## 4 Results and Discussion
### Variable Evaporation Pressure  
Figure 8 shows the change rule for each phase area ratio in the evaporator with \(P_{e}\). With increasing evaporation pressure, the saturation temperature increases. It boils more easily and more bubbles form in the evaporator. At the same time, saturated gaseous working fluid also becomes more superheated. That is the reason why the ratio of the two-phase zone and superheated zone gradually rises. The two-phase zone represented the biggest share, increasing from 70.22% to 75.83%. The supercooled zone followed, decreasing from 27.56% to 20.72%. With the smallest percentage, the superheated zone rose from 1.53% to 3.44%. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{(**a**)} \\ \hline
**Parameter** & **Value** & **Unit** \\ \hline \(T_{lux\_in}\) & 125 & \({}^{\circ}\)C \\ \(T_{c}\) & 45 & \({}^{\circ}\)C \\ Interval ranges of \(P_{e}\) & 600–1410 & kPa \\ \hline \multicolumn{2}{c}{(**b**)} \\ \hline
**Parameter** & **Value** & **Unit** \\ \hline \(T_{lux\_in}\) & 125 & \({}^{\circ}\)C \\ \(T_{e}\) & 104 & \({}^{\circ}\)C \\ Interval ranges of \(T_{c}\) & 28–48 & \({}^{\circ}\)C \\ \hline \multicolumn{2}{c}{(**c**)} \\ \hline
**Parameter** & **Value** & **Unit** \\ \hline \(W_{exp}\) & 153.11 & kW \\ \(m_{r}\) & 9.09 & kg/s \\ Interval ranges of \(T_{lux\_in}\) & 125–137 & \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 4: (**a**) Working conditions with the variable \(P_{e}\). (**b**) Working conditions with the variable \(T_{c}\). (**c**) Steady adjustment of the ORC system with the variable \(T_{lux\_in}\). Figure 7: Model validation. The heat flux and mass flow rate have a direct impact on the heat transfer coefficient. Bubbles form more quickly when the heat flux rises. An increase in the mass flow rate expedites the removal of bubbles produced in the evaporator and promotes convective heat transfer. Consequently, the heat transfer coefficient increases. All of that can be seen in Figure 9. The values for the heat transfer coefficient, mass flow rate, and heat flux were 2264.65-3230.40 W/(m\({}^{2}\).K), 3.14-11.55 kg/s, and 14.04-46.32 kW/m\({}^{2}\), respectively. As Figure 10b illustrates, the mass flow rate of the working fluid decreased when the evaporation pressure increased. From the previous analysis, a drop in the mass flow rate can cause bubbles to deposit, which makes the utilization ratio of two heat exchangers decrease, as shown in Figure 10a. Among them, the evaporator utilization ratio decreased from 74.85% to 38.32% and the condenser utilization ratio decreased from 66.61% to 13.69%. The output power of the expander is the product of the mass flow rate and the enthalpy difference between the inlet and outlet. The latter increases with evaporation pressure. When the evaporation pressure was less than 827.46 kPa, the increase in specific enthalpy difference was greater than the decrease in the mass flow rate, so the output power showed an increasing trend. The impact of mass flow on the output power started to outweigh the specific enthalpy difference when the evaporation pressure rose over 827.46 kPa, resulting in a decrease in output power. As a result, the output power had a maximum value of 153.11 kW. The system efficiency was 7.78% and mass flow rate was 9.13 kg/s when the output power reached its maximum. Figure 8: The curves of the evaporator-phase zone ratios varying with \(P_{e}\). Figure 9: The linear relationship between the \(K_{e}\), \(m_{r}\), and heat flux in the evaporator. As the evaporation pressure rises, the heat transfer amount of the evaporator is the product of the heat transfer coefficient, heat transfer area, and temperature difference. The decrease in the heat transfer coefficient and actual heat exchange area lead to the decrease in the heat transfer amount in the evaporator. System efficiency is the ratio of the net output work to the evaporator heat transfer.