Experimental vapor pressures and thermodynamic models of perfluorocarbons PP80 and PP90

Complete thermodynamic models are developed for the perfluorocarbons PP80 (perfluoro-2-methyl-3-ethylpentane, C8F18, CASRN: 354-97-2) and PP90 (perfluoro-2,4-dimethyl-3-ethylpentane, C9F20, CASRN: 50285-18-2). These perfluorocarbons can be used as working fluids in energy conversion applications, like organic Rankine cycle (ORC) power systems operating at medium and high temperatures. Other areas of use of PP80 and PP90 are in the electronic industry for component testing, in the chemical industry as a hazardous reaction suppressant and as tracers in the oil and gas industry. The improved equation of state of Peng–Robinson modified by Stryjek–Vera (iPRSV) is adopted, supplemented with a third order polynomial for the ideal gas isobaric heat capacity as a function of temperature. Vapor–liquid pressures for both fluids were measured in a temperature range spanning 358–508 K. The vapor–pressure temperature range for the fitting of the equation of state is extended down to 270 K by extrapolation of the Wagner–Ambrose equation that is used for the correlation of the aforementioned measured data. Ideal gas isobaric heat capacities data are estimated with the Joback method. The obtained thermodynamic models are arguably sufficiently accurate for preliminary engineering calculations, for example for the thermodynamic design of ORC power systems.