## 3 Results
Note that the net heat transfer rate shows a similar pattern when compared to the available solar power (\(\lx@overaccentset{{\circ}}{\circ}\)) in Figure 10 (as generated with SolTrace when \(I_{sun}\) is set to 1000 W/m\({}^{2}\)). Finally, Figure 11 shows the working fluid outlet temperature per element along the lengths of the cavity receivers. It should be mentioned that pure thermal oil was investigated as heat transfer fluid in this section of analyses. It is concluded that the outlet temperature of the hemispherical cavity receiver is the highest. According to Figure 11, the elemental outlet temperatures always increase along the cavity tube, since the heated working fluid from a previous element enters the next element. The outlet temperature increases more rapidly at the top wall elements of the cubical and cylindrical cavity receivers. This is because of higher solar heat flux at the cavity top wall as stated previously. Similar achievements are reported by other papers including [17; 18] for a solar dish concentrator with rectangular and cylindrical cavity receiver. A comparison study was presented in this research for different thermal performance parameters such as solar heat flux, absorbed heat, and outlet temperature for three investigated cavity receivers including the hemispherical, cubical, and cylