Compressibility and sound velocity measurements on N2 up to 1 GPa

A gas expansion technique has been used to determine the pVT properties of N₂ up to 1 GPa at 298.15 K, with an accuracy of 0.08% in density, 1 mK in temperature, and 0.05%+0.2 MPa in pressure. The sound velocity has been measured by a phase-comparison pulse-echo technique between 123 and 298 K at intervals of 25 K and at pressures up to 1 GPa, with an accuracy of better than 0.02% in sound velocity, 10 mK in temperature, and 0.05%+0.2 MPa in pressure. An equation of state is presented that correlates the density data over the wide pressure range of 36–1000 MPa with maximum deviations between the calculated and the experimental densities of less than 0.05%.     

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.     

Correlation of the volumetric properties of fluorinated ethers by the group-contribution volume-ratio method

(p, V, T) data obtained with simple volmnometers are usually restricted to a small range of temperatures below and above ambient temperature. The modified Tait equation has been very useful for extrapolating (p, V, T) data for individual liquids. The available volumetric data for fluorinated ethers is reviewed and is expressed as a correlation by using the Tait equation and the group-contribution volume-ratio method. Volume ratios obtained from this correlation used in combination with the densities of the liquid along the saturation boundary should provide the densities for a wide temperature and pressure range for the fluorinated ethers, including some which may be useful as longterm replacements for existing alternative refrigerants.Paper presented at the Twelfth Symposium on Thermophysical Properties. June 19–24, 1994, Boulder, Colorado. U.S.A.     

Analytical Equation of State for Solid-Liquid-Vapor Phases

A simple analytical equation of state has been proposed for describing the phase behavior of three thermodynamic states (solid, liquid, and vapor) of matter. In terms of reduced parameters, it can be written as:

Equation of state for compressed liquids from surface tension

A method for predicting an analytical equation of state for liquids from the surface tension and the liquid density at the freezing temperature ( ₁, ₁) as scaling constants is presented. The reference temperature. T_ref. is introduced and the product (T _ref T ₁ ^{1 2} ) is shown to be an advantageous corresponding temperature for the second virial coeflicienls. B₂(T). of spherical and molecular fluids. Thus, B₂(T) follows a promising corresponding states principle and then calculations for(T) andb(T), the two other temperature-dependent constants of the equation of state, are made possible by scaling. As a result, ( ₁, ₁) are sufficient for the determination of thermophysical properties of fluids from the freezing line up to the critical temperature. The present procedure has the advantage that it can also be used in cases whereT _c andP _c are not known or the vapor pressure is too small to allow accurate measurements. We applied the procedure to predict the density of Lennard-Jones liquids over an extensive range of temperatures and pressures. The results for liquids with a wide range of acentric factor values are within 5%.     

Densities of tetramethylsilane,tetraethylsilane, and tetraethoxysilane under high pressures

Accurate density data for tetramethylsilane, tetraethylsilane, and tetraethoxysilane in the temperature range from 283.15 to 333.15 K under pressure up to 100 MPa have been measured in order to test existing correlation methods. We have also measured the saturated liquid densities of tetramethylsilane, tetraethylsilane, and tetraethoxysilane in the temperature range from 283 to 343 K. The modified Rackett equation and the COSTAD correlation were used to correlate the saturated liquid density data. The Tait equation and a modified van der Waals equation of state were used to correlate the liquid density data under pressure. It was found that the average absolute deviations of the experimental values from those calculated with the Tait equation and the modified van der Waals equation of state were less than 0.01 and 0.21%, respectively. The effective hard sphere diameters for these three silane compounds were determined from the modified van der Waals equation of state parameter. It was found that the effective hard-sphere diameter decreases with temperature.     

A general equation of state for dense fluids

A general equation of state, originally proposed for compressed solids by Parsafar and Mason, has been successfully applied to dense fluids. The equation was tested with experimental data for 13 fluids, including polar, nonpolar, saturated and unsaturated hydrocarbons, strongly hydrogen bonded, and quantum fluids. This equation works well for densities larger than the Boyle density ρ_B [1/ρ_B=T _B d B ₂(T _B)/T], where B₂(T_B) is the second virial coefficient at the Boyle temperature, at whichB ₂=0 and for a wide temperature range, specifically from the triple point to the highest temperature for which the experimental measurements have been reported. The equation is used to predict some important known regularities for dense fluids, like the common bulk modulus and the common compression points, and the Tait-Murnaghan equation. Regarding the common points, the equation of state predicts that such common points are only a low-temperature characteristic of dense fluids as verifed experimentally. It is also found that the temperature dependence of the parameters of the equation of state differs from those given for the compressed solids. Specifically they are given byA ₁ (T)=a ₁+b₁T+c₁T²-d₁ T ln (T).     

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 2,2,4-trimethylpentane

p, V, T data for 2,2,4-trimethylpentane (TMP) 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. There are strong indications that the combination of the present results with literature data at 348 and 373 K enable accurate extrapolations in the liquid range up to 473 K, and possibly to as low as 170 K, for pressures up to 980 MPa; use of only the present results 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 of comparable accuracy. It is suggested that 2,2,4-trimethylpentane is a suitable secondary reference material (because of its large liquid range at atmospheric pressure and the similarity of its volumetric properties to a wide range of fluids) for calibration of measuring cells used for determining volumes of fluids under pressure.     

