## 4 Results and Discussion
### Comparison of the Steam-CO\({}_{2}\) Mixture Condensation Features with Steam-Air  
Figure 8 shows the variation in condensation parameters of steam-CO\({}_{2}\) (CG model) and steam-air condensation mixtures at 1 atm and 10 MPa on the surface of a 0.2 m long horizontal plate. The velocity of the mixture is 1 m/s, and the CO\({}_{2}\) and air mass percentages at the inlet mixture gas are taken as 2% and 30%. As shown in Figure 8a, for the same mass percentage and other conditions of steam-CO\({}_{2}\) and steam-air mixtures, there is a remarkable difference in their condensation heat transfer parameters, which is only caused by the different components of CO\({}_{2}\) and air. The gas-liquid interface temperature of steam-CO\({}_{2}\) mixture condensation is higher than that of a steam-air mixture. Figure 8c shows that the percentage of CO\({}_{2}\) at the gas-liquid interface is higher than that of air. Since the solubility of CO\({}_{2}\) is small, its effect on condensation can be negligible in low-pressure conditions. Moreover, 10 MPa is selected as the total pressure of this part for the following data comparison. Figure 8b uses \(\Delta NDT_{i}\) (the deviation in non-dimensional \(T_{i}\)) to compare the ratio of thermal resistance in the gas phase of NG or CG with air at 10 MPa. \[ \begin{array}{c}\Delta NDT_{i}=\frac{(T_{\rm air}-T_{\rm NG/CG})_{\alpha}-(T _{\rm NG/CG}-T_{\rm air})_{\alpha}}{T_{\infty}-T_{\rm air}}\\ =(\frac{T_{\infty}-T_{i}}{T_{\infty}-T_{\rm air}})_{\rm air}-(\frac{T_{\infty} -T_{i}}{T_{\infty}-T_{\rm air}})_{\rm NG/CG}\end{array}  \tag{26}\]  
Figure 6: Comparison of \(\Delta HTC\) and CO\({}_{2}\) solubility values at CO\({}_{2}\) inlet fractions of 2%, 30%, and 80% (\(L\)\(\alpha_{\infty}\) = 1 m/\(s\); \(L\) = 0.2 m). (**a**) Comparison of \(\Delta HTC\) at different \(\alpha_{\infty}\); (**b**) Comparison of \(S\) at different \(\alpha_{\infty}\). The physical significance of the first term represents the proportion of the gas-phase thermal resistance of steam-air total thermal resistance, and the second term represents the proportion of the gas-phase thermal resistance of steam-CO\({}_{2}\) (CG model or NG model) in the total resistance. Both terms are dimensionless parameters. Due to the differences in physical properties, under the same condition in \(\alpha_{\infty}\), the gas-phase thermal resistance of steam-air mixture condensation is greater than that of the steam-CO\({}_{2}\) mixture. Given the micro-soluble nature of CO\({}_{2}\), the gas-phase thermal resistance calculated by the CG model is lower than that calculated by the NG model, as shown in Figure 8a,b, due to the entry of CO\({}_{2}\) into the liquid phase. Figure 8d shows \(\Delta ND\alpha_{i}\) (the deviation in non-dimensional \(\alpha_{i}\)), as given below:  
\[\Delta ND\alpha_{i}=\frac{\alpha_{i,\text{air}}-\alpha_{i,\text{NG/CG}}}{( \alpha_{i}-\alpha_{\infty})_{\text{air}}}=1-\frac{(\alpha_{i}-\alpha_{\infty} )_{\text{air}}}{(\alpha_{i}-\alpha_{\infty})_{\text{NG/CG}}} \tag{27}\]  
Figure 7: Comparison of \(T_{i}\), \(\alpha_{i}\), and \(\delta\) curves at total pressures of 10 MPa. (**a**) \(T_{i}\) versus subcooling; (**b**) \(\alpha_{i}\) versus subcooling; (**c**) Film thickness along the horizontal plate at 7 K subcooling (\(U_{\infty}=1\) m/s; \(L=0.2\) m). \(\Delta ND\alpha_{i}\) represents the CO\({}_{2}\) fraction difference at the steam-CO\({}_{2}\) and steam-air gas-liquid interface. In Figure 8d, the difference in \(\Delta ND\alpha_{i}\) increases with an increase in the CO\({}_{2}\) concentration and subcooling rate. Figure 8a-d indicate that the impact of CO\({}_{2}\) solubility at  
Figure 8: Comparison of steam–CO\({}_{2}\) and steam–air mixture condensation on horizontal plate at the same inlet CO\({}_{2}\) and air mass percentage (\(U_{\infty}=1\) m/s; \(L=0.2\) m).