Apparatus based on a compact single-sinker densimeter and measurements of the (p, ρ, T) relation of difluoromethane

•An apparatus based on a single-sinker densimeter for gas and liquid was described.•Measurements of the (p, ρ, T) relation of ethane were carried out.•Experimental results demonstrate the good performance of the apparatus.•Measurements of the (p, ρ, T) relation of difluoromethane were carried out.•Equations were established by correlating the (p, ρ, T) data of difluoromethane.

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 T = (215 to 293) K and pressures up to 2.2 MPa. The relative standard uncertainty in density is (0.01 to 0.08)% for vapor and 0.01% for liquid. The standard uncertainty in temperature is 5 m · K, and that in pressure is (177 and 493) Pa for vapor and liquid, respectively. The experimental results were compared with selected literature data and were correlated by the virial equation and Tait equation for vapor and liquid, respectively. The calculated results show good agreement with the experimental values.