Isochoric p–ρ–T and Heat Capacity Cv Measurements for Ternary Refrigerant Mixtures Containing Difluoromethane (R32), Pentafluoroethane (R125), and 1,1,1,2-Tetrafluoroethane (R134a) from 200 to 400 K at Pressures to 35 MPa

The p \ T relationships and constant volume heat capacity Cv were measured for ternary refrigerant mixtures by isochoric methods with gravimetric deter- minations of the amount of substance. Temperatures ranged from 200 to 400 K for p \ T and from 203 to 345 K for Cv , while for both data types pressures extended to 35 MPa. Measurements of p \ T were carried out on compressed gas and liquid samples with the following mole fraction compositions: 0.3337 R32+0.3333 R125+0.3330 R134a and 0.3808 R32+0.1798 R125+0.4394 R134a. Measurements of Cv were carried out on liquid samples for the same two compositions. Published p \ T data are in good agreement with this study. For the p \ T apparatus, the uncertainty is 0.03 K for temperature and is 0.010 for pressure at p>3 MPa and 0.050 at p<3 MPa. The principal source of uncer- tainty is the cell volume (t28.5 cm3), with a standard uncertainty of 0.003 cm3. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and, thus, a two-standard deviation estimate) of the density measurements is estimated to be 0.050. For the Cv calorimeter, the uncertainty of the temperature rise is 0.002 K and for the change-of-volume work it is 0.20; the latter is the principal source of uncer- tainty. When all components of experimental uncertainty are considered, the expanded relative uncertainty of the heat capacity measurements is estimated to be 0.70.