Speeds of sound for (CH4 + He) mixtures from p = (0.5 to 20) MPa at T = (273.16 to 375) K Lozano-Martín, D.; Rojo, A.; Martín, M.C.; Vega-Maza, D.; Segovia, J.J.; The Journal of Chemical Thermodynamics 2019, 139, 105869