ps_models.md

Vapor pressure models

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Functions of $p=\mathrm{f}(T)$
where $p$ is vapor pressure [kPa] and $T$ is temperature [K].

Content

1. Antoine
2. Wagner

Antoine (extended)

$$\ln p = A + \frac{B}{T + C} + D T + E \ln T + F T^G$$

The basic Antoine is the same, but with only first 3 parameters $A,B,C$, the rest are zero.

Params table

	$A$	$B$	$C$	$D$	$E$	$F$	$G$
UoM	ln kPa	ln kPa·K	K	1/K	ln kPa / ln K	ln kPa · K^-G	1

Antoine parameters conversion

When importing parameters from external source, it is imperative to carefully check the formula they use!
Unfortunately, there is no single convention for the equation format, so a guide on the most common $A,B,C$ parameter transformations might come in handy.
Only the basic parameters are covered; the extended form complies with Aspen Plus and you'd have to transform the $D,E,F,G$ parameters yourself if it is in different format.

• If $B$ or $C$ are presented with a minus sign in the formula, switch their sign accordingly.
• In case of different log base, for example 10: $\log_{10} p = A' + B'/(T + C)$
  • $A = A' \cdot \ln 10$
  • $B = B' \cdot \ln 10$
  • $C$ is identical
• In case of different pressure units, for example [Pa]: $\ln p = A' + B/(T + C)$
  • $A = A' + \ln 1000$
    • 1000 is for [Pa] as example, substitute $\mathrm{kPa}/\mathrm{UoM}$ for other units
  • $B$ is identical
  • $C$ is identical
• In case of different temperature units, for example [°C]: $\ln p = A + B/(T + C')$
  • $A$ is identical
  • $B$ is identical
  • $C = C' + 273.15$

Wagner

$$\ln p = \ln p_c + \frac{A \tau + B \tau^{1.5} + C \tau^{2.5} + D \tau^5}{1-\tau}$$

Where $\tau = 1 - T/T_c$.
Note that $p_c$ is critical pressure [kPa] and $T_c$ is critical temperature [K].
Those must be provided and won't be optimized.

Params table

	$A$	$B$	$C$	$D$	$p_c$	$T_c$
UoM	1	1	1	1	kPa	K