基于注塑机的聚苯乙烯pVT特性在线测试

利用一种新的基于注塑成型机的聚合物P-V-T(压力-体积-温度)特性在线测试技术,对无定形聚合物聚苯乙烯(PS)的P-V-T特性进行了测试。测试得到了PS在线PVT特性结果,并同软件Moldflow数据库中的一种PS的P-V-T数据结果做了比较,其曲线趋势一致性证明了的结果的正确性以及测试技术的可行性,而其曲线的不同性则证明同种材料不同牌号的P-V-T特性具有不同性。利用修正的双域Tait状态方程对实验结果进行了关联对比,很好的拟合了测试结果,并获得了状态方程的参数值。     

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.     

Common intersection point independent of mole fraction: A new regularity

A new regularity has been found for compressed liquid mixtures, namely, a common intersection point for the isotherms of the reduced bulk modulus of a compressed liquid mixture as a function of composition. The regularity holds over a specific range of densities from a particular liquid mixture. The regularity has been tested for a LJ (12,6) mixture, Ar+Kr, Kr+Xe, and CO₂+C₂H₆ based on equations of state derived from statistical mechanics and it is valid close to within experimental accuracy.     

Diffusion and viscosity equations of state for a Lennard-Jones fluid obtained from molecular dynamics simulations

Equilibrium molecular dynamics simulations were performed for a Lennard-Jones fluid at 171 conditions spanning the range 0≤p ⁺≤1.0 and 0.8≤T ⁺≤4.0. The Einstein or, mean-squared-displacement (MSD) formula was used to compute the self-diffusion coefficient and a recently suggested, modified MSD equation was used to compute the shear viscosity at each condition. Analytical equations for the self-diffusion and viscosity coefficients were then fitted to the simulated data as polynomial functions ofp ⁺ andT ⁺. The resultant smoothing equations correlate the simulated data quite well and agree with argon experimental data within the uncertainty of the data.     

Tait's Equation of State for Liquid Mixtures

The methods of statistical theory of liquid state are used to validate the well-known Tait's equation of state for liquid mixtures. An expression is derived which relates the coefficients A and B of Tait's equation of state to the parameters of steepness of repulsion forces m and to the thermodynamic properties of the system. P–V–T–x measurements for a water-acetone system are performed to check the theoretical results. The method of molecular dynamics is used to calculate the parameters of steepness of repulsion forces of a water-acetone mixture at different temperatures and concentrations. It is demonstrated that m in the treated ranges of temperature and pressure assumes a constant value of 15. The theoretically obtained coefficient A coincides with the experimentally obtained value within the experimental error, and the coefficient B describes qualitatively correctly the temperature and concentration dependences obtained as a result of P–V–T–x measurements.     

Equation of state for compressed liquids and their mixtures from the cohesive energy density

A procedure is presented, based on statistical-mechanical theory, for predicting the equation of state of compressed normal liquids and their mixtures from two scaling constants that are available from measurements at ordinary pressures and temperatures. The theoretical equation of state is that of Ihm, Song, and Mason, and the two constants are the enthalpy of vaporization and the liquid density at the triple point, which are related to the cohesive energy density of regular solution theory. The procedure is tested on a number of substances ranging in complexity from Ar and CO₂ to n-heptane and toluene. The results indicate that the liquid density at any pressure and temperature can be predicted within about 5%, over the range from T _tp to T _c and up to the freezing line. Possible methods of determining the scaling constants are discussed, as well as other possible choices for scaling constants.Paper dedicated to Professor Joseph Kestin.     

新型聚酯材料状态方程的研究

聚酯材料在航空航天领域有着较广泛的应用,其高压力学性能的研究逐渐受到人们的关注。针对一种新型聚酯材料通过轻气炮(LGG)实验开展其冲击压缩力学性能研究。采用非对称碰撞直接测量法测量并计算激波速度(D)与波后质点速度(u)的D-u型Hugoniot曲线,并由此推导出P-η型Hugoniot曲线。建立了该材料的Murnagham状态方程,求得了相应的材料参数。并对新型聚酯材料的Murnagham状态方程和P-η型Hugoniot状态方程进行了比较和分析。     

An Analytical Equation of State for Some Saturated Liquid Metals

An analytical equation of state (EoS) is developed for some saturated molten metals. The equation is that of Ihm, Song and Mason in which the three temperature–dependent parameters, second virial coefficient, van der Waals co–volume, and a scaling parameter, are calculated by means of corresponding states correlations. The required characteristic constants are the heat of vaporization and the density at the melting point, H _vap and _m, respectively. The EoS is applied to these liquid metals to calculate the density at temperatures higher than their melting points. The results are fairly consistent with experiment, maximum difference less than ±4%.     

Volumetric properties under pressure for 1,2-dichlorofluoroethane (R141), 1-fluoro-1,1,2-trichloroethane (R131a), and 1,2-dichloro-1,1-difluoroethane (R132b)

The effect of pressure on the volume of R141, R131, and R132b is reported as volume ratios (the volume under pressure relative to its value at atmospheric pressure) at six temperatures covering the range 278.15 to 338.13 K and pressures up to 380 MPa for R141 and R131a. For R132b the same temperature range has been used, but above its normal boiling point experimental arrangements have limited maximum pressures to below 300 MPa, with some loss of accuracy. Densities have been measured at atmospheric pressure for each liquid. The experimental data have been used to calculate isothermal compressibilities, thermal expansivities, and internal pressures: the change in isobaric heat capacity from its value at atmospheric pressure has also been estimated. The volume ratios for all three compounds can be represented by a version of the Tait equation based on previously reported data for 1,2-dicloroethane and 1,1,2-trichloroethane with the inclusion of allowances for the substitution in the former of chlorine or fluorine for the hydrogens on one of the carbons.