Measurement of the (pressure, density, temperature) relation of a (methane + nitrogen) gaseous mixture using an accurate single-sinker densimeter

A single-sinker magnetic suspension densimeter based on Archimedes’ buoyancy principle is described. Density measurements on high-purity nitrogen demonstrate the performance of the densimeter. Comprehensive (p, ρ, T) measurements at low densities on a gaseous mixture with mole fraction of (0.8977CH4 + 0.1023N2) were carried out on this densimeter at six temperatures from (170.586 to 270.054) K and at pressures ranging from (0.1333 to 1.5945) MPa. The overall uncertainty in density is estimated to be 0.1%. The uncertainty in temperature is estimated to be 5 mK and that in pressure is 250 Pa for (0 to 1.5) MPa and 390 Pa for (1.5 to 3) MPa, respectively. The experimental results of the (methane + nitrogen) mixture were compared with REFPROP 9.0, which used GERG-2008 and AGA8 equations of state to predict thermophysical properties of natural gas. The absolute relative deviations of density measurements are all within 0.1%. Meanwhile the experimental results were correlated using the virial equation of state (Virial EOS) with three different mixing rules. The calculated results using the virial EOS combined with VDW mixing rule show good agreement with the experimental data.

► A single-sinker densimeter was described.
► The densimeter is based on Archimedes’ buoyancy principle.
► (p, ρ, T) Data for a (CH4 + N2) gaseous mixture were measured at six temperatures.
► Experimental results show good agreement with values calculated from REFPROP 9.0.
► A correlation of (p, ρ, T) data was made using the virial equation of state.