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

Abstract

This work provides accurate experimental (p, ρ, T) values 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) values for the (0.95 CH4+0.05 He) and the (0.90 CH4+0.10 He) binary mixtures over the temperature range from (250 to 400)K. All density measurements were performed by using a single-sinker densimeter with magnetic suspension coupling at pressures up to 20MPa. Experimental values were compared with the corresponding densities calculated from the GERG-2008 and the AGA8-DC92 equations of state, respectively. Deviations from the GERG-2008 are much larger than from the AGA8-DC92 (up to −6.5%). These deviations increase 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 and the third virial coefficients, B(T,x) and C(T,x), as well as the second interaction virial coefficient B12(T) for this mixture.