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An equation of state (EOS) explicit in Helmholtz free energy has been improved to calculate the PVTx and vapor–liquid phase equilibrium properties of CH 4 –CO 2 fluid mixture. This EOS, where four mixing parameters are used, is based on highly accurate EOSs recommended by NIST for pure components (CH 4 and CO 2 ) and contains a simple generalized departure function presented by Lemmon and Jacobsen (1999). Comparison with experimental data available indicates that the EOS can calculate both vapor–liquid phase equilibrium and volumetric properties of this binary fluid system with accuracy close to that of experimental data up to high temperature and pressure within full range of composition. The EOS of CH 4 –CO 2 fluid, together with the updated Gibbs free energy model of solid CO 2 (dry ice), is applied to calculate the CH 4 content ( x CH4 ) and molar volume ( V m ) of the CH 4 –CO 2 fluid inclusion based on the assumption that the volume of an inclusion keeps constant during heating and cooling. V m − x CH 4 diagrams are presented, which describe phase transitions involving vapor, liquid and CO 2 solid phases of CH 4 –CO 2 fluid inclusions. Isochores of CH 4 –CO 2 inclusions at given x CH 4 and V m can be easily calculated from the improved EOS. [ABSTRACT FROM AUTHOR]

Abstract: The IAPWS-95 formulation explicit in Helmholtz free energy proposed by Wagner and Pruß (The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use, Journal of Physical and Chemical Reference Data 2002 31(2), 387–535) is extended to calculate the volumetric property of the fluid water from 1GPa and 273K to 20GPa and 4273K. Comparison with large experimental and molecular dynamic simulation data above 1GPa shows that the equation of state can reproduce the volume of the fluid water with an average absolute deviation of 0.52%. Thus the original IAPWS-95 formulation together with the extended part can be used in a much larger temperature–pressure region: 273–4273K and 0–20GPa. In addition, this paper also reports a reliable and highly efficient method to calculate the saturated properties of water so that the equation of state can be conveniently applied in the study of fluid inclusion: calculating homogenization pressures, homogenization densities (or molar volumes) and isochores. Computer code of the model can be obtained from the first author. [Copyright &y& Elsevier]