Thermodynamic properties of simple molecular fluids: tetrafluoromethane and trifluoromethane

Abstract

The thermodynamic properties of CF, and CHF, have been cakuiated from an equation of state of the Strobrldg. type, fitted to extenrlve p-Y-Tdata sets recently publbhed. The thormodynamic properties under saturation condltlons have been compared with previously pubitshed data, the agreement being satisfactory except In the neartrlticai region. The results have been used to dkcusr the performance of a monatomic fluid model, whkh k shown to be unsatisfactory.

The speed of sound, and derived thermodynamic properties of liquid trifluoromethane (HFC23) fromT=(258 to 303)K at pressures up to 65MPa

“…Although not obvious from figure 1, the temperature dependence of the speed of sound shows an inflection point at high pressures, (4) A few measurements were randomly repeated, yielding a precision of ±0.1 m·s −1 . We have fitted the data to equation (1) and obtained an overall standard deviation of 1.2 m·s −1 , which corresponds to an uncertainty of ±0.18 per cent.…”

“…The region covered extended from T = (125 to 350) K, and from the vapour pressure up to 90 MPa, with a total of 292 experimental values obtained from literature. (4)(5)(6)(7)(8)(9)(10)(11) The standard deviation of this fit is 3.5 kg·m −3 . Combining both fits (speed of sound and density), we have calculated the isentropic compressibility by using equation (2).…”

“…Both the isothermal compressibility (figure 4) and the cubic expansion coefficient (figure 5) were calculated by analytical derivation of equation (1) and by using equations (3) and (4). In view of the high quality of the available density data and the analytical method used for the derivatives, we estimate an accuracy of ±0.4 per cent for the isothermal compressiblity and the cubic expansion coefficient.…”

“…The present speed of sound data together with published density ρ data (4)(5)(6)(7)(8)(9)(10)(11) were used to calculate thermodynamic properties such as the isentropic compressibility κ s , the isothermal compressibility κ T , the cubic expansion coefficient α p , and the specific heat capacity at constant pressure c p .…”

“…(3) Derived thermodynamic properties such as the isentropic compressibility κ s , the isothermal compressibility κ T , the cubic expansion coefficient α p , and the specific heat capacity at constant pressure c p are calculated by combining the present experimental data with the density values published by other authors. (4)(5)(6)(7)(8)(9)(10)(11) The estimated properties are compared, where possible, with literature data. …”