Properties of Gases and Liquids

Source

Methods for calculating pure component properties from:

The Properties of Gases & Liquids, 4th Edition Reid, Prausnitz and Polling, 1987, McGraw-Hill

Ideal Gas Molar Heat Capacity (Constant Pressure)

Properties of Gases and Liquids uses the following correlation for the ideal gas molar heat capacity:

\[c_{\text{p ig}} = A + B \times T + C \times T^2 + D \times T^3\]

Parameters

Symbol Parameter Name Indices Description
\(A, B, C, D\) cp_mol_ig_comp_coeff component, [‘A’, ‘B’, ‘C’, ‘D’]  

Ideal Gas Molar Enthalpy

The correlation for the ideal gas molar enthalpy is derived from the correlation for the molar heat capacity and is given below:

\[h_{\text{ig}} - h_{\text{ig ref}} = A \times (T-T_{ref}) + \frac{B}{2} \times (T^2 - T_{ref}^2) + \frac{C}{3} \times (T^3 - T_{ref}^3) + \frac{D}{4} \times (T^4 - T_{ref}^4) + \Delta h_{\text{form, Vap}}\]

Parameters

Symbol Parameter Name Indices Description
\(A, B, C, D\) cp_mol_ig_comp_coeff component, [‘A’, ‘B’, ‘C’, ‘D’]  
\(\Delta h_{\text{form, Vap}}\) enth_mol_form_vap_comp_ref phase, component Molar heat of formation at reference state

Note

This correlation uses the same parameters as the ideal gas heat capacity correlation.

Ideal Gas Molar Entropy

The correlation for the ideal gas molar entropy is derived from the correlation for the molar heat capacity and is given below:

\[s_{\text{ig}} = A \times ln(T/T_{ref}) + B \times (T - T_{ref}) + \frac{C}{2} \times (T^2 - T_{ref}^2) + \frac{D}{3} \times (T^3 - T_{ref}^3) + s_{\text{form, Vap}}\]

Parameters

Symbol Parameter Name Indices Description
\(A, B, C, D\) cp_mol_ig_comp_coeff component, [‘A’, ‘B’, ‘C’, ‘D’]  
\(s_{\text{form, Vap}}\) entr_mol_form_vap_comp_ref phase, component Standard molar entropy of formation at reference state

Note

This correlation uses the same parameters as the ideal gas heat capacity correlation .

Saturation (Vapor) Pressure

Properties of Gases and Liquids uses the following correlation to calculate the vapor pressure of a component:

\[ln(\frac{P_{sat}}{P_{crit}}) \times (1-x) = A \times x + B \times x^1.5 + C \times x^3 + D \times x^6\]

where \(x = 1 - \frac{T}{T_{crit}}\).

Symbol Parameter Name Indices Description
\(A, B, C, D\) pressure_sat_comp_coeff component, [‘A’, ‘B’, ‘C’, ‘D’]  
\(P_{crit}\) pressure_crit_comp None Critical pressure
\(T_{crit}\) temperature_crit_comp None Critical temperature

Note

This correlation is only valid at temperatures below the critical temperature. Above this point, there is no real solution to the equation.