# Analysis of Nanofluids Behavior in Concentrated Solar Power Collectors with Organic Rankine Cycle
## 3 Discussion and Analysis  
Samples of the predicted results for the CSP, thermal oil loop and ORC cycle are presented under different inlet conditions, and are analyzed and discussed in the following sections for different solar radiations--550, 750, 1000 and 1200 w/m\({}^{2}\)--and different angles of incidence at 8 a.m., 12 p.m. and 16.00 p.m., and with different nanofluids-- Al\({}_{2}\)O\({}_{3}\) CuO, Fe\({}_{3}\)O\({}_{4}\) and SiO\({}_{2}\)--with a mainly thermal oil supply with exit temperatures of the CSP collector of 166.5 \({}^{\circ}\)C (331 \({}^{\circ}\)F) and 149.5 \({}^{\circ}\)C (301 \({}^{\circ}\)F), respectively, and an ambient temperature of 25 \({}^{\circ}\)C (77 \({}^{\circ}\)F). Other output temperatures of the CSP solar collector were considered: 182 \({}^{\circ}\)C (361 \({}^{\circ}\)F), and 199 \({}^{\circ}\)C (391 \({}^{\circ}\)F). Figures 4-6 present the results of the characteristics of the CSP hybrid system, including absorbed thermal energy, collected thermal energy by the CSP, thermal energy stored, thermal energy delivered to the waste heat boiler of the ORC and finally work produced by ORC, where the thermal oil is the  
Figure 3: Logical diagram for numerical model. base fluid at three different times during the day, and with different angles of incidence of the solar radiation: 17.44\({}^{\circ}\) at 8:00 a.m., 77.44\({}^{\circ}\) at 12:00 p.m. and 137.44\({}^{\circ}\) at 16:00 p.m. Specifically, Figure 3 displays the power absorbed by the CSP at different times during the day and at different angles of incidence in the month of January 2018. It is apparent that the maximum power absorbed by the CSP occurs at midday--12:00 p.m. However, the highest power was observed at 8:00 a.m. due to the solar radiation being higher at 8:00 a.m. compared to at 4:00 p.m. On the other hand, Figure 4 shows the power produced by the ORC at different times during the day and at different angles of incidence. This figure also confirms that the maximum power produced by the ORC occurs at midday. Furthermore, the main parameters of the CSP system--power absorbed, power collected, storage tank thermal energy and work generated by the ORC at different direct normal insolation and angles of incidence--are depicted in Figures 3 and 4. Solar radiations depicted in Figure 4 were measured at the site using a Hobo environmental station. It is quite evident from the results displayed in these figures that the higher the solar radiation, the higher the characteristics of the CSP system and the power produced by the ORC with the use of thermal oil as base fluid. In addition, the solar radiation intensities corresponding to the different angle of incidences are shown in Figure 3. Figure 4 demonstrates that the higher the solar radiation, the higher the efficiencies of CPS and hybrid systems. Furthermore, the results displayed in this figure also demonstrate the maximum efficiencies of the CSP and the hybrid system occur at mid-dia. This can be attributed to the fact that higher solar radiation at higher angles of incidence increases the thermal energy absorbed by the CPS collector and the thermal energy delivered to the waste heat boiler of the ORC. This, in turn, increases the ORC work produced and the efficiencies of the CPS and the hybrid system as shown in Figure 5, where the efficiency of CSP collector and hybrid system are plotted against different angle of incidence and thermal oil as base fluid. The results in this figure also clearly demonstrate that the maximum efficiencies occur at 12:00 and solar radiation of 599.67 w/m\({}^{2}\). Al\({}_{2}\)O\({}_{3}\) is one of the most studied nanofluid in the literature [17; 26; 29; 30]; in the following sections, we present first samples of the results in Figures 7-11 for 5% and 20% concentrations of nanofluid Al\({}_{2}\)O\({}_{3}\).