Measurement of the compressibility and sound velocity of helium up to 1 GPa

By using a gas expansion technique, the density of helium has been determined at 298.15 K as a function of pressure from 100 MPa to 1 GPa. The precision of the measurements is 0.02%, while the estimated absolute accuracy is about 0.08%. The sound velocity has been measured by a phase-comparison pulseecho technique between 98 and 298 K with intervals of 25 K and at pressures up to 1 GPa, with an accuracy generally better than 0.04%. By combining pVT with velocity-of-sound data at 298 K, the adiabatic compressibility and the ratio of the specific heats are calculated. The experimental sound velocities are compared with the values, predicted from an equation of state as proposed by Hansen.     

Measurement of the compressibility and sound velocity of neon up to 1 GPa

The density of neon has been determined at 298.15 K as a function of pressure from 80 MPa to 1 GPa. The precision of the measurements is 0.03%, while the estimated absolute accuracy is between 0.05 and 0.09%. The sound velocity has been measured between 98 and 298 K with intervals of 25 K and at pressures up to 1 GPa, with an accuracy generally better than 0.06%. The adiabatic compressibility and the ratio of the specific heats are calculated by combining pVT with velocity-of-sound data at 298 K. Several equations of state are fitted to the density data at 298.15 K.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Measurements of the compressibility and sound velocity in methane up to 1 GPa,revisited

New density measurements of methane (CH₄) at 298.15 K up to 1 GPa are reported. The precision of the measurements is 0.03%, while the estimated accuracy is between 0.05 and 0.1%. Velocities of sound have been remeasured between 148.15 and 298.15 K at intervals of 25 K and at pressures up to 1 GPa, with an estimated accuracy of 0.12% at 100 M Pa, 0.10% at 150 MPa, and 0.08% above 150 MPa. Comparisons with experimental results and equations of state of other workers are presented. The isothermal and the adiabatic compressibility and the ratio of specific heats have been calculated at 298.15 K.     

Equation-of-state measurements for crude oils at pressures up to 1 GPa

Equation-of-state measurements of two crude oils with different compositions and viscosity were performed at room temperature in the pressure range 0<P<1.0 GPa. We found large compressibilities and a strong dependence of the compressibility on oil content and viscosity. The bulk modulus changed with pressure from 2.0 to 12.1 GPa for one oil and from 1.3 to 9.5 GPa for the other. We discuss the possibility of detecting phase transitions in the region under investigation. The Tait and Murnaghan equations of state were fitted to the data, and residuals are presented.     

Compressibilities of ternary mixtures C1-nC16-CO2 under pressure from ultrasonic measurements of sound speed

Speed of sound measurements have been performed on three mixtures of the ternary system methane + carbon dioxide + normal hexadecane. The systems have been investigated from 12 to 70 MPa in the temperature range from 313 to 393 K. Furthermore, these measurements have allowed the evaluation of the isothermal and the isentropic compressibilities up to 70 MPa from low pressure (<40-MPa) density data.     

Velocity of sound in supercritical water up to 700°C and 300 MPa

The velocity of sound in water was measured up to 700°C and 300 MPa. A classical pulse method has been used. The frequency was typically 5 MHz. The mean accuracy of the data is 0.5% of the velocity. The greatest error in velocity is due to the uncertainty in the temperature measurements at high pressures.     

Volume ratios for n-pentane in the temperature range 278–338 K and at pressures up to 280 MPa

Volume ratios (V _P/V _0.1), and isothermal compressibilities calculated from them, are reported for n-pentane for seven temperatures in the range 278 to 338 K for pressures up to 280 MPa. The isobaric measurements were made with a bellows volumometer for which a novel technique had to be devised to enable measurements to be made above the normal boiling point (309.3 K). The accuracy of the volume ratios is estimated to be ±0.05 to 0.1% up to 303.15 K and ±0.1 to 0.2% from 313.15 to 338.15 K. The volume ratios are in good agreement with those calculated from recent literature data up to the maximum pressure of the latter, viz., 60 MPa.     

