Experimental investigation on critical parameters of two binary CO₂-based mixtures containing hydrofluorocarbon (HFC) and modification of the CO₂ + HFC prediction model.

The critical parameters of carbon dioxide (CO2) + fluoroethane (R161) and carbon dioxide (CO2) + 1,1-difluoroethane (R152a) binary mixtures, including critical temperature and critical pressure, have been determined by variable volume method. The critical point is determined by observing the disappearance and recurrence of the vapor-liquid phase interface in the middle of the sapphire image. The extended uncertainties of mixture composition, critical temperature, and critical pressure are <0.00023, 0.27 K, 0.03 MPa (k = 2, 0.95 confidence level), respectively. The experimental results are compared with the prediction results of Peng-Robinson equation of state (PR EOS), Helmholtz energy equation of state (HEOS), Modified Extended Chueh and Prausnitz (MECP) method, which prove the accuracy of the results for the two mixtures. The coefficients of the MECP method are modified for CO2+HFC mixtures, and the prediction accuracy of the method is improved. The Redlich-Kister (RK) equations are used to correlate the experimental data, and the results are in good agreement with the experimental data. The average absolute relative deviation (AARD) of the critical temperature and critical pressure fitted to the RK equation are 0.223% and 0.450% (CO2/R161), 0.231% and 0.255% (CO2/ R152a), respectively, which are basically consistent with the experimental results.