## 6 Results and Discussion
### Parametric Study
#### 6.3.2 Effect of the Working Fluids in ORC  
The quality of the working fluid affects the power output and cycle efficiency significantly. The candidate of working fluid is selected in consideration with aspects from environmental friendliness, safety, availability and suitable for working condition of marine vessels and working performance. According to the recommendation from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and related technical documents, the five working fluids, R134a, R600, R601, R152a, and R124, were chosen to improve the ORC cycle performance. The properties of proposed candidates working fluids are presented on Table 11.  
The impacts of the specified expander inlet temperature on the ORC performance were investigated to determine the net power, thermal efficiency, scroll expander rotational speed, and condenser load of the ORC system, as shown in Figure 8. After the heat exchange on E-103, the temperature of stream 18 is approximately 311.1 \({}^{\circ}\)C. Therefore, the maximum evaporation temperature of the working fluids in the ORC was set at 305 \({}^{\circ}\)C to recover the waste heat energy completely. The specified evaporating temperature of the ORC equals the expander inlet temperature when the expander inlet temperature lies between 150 and 305 \({}^{\circ}\)C, and the expander inlet condition is positioned at the saturated vaporization line of the working fluid. As shown in Figure 8, the net power generation of the ORC increased from 11.72 kW to approximately 110.9 kW as the specified turbine inlet temperature increased from 110 to 290 \({}^{\circ}\)C, according to the results. The performance of the ORC systems using R600 and R601 changes slightly when superheated from 100 to 166 \({}^{\circ}\)C. Subse  
Figure 8: Power output of ORC under different working fluids. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \begin{tabular}{c} **Working** \\ **Fluid** \\ \end{tabular}  & **ODP** & **GWP** & \begin{tabular}{c} **Molecular** \\ **Mmass (g/mol)** \\ \end{tabular}  & \begin{tabular}{c} **Safety Class** \\ **(ASHRAE 34)** \\ \end{tabular}  & \begin{tabular}{c} **Boiling** \\ **Temperature** \\ **[°C]** \\ \end{tabular}  & \ \begin{tabular}{c} **Critical** \\ **Temperature** \\ **[°C]** \\ \end{tabular}  & \begin{tabular}{c} **Critical** \\ **Pressure [kPa]** \\ \end{tabular}  \\ \hline R134a & 0 & 1320 & 102.03 & A1 & \(-\)26.1 & 101.1 & 4059 \\ \hline R124 & 0.02 & 609 & 136.48 & A1 & \(-\)11 & 122.4 & 3624 \\ \hline R152a & 0 & 124 & 66.05 & A2 & \(-\)14 & 113 & 4517 \\ \hline R600 & 0 & 20 & 58.13 & A3 & \(-\significantly with the temperature of the turbine inlet. When R152a is utilized as the ORC working fluid, the best performance of the system is 110.9 kW at 290 \({}^{\circ}\)C under the intended superheated inlet temperature. However, the LMTD of the heat exchanger E108 increases with the evaporator temperature and consequently, the contact areas of the heat exchanger become insufficient. Figure 9 shows that for various working fluids, the average energy efficiency of the ORC system ranged from 11.85% to 25.29% when the superheated temperature of the working fluid increased. R152a and R601 exhibit the maximum and minimum energy efficiencies, respectively, across the entire spectrum of superheated temperatures because different working fluids have varying boiling points. Owing to the enthalpy change, it makes different exchangers duty after heat exchange E-108. Consequently, different operating fluids exhibit different exergy efficiencies. As shown in Figure 10, the exergy efficiency tends to increase with the superheated temperature. R152a exhibited the highest energy efficiency among the five working fluids tested. Therefore, considering the effects of each working fluid on the performance of the system, R152a was selected for the ORC cycle. Figure 10: Exergy efficiency of ORC under different working fluids. Figure 9: Energy efficiency of the ORC under different working fluids.