Accurate experimental (p, ρ, T) data and virial coefficients for the (methane and helium) binary system

Abstract

The quality and the availability of experimental data limit the achievable accuracy of multiparameter equations of state, such as the GERG-2008. Referring to the fundamentals of this wide-range equation of state, no suitable data were available for many mixtures containing helium. This work provides accurate experimental (p, ρ, T) data for three binary mixtures of methane with helium: (0.95 (amount-of-substance fraction) CH4 + 0.05 He) and (0.90 CH4 + 0.10 He) at temperatures of (240, 250 and 260) K, and (0.50 CH4 + 0.50 He) from (240 to 400) K. This work is a continuation of a previous one which reported accurate experimental (p, ρ, T) data for the (0.95 CH4 + 0.05 He) and the (0.90 CH4 + 0.10 He) binary mixtures in the temperature range from the (250 to 400) K. All density measurements were performed by using a single-sinker densimeter with magnetic suspension coupling at pressures up to 20 MPa. Experimental data were compared with the corresponding densities calculated from the GERG-2008 and the AGA8-DC92 equations of state. Deviations from the GERG-2008 are much larger than from the AGA8-DC92 (up to –6.5 %). These deviations increased with decreasing temperature, with increasing pressure, and with increasing helium fraction. In contrast, deviations from the AGA8-DC92 are within the 0.5 % band. The experimental values were also used to calculate the second interaction virial coefficient for this mixture.