THERMOPHYSICAL PROPERTIES OF GASEOUS REFRIGERANTS FROM SPEED-OF-SOUND MEASUREMENTS .3. RESULTS FOR 1,1-DICHLORO-2,2,I-TRIFLUOROETHANE (CHCL2-CF3) AND 1,2-DICHLORO-1,2,2-TRIFLUOROETHANE (CHCLF-CCLF2)

The speed of sound in gaseous 1,1-dichloro-2,2,2-trifluoroethane (CHCl2CF3, commonly known as R123) has been measured at temperatures T between 260 and 335 K at pressures p from 1.6 to 77 kPa. Perfect-gas heat capacities and second and third acoustic virial coefficients have been calculated from the results. The second and third acoustic virial coefficients are used to estimate the density virial coefficients B(T) and C(T) and an effective square-well potential. The acoustic estimates of B(T) and C(T) are consistent with B(T) and C(T) deduced from high-quality (p,V(m),T) results. The combined values of B(T) and C(T) cover a reduced temperature range of 0.57 to 0.99. We have also measured the speed of sound in 1,2-dichloro-1,2,2-trifluoroethane (CHClF-CClF2, commonly known as R123a). This isomer of R123 is a significant impurity in R123 as manufactured and used. We provided estimates of the vibrational relaxation time for R123.