## 3 Results and Discussion
### Parametric Study  
After analysing all the graphs in the previous section for each mixture, R245 fa/propane and butane/propane are chosen for parametric study. As per the graphs above, these mixtures have significantly higher cycle efficiency at lower operating conditions (T-Hot = 85 \({}^{\circ}\)C; T-Cold = 25 \({}^{\circ}\)C)  
Figure 11: (**a**) Cycle efficiency and net work output; (**b**) temperature glides and volume ratio vs. mass fraction for R245 fa/propane mixture.  
Figure 12: (**a**) Cycle efficiency and net work output; (**b**) temperature glides and volume ratio vs. mass fraction for butane/propane mixture.  
and also have lowest volume ratio and highest temperature glides among other fluids operating at the same conditions. This parametric study is carried out by varying three parameters: hot and cold source temperatures of the ORC and the mass fraction of the mixtures. This study also considers the second law efficiency of the ORC system that is being evaluated at the dead-state temperature of 20 \({}^{\circ}\)C. The conditions are outlined in Table 7. The hot source temperature between 80 \({}^{\circ}\)C to 95 \({}^{\circ}\)C is selected for the use with a flat plate solar collector and the cold source temperature between 20 \({}^{\circ}\)C to 35 \({}^{\  
Figure 15a,b present the effects of mass fraction and hot source temperatures on the cycle efficiency for the two working fluid mixtures. Figure 15a shows that for hot source temperatures of 80 \({}^{\circ}\)C and 85 \({}^{\circ}\)C there is a local minimum cycle efficiency at R245 fa/propane ratio of 0.6/0.4. However, for hot source temperatures of 90 \({}^{\circ}\)C and 95 \({}^{\circ}\)C there is a local maximum cycle efficiency at the same ratio (0.6/0.4). In Figure 15b it can be seen that highest cycle efficiency is at mixture butane/propane (0.8/0.2). There is a local minimum at mixture butane/propane (0.6/0.4). The trend shifts vertically up with increasing hot temperature.  
Figure 16a,b depict the effects of hot and cold source temperatures on the second law cycle efficiency. It can be seen that the second law cycle efficiency is directly proportional to hot source temperatures and as the cycle efficiency trends in Figure 15a,b show, decreasing the cold temperatures tends to trigger an upward vertical movement of the cycle efficiency. The highest second law efficiency is achieved at hot temperature of 95 \({}^{\circ}\)C and cold temperature of 20 \({}^{\circ}\)C.  
Figure 17a,b show the effects of mass fraction and hot source temperature on the second law cycle efficiency for the two working fluid mixtures. Figure 17a shows that the second law cycle efficiency decreases as the mass fraction of R245 fa is increased. In compositions between 0.2 and 0.4, the second law efficiency is almost identical at different hot source temperatures, which shows that hot source temperature does not significantly affect the second law efficiency in these compositions. In Figure 17b the highest second law efficiency is achieved at the mixture butane/propane (0.2/0.8). There is a local minimum at the mixture butane/propane (0.6/0.4). The trend shifts vertically up when the hot temperature increases; however, the shift is small which shows that changing hot temperatures have little effect on the second law efficiency.  
Figure 14: Net work output vs. hot source temperature for different cold source temperatures and with regenerator for mixtures: (**a**) R245 fa/propane (0.6/04); (**b**) butane/propane (0.8/0.2).  
Figure 16: Second law cycle efficiency vs. hot source temperatures for different cold source temperatures for (**a**) R245 fa/Propane (0.6/0.4); (**b**) butane/propane (0.8/0.2).  
Figure 15: Cycle efficiency vs. mass fraction for different hot source temperatures at cold source temperature of 20 \({}^{\circ}\)C and with regenerator: (**a**) R245 fa/propane and (**b**) butane/propane.