density changes of less than 5 x g ~m -~and allows densities of low viscosity materials to be determined to an accuracy of f 5 x g ~m -~if a suitable calibration standard is available. The effect of t h e viscosity of the samples on the density readings has been found to be significant when the viscosity is greater than ca. 1 mPa s. A correction procedure has been devised for such liquids. Excess volumes of the cyclohexanetoluene system have been measured at 298.15 K and agree with literature data, t h u s confirming the suitability of the apparatus for the determination of density differences.

Tris(2-Ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part II: Density measurements at temperatures from (293 to 373)K and pressures up to 68MPa

“…Several studies of this effect [11][12][13][14][15][16][17][18][19] have shown that the shape of the deviation is similar for all the studied vibrating-tube densimeters from Anton Paar. However, the reasons for this do not seem to be well understood.…”

“…The effect of viscosity on the density measurements made by U-tube densimeters has been extensively studied experimentally [11][12][13][14][15][16][17][18][19] and, recently, the increasing interest in high viscosity liquids has intensified the awareness in this effect [15][16][17][18]. However, to the knowledge of the authors, no theoretical study has been published.…”

“…Retsina et al [20] also note that an analytical treatment of the oscillation of a U-tube is not feasible. As a consequence of the complexity of a theoretical description of the liquid viscosity effect on U-tube density measurements, only empirical studies [11][12][13][14][15][16][17][18][19] about this phenomenon have been found in the literature. The viscosity effect on density measurements depends on the tube characteristics, which implies that the correction to the density readings has to be obtained for every particular instrument.…”

Density and refractive index in mixtures of ionic liquids and organic solvents: Correlations and predictions

“…The earliest attempts at determining this quantity in RTILs resulted in large differences between the results obtained by some authors, which has been ascribed to an unusually strong influence of impurities on density [14]. Also the most commonly used technique for determining density, which uses a vibratingtube densimeter, is allegedly subject to systematic errors due to the ''damping effect" arising from the typically high viscosity of RTILs [15]. By now, impurities in RTILs have been substantially reduced, their influence on density at least partly elucidated and the consequences of the damping effect avoided by using a variety of techniques most of which require the knowledge of the sample viscosity [16][17][18].…”

Low‐Viscosity Paramagnetic Ionic Liquids with Doubly Charged [Co(NCS)4]2− Ions

“…[5,7] The density of 1 was measured in the temperature range of 15-50 8C in steps of 5 K using a vibrating-tube densiom- eter. [16] The linear temperature dependence is given by Equation (1):…”