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.     

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.     

Pressure Dependence of the Thermophysical Properties of n-Pentadecane and n-Heptadecane

The speed of sound in liquid n-pentadecane and n-heptadecane was measured using a pulse technique operating at 3 MHz. The measurements were carried out at pressures up to 150 MPa in the temperature range from 293 to 383 K. The experimental results have been used to evaluate various thermophysical properties such as density and isentropic and isothermal compressibilities up to 150 MPa with the help of additional density and heat capacity data at atmospheric pressure.     

Density and speed of sound of R-406A refrigerant in the vapor phase

The speed of sound and the density of the gaseous R-406A refrigerant within the temperature range 293–373 K and at the pressures from 0.05 MPa up to 0.6–2.3 MPa were investigated by means of an ultrasound interferometer and a constant volume piezometer. The measurement errors for the temperature, the pressure, and the speed of sound were ±20 mK, ±4 kPa, and ±(0.1–0.3)%, respectively. The approximation dependences of the investigated properties of the R-406A vapor are obtained and their errors are estimated. The obtained results are compared with the calculations using the REFPROP software.     

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.     

Thermodynamic Properties of HFC-236ea

The density of gaseous and liquid 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and the speed of sound in liquid HFC-236ea have been studied by a γ-attenuation technique, an ultrasonic interferometer, and an isochoric piezometer method over the temperature range of 263–423 K at pressures up to 4.05 MPa. The purity of the samples used throughout the measurements is 99.68 mol%. The pressures of the saturated vapor were measured over the same temperature range. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound measurements were estimated to be within ±20 mK, ±1.5 kPa, ±(0.05–0.30)%, and ±(0.05–0.10)%, respectively.     

Thermodynamic properties of the R-415A refrigerant in the vapor phase and on the condensation line

The speed of sound in the R-415A refrigerant vapor and its density and pressure on the condensation line were measured by the ultrasonic interferometer and constant-volume piezometer methods within a range of temperatures from 293 to 373 K and pressures from 0.04 to 0.5–2.45 MPa. The temperature, pressure, density and speed of sound measurement errors were ±20 mK, ±4 kPa, and ±(0.1–0.2)%, respectively. The temperature dependence of the ideal-gas heat capacity was calculated on the basis of the obtained data. The obtained results were compared with the properties calculated by the REFPROP software.     

New Fundamental Equations of State with a Common Functional Form for 2,3,3,3-Tetrafluoropropene (R-1234yf) and <Emphasis Type="Italic">trans</Emphasis>-1,3,3,3-Tetrafluoropropene (R-1234ze(E))

New fundamental equations of state explicit in the Helmholtz energy with a common functional form are presented for 2,3,3,3-tetrafluoropropene (R-1234yf) and trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)). The independent variables of the equations of state are the temperature and density. The equations of state are based on reliable experimental data for the vapor pressure, density, heat capacities, and speed of sound. The equation for R-1234yf covers temperatures between 240 K and 400 K for pressures up to 40 MPa with uncertainties of 0.1 % in liquid density, 0.3 % in vapor density, 2 % in liquid heat capacities, 0.05 % in the vapor-phase speed of sound, and 0.1 % in vapor pressure. The equation for R-1234ze(E) is valid for temperatures from 240 K to 420 K and for pressures up to 15 MPa with uncertainties of 0.1 % in liquid density, 0.2 % in vapor density, 3 % in liquid heat capacities, 0.05 % in the vapor-phase speed of sound, and 0.1 % in vapor pressure. Both equations exhibit reasonable behavior in extrapolated regions outside the range of the experimental data.     

Thermodynamic Properties of Air from 60 to 2000 K at Pressures up to 2000 MPa

A thermodynamic property formulation for standard dry air based upon experimental P––T, heat capacity, and speed of sound data and predicted values, which extends the range of prior formulations to higher pressures and temperatures, is presented. This formulation is valid for temperatures from the solidification temperature at the bubble point curve (59.75 K) to 2000 K at pressures up to 2000 MPa. In the absence of experimental air data above 873 K and 70 MPa, air properties were predicted from nitrogen data. These values were included in the fit to extend the range of the fundamental equation. Experimental shock tube measurements ensure reasonable extrapolated properties up to temperatures and pressures of 5000 K and 28 GPa. In the range from the solidification point to 873 K at pressures to 70 MPa, the estimated uncertainty of density values calculated with the fundamental equation for the vapor is ±0.1%. The uncertainty in calculated liquid densities is ±0.2%. The estimated uncertainty of calculated heat capacities is ±1% and that for calculated speed of sound values is ±0.2%. At temperatures above 873 K and 70 MPa, the estimated uncertainty of calculated density values is ±0.5%, increasing to ±1% at 2000 K and 2000 MPa.     

Speed-of-Sound Measurements in n-Nonane at Temperatures between 293.15 and 393.15 K and at Pressures up to 100 MPa

Speed-of-sound measurements in liquid phase n-nonane (C₉H₂₀) are reported along six isotherms between 293.15 and 393.15 K and at pressures up to 100 MPa. The experimental technique is based on a double reflector pulse-echo method. The acoustic path lengths were obtained by comparison with measurements carried out at atmospheric pressure and ambient temperature in pure water. The values of the speed of sound are characterized by an overall estimated uncertainty of less than 0.2 %. These results were compared with literature values and with predictions of a dedicated equation of state.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Pressure and Temperature Dependence of the Speed of Sound and Related Properties in Normal Octadecane and Nonadecane

The speed of sound was mesured in liquid n-octadecane and n-nonadecane using a pulse technique operating at 3 MHz. The measurements were carried out at pressures up to 150 MPa in the temperature range from 313 to 383 K. The experimental results combined with atmospheric density measurements were then used to evaluate volumetric properties such as the density and the isentropic and isothermal compressibilities up to 150 MPa in the same range of temperature. The density data were fitted with a six-parameter modified Tait equation within the experimental uncertainty.     

PVT measurements of liquid ethanol in the temperature range from 310 to 363 k at pressures up to 200 MPa

Density measurements in the compressed liquid phase for ethanol were performed with a metal-bellows variable volumometer for temperatures between 310 and 363 K at pressures from the vapor pressure to 200 MPa. The results cover the high-density region from 737 to 882 kg m_–3. The experimental uncertainties (total errors) of temperature, pressure, and density were estimated to be no greater than 3 mK, 0.1 %, and 0.1 %, respectively. Measurements of saturated liquid density at temperatures of 310, 340, and 360 K are also reported.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Vapor pressure and liquid and gas densities of 2,2,2-trifluoroethanol

Forty-three vapor pressures were measured for temperatures from the normal boiling point to the critical point. These data were obtained with a phase-equilibrium cell designed for precise static measurements at pressures up to 20 MPa. The cell is located within an oil-operated thermostatic bath which provides a homogeneous temperature field with variations less than ±1 mK. The vapor pressure data were fitted to a Wagner-type equation. Sixty-two liquid densities were measured on seven isotherms between 20 and 140°C for pressures up to 16 MPa. These measurements were carried out with a precision density meter operating on a vibrational technique. Sixty-nine gas-PVT triples were determined from Burnett expansion series on five isotherms between 140 and 200°C for pressures up to the saturation line. In all experiments, temperature measurements were made with platinum resistance thermometers. Precise pressure measurements were performed using a mercury column of 6-m height and a standard deadweight gauge for the higher pressures.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

P-V-T-x measurements of aqueous mixtures at supercritical conditions

We report P-V-T-x measurements for five binary systems: water+methane, water+n-hexane, water+n-octane, water+benzene, and water+nitrogen at supercritical conditions for several compositions. The experimental data were obtained along isotherms with a phase-equilibrium cell designed for accurate measurements at pressures up to 100 MPa. The uncertainties in temperature, pressure, density, and concentration are ±0.01 K, ±0.2%, ±0.2%, and ±0.002 mole fractions, respectively. The behavior of the second virial coefficient, the excess volume, and the excess Gibbs free energy is also discussed.     

Speed of Sound and Some Thermodynamic Properties of Liquid Methylcyclopentane and Butylcyclohexane in a Wide Range of Pressure

Ultrasonic velocity measurements were performed on liquid methylcyclopentane and butylcyclohexane at pressures from atmospheric up to 150 MPa in the temperature range from 293 to 373 K using a pulse echo technique operating at 3 MHz. The data were used to evaluate various thermophysical properties such as density, and isentropic and isothermal compressibilities up to 150 MPa with the help of additional density measurements.     

Sound velocity of equimolar dense noble-gas mixtures

The sound velocity in argon-helium, argon-neon, argon-krypton, and argon-xenon equimolar dense mixtures has been measured with a pulse-echoes overlap method at room temperature, 298.15 K, and at pressures up to 800 MPa. The accuracy of these results is 0.2%. Furthermore, the validity of the one-fluid compared with these experimental data is examined.     

Thermophysical Properties of Gaseous HBr and BCl3 from Speed-of-Sound Measurements

The speed of sound in gaseous hydrogen bromide (HBr) and boron trichloride (BCl₃) was measured using a highly precise acoustic resonance technique. The HBr speed-of-sound measurements span the temperature range 230 to 440 K and the pressure range from 0.05 to 1.5 MPa. The BCl₃ speed-of-sound measurements span the temperature range 290 to 460 K and the pressure range from 0.05 MPa to 0.40 MPa. The pressure range in each fluid was limited to 80% of the sample vapor pressure at each temperature. The speed-of-sound data have a relative standard uncertainty of 0.01%. The data were analyzed to obtain the ideal-gas heat capacities as a function of temperature with a relative standard uncertainty of 0.1%. The heat capacities agree with those calculated from spectroscopic data within their combined uncertainties. The speeds of sound were fitted with the virial equation of state to obtain the temperature-dependent density virial coefficients. Two virial coefficient models were employed, one based on the hard-core square-well intermolecular potential model and the second based on the hard-core Lennard–Jones intermolecular potential model. The resulting virial equations of state reproduced the speed-of-sound measurements to 0.01% and can be expected to calculate vapor densities with a relative standard uncertainty of 0.1%. Transport properties calculated from the hard-core Lennard–Jones potential model should have a relative standard uncertainty of 10% or less.     

The thermodynamic properties of liquid binary mixtures of <Emphasis Type="Italic">n</Emphasis>-alkanes: <Emphasis Type="Italic">n</Emphasis>-decane + <Emphasis Type="Italic">n</Emphasis>-hexadecane

Data on sound velocity are used for determining the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacity, and the isothermal compressibility of liquid binary mixture of n-decane + n-hexadecane of three compositions in the temperature range of 298–433 K and pressure range of 0.1–100 MPa. The coefficients of Tait equation are calculated in the above-identified range of parameters. The calculation results are compared with experimental data on density. The divergence does not exceed 0.2% for the most reliable data.