Bubble point pressure for binary mixtures of difluoromethane with pentafluoroethane and 1,1,1,2-tetrafluoroethane

Bubble point pressures for the two binary hydrofluorocarbon mixtures difluo romethane, CH2F2 with pentafluoroethane CHF2CF3 and 1,1,1,2-tetrafluoroetha ne CF3CH2F were measured using an acoustic absorption technique. Results co ver the temperature range from 243 K to 333 K with an uncertainty of +/- 20 kPa except at 333.15 K. For the (1 - x) CH2F2 + xCHF(2)CF(3) system, bubbl e point pressures show a maximum around x = 0.2 at 248.15 K, corresponding to the azeotropic mixture. This point shifts to the CH2F2-rich region with increasing temperature, and finally vanishes out at temperatures higher tha n 313.15 K. Bubble pressures for the (1 - x) CH2F2 + xCF(3)CH(2)F system de crease monotonously with increasing composition of CF3CH2F at each temperat ure. These experimental data were fairly well correlated with the Peng-Robi nson equation of state including the azeotropic point. (C) 1999 Elsevier Sc ience B.V. All rights reserved.