COCO - CAPE-OPEN to CAPE-OPEN simulation environment

Vapor Pressure

The vapor pressure routines are specified per compound in the compounds tab, if the vapor pressure calculations are enabled.


The Antoine Equation is:

\begin{displaymath}\ln P^{*}_i = A_i - {B_i \over T + C_i}\end{displaymath}

Note the natural logarithm. This option should be selected if you are using activity coefficient models with parameters from the DECHEMA series. Antoine parameters are available in the TEA PCD data files.

Extended Antoine

The Extended Antoine equation incorporated in TEA's thermodynamic routines is:

\begin{displaymath}\ln P^{*}_i = A_i + {B_i \over C_i + T} +D_i T + E_i \ln T + F_i T^G_i\end{displaymath}

The parameters A through G must be supplied by the user.

Temperature Correlation

The temperature correlation for vapor pressure is given by

\begin{displaymath}\ln P^{*}_i = A_i + {B_i \over T} + D_i T + C_i \ln T + D_i T^E_i\end{displaymath}

Parameters A through E are available in the TEA PCD data files.


The Riedel equation is best suited to non-polar mixtures:

$\displaystyle \zeta_T$ $\textstyle =$ $\displaystyle 36 / T_r + 96.7 \log T_r - 35 - T_r^6$
$\displaystyle \zeta_{Tb}$ $\textstyle =$ $\displaystyle 36 / T_{rb} + 96.7 \log T_{rb} - 35 - T_{rb}^6$
$\displaystyle \phi$ $\textstyle =$ $\displaystyle 0.118 \zeta_T - 7 \log T_r$
$\displaystyle \psi$ $\textstyle =$ $\displaystyle 0.0364 \zeta_T - \log T_r$
$\displaystyle \alpha$ $\textstyle =$ $\displaystyle {0.136 \zeta_{Tb} + \log P_c - 5.01 \over0.0364 \zeta_{Tb} - \log T_{rb}}$
$\displaystyle \log P^*_r$ $\textstyle =$ $\displaystyle - \phi - (\alpha-7) \psi$


Lee and Kesler used a Pitzer expansion to obtain:

$\displaystyle \ln P^{*}_i$ $\textstyle =$ $\displaystyle f^{(0)} + \omega_i f^{(1)}$
$\displaystyle f^{(0)}$ $\textstyle =$ $\displaystyle 5.92714 - {6.09648 \over T_r}- 1.28862 \ln{T_r} + 0.169347 T_r^6$
$\displaystyle f^{(1)}$ $\textstyle =$ $\displaystyle 15.2518 - {15.6875 \over T_r}- 13.4721 \ln{T_r} + 0.43577 T_r^6$



Both the Riedel and Lee-Kesler models are recommended for hydrocarbon mixtures in particular.