Gas viscosities and intermolecular interactions of replacement refrigerants HCFC 123 (2,2-dichloro-1,1,1-trifluoroethane), HCFC 124 (2-chloro-1,1,1,2-tetrafluoroethane) and HFC 134a (1,1,1,2-tetrafluoroethane)

Abstract

A capillary-flow gas viscometer has been used to measure the shear viscosities of gaseous HCFC 123 (2,2-dichloro-1,1,1-trifluoroethane), HCFC 124 (2-chloro-1,1,1,2-tetrafluoroethane) and HFC 134a (1,1,1,2-tetrafluoroethane) at pressures up to 0.1 MPa relative to a nitrogen standard. The experimental temperature ranges were within the limits imposed by the boiling points and decomposition temperatures of the samples, the precise ranges being 308.15–363.15 K for HCFC 123, 283.15–403.15 K for HCFC 124 and 308.15–403.15 K for HFC 134a. The flow times were corrected for small temperature drifts, kinetic-energy and gas-imperfection effects, and slip flow. Pressure conditions were chosen such that curved-pipe flow and turbulence effects were negligible. The accuracy of the viscometer, in terms of its function and our experimental procedure, was confirmed by measuring the relative viscosities of nitrogen and argon. These results were found to be within 0.1% of published data. Our measurements of the viscosity of HFC 134a are shown to agree to a limited degree with other workers' results within combined experimental uncertainty. Our measurements for HCFC 123 agree within experimental uncertainties with other measurements, and no other measurements of HCFC 124 viscosity have been found. Within the framework of the rigorous Chapman–Enskog kinetic theory of gases, we calculate approximate self-diffusion coefficients and hard-sphere collision diameters for the molecules. An analysis of HFC 134a and HCFC 123 viscosities by the extended law of corresponding states allows us to calculate the well depths of the intermolecular interactions using collision diameters suggested by Nabizadeh and Mayinger (Proc. 12th European Conference on Thermophysical Properties, 1990). The use of Schramm, Hauck and Kern (Ber. Bunsenges. Phys. Chem., 1992, 96, 745) of a Stockmayer potential-energy function is discussed. Finally, an application of the Mason–Monchick approximation to the Stockmayer function is used to calculate the percentage effect of the dipole moments on the collision integrals.