## 5 Model Validation  
Figures 25 and 26 have been constructed to validate the predicted numerical results by this model with the data presented in the literature on solar PV-Th, magnetic fields, and nanofluids. Experimental data on the magnetic field and nanofluids are scarce and hardly reported in the literature. The thermal energy was calculated using Equation (10) through Equation (17) under a magnetic field up to 3000 Gauss and with nanofluids as heat transport fluid and compared to experimental data reported in the literature. The data reported by reference [49] on Fe\({}_{3}\)O\({}_{4}\) nanofluid were considered and compared with the different magnetic fields up to 7000 Gauss and at a temperature difference of 15 \({}^{\circ}\)C (Figure 25). [PERSON] [49] reported that the stability of the results under a magnetic field was found to be less certain for nanofluids at a lower volume concentration, coupled with the possibility of higher settlement rates due to the additional magnetic force on the nanoparticles. The Fe\({}_{3}\)O\({}_{4}\) nanofluid, the choice for his study, was found to be the nanofluid with a 0.1% volume concentration. The results of our model prediction were compared to the data of reference [49] at similar conditions and are plotted in Figure 25. The comparison showed some discrepancy and it varied between 8% to 14% with the model when predicting the experimental data of reference [49] with higher magnetic fields. We believed that these discrepancies stemmed from the heat transfer coefficient under the magnetic field not being similar and the thermophysical properties of Fe\({}_{3}\)O\({}_{4}\)[54], as well as the PV-thermal heat transfer efficiency, which were not fully disclosed for each nanofluid concentration by reference [50].  
An experimental investigation reported by [PERSON] and [PERSON] [54] on the performance effect of the magnetic field applied to oscillating heat pipes (OHPs) using kerosene with Fe\({}_{2}\)O\({}_{3}\) nanoparticles as the working fluid has been predicted by this model and the comparisons are shown in Figure 26. The heat pipe configuration used in reference [54] was used to conduct the simulation presented in Figure 26. The thermal resistance is a measure of thermal performance and was calculated by the difference in the wall temperature of the evaporator and the wall temperature of the condenser divided by the input heat load. It appears from the comparison presented in this figure that the model overpredicted the heat pipe data by an average of 10%. As per the previous discussion in this paper, and as reported by reference [54], the addition of a magnetic field resulted in a further reduction in the thermal resistance and consequently increased the heat load. We agree with reference [54] that this is due to the ability of the magnetic field to destabilize the vapor film formed on the heat transfer surface at higher heat loads, and the addition of Fe\({}_{2}\)O\({}_{3}\) nanoparticles enhanced the heat transfer to the heat pipe evaporator section. This  
Figure 24: Heat pipe efficiency with different nanofluids.  
effect was fully considered in our prediction of the experimental data of reference [54] and this explained the discrepancies in Figure 26.