Thermophysical Properties of Methane

New correlations for the thermophysical properties of fluid methane are presented. The correlations are based on a critical evaluation of the available experimental data and have been developed to represent these data over a broad range of the state variables. Estimates for the accuracy of the equations and comparisons with measured properties are given. The reasons for this new study of methane include significant new and more accurate data, and improvements in the correlation functions which allow increased accuracy of the correlations especially in the extended critical region. For the thermodynamic properties, a classical equation for the molar Helmholtz energy, which contains terms multiplied by the exponential of the quadratic and quartic powers of the system density, is used. The resulting equation of state is accurate from about 91 to 600 K for pressures <100 MPa and was developed by considering PVT, second virial coefficient, heat capacity, and sound speed data. Tables of coefficients and equations are presented to allow the calculation of these and other thermodynamic quantities. Ancillary equations for properties along the liquid–vapor phase boundary, which are consistent with the equation of state and lowest order scaling theory, are also given. For the viscosity of fluid methane, a low-density contribution based on theory is combined with an empirical representation of the excess contribution. The approximate range of the resulting correlation is 91 to 400 K for pressures <55 MPa. The correlation for the thermal conductivity includes a theoretically based expression for the critical enhancement; the range for the resulting correlation is about 91 to 700 K for pressures below 100 MPa.