Calculation of state equation isobars of carbon dioxide and methane in pressure interval from 2 to 20 MPa

Abstract

The paper presents the calculation results for the state equation isobars of carbon dioxide and methane in the pressure range from 2 to 20 MPa. The calculations have been performed by using the fractal equation of state and the Fract EOS software. It was previously shown that for carbon dioxide there is no temperature dependence of the fitting parameter α. For methane, it was found that the temperature dependence is not significant and weakens approaching to 1000 K. This allowed for considered substances to approximate the dependence of α on the density by a polynomial and use it in calculations at any temperature. Next, in order to apply the proposed model for calculating isobars, a set of isotherms with a small temperature step has been calculated. Then, a point with the required pressure was selected on each isotherm. The obtained results show a good agreement with experimental data. The proposed equation of state is suitable for studying industrially important substances such as carbon dioxide and methane.

Keywords

• equation of state
• integral-differentiation of fractional order
• maxwell relations
• helmholtz potential
• partition function
• carbon dioxide
• methane
• isobar
• isotherm
• thermophysical properties