Measurements of the Vapor-Liquid Coexistence Curve in the Critical Region and the Critical Parameters of 1,1,2,2-Tetrafluoroethane

The vapor-liquid coexistence curve in the critical region of 1,1,2,2-tetrafluoroethane (HFC-134) was measured by a visual observation of the meniscus in an optical cell. Eighteen saturated liquid densities and 10 saturated vapor densities have been obtained in a temperature range from 364 K to the critical temperature, corresponding to a density range from 243 to 1001 kg·m⁻³. The experimental uncertainties of temperature and density measurements are estimated to be within ±10 mK and between ±0.11% and ±0.44%, respectively. Not only the level where the meniscus disappeared but also the intensity of the critical opalescence was considered in the determination of the critical temperature and density being 391.74 ± 0.02 K (ITS-90) and 536 ± 2 kg·m⁻³, respectively. The critical exponent of the power law, β, was also determined as 0.347 ± 0.002. A saturated vapor-liquid density correlation has been developed on the basis of the present measurements.