A Decade of Progress in Calorimetry, Halogenated Hydrocarbons and Their Mixtures
Joe W. Magee
A knowledge of accurate thermodynamic properties is a prerequisite to design efficient and cost-effective refrigeration systems which use halogenated hydrocarbons as working fluids. A review is presented of a NIST Project concerning experimental methods and measurements of thermodynamic properties. These measurements were conducted on selected pure components and their mixtures. Key properties include vapor pressures of vapor-liquid equilibrium, densities, and heat capacities. Because of their significance, the review emphasizes calorimetric measurements of heat capacities at constant volume Cv with an adiabatic method, while also discussing a concurrent effort that produced vapor pressures and densities. This measurement program produced thermodynamic measurements for pure halogenated hydrocarbons including HCFC-13, HFC-23, HFC-32, HFC-41, HCFC-123, HCFC-124, HFC-125, HFC-134a, HFC-143a, and HFC-152a, and for their binary and ternary mixtures including HFC-32+HFC-125, HFC-32+HFC-134a, HFC-125+HFC-134a, HFC-125+HFC-134a, and HFC-32+HFC-125+HFC-134a. In addition to heat capacities, calorimetric studies produced the first reliable measurements of triple point temperatures and enthalpies of fusion for seven pure compounds. Also, heat capacities measured in the two-phase region have provided a useful means of calculating thermodynamically consistent vapor pressures at temperatures between the triple-point and the normal boiling-point temperatures. Taken as a whole, this body of calorimetric measurements had a significant impact on the development of accurate predictive models. Because of the sensitivity of the mathematical models to the behavior of the heat capacity, the heat capacieites from this project have strongly influenced the selection by an international panel, of the most reliable equation of state formulations for HFC-32, HCFC-123, HFC-125, HFC-134a, HFC-143a, and HFC-152a. The heat capacities measured for the mixture systems have had an equal impact on the development of accurate mixture models.