In a preceding project, functional forms for “short” Helmholtz energy equations of state for typical nonpolar and weakly polar fluids and for typical polar fluids were developed using simultaneous optimization. In this work, the coefficients of these short forms for the equations of state have been fitted for the fluids acetone, carbon monoxide, carbonyl sulfide, decane, hydrogen sulfide, 2-methylbutane (isopentane), 2,2-dimethylpropane (neopentane), 2-methylpentane (isohexane), krypton, nitrous oxide, nonane, sulfur dioxide, toluene, xenon, hexafluoroethane (R-116), 1,1-dichloro-1-fluoroethane (R-141b), 1-chloro-1,1-difluoroethane (R-142b), octafluoropropane (R-218), 1,1,1,3,3-pentafluoropropane (R-245fa), and fluoromethane (R-41). The 12 coefficients of the equations of state were fitted to substance specific data sets. The results show that simultaneously optimized functional forms can be applied to other fluids out of the same class of fluids for which they were optimized without significant loss of a...

Short Fundamental Equations of State for 20 Industrial Fluids

The “Tait equation,” which is now widely used to fit liquid density data over wide pressure ranges, is a modification of the original equation of Tait, published 100 years ago, to fit his results on the compressibility of fresh water and seawater at different pressures. The range of applicability of these different equations is discussed and it is concluded that their simplicity and accuracy in reproducing high pressure density data for dense gases, liquids, solids, and liquid mixtures will ensure their continued use.

The Tait equation: 100 years on

New functional forms have been developed for multiparameter equations of state for non- and weakly polar fluids and for polar fluids. The resulting functional forms, which were established with an optimization algorithm which considers data sets for different fluids simultaneously, are suitable as a basis for equations of state for a broad variety of fluids. The functional forms were designed to fulfil typical demands of advanced technical application with regard to the achieved accuracy. They are numerically very stable and their substance-specific coefficients can easily be fitted to restricted data sets. In this way, a fast extension of the group of fluids for which accurate empirical equations of state are available is now possible. This article deals with the results found for the polar fluids CFC-11 (trichlorofluoromethane), CFC-12 (dichlorodifluoromethane), HCFC-22 (chlorodifluoromethane), HFC-32 (difluoromethane), CFC-113 (1,1,2-trichlorotrifluoroethane), HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane), HFC-125 (pentafluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-143a (1,1,1-trifluoroethane), HFC-152a (1,1-difluoroethane), carbon dioxide, and ammonia. The substance-specific parameters of the new equations of state are given as well as statistical and graphical comparisons with experimental data. General features of the new class of equations of state such as their extrapolation behavior or their numerical stability and results for non- and weakly polar fluids have been discussed in preceding articles.

Equations of state for technical applications. III. Results for polar fluids

Advanced calibration, adjustment, and operation of a density and sound speed analyzer

The current study focuses on 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [C3mim][NTf2], and 1-pentyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [C5mim][NTf2]. The objective is to study the influence of pressure as well as that of the cation's alkyl chain length on several properties of this type of ionic liquids. Speed of propagation of ultrasound waves and densities in pure ionic liquids as a function of temperature and pressure have been determined. Other thermodynamic properties such as compressibilities and expansivities have been obtained. Speed of sound measurements have been carried out in broad ranges of temperature (298 < T/K < 338) and pressure (0.1 < p/MPa < 200). A novel high-pressure ultrasonic cell was designed and built to allow for precise speed of sound measurements in liquids. The uncertainty of the speed of sound measurements is 0.05 %. A detailed description of the cell is presented. Density measurements have been performed over a broad range of temperat...

Density, Speed of Sound, and Derived Thermodynamic Properties of Ionic Liquids over an Extended Pressure Range. 4. [C3mim][NTf2] and [C5mim][NTf2]

The sound velocity in toluene has been measured up to 2634 bar and at temperatures from 173 to 320 K using the pulse-echo overlap method. The sound velocity in n-heptane has been measured up to 2634 bar and at temperatures from 185 to 310 K by the phase comparison pulse-echo method. The density, the isothermal compressibility, the isobaric thermal expansion and the specific heat at constant pressure of both liquids have been evaluated from the measured sound velocity, following the method of Davis and Gordon. From a comparison of the calculated densities with those obtained previously from direct measurements, it is concluded that the method is very suitable for precise determination of liquid densities under elevated pressures.

The effect of pressure on the sound velocity and density of toluene and n-heptane up to 2600 bar

The P-T melting curves of methanol and ethanol have been measured precisely at pressures up to 270 MPa and 200 MPa respectively, using the ultrasonic method developed previously. The accuracy of the experimental melting temperatures is about 0.1 K and of the melting pressures about 0.8 MPa for both liquids. The accuracy of the experimental results, fitted to the Simon-Glatzel equation, is sufficient for the precise calculation of thermodynamic properties along the melting line.

Accurate measurement of the melting line of methanol and ethanol at pressures up to 270 MPa

Accurate Measurement of the Melting Line of Methanol and Ethanol at Pressures up to 270 MPa

The nuclear magnetic resonance (NMR) pulse technique was used to study phase transitions in solid methane up to 60 kbar. NMR offers many advantages for studying the phase diagram of molecular species which contain magnetic nuclei. It may also be used at high pressures. In a separate experiment, at pressures up to 100 kbar in solid methane, the diamond anvil cell method was used to ascertain which are the stable solid phases of CH/sub 4/ at pressures in excess of 10 kbar. The CH/sub 4/ phase diagram is presented.

Phase Transitions in Solid Methane Up to 60 Kbar

The critical line of a nearly ideal binary system generally moves from the critical point of one of the components directly to the critical point of the other component (curve 1 Fig. 1). In a less ideal system, however, the behaviour is quite different. In some cases the curves move from the critical point of the less volatile component (component 2) to lower temperatures and higher pressures (curve 2) and rise again to higher temperatures via a temperature minimum, the critical double point. In other systems, the critical temperature increases continuously from the critical point of the less volatile component when the pressure is increased (curve 3). We assume here that the critical line is not interrupted by the appearance of a solid phase.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400397779

N. J. Trappeniers

Papers

The effect of pressure on the sound velocity and density of toluene and n-heptane up to 2600 bar

Accurate measurement of the melting line of methanol and ethanol at pressures up to 270 MPa

Accurate Measurement of the Melting Line of Methanol and Ethanol at Pressures up to 270 MPa

Phase Transitions in Solid Methane Up to 60 Kbar

Investigation of the Phase Equilibria in the System Neon-Xenon Using a Diamond-Anvil System