## 4 Results and Discussion  
### The Effect of CO2 Solubility on Steam-CO2 Mixture Condensation  
The effect of CO2 solubility on the condensation of the steam-CO2 mixture is analyzed by comparing the simulation results of boundary layer models with and without considering CO2 solubility, which have been marked as the CG model and the NG model, respectively. By taking the horizontal plate as an example, Figure 5 gives the average HTC and \(q/q_{0}\) curves versus the subcooling. The inlet CO2 mass percentages shown in Figure 5 are taken at 2%, 30%, and 80%, and the simulation results of CG and NG models are both given and compared under total pressure conditions of 1 atm, 1 MPa, and 10 MPa. Steam-CO2 mixture condensation data curves calculated by CG (solid curve) and NG (dash curve) boundary layer models are different. Although the solid and dash curves are closer to each other at total pressure conditions of 1 atm and 1 MPa, they can be distinguished under 10 MPa conditions. All the distinguishable curves presented in Figure 5 show that the average HTC and \(q/q_{0}\) curves calculated by the CG model are larger than those calculated by the NG model under the same conditions. Moreover, under 10 MPa, increases in the concentration and differences in the average HTC curve between the CG and NG models are found. This indicates that the solubility of CO2 is an enhancement or reduction alleviation effect of the steam-CO2 condensation heat transfer. The effect of CO2 solubility on steam-CO2 mixture condensation is different under different conditions, partly because of the different CO2 solubility itself, which increases with increasing CO2 partial pressure and decreases with temperature. For the small calculation range of subcooling in this study (\(\leq\)20 K), the solubility of CO2 is mainly controlled by the total pressure and the CO2 percentage. When the total pressure is 1 atm and 1 MPa, the solid and dash curves are almost coincident in Figure 5, especially for Figure 5a,b; this is because the solubility of CO2 is small under this condition. Thus, it is reasonable to regard CO2 as an NCG under low-pressure conditions. As the pressure increases, the partial pressure of CO2 on the surface of the condensate also gradually increases. At a total pressure of 10 MPa, the CG and NG models show significantly different simulation results. By comparing the curves in Figure 5a,c,e, with an increase in the CO2 concentration, the differences in the average HTC values of the CG and NG models become more significant under the same total pressure levels. When the concentration reaches 80%, a reduction in the condensate heat transfer is significant, and \(q/q_{0}\) is not discussed here. The effect of CO2 solubility on mixture condensation will influence the average HTC data. Figure 6a shows the average HTC deviations between CG and NG models and Figure 6b shows CO2 solubility values under a total pressure of 10 MPa, in which \(\Delta\)_HTC_ is:  
\[\Delta\emph{HTC}=\frac{\overline{h}_{CG}-\overline{h}_{NG}}{\overline{h}_{CG}} \tag{25}\]  
For the inlet condition of 2% CO2, the CO2 solubility is around 0.6508-1.6401 g/kg water, and \(\Delta\)_HTC_ is the range of 0.218-4.4%; meanwhile, for the inlet condition of 30% CO2, the CO2 solubility is around 10.8774-25.3173 g/kg water and \(\Delta\)_HTC_ is around 1.4-3.5%; and for the inlet condition of 80% CO2, the CO2 solubility is around 36.1272-39.6 g/kg water and \(\Delta\)_HTC_ is around 2.117-3.005%. It can be found that with the increase in subcooling, the growth rate of low \(\alpha_{\infty}\) is faster. This is because the mixed gas with lower \(\alpha_{\infty}\) has better condensation and heat transfer conditions, the condensation mass flux is larger, and \(\Delta\)_HTC_ may show a faster growth trend. In conclusion, when subcooling increases, the solubility of CO\({}_{2}\) reduces the reduction in condensation heat transfer more obviously.