Experimental And Theoretical Investigation Of The Virial Coefficients Of Fluids

The virial coefficients are basic thermophysical properties that can be used to define a wide range of thermodynamic properties and are important in molecular theory. This dissertation presents accurate experimental investigations, empirical correlations and theoretical models of the virial coefficients.The virial coefficient measurements are based on an improved pvT measurement system whose accuracy was significantly enhanced by the minimization of the influence of nonideal factors. The Burnett-isochoric method was used to precisely measure the pvT properties of HFC-236fa. The second and third virial coefficients were then determined along with a truncated virial EOS from the data. The pvTx properties of HFC-32/HFC-125 mixtures were also measured to determine the mixture and cross virial coefficients. The uncertainties of the pvT measurements were carefully analyzed.A new correlation for the second virial coefficients for a variety of fluids was developed based on the corresponding-states principle which can be used for nonpolar, polar, associated and quantum fluids. The convenient correlation corrects the systematic negative errors at subcritical temperatures of existing correlations with enhanced accuracy. A new correlation for the third virial coefficients of various fluids was also developed that is accurate for both nonpolar and polar fluids. With the second virial coefficient correlation, it can provide a very good fit to precise pvT data for low and medium densities.The binary interaction parameters, kij, of 379 nonpolar mixtures were determined by fitting the second cross virial coefficients with the new correlation for pure compounds using classical mixing rules. The kij values for n-alkane/n-alkane binaries have a regular distribution and were successfully correlated with the carbon numbers as the correlating parameters. The correlation was found to perform very well, even for binaries with carbon numbers up to 30. The binary interaction parameters were also successfully correlated for N₂, CO₂, H₂O/n-alkane binaries, CO/nonpolar binaries, fluorocarbon/fluorocarbon binaries and quantum contained binaries.A new theoretical model, the 2CLJDQP potential function, was developed for linear molecules, which takes into account dipole, quadrupole and induction effects as well as the rotation of the dipole out of the molecular axis. The energy parameters were optimized for various types of fluids. With the modified mixing rules, the potential parameters obtained from homonuclear molecules can be used to calculate the second virial coefficients of heteronuclear molecules. The model was also successfully extended to triatomic molecules. Analysis of the contributions to the second virial coefficients of long-range interactions shows that the molecular interactions introduced in the present model, such as, the induction effects, cannot be neglected.