# Analysis of Nanofluids Behavior in Concentrated Solar Power Collectors with Organic Rankine Cycle
## 3 Discussion and Analysis
The data displayed in this figure clearly demonstrated that the refrigerant flow is maximized at midday, which reflects on the work produced at the ORC vapor turbine, where its maximum value also occurs at same time. Furthermore, simulated results of characteristics of the CSP collector system under solar radiations of 500, 750, 1000, and 1200 w/m\({}^{2}\) occurring at different times of day and 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. have been conducted. The purpose of this exercise is to predict the impact of a wide range solar radiations other than those in the previous figures on the characteristics of the CSP collector system. Figure 19 and Figure 24 present these characteristics at midday. As anticipated, the results displayed in these figures show that higher concentration of the nanofluid Al\({}_{2}\)O\({}_{3}\) enhance the different key parameters  
Figure 3.4 Efficiencies of the CSP hybrid system at different concentrations of Al\({}_{2}\)O\({}_{3}\). of the characteristics of the CSP collector such and power absorbed and collected, thermal storage energy, the output work at the ORC, over thermal oil as base fluid. It is noticeable from the results that the ORC key parameters, such as waste heat boiler thermal energy and work produced (cf. Figures 22 and 23), are enhanced with the increase of the solar radiation and the nanofluid concentrations. However, the CSP power absorbed and storage tank thermal energy are only enhanced with the solar radiation. However, it is worthwhile pointing out that nanofluid concentration higher than 20% could result in higher pressure head losses and pumping power losses in the thermal oil loop and that is undesirable. Therefore, it is important for the designer of such systems to exercise caution when using the Al\({}_{2}\)O\({}_{3}\) nanofluid [25; 26; 30]. The data presented in Figures 19-21 illustrate that the power absorbed, and power collected by the CSP collector and thermal energy stored in the storage tank are enhanced with the increase of the solar radiation; however, they are independent from the nanofluid Al\({}_{2}\)O\({}_{3}\) concentrations and thermophysical properties. This can be interpreted in light of Equations (1)-(6). Figures 22 and 23 illustrate that the key parameters of the ORC are waste heat boiler thermal energy supplied to ORC, and the work produced by the vapor turbine of the ORC. The data is as follows. Figure 3.5 Thermal energy stored in thermal tank at different concentrations of Al\({}_{2}\)O\({}_{3}\). Figure 3.6 ORC waste heat boiler thermal energy at different concentrations of Al\({}_{2}\)O\({}_{3}\). The figures clearly demonstrate that these key parameters are enhanced by solar radiation and the nanofluid concentrations. Also, in Figure 24, the CSP system hybrid efficiency is plotted at different concentrations of Al\({}_{2}\)O\({}_{3}\) and solar radiations, showing that hybrid system efficiency was mainly enhanced by the increase of the solar radiation and at higher nanofluid Al\({}_{2}\)O\({}_{3}\) concentrations over the thermal oil as base fluid. As expected, the maximum efficiency was observed at a solar radiation of 1200 w/m\({}^{2}\). Other nanofluids, such as CuO, Fe\({}_{3}\)O\({}_{4}\) and SiO\({}_{2}\), have received significant attention in the literature, namely, [25; 26; 30]. In the following section, we will discuss the impact of using these nanofluids as heat transfer fluid in the thermal oil loop of the CSP solar collector on the characteristics of the CSP hybrid system; Figures 25-28. It evident from the results depicted in these figures that the nanofluid CuO has the highest characteristic performance among the other nanofluids in the CSP solar collector system over the thermal oil as base heat transfer fluid. This can obviously be attributed to the  
Figure 3.7 ORC work produced at different concentrations of Al\({}_{2}\)O\({}_{3}\) and solar radiations.