Alternative refrigerants difluoromethane and pentafluoroethane: critical temperature, refractive index, surface tension, and estimates of liquid, vapor, and critical densities

Refractive index data and capillary rise data are reported for CH[sub 2]F[sub 2] and C[sub 2]HF[sub 5], which are denoted as R32 and R125 by the refrigeration industry. For each fluid, the data extend from 296 K to the critical point and yield the critical temperature T[sub c] and the temperature-dependent capillary length. The refractive index data were combined with liquid density data at 303 K to determine the Lorentz-Lorenz constant k. This constant and the data were used to estimate the liquid, vapor, and critical densities, and the surface tension [sigma] up to the critical point. For both fluids, the surface tension [sigma] is given by the expression [sigma] = S[sub 0]t[sup 1.26]k[sub B]T[sub c](N[sub A]/V[sub c][sup 2/3]) with S[sub 0] = 5.5 for R32 and S[sub 0] = 6.0 for R125. Here k[sub B], N[sub A], T[sub c], and V[sub c] are the Boltzmann constant, the Avogadro constant, the critical temperature, and the molar critical volume, respectively, and t [triple bond] (T[sub c] [minus] T)/T[sub c]. The present values for S[sub 0] are close to the average value S[sub 0] = 5.7 for seven other refrigerants.