Calibration Fluids and Calibration Equations: How Choices May Affect the Results of Density Measurements Made with U-Tube Densimeters (original) (raw)
Related papers
Journal of Research of the National Institute of Standards and Technology
The viscosities of three pentaerythritol tetraalkanoate ester base oils and one fully formulated lubricant were measured with an oscillating piston viscometer in the overall temperature range from 275 K to 450 K with pressures up to 137 MPa. The alkanoates were pentanoate, heptanoate, and nonanoate. Three sensing cylinders covering the combined viscosity range from 1 mPa·s to 100 mPa·s were calibrated with squalane. This required a re-correlation of a squalane viscosity data set in the literature that was measured with a vibrating wire viscometer, with an estimated extended uncertainty of 2 %, because the squalane viscosity formulations in the literature did not represent this data set within its experimental uncertainty. In addition, a new formulation for the viscosity of squalane at atmospheric pressure was developed that represents experimental data from 169.5 K to 473 K within their estimated uncertainty over a viscosity range of more than eleven orders of magnitude. The viscosi...
The pressure-viscosity coefficient of a traction fluid is determined by fitting calculation results on accurate film thickness measurements, obtained at different speeds, loads, and temperatures. Through experiments, covering a range of 5.6 < M < 12000, 2.1 < L < 17.5, film thickness values are calculated using a numerical method and approximation formulas from twelve models. It is concluded that, to assess the pressure-viscosity coefficient of the fluid, the Chittenden et al. approximation formula applied to circular contacts is the best choice, having an inaccuracy in between (-15%, +11%). This expression has been used far outsides the regime of the numerical data where it was based upon.
Compressed-Liquid Density Measurements of Four Polyol Ester-Based Lubricants
Energy & Fuels, 2018
A vibrating-tube densimeter has been used to measure compressed-liquid densities of the fluids pentaerythritol tetrapentanoate (POE5), pentaerythritol tetraheptanoate (POE7), pentaerythritol tetranonanoate (POE9), and a fully qualified lubricant within a temperature range of 270 to 470 K at pressures within 0.5 to 50 MPa. The compressed-liquid densities of the lubricants studied cover a density range from 829 kg/m 3 to 1063 kg/m 3. The data have been extrapolated to atmospheric pressure and correlated with a Racket equation and the compressed-liquid density data have been correlated to Tait equations for comparison to existing literature data.
2011
The pressure-viscosity coefficients of two commercial traction fluids are determined by fitting calculation results on accurate film thickness measurements, obtained at a wide range of speeds, and different temperatures. Film thickness values are calculated using a numerical method and approximation formulas from twelve models. It is concluded that, to assess the pressure-viscosity coefficient of these traction fluids, the Hamrock and Dowson approximation formula, and derivatives: Hamrock et al. and Chittenden et al., are the best choice, having an inaccuracy in between (-12%, +7%). These equations have been used far outsides the regime of the numerical data where they were based on.
Journal of Chemical Thermodynamics, 2011
A new method for accurately converting vibrating tube periods of oscillation in density values is presented. This method is based on the fundamental requirement of the non-dependence on pressure of the vibration period of the cell under vacuum. An analytical method permits to correctly evaluate the evacuated vibrating tube periods of the Anton Paar cells namely the high pressure cells, 512 and 512P, as a function of temperature. It is further shown that the previously experimental method for the determination of this parameter is not suitable for obtaining reliable density values. A new simple calibration procedure is described and tested over wide ranges of temperature, T = (283.15 to 323.15) K and pressure, P = (0.1 to 60) MPa. New recommended density values for n-alkanes (C 6 , C 7 , C 8 , and C 10) and tetrachloromethane, calculated by the proposed method, are given and compared with literature values in terms of mutual uncertainties.
Fluid Phase Equilibria, 2014
The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate or 1,2,4-Benzenetricarboxylic acid, tris(2-ethylhexyl) ester (TOTM) which is an important plasticizer in the polymer industry and has wide applications as a lubricant. Nevertheless, the main motivation for the present work is to propose TOTM as a plausible candidate for an industrial viscosity reference fluid for high viscosity, high pressure and high temperature. This kind of reference fluid is presently on demand by oil industries and the International Association for Transport Properties is developing efforts aiming to select appropriate candidates and to establish the corresponding reference data. The viscosity measurements were performed with a novel vibrating wire sensor. The new instrument was designed for operation at high pressures (up to 100 MPa) and temperatures up to 373 K. The present measurements were obtained using the vibrating wire sensor in the forced oscillation or steady-state mode of operation. The viscosity measurements were carried out up to 65 MPa and at six temperatures from (303 to 373) K. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is 0.53% and the maximum absolute relative deviation was less than 1.7%. The expanded uncertainty of the present viscosity results, at a 95% confidence level, is estimated to be less than AE2% for viscosities up to 68 mPa s, less than AE2.6% for viscosities between (69 and 268) mPa s and less than AE3% for higher viscosities. The TOTM density data necessary to compute the viscosity results were measured using a vibrating Utube densimeter, model DMA HP and are described in part II of the present work. No literature data above atmospheric pressure could be found for the viscosity of TOTM. As a consequence, the present viscosity results could only be compared upon extrapolation of the vibrating wire data to 0.1 MPa. Independent viscosity measurements were performed, at atmospheric pressure, using an Ubbelohde capillary in order to compare with the vibrating wire results, extrapolated by means of the above mentioned correlation. The two data sets agree within AE1%, which is commensurate with the mutual uncertainty of the experimental methods. Comparisons of the literature data obtained at atmospheric pressure with the present extrapolated vibrating-wire viscosity measurements have shown an agreement within AE2% for temperatures up to 339 K and within AE3.3% for temperatures up to 368 K.
