## 4 Conclusions  
The desire to minimize water consumption led to the power plant integrated with a dry cooling system. This is also true for a power plant using supercritical CO\({}_{2}\) power cycle. However, this will result in a higher compressor inlet temperature (CIT). Thus, an S-CO\({}_{2}\) Brayton cycle with the dry cooling system inevitably faces substantial deterioration of the cycle efficiency due to losing the benefit of reduced compression work when dry cooling is necessary. This study suggests how to improve aerodynamic performance of an S-CO\({}_{2}\) centrifugal compressor when the compressor inlet temperature can be high to recover the cycle efficiency eventually. A conventional air centrifugal compressor can achieve higher efficiency as backsweep angle increases, however, the maximum allowable backsweep angle is restricted due to the structural issue to the values of about \(-50^{\circ}\). In this study, an S-CO\({}_{2}\) centrifugal compressor performance was examined while changing the backward sweep angle at impeller exit to investigate the same maximum backsweep angle should be applied to the S-CO\({}_{2}\) centrifugal compressor as in the air centrifugal compressor. It was found that an S-CO\({}_{2}\) compressor can achieve the highest efficiency at \(-70^{\circ}\) backsweep angle, which is greater than the typical design value of the air centrifugal compressor. This is because an S-CO\({}_{2}\) compressor can be less limited by the structural integrity compared to the air compressor because S-CO\({}_{2}\) requires only a few hundredths of the enthalpy rise of air when it increases the same amount of pressure. Consequently, the S-CO\({}_{2}\) compressor has lower relative Mach number even though S-CO\({}_{2}\) has lower speed of sound near the critical point. It was also quite surprising that the variation of compressibility factor near the critical point does not impact on its total to total efficiency since its Mach number is still lower than unity. A backward sweep impeller can achieve higher pressure ratio and operate stably in wider range as the mass flow rate is decreased, thus it is recommended to have larger backsweep angle when designing an S-CO\({}_{2}\) centrifugal compressor. As further works, the suggested concept will be proved by more detail structural analysis and the compressor performance test experimentally. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{**Cycle Design Constraints**} \\ \hline Maximum Pressure [MPa] & 20 & \(\eta_{T}\)s [\%] & 90 \\ TIT [\({}^{\circ}\)C] & 350–750 & \(\varepsilon\) of redeperators [\%] & 95 \\ Pressure drop in heat exchangers [MPa] & 0.15 & Generator efficiency [\%] & 98 \\ \(\eta_{\text{COM}}\) [\%] & 81/84 & CIT [\({}^{\circ}\)C] & 31–70 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Design conditions for cycle optimization. Figure 26: Contour of cycle efficiency increase. **Author Contributions:** Conceptualization, S.K.C. and J.I.L. ; methodology, S.K.C., J.L. and J.L. ; validation, S.K.C. and J.L. ; formal analysis, S.K.C., S.J.B. and Y.J. ; manuscript writing, S.K.C. and J.I.L. **Funding:** This research was funded by Civil-Military Technology Cooperation Program (Project No. : 17-CM-EN-04, Development of the supercritical CO\({}_{2}\) power generation system for the exhaust heat recovery of surface ships) as part of the core industrial technology development project supported by the Ministry of Trade, Industry and Energy. **Conflicts of Interest:** The authors declare no conflict of interest.