Critical temperature and density from liquid-vapor coexistence data: application to refrigerants R32, R124, and R152a

Liquid-vapor coexisting density and temperature data within 3 to 20 K of the critical point at approximately 1 K intervals are used to obtain the critical temperature (Tc) and the critical density (ϱc) of the refrigerants R32, R124, and R152a. The difference between the saturated liquid density and the saturated vapor density is used to obtain Tc which is, in turn, used in an equation for the rectilinear diameter to obtain ϱc. For the determination of Tc, coexisting densities and temperature are allowed to vary as normally distributed variables about a mean, the reported experimental value, with a standard deviation equal to one-third the reported experimental uncertainty. For the determination of ϱc, Tc is similarly allowed to vary based on its previously determined value and uncertainty. Equally probable data subsets are chosen randomly from the complete data set. Consistent results for Tc and ϱc, obtained as averages, and their uncertainties expressed at the 2σ level based on deviations from these averages, are achieved when the data selection-data fitting procedure is repeated two to three hundred times. The critical values obtained agree with those in the literature within the estimated uncertainties. This method yields critical properties consistent with experimental coexisting properties using data removed from the critical point and can complement various methods of determining Tc and ϱc that include the direct observation of the critical point.