The Journal of Chemical Thermodynamics, 2010
A specific calibration procedure that allows the accurate determination of densities of room temperature ionic liquids, RTILs, as a function of temperature and pressure using vibrating tube densimeters is presented. This methodology overcomes the problems of common calibration methods when they are used to determine the densities of high density and high viscosity fluids such as RTILs. The methodology is applied for the precise density determination of RTILs 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF 4 ], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF 4 ], 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF 4 ], and 1-octyl-3-methylimidazolium tetrafluoroborate [Omim][BF 4 ] in the temperature and pressure intervals (283.15 to 323.15) K and (0.1 to 60) MPa, respectively. The viscosities of these substances, needed for the estimation of the viscosity-induced errors, were estimated at the same conditions from the experimental measurements in the intervals (283.15 to 323.15) K and (0.1 to 14) MPa and from a specific extrapolation procedure. The uncertainty in the density measurements was estimated in ±0.30 kg Á m À3 which is an excellent value in the working intervals. The results of these RTILs have demonstrated that viscosity-induced errors are relevant and they must be taken into account for a precise density determination. Finally, an alternative tool for a simpler application of this procedure is presented.
Industrial & Engineering Chemistry Research, 2007
The dynamic viscosity under pressure of three mixtures of pentaerythritol ester lubricants (PEs) has been measured using a rolling-ball viscometer for several temperatures with an experimental uncertainty of 3%. The first one is a multicomponent mixture of several PEs named in the present work as PEC5-C9 lubricant; the second one is a binary mixture of pentaerythritol tetra(2-ethylhexanoate), PEB8, and pentaerythritol tetraheptanoate, PEC7, with a PEB8 mole fraction of 0.6670; and the third one is another binary mixture of PEB8 and pentaerythritol tetrapentanoate, PEC5, with a PEB8 mole fraction of 0.6911. The two binary mixtures, xPEB8 + (1x)PEC7 and xPEB8 + (1x)PEC5, have been prepared with the same viscosity grade as the PEC5-C9 lubricant (VG32). A total of 1176 experimental measurements of the rolling time have been performed at pressures up to 60 MPa for the determination of 196 dynamic viscosity data points. The viscosities of these binary mixtures have been compared with the predicted values obtained by using several viscosity models (Grunberg-Nissan and Katti-Chaudhri mixing laws, self-referencing model, hard-sphere theory, and free-volume model). All methods predict dynamic viscosity values for the two binary mixtures that agree with the experimental data within an average mean deviation of 10% over the entire temperature and pressure ranges. The best predictions were found with the free-volume model, for which the average mean deviation for both mixtures is lower than 4%. Parameter values for the self-referencing model were determined from experimental viscosity data of several pure PEs. These parameters permit the estimation of viscosity values of PE lubricant of unknown composition, when a viscosity value at any temperature and pressure is available. This model predicts the viscosities of PEC5-C9 lubricant with an average deviation of 4%.
In pursuit of a high temperature, high pressure, high viscosity standard: the case of TOTM!
Journal of Chemical & Engineering Data, 2017
This paper presents a reference correlation for the viscosity of tris(2-ethylhexyl) trimellitate designed to serve in industrial applications for the calibration of viscometers at elevated temperatures and pressures such as those encountered in the exploration of oil reservoirs and in lubrication. Tris(2-ethylhexyl) trimellitate has been examined with respect to the criteria necessary for an industrial standard reference material such as toxicity, thermal stability, and variability among manufactured lots. The viscosity correlation has been based upon all of the data collected in a multinational project and is supported by careful measurements and analysis of all the supporting thermophysical property data that are needed to apply the standard for calibration to a wide variety of viscometers. The standard reference viscosity data cover temperatures from 303 to 473 K, pressures from 0.1 to 200 MPa, and viscosities from approximately 1.6 to 755 mPa s. The uncertainty in the data provided is of the order of 3.2% at 95% confidence level, which is thought to be adequate for most industrial applications.