The speed of sound in gases

The speed of sound in various gases was measured using two different acoustic resonators. The first, a fixed-pathlength variable-frequency cylindrical resonator, was operated between 50 and 100 kHz, while the second, a spherical resonator of radius 60 mm, was operated between 2 and 15 kHz. The temperatures and pressures of the gases were accurately controlled and measured. Measurements were made on argon, xenon, helium, and 2,2-dimethylpropane at various temperatures between 250 and 340 K, and at pressures below 110 kPa. The results obtained in 2,2-dimethylpropane were used to derive values of the perfect-gas heat capacity and the second acoustic virial coefficient at temperatures between 250 and 340 K. The second acoustic virial coefficients determined using the spherical resonator have a precision of about ±0.1 per cent and have been used to calculate second virial coefficients. Measurements of the acoustic losses in the spherical resonator indicate that the vibrational relaxation time of 2,2- dimethylpropane at 298.15 K and 100 kPa is 4 ns. Detailed measurements of the speed of sound in argon indicate that a precision approaching 1 x10-6 is possible in acoustic thermometry using a spherical acoustic resonator. The second acoustic virial coefficients obtained in argon are in close agreement with values calculated from the interatomic pair-potential-energy function

Reference materials for phase equilibrium studies. 1. Liquid–liquid equilibria (IUPAC Technical Report)

This article is the first of three projected IUPAC Technical Reports resulting from IUPAC Project 2011-037-2-100 (Reference Materials for Phase Equilibrium Studies). The goal of this project is to select reference systems with critically evaluated property values for the validation of instruments and techniques used in phase equilibrium studies of mixtures. This report proposes seven systems for liquid–liquid equilibrium studies, covering the four most common categories of binary mixtures: aqueous systems of moderate solubility, non-aqueous systems, systems with low solubility, and systems with ionic liquids. For each system, the available literature sources, accepted data, smoothing equations, and estimated uncertainties are given

A kinetic theory description of the viscosity of dense fluids consisting of chain molecules

Contains fulltext : 72707.pdf (publisher's version ) (Open Access)8 p

Densities and bubble points of binary mixtures of carbon dioxide and n-heptane and ternary mixtures of n-butane, n-heptane and n-hexadecane

The densities of three mixtures of carbon dioxide and n-heptane and three mixtures of n-butane, n-heptane and n-hexadecane were measured. The binary mixtures were studied over the temperature range of 302–459 K and the pressure range of 3.61–55.48 MPa at the following carbon dioxide mole fractions: 0.2918, 0.3888 and 0.4270. The ternary mixtures were studied over the temperature range of 405–469 K and the pressure range of 0.7–24 MPa at the following n-butane mole fractions: 0.0904, 0.1564 and 0.1856 and corresponding n-heptane mole fractions: 0.7358, 0.6825 and 0.6588. The measurements were carried out in an automated isochoric instrument and their accuracy is estimated to be better than ±0.1%. The bubble points of the mixtures were also determined from an analysis of the experimental isochores in the one- and two-phase regions. The new measurements have been used to assess the performance of the Peng–Robinson equation of state and the one-fluid corresponding states model. In single phase regions, the performance of the one-fluid model is found to be superior to that of the Peng–Robinson equation. The latter performs well for bubble points provided that optimised interaction parameters are used. As an interpolation tool, the one fluid model is found to reproduce the ternary mixtures within the experimental uncertainty

Measurement of the universal gas-constant R using a spherical acoustic resonator

We report a new determination of the Universal Gas Constant R: (8.314 471 ±0.000 014) J·mol−1K−1. The uncertainty in the new value is 1.7 ppm (standard error), a factor of 5 smaller than the uncertainty in the best previous value. The gas constant was determined from measurements of the speed of sound in argon as a function of pressure at the temperature of the triple point of water. The speed of sound was measured with a spherical resonator whose volume was determined by weighing the mercury required to fill it at the temperature of the triple point. The molar mass of the argon was determined by comparing the speed of sound in it to the speed of sound in a standard sample of argon of accurately known chemical and isotoptic composition

Densities and bubble points of ternary mixtures of methane, n-butane and n-hexadecane and quaternary mixtures of methane, n-butane, n-heptane and n-hexadecane

The densities of three ternary mixtures of methane, n-butane and n-hexadecane and three quaternary mixtures of methane, n-butane, n-heptane and n-hexadecane were measured. The ternary mixtures were studied over the temperature range 295–350 K and the pressure range 8.3–49.3 MPa at the following methane mole fractions: 0.0185, 0.0358 and 0.0478 and corresponding n-butane mole fractions: 0.8680, 0.8527 and 0.8422. The quaternary mixtures were studied over the temperature range 317–460 K and the pressure range 26.9–49.7 MPa at the following methane mole fractions: 0.1210, 0.1717 and 0.2186 and corresponding n-butane mole fractions: 0.1632, 0.1537 and 0.1450 and n-heptane mole fractions: 0.5791, 0.5457 and 0.5148. The measurements were carried out in an automated isochoric instrument and their accuracy is estimated to be better than ±0.1%. The bubble points of the quaternary mixtures were determined from an analysis of the experimental isochores in the one- and two-phase regions. The new measurements have been used to assess the performance of the Peng–Robinson equation of state and the one-fluid corresponding states model. In single phase regions, the performance of the one-fluid model is found to be superior to that of the Peng–Robinson equation

The viscosity and density of n-dodecane and n-octadecane at pressures up to 200 MPa and temperatures up to 473 K

A vibrating-wire instrument for simultaneous measurement of the density and viscosity of liquids under conditions of high pressure is described. The instrument is capable of operation at temperatures between 298.15 and 473.15 K at pressures up to 200 MPa. Calibration was performed by means of measurements in vacuum, air, and toluene at 298.15 K. For n-dodecane measurements were made along eight isotherms between 298.15 and 473.15 K at pressures up to 200 MPa while for n-octadecane measurements were measured along seven isotherms between 323.15 and 473.15 K at pressures up to 90 MPa. The estimated uncertainty of the results is 2% in viscosity and 0.2% in density. Comparisons with literature data are presented

Predicting the viscosity of liquid refrigerant blends: comparison with experimental data. Mélanges de frigorigènes liquides: prévision de la viscosité et comparaison avec des données expérimentales

A method is presented for predicting the viscosity of liquid refrigerant mixtures. The method has no adjustable parameters and, in essence, relies upon the knowledge of the viscosity of the pure components to predict the viscosity of a mixture by means of kinetic theory and rigid-sphere formalism. The predictions have been compared with the available experimental data for a number of refrigerant mixtures. Based on this comparison and previous studies, the accuracy of the proposed method is assessed to be of the order of ±7%