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

A pVT apparatus based on a combination of gas expansion and isochoric method and an ultrasonic apparatus for sound velocity measurements based on phase comparison pulse-echo technique have been developed for precise measurements of isothermal and adiabatic compressibility of gases at pressures up to 10 kbar and temperatures down to the melting line.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400397767

S. N. Biswas

Papers

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

Apparatus for the Measurement of Isothermal and Adiabatic Compressibility of Gases up to 10 Kbar