## 2 Basic Analysis of Prediction Models and Model Verification
### Prediction Models of Saturated Vapor Pressure and Saturated Density
#### 3.2.4 Comparison and Discussion of Different Models of Saturated Liquid Density  
The nine prediction models summarized in Table 3 were used to calculate the saturated liquid densities of the three electronic fluoride liquids. The results are shown in Figures 5-7. The experimental data on the saturated liquid densities were taken from the literature [60, 66, 71], and the combined uncertainties in measurements (level of confidence = 0.95, coverage factor = 2) of FC-72, Novec 649 and HFE-7100 were 0.029% [60], 0.0075% [66] and 0.02% [71], respectively. Table 6 shows the MRDs and ARDs between the predicted and reference values of different prediction models for the saturated liquid densities.  
From Figures 5-7, it can be known that compared with the PR model, the modification of the \(\alpha\) function (MAPR1 model and MAPR2 model) cannot significantly improve the predictive accuracy of saturated liquid densities, which is exactly as some have scholars proposed, that the modification of the \(\alpha\) function was more beneficial for predicting saturated vapor pressure, but for liquid density, this modification did not seem to work [89, 90, 91, 92]. The specific volume translation modification method of the PR equation has a direct impact on the prediction of liquid densities. Except for the VTPR3 model, the VTPR1 and VTPR2 models have higher predictive accuracy than the PR model, and the VTPR1 model has the highest accuracy. In most cases, the PT model has a poor accuracy when saturated liquid densities are predicted. Furthermore, for some models, a good predictability of saturated vapor pressures does not mean a good predictability of saturated liquid densities. For  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Electronic Fluoride Liquid** & **PR** & **MAPR1** & **MAPK2** & **MPPR** & **PT** & **NEOS** \\ \hline \multirow{3}{*}{FC-72} & ARD (\%) & 1.03 & 0.60 & 0.26 & 0.36 & 1.39 & 4.44 \\  & MRD (\%) & 3.57 & 1.65 & 1.07 & 0.69 & 1.93 & 5.22 \\ \multirow{3}{*}{Novec 649} & ARD (\%) & 0.98 & 0.92 & 0.40 & 0.56 & 1.62 & 4.07 \\  & MRD (\%) & 3.61 & 1.94 & 1.66 & 1.25 & 2.29 & 4.49 \\ \multirow{3}{*}{HFE-7100} & ARD (\%) & 1.22 & 1.06 & 0.58 & 0.82 & 1.49 & 2.29 \\  & MRD (\%) & 5.80 & 4.02 & 3.32 & 3.37 & 3.79 & 4.02 \\ \hline \hline \end{tabular}
\end{table}
Table 5: ARDs and MRDs between the predicted and reference values of different prediction models of the saturated vapor pressures of electronic fluoride liquids.  
instance, the MPPR model has a high accuracy ranking only second to the MAPR2 model for saturated vapor pressures, while its accuracy is really low for saturated liquid densities. These results were also summarized by [PERSON] et al., who showed a low accuracy of the PT model [98] and the MPPR model [94] when liquid densities were predicted, especially for some fluorinated compounds, such as \([-(\mathrm{CF}_{2})_{4}\)-]. The predictive accuracy of the NEOS model was better than that of the PR equation for FC-72 and Novec 649 for the saturated liquid densities, but its relative deviations between the predicted and reference values were the largest of all the models in most cases when saturated vapor pressures were predicted. Therefore, in consideration of versatility, the MPPR and NEOS models are not recommended.  
Figure 4: Relative deviations between the predicted and reference values [73] of the saturated vapor pressures of HFE-7100.  
Figure 5: Relative deviations between the predicted and reference values [60] of the saturated liquid densities of FC-72.  
In summary, when saturated liquid densities are predicted, the specific volume translation modification model is recommended and the VTPR2 model has the best accuracy out of all the models reviewed in this work.