Peng-Robinson equation of state.

This class implements the Peng-Robinson equation of state (PR-EOS), a widely used cubic equation of state for describing the behaviour of real gases, particularly hydrocarbons. It accounts for non-ideal behaviour of fluids over a range of temperatures and pressures.

The equation is given in terms of the molar density \(\rho\) as:

\[ P = \frac{R T \rho}{1 - b \rho} - \frac{a \rho^2}{1 + 2b \rho - b^2 \rho^2} \]

where \(P\) is the pressure, \(T\) the temperature, \(\rho\) the molar density, \(R\) the universal gas constant, and \(a\), \(b\) are substance-specific parameters.

The parameters \(a\) and \(b\) are computed from the critical temperature \(T_c\) in Kelvin, critical pressure \(p_c\) in Pascal, and (dimensionless) acentric factor \(\omega\) as follows:

\[ a = 0.457235 \frac{R^2 T_c^2}{p_c} \]

\[ b = 0.077796 \frac{R T_c}{p_c} \]

The Peng-Robinson equation is applicable for a wide range of substances (gases and liquids), particularly hydrocarbons, at conditions ranging from subcritical to supercritical. The EOS is not suitable for solid phases or very low-temperature applications where real gases behave ideally.

All input parameters (temperature, pressure, density) are assumed to be in SI units:

Temperature \(T\) in Kelvin [K]
Pressure \(P\) in Pascal [Pa]
Mass density \(\rho\) in \([kg/m^3]\)
The resulting properties will also follow SI units.

Original source: D.-Y. Peng and D.B. Robinson, "A New Two-Constant Equation of State," Industrial & Engineering Chemistry Fundamentals, vol. 15, pp. 59-64, 1976.

Child parameters, attributes and cases

Additional info

Used in the following test data files