Liquid-Phase Speed of Sound Measurements of Octafluorocyclobutane (RC-318) and Hexafluoroethane (R-116)

Sound speed data measured using a dual-path pulse-echo instrument are reported for octafluorocyclobutane (RC-318) at temperatures ranging from 240 to 390 K and at pressures up to 49.01 MPa, and for hexafluoroethane (R-116) at temperatures ranging from 230 to 320 K and at pressures up to 50.27 MPa. The combined expanded uncertainty in the speed of sound varies from 0.035% to 0.102% for RC-318 and 0.039% to 0.097% for R-116 of the measured speed of sound value. The data reported in the present study and those available in the literature are compared to reference equations of state (EOS) for RC-318 and R-116 included in REFPROP version 10.0. The overall performance of both EOS is characterized by an average absolute relative deviation and the maximum deviation. The RC-318 EOS compared to the reported sound speed data with an absolute average relative deviation of 0.56% and a maximum deviation of 1.62%. The R-116 EOS compared to the reported sound speed data with an absolute average relative deviation of 4.85% and a maximum deviation of 6.35%. In both cases, these comparisons show that a refitting of both EOS is required to accurately reproduce the liquid-phase speed of sound for RC-318 and R-116.