# Analysis of Nanofluids Behavior in Concentrated Solar Power Collectors with Organic Rankine Cycle
## 3 Discussion and Analysis
### Model Validation  
Among a few experimental data that have been reported in the literature on the use of nanofluids in CSP solar collectors, we compared the present model's prediction of the enhancement ratio of the ORC work produced due to the use of the nanofluids; CuO and Al\({}_{2}\)O\({}_{3}\) with the data reported by [PERSON] and [PERSON] [35]. This comparison is presented in Figures 32 and 33, under nanofluid concentrations of 1-6%. The objective of their work was to optimize and evaluate a solar-driven trigeneration system that uses nanofluid-based parabolic trough solar collectors. The trigeneration system studied in reference [35] included an organic Rankine cycle (ORC) and an absorption heat pump operating with LiBr-H\({}_{2}\)O, which is powered by heat dissipated from condenser of the ORC. The comparison between the data of [PERSON] and [PERSON] [35] and our model's prediction was conducted for the nanofluids CuO and Al\({}_{2}\)O\({}_{3}\) on the basis of the enhancement of the work produced by the ORC with each nanofluid, respectively. It was found that the data and the model have the same trend; however, some discrepancies exit between the model's prediction and the experimental data. It is believed that the selection of the basic operating parameters: the pressure in the turbine inlet, the temperature in the ORC condenser and the nanofluid concentration attributed to the discrepancies between model's prediction and the data. In addition, reference [35] did not disclose the aforementioned parameters, which are critical in the validation of the current model. Therefore, other references were consulted [38; 39; 40].  
[PERSON] et al. [31] presented an optical and thermal analysis of parabolic trough solar collector (PTC) and evaluated the performance of the PTC, using four cities with different weather conditions. The analysis was performed using MATLAB software and shows an average annual thermal efficiency of 13.91%. Also, their work concluded that using the nanofluids CuO, SiO2 and Al\({}_{2}\)O\({}_{3}\) as heat transfer fluid increased the heat transfer and system efficiency under average solar radiations of 344 w/m\({}^{2}\). Those results and conclusions were compared to our model's predictions under similar average solar radiations and it was found that our prediction of the system efficiency was, on average, 13.15%, compared to 13.91% reported by reference [31]. In addition, our model predictions were in agreement with the results of reference [31] that nanofluids; CuO, SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) enhanced the heat transfer.  
Other comparisons between our model's prediction for the convection heat transfer coefficient and the data reported by [PERSON] et al. [31] on Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\) are presented in Figures 34 and 35, respectively, at a solar radiation of 425 w/m\({}^{2}\). The comparison displayed in these figures shows that as the nanofluid concentration increases the heat transfer coefficient increases. Our model compares fairly with the data of reference [31]; however, our model underpredicted the heat transfer coefficient by  
Figure 32: Comparison between model and data of [PERSON] and [PERSON] [35].  
9.3% and 8.8% for the nanofluids Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\), respectively. This could be attributed to the different relationships used to calculate the thermophysical properties of the nanofluids in question and used in the Dittus-Bolter correlation [36] to calculate the heat transfer coefficient.  
Figure 34: Comparison between model and data of [PERSON] et al. [31] for Al\({}_{2}\)O\({}_{3}\) as in text is (Al\({}_{2}\)O\({}_{3}\)) and applies to all other Figures.  
Figure 33: Comparison between model and data of [PERSON] and [PERSON] [35] as in text is (Al\({}_{2}\)O\({}_{3}\)) and applies to all other Figures.