Determination of the thermodynamic properties of liquid ethanol from 193 to 263 K and up to 280 MPa from speed-of-sound measurements

The sound velocity in liquid ethanol has been measured up to 280 MPa and at temperatures between 193 and 263 K, using a phase-comparison, pulse-echo technique operating at 2 MHz. The density, isothermal compressibility, isobaric thermal expansion coefficient, and specific heat have been evaluated from the measured speed of sound starting from the density and specific heat data at 0.1 MPa and making use of a modified computational method originally developed by Davis and Gordon. The derived density data have been used to examine the validity of several empirical equations of state.     

Determination of the thermodynamic properties of liquid <Emphasis Type="Italic">n</Emphasis>-hexadecane from the measurements of the velocity of sound

The density, the isobaric expansion coefficient, the specific heats at constant pressure and constant volume, and the isothermal compressibility coefficient of liquid n-hexadecane have been calculated in the range of temperatures 298–433 K and pressures 0.1–140 MPa from the data on the velocity of sound. The coefficients of the Tate equation in the above parametric range have been determined. The table of the thermodynamic properties of n-hexadecane has been presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 150–156, January–February, 2009.     

The pressure-volume relation of ytterbium up to 9 GPa

The pressure-volume relation of ytterbium has been determined up to 9 Gpa using tungsten carbide opposed anvil high pressure x-ray camera. The fcc phase of ytterbium is observed between one atmosphere and 4 GPa and the bcc phase above 3·5 GPa. The bcc phase can be metastably retained down to 1 GPa by gradually decreasing the pressure from a region where only bcc phase alone is observed. The bulk modulus,B ₀, at zero pressure and the pressure derivative of the bulk modulus,B’ ₀, are determined by fitting Murnaghan equation to the pressure-volume data. The following values were obtained:B ₀=16·3 GPa andB’ ₀=3·6 for the fcc phase, andB ₀=14·7 GPa andB’ ₀=1·5 for the bcc phase. Based on the present data it is suggested that the thermodynamic equilibrium pressure for fcc ⇆ bcc transformation in ytterbium is below 3·5 GPa. The valence change under pressure has been discussed.     

Freezing pressures,p, V,T, and self-diffusion data at 298 and 313 K and pressures up to 300 MPa for 1,3,5-trimethylbenzene

Mesurements are reported for the melting point of 1,3,5-trimethylbenzene at pressures up to 345 MPa. Self-diffusion coefficients and p, V, T data have been obtained at 298 and 313 K for pressures up to 280 MPa. Isothermal compressibilities have been calculated from the p, V, T results. The freezing pressures at 0.1 MPa correspond to previously reported values for modification III of trimethylbenzene. Equivalent hard-sphere diameters estimated from the melting point and p, V, T data are used to apply the rough hard-spheres theory to the self-diffusion data; the calculations indicate that there is random packing of the particles.On leave from Department of Chemistry, University of Auckland, Auckland, New Zealand.     

Volumetric properties of 1-alkanols at temperatures in the range 298–348 K and pressures up to 40 MPa

Molar volumes, thermal expansion coefficients, and isothermal compressibilities of six higher 1-alkanols (1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, and 1-hexadecanol) have been determined at temperatures from 298 to 348 K and pressures up to 40 MPa. The density measurements were performed using a vibrating densitometer with an uncertainty of ±0.06%. The relationship between the properties and the structures of these alkanols is discussed in terms of the carbon-chain lengths.     

p,V, T and derived thermodynamic data for bromobenzene at temperatures from 278 to 323 K and pressures up to 280 MPa

Experimentally determined p, V, T data are reported for bromobenzene at 278, 288, 298, 313, and 323 K, at pressures up to about 280 MPa or (at 278 and 288 K) a lower pressure slightly below the freezing pressure at the temperature of measurement. Values of the isobaric expansivity, isothermal compressibility, internal pressure, and equivalent hard-sphere diameter, derived from the p, V, T data, are presented.On leave from the Department of Chemistry, The University of Auckland, Auckland, New Zealand.     

Thermodynamic properties of 2,2,2-trifluoroethanol

(p, V, T) data for 2,2,2-trifiuoroethanol (TFE) have been obtained in the form of volume ratios for six temperatures in the range 278.15 to 338.15 K for pressures up to 280 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The compressibilities and internal pressures indicate that the behavior of TFE is closer to that of methanol than of ethanol for most of the pressure range. The use of only the present volumetric results together with the requirement that the B coefficient of the Tait equation should become equal to the negative of the critical pressure at the critical temperature provides interpolations and extrapolations up to 413 K of comparable accuracy.     

Thermal conductivity and thermal diffusivity of xylene isomers in the temperature range 308–360 K at pressures up to 0.38 GPa

New, absolute measurements of the thermal conductivity of the three xylene isomers within the temperature range 308–360 K for pressures up to 0.38 GPa are reported. In addition, for two of the isomers, m-xylene and p-xylene, it has been possible to measure the thermal diffusivity simultaneously within the same range of conditions. The accuracy of the thermal conductivity data reported is one of ±0.3%, whereas for the thermal diffusivity the estimated accuracy is ±6%. It is found that the density dependence of the thermal conductivity for all of the xylenes can be well represented by one equation based on a rigid-sphere model in the same way that has proved successful for normal alkanes. The thermal diffusivity data have been employed to derive heat capacities for the xylenes over a range of pressures.     

Accurate measurements of the PVT properties of methane from —20 to 150 °C and to 690 MPa

The density of methane has been measured in the temperature range -20 to 150°C and in the pressure range 130–690 MPa, using a substitution method. The overall uncertainty in the results of 0.03% at the 95% confidence level. The data are presented in the form of a modified Benedict-Webb-Rubin equation of state and are compared with the results of other workers.     

Thermodynamic Properties of Heavy n-Alkanes in the Liquid State: n-Dodecane

A grid algorithm based on sound speed data, was used to calculate the thermodynamic properties of liquid n-dodecane. The density, isobaric expansion coefficient, isothermal compressibility, isobaric and isochoric heat capacities, enthalpy, and entropy of liquid n-dodecane were calculated in the range of temperatures from 293 to 433 K and pressures from 0.1 to 140 MPa. Coefficients of the Tait equation were determined in the above-identified range of parameters. A table of the thermodynamic properties of n-dodecane is presented.     

Experimental study of the ultrasonic velocity in liquid cesium at high temperatures and pressures

The sound velocity in liquid cesium under pressures up to 60 MPa and temperatures to 1500 K is measured using a modified-pulses phase-sensitive technique. The sound velocity (at frequency 10 MHz) is determined by means of the pulse propagation time measurement through the cesium sample. The experimental error is 0.2%. The results obtained are discussed.Paper submitted to the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

自由体积理论下液体声速、声速系数及非线性声参量B/A的研究

用液体自由体积理论研究了有机液体的声速、声速系数及非线性声参量与分子结构和分子势能的关系。结果表明分子间的作用力是影响声速、声速系数及非线性声参量的主要原因。同时非线性声参量Ｂ／Ａ也体现了液体分子结构方面的信息。本文有助于对自由体积理论下液体状态方程的进一步研究。为揭示声速及其相关特性与微观机制的关系并为其定量计算作了有益的探索。     

Density and Viscosity of Mixtures of n-Hexane and 1-Hexanol from 303 to 423 K up to 50 MPa

Experimental results for the density and viscosity of n-hexane+1-hexanol mixtures are reported at temperatures from 303 to 423 K and pressures up to 50 MPa. The binary mixture was studied at three compositions, and measurements on pure 1-hexanol are also reported. The two properties were measured simultaneously using a single vibrating-wire sensor. The present results for density have a precision of ±0.07% and an estimated uncertainty of ±0.3%. The viscosity measurements have a precision of ±1% and an estimated uncertainty of ±4%. Representations of the density and viscosity of the mixture as a function of temperature and pressure are proposed using correlation schemes.