## 5 Results and Analysis
### Results under Typical Conditions  
Due to the physical property changes of CO\({}_{2}\), it is necessary to consider the pinch point in each heat exchanger. Figure 3 clearly shows the temperature profiles of both the hot side and the cold side in the TES. As to water and molten salt, their specific heat capacities change slightly and the temperatures show linear variations. For CO\({}_{2}\), the specific heat capacity rises intensely and the temperature varies smoothly when CO\({}_{2}\) approaches the critical point. In the TES1 and TES2, CO\({}_{2}\) releases the heat with a constant pressure of 7.0 MPa, and the maximum specific heat capacity occurs at 29 \({}^{\circ}\)C. Thus, the decrease in temperature in the TES2 narrows during the heat transfer process and the pinch point appears in the middle position of the heat exchanger. And the temperature of CO\({}_{2}\) in the TES1 shows an approximately linear change, as the temperature is far from 29 \({}^{\circ}\)C, and the minimum temperature difference (pinch point) appears in the hot terminal. In the TES3 and TES4, CO\({}_{2}\) absorbs the heat with a constant pressure of 5.5 MPa, and the maximum specific heat capacity occurs at 18 \({}^{\circ}\)C. Hence, the temperature of CO\({}_{2}\) in the TES3 shows a similar variation in the TES2, and the pinch point occurs in the cold terminal. In the TES4, the temperature of CO\({}_{2}\) shows a linear change for the same reason in the TES2, and the pinch point also occurs in the hot terminal. Above all, CO\({}_{2}\) has a different variation trend during distinct temperature ranges, indicating that two sets of heat transferring units are necessary to diminish the temperature difference in the heat exchangers. Therefore, molten salt is used in the high-temperature range and water is used in the middle-temperature range. Table 6 demonstrates the thermodynamic and the exergoeconomic values of system state points under typical operation. Table 7 clearly lists the exergy and exergoeconomic results of system components under typical conditions, while Figure 4 presents the \(\dot{E}_{\rm D}\) ratio of system components. It is clear that the \(\dot{E}_{\rm D}\) proportions of the turbine and the compressor are the highest, representing 34.19% and 28.43%, respectively. It is mainly due to the large pressure drops of the power components, which cause high irreversible losses during CO\({}_{2}\) flow. Large exergy destructions occur in the cooler, TES3, TES2, TES4, and condenser, with values of about 11.19%, 9.97%, 4.67%, 4.27%, and 2.24%, respectively. For the TES3, its specific heat capacity varies greatly during the heat exchange, since the inlet state of the cold fluid is close to the critical state, resulting in the large changes in temperature difference between the cold and hot fluid (\(\Delta\)T), and \(\dot{E}_{\rm D}\) is increased accordingly. For the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Unit** & **Value** \\ \hline Reference temperature & \({}^{\circ}\)C & 25.0 \\ Reference pressure & MPa & 0.1 \\ Water storage tank pressure & MPa & 5.0 \\ System output power & MW & 10.0 \\ Storage pressure of CO\({}_{2}\) & MPa & 7.0 \\ Temperature of cold molten salt & \({}^{\circ}\)C & 260.0 \\ Evaporation pressure of CO\({}_{2}\) & MPa & 5.5 \\ Terminal differences of TES1 & \({}^{\circ}\)C & 5.0 \\ Hot terminal difference of TES2 & \({}^{\circ}\)C & 20.0 \\ Cold terminal difference of TES2 & \({}^{\circ}\)C & 25.0 \\ Cold terminal difference of TES3 & \({}^{\circ}\)C & 5.0 \\ Charging and discharging time & hour & 8.0 \\ Compressor isentropic efficiency & \% & 80.0 \\ Turbine isentropic efficiency & \% & 85.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: System parameter settings under typical conditions [36; 42; 56; 57]. TES1, the \(\dot{E}_{\rm D}\) proportion is the smallest and the value is about 0.87%. It is because of the fact that \(\Delta T\), during the flowing process, is kept in a low range.