## 5 Result and Discussion
### Thermal Performance
The optimal HTL evaporation temperature reaches the upper limit, and the PPTD of the HTL evaporator is at VPP when \(T_{\text{g1}}\) rises to 618.15 K. Furthermore, \(T_{\text{g3}}\) rapidly decreases with the increase in \(T_{\text{g1}}\), thereby increasing the increment rate of the net power output. The optimal HTL evaporation temperature does not reach the upper limit, and the PPTD of the HTL evaporator occurs at VPP when toluene is used for the HTL, and \(T_{\text{g1}}\) is 523.15-623.15 K. Therefore, the net power output increases with \(T_{\text{g1}}\). Figure 6 illustrates that thermal efficiency increases with \(T_{\text{g1}}\) because the increment rate is larger in the net power output than in heat absorption. The maximal thermal efficiency is 14.6-19.6% with the \(T_{\text{g1}}\) of 523.15-623.15 K when toluene and R601a are used for HTL and LTL, correspondingly. The thermal efficiencies of cyclopentane, cyclohexane, and benzene system are also maximal when R601a is used for LTL. The R1234 ze(E) used for the LTL will cause minimal thermal efficiency. Figure 6a shows that the optimal HTL evaporation temperature does not reach the upper limit when cyclopentane is used for HTL, and \(T_{\text{g1}}\) is 523.15-553.15 K. The thermal efficiency increases with \(T_{\text{g1}}\). The net power output increases rapidly when \(T_{\text{g1}}\) is 558.15-563.15 K, thus also rapidly \begin{table}
\begin{tabular}{c c c c} \hline \hline \(T_{\text{g1}}\)/K & HTL Working Fluid & LTL Working Fluid &
\begin{tabular}{c} **Maximal Net Power** \\ **Output/KW** \\ \end{tabular} \\ \hline
523.15–598.15 & cyclopentane & R1234 ze(E) & 56.9–117.3 \\
603.15–618.15 & cyclohexane & R1234 ze(E) & 125.6–133.4 \\
623.15 & benzene & R1234 ze(E) & 142.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Optimal working fluids and net power output with \(T_{\text{g1}}\) of 523.15–623.15 K.  
Figure 6: Effects of \(T_{\text{g1}}\) on the thermal efficiency. increasing thermal efficiency. The HTL evaporation temperature is unsuitable for the increase in \(T_{\text{g1}}\), the increment rates of the net power output and thermal efficiency decrease when \(T_{\text{g1}}\) increases to 568.15 K. When cyclohexane is used and \(T_{\text{g1}}\) is 523.15-593.15 K, the optimal HTL evaporation temperature does not reach the upper limit, and the thermal efficiency increases with \(T_{\text{g1}}\). When \(T_{\text{g1}}\) increases to 598.15 K, the optimal HTL evaporation temperatures of the R600a, R245 fa, and R601a systems reach the upper limit; moreover, the irreversibilities between exhaust gas and HTL increase, and the increment rate of thermal efficiency decreases. For the R1234 ze(E) system, the optimal HTL evaporation temperature reaches the upper limit with the \(T_{\text{g1}}\) of 603.15 K.  
Figure 6b demonstrates that, when benzene is used for HTL, and \(T_{\text{g1}}\) is 523.15-613.15 K, the optimal HTL evaporation temperature does not reach the upper limit, and the thermal efficiency increases with \(T_{\text{g1}}\). When \(T_{\text{g1}}\) increases to 618.15 K, the optimal HTL evaporation temperature reaches the upper limit, and the increment rate of thermal efficiency decreases. When toluene is used for HTL, and \(T_{\text{g1}}\) is 523.15-623.15 K, the optimal HTL evaporation temperature does not reach the upper limit, and the increment rate of thermal efficiency remains unchanged. Figure 7 displays that the variations in exergy efficiency with \(T_{\text{g1}}\) are different with various HTL working fluids. Furthermore, Figure 7a illustrates that, when cyclopentane is used for HTL, and \(T_{\text{g1}}\) is 523.15-553.15 K, the optimal HTL evaporation temperature does not reach the upper limit, the increasing \(T_{\text{g1}}\) improves net power output, and the exergy efficiency increases with increasing \(T_{\text{g1}}\).