Description of thermodynamic properties of liquids over wide ranges of pressure and temperature

A novel method for estimating the behavior of liquids at the moderate and high pressures within the range from a melting line to a critical isotherm has been developed on the base of the fluctuation thermodynamics model. The knowledge of accurate data for the thermal (PCXS(T), ρℓ(T)) properties along the liquid branch of the coexistence curve and the caloric (CPa(T), W0(T), ρ0(T)) properties along the initial supercritical isobar P0 allow one to achieve a reasonable description of the complete set of thermodynamic properties (CP, CV, ρ, W, αP, χT, h, s) at the arbitrary given values (P, T) in an easy way. The simple equations of the fluctuation thermodynamics model allow one to describe a characteristic curve (specific isentrope) passing through an arbitrary point (P, T) by calculation of only three coefficients: (A0, G0) (from the initial isobar P0) and Bs (from the liquid branch of the coexistence curve). All thermodynamic properties can be expressed in that point. Argon and carbon dioxide have been used to test the ability of the fluctuation thermodynamics model to represent the thermodynamic behavior of compressed liquids at low temperatures and high pressures up to 300 MPa (the initial isobar P0 has been selected at the pressure 20 MPa for Ar and 30 MPa for CO2). It appears to be the simple method able to predict a common crossing point of the αP(P)-isotherms and a point of minimum of the CP(P)-isotherms experimentally observed for real liquids.