An apparatus for accurate pressure-density-temperature (p, ρ, T) measurements was modified according to the requirement that liquid can be measured. The new instrument is based on a compact single-sinker densimeter which applies the Archimedes’ buoyancy principle. The whole apparatus includes the magnetic suspension balance, thermostat system, measured fluid filling system, temperature and pressure measuring system, vacuum and auxiliary system. It covers a density range from (0 to 2000) kg m^-3 at temperatures from (210 to 300) K and pressures up to 6.0 MPa. In order to verify the new apparatus, comprehensive (p, ρ,T) measurements of pure ethane were carried out. The experimental data were compared with selected literature data and the results demonstrate the good performance of the apparatus. Comprehensive (p, ρ, T) measurements on high purity difluoromethane (HFC32) were measured along different isotherms from (215 to 293) K and pressures up to 2.2 MPa. The relative standard uncertainty in density is (0.01 to 0.08) % for vapour and 0.01 % for liquid. The standard uncertainty in temperature is 5 mK, and that in pressure is 177 Pa and 493 Pa for vapour and liquid, respectively. The experimental results were compared with selected literature data and were correlated by the virial equation and Tait equation for vapour and liquid, respectively. The calculated results show good agreement with the experimental values.

The Journal of Chemical Thermodynamics, 2014