Abstract
On the basis of the Clapeyron equation and the scale theory, expressions are developed for the “apparent” heat of vaporization r
* = r
* (T), vapor ρ- = ρ- (T) and liquid ρ+ = ρ+ (T) branches of the saturation line of individual substances for the range of state parameters from the triple point (pt,Tt,ρt
) to the critical (pc,Tc,ρc
). The peculiarity of the proposed approach to the description of the saturation line is that all exponents of the components of the equations ρ- = ρ- (T) and ρ+ = ρ+ (T) are universal up to the universality of the critical indices α, β and Δ. In this case, the order parameter ds
= (ρ+ − ρ-)/(2ρc) and the average diameter df
= (ρ+ + ρ-)/(2ρc) − 1 of the saturation line satisfy the saturation line model [2β,1−α], which follows from the modern theory of critical phenomena. The method is tested on the example of describing the phase equilibrium line of refrigerant R1233zd(E) in the range from Tt
= 195.15 K to Tc
= 439.57 K. It is found that in the temperature range [Tt,Tc
], the developed system of the mutually consistent equations ps
= ps
(T), r
* = r
* (T), ρ- = ρ- (T) and ρ+ = ρ+ (T) allows describing the data on the saturated vapor pressure ps
and densities ρ- and ρ+ on the saturation line within the experimental uncertainty of these data.
Analysis of the saturation line on the basis of Clapeyron–Clausius and Gibbs–Duhem equations
