Crossover equation of methane state for calculation of heat capacity and sound velocity in regular and critical state regions up to 30 mpa
P.P. Bezverkhii1, O.S. Dutova2
1Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: methane, combined equation of state, critical point, heat capacities, speed of sound
Abstract
A new thermal equation of state for methane is proposed in explicit form, including a crossover function. This function comprises new regular and scaling parts with 22 adjustable coefficients written in real temperature-density variables. The coefficients are determined from the ρ, ρ, T-data for CH4. Data on the heat capacities Cv, Cp and the speed of sound W were not involved in calculations, except for the data on the isochoric heat capacity Cv in the ideal gas state and the Cv value at 100 K on the liquid branch of the liquid-gas equilibrium curve. In the regular region, the calculated values of Cv, Cp, 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 σp = 0,5 %, and the error in Cv is less than 5%. The calculation results are compared with the known crossover equations of state for CH4. It is concluded that the proposed model of the equation of state is preferable for calculating the thermophysical properties of methane.
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