Some group of equations F(τ,D,C) is investigated in the report. Models F(τ,D,C) are connected with thermodynamic properties, F=( ρ l, ρg ρs, fd…), between them the densities, ρ l, ρg, the order parameter, fs, the coexistence curve diameter, fd, related to the coexistence curve (CC). The models F(τ,D,C) are chosen as equations those follow to the scaling theory of critical phenomena (ST) and include critical characteristics, D=(α,β, …). The models of densities ( ρ l,ρg) are represented by equations of Wegner (1985), Anisimov et al. (1990), Rabinovich and Sheludiak (1995), Shimanskaya et al. (1996), Bazaev, Abdulagatov et al. (2007). One more model F(τ,D,C) is named as a combined model (CM) and discussed in the work. It combines scaling, Fscale, and regular, Freg, parts. The structure of Fscale is chosen dew to ST. Fscale represents measured (Fexpk,Tk) -values those are placed in the range: from the high level of temperature, Thigh, to a border, Tscale, of the critical region (the relative interval is △τscale=τscale-τlow=0.1). The part, Freg, is involved and adopted with the aim to compensate systematic deviations of Fscale from ( ρ l,ρg,T)exp data those are placed at temperatures τ > 0.1. Fitting parameters, D,C, of model CM is determined with the help of a statistical treaty of experimental ( ρ l,ρg,T) data. Optimal values of critical characteristics Dopt include α,β,Tc and ρc. CM can represent ( ρ l,,T) exp data those are placed in the interval τlow…τhigh=0.0001…0.5 in the liquid phase. It can represent (ρg,,T)exp data those are placed in the interval τlow…τhigh=0.0001…0.12 in the gas phase. We have considered a model suggested by Vorobev et al. (2009). The model uses ρB and TB-adjustable coefficients those correlate with the density and the temperature in the Boyle point. One more analytical expression F=fs is studied. It is developed in Zhelezny et al. (1994), based on a degree function β(τ) and named as a crossover model. The models mentioned have been tested and compared in similar border conditions. Input ( ρ l,ρg,T)exp data are selected for the tests and involve reliable experimental data of some substances including CH4, HFC 134a, HFC 143a, HFC 236ea, H2O, NH3, SF6, alcohols, ethers and metals. Some functions were investigated among them: the scaling function Z and degree function β(τ) those are connected with the models and the substances. Numerical data on F=( ρ l, ρg fs, fd…) are got in the critical region and analyzed.
Thermophysics Engineering Department Moscow Power Engineering Institute (TU) Krasnokazarmennaya, 14 Joint Institute of high temperatures RAS Lapina, 4 Moscow, Russia, 111250 Thermophysics Engineering Department Moscow Power Engineering Institute (TU) Moscow, Russia, 111250 Geothermal Research Institute of the Dagestan Scientific Center, Makhachkala, Russia, Thermophysics Engineering Department Moscow Power Engineering Institute (TU) Krasnokazarmennaya,14 M State Key Laboratory of Multiphase Flow in Power Engineering Xian Jiaotong University Xian, China,