Crossover equation of methane state for calculation of heat capacity in regular and critical state regions up to 30 MPa

A new thermal equation of state for methane is proposed in explicit form, including a crossover function. This equation of state comprises new regular and scaling parts with 22 adjustable coefficients written through the real temperature-density variables. The coefficients are determined from the p, ρ, T data for CH 4 . Data on the heat capacities C v , C p , and the speed of sound W were not involved in coefficient calculations, except for the data on the isochoric heat capacity C v for the ideal gas state and the C v value (at 100 K) on the liquid branch of the liquid-gas equilibrium curve. In the regular region, the calculated values of C v , C p , and W are close to the experimental and tabulated values. In the critical region, the discrepancies with the tabulated values are no more than 5 %, which is associated with the use of the scaling equation of state. The average absolute deviation is 0.3 % in the pressure description, the r.m.s. error σ p = = 0.5 %, and the error in C v is less than 5 %. The calculation results are compared with the known crossover equations of state for CH 4 . It is concluded that the proposed model of the equation of state is preferable for calculating the thermophysical properties of methane.