The fluid database consists of a set of .json-files in the fluids directory. These files are are used to auto-generate the FORTRAN-files compdatadb.f90 and saftvrmie_datadb.f90 by running the respective python scripts compdata.py and saftvrmie.py found in the directory addon/pyUtils/datadb/. The files are generated in the current working directory and must be copied to the src-directory before recompiling ThermoPack to make the fluids available.

A <fluid\>.json file must contain a minimal set of data to be valid. This includes the critical point, accentric factor, mole weight and ideal gas heat capacity.

Ideal gas heat capacity

Several different correlations for the heat capacity are available, selected by the “correlation”-key in the “ideal-heat-capacity-1” field of the fluid files. These are summarized in the table below.

Ideal gas heat capacity correlations, and the corresponding keys used in the fluid-database.

Key	Correlation	Equation	Unit
1	Sherwood, Reid & Prausnitz(a)	$A + BT + CT^2 + DT^3$	$\text{cal mol}^{-1} \rm{K}^{-1}$
2	API-Project	44	-
3	Hypothetic components	-	-
4	Sherwood, Reid & Prausnitz(b)	$A + BT + CT^2 + DT^3$	$\rm{J mol}^{-1} \rm{K}^{-1}$
5	Ici (Krister Strøm)	$A + BT + CT^2 + DT^3 + ET^{-2}$	$\rm{J g}^{-1} \rm{K}^{-1}$
6	Chen, Bender (Petter Nekså)	$A + BT + CT^2 + DT^3 + ET^4$	$\rm{J g}^{-1} \rm{K}^{-1}$
7	Aiche, Daubert & Danner(c)	$A + B [ (C / T) \sinh(C/T) ]^2 + D [ (E / T) \cosh(E / T) ]^2$	$\rm{J kmol}^{-1} \rm{K}^{-1}$
8	Poling, Prausnitz & O’Connel(d)	$R ( A + BT + CT^2 + DT^3 + ET^4 )$	$\rm{J mol}^{-1} \rm{K}^{-1}$
9	Linear function and fraction	$A + BT + C(T + D)^{-1}$	$\rm{J mol}^{-1} \rm{K}^{-1}$
10	Leachman & Valenta for H2	-	-
11	Use TREND model	-	-
12	Shomate equation $^{(*)}$	$A + B T_{\rm{s}} + C T_{\rm{s}}^2 + D T_{\rm{s}}^3 + E T_{\rm{s}}^{-2}$	$\rm{J mol}^{-1} \rm{K}^{-1}$
13	Einstein equation sum	$R (A + \sum_i B_i (C_i / T)^2 \exp[C_i / T] / (\exp[C_i / T] - 1)^2)$	$\rm{J mol}^{-1} \rm{K}^{-1}$

(a) 3rd ed.(c) DIPPR-database

(b) 4th ed.(d) 5th ed.

${(*)}$ Note:$T_{\rm{s}}= 10^{-3} T$

Melting and sublimation curve correlations

$T_{\rm{reducing}} (K), p_{\rm{reducing}} (Pa), \mathbf{a}, \mathbf{c}, n, n_1, n_2$ and $n_3$ are read from the <fluid\>.json file, while $n_4 = n-n_1- n_2-n_3$. Currently a maximum of 6 parameters can be given, $n \leq 6$. The correlation type is defined by a four character string with the format XX-X, where ML-X and SL-X are the default melting curve ($\sigma_{\rm{melt}}$) and sublimation curve ($\sigma_{\rm{sub}}$) correlations, respectively. See the Methane.json file for an working example of both the melting_curve and sublimation_curve parameters.

The reduced temperature used in the correlations is defined as

\[\tau = \frac{T}{T_{\rm{reducing}}}.\]

The last character in the correlation string defines how the reducing pressure combines with $\sigma$ to give the melting/sublimation pressure,

\[p(\sigma) = p_{\rm{reducing}} \times \begin{cases} \sigma & \text{correlation is XX-1} \\\\ \exp(\sigma) & \text{correlation is XX-2}\\\\ \exp(\frac{\sigma}{\tau}) & \text{correlation is XX-3} \end{cases}\]

For the melting curve calculation $\sigma$ is calculated from

\[\sigma_{\rm{melt}} = \sum_{i=1}^{n_1} a_i \tau^{c_i} + \sum_{j=1}^{n_2} a_j (\tau-1)^{c_j} + \sum_{k=1}^{n_3} a_k (\ln \tau)^{c_k} + \sum_{l=1}^{n_4} a_l (\tau^{c_l} - 1)\]

For the sublimation curve calculation $\sigma$ is calculated from

\[\sigma_{\rm{sub}} = \sum_{i=1}^{n_1} a_i \tau^{c_i} + \sum_{j=1}^{n_2} a_j (1-\tau)^{c_j} + \sum_{k=1}^{n_3} a_k (\ln \tau)^{c_k} + \sum_{l=1}^{n_4} a_l (\tau^{c_l} - 1)\]

The melting/sublimation curves can be scaled to match the saturation pressure at the triple temperature, $p_{\rm{sat}}(T_{\rm{triple}})$. The scaled pressure, $\tilde{p}(\sigma)$, is then calculated as

\[\tilde{p}(\sigma) = \frac{p_{\rm{sat}}(T_{\rm{triple}}) }{p(\sigma(T_{\rm{triple}}))} p(\sigma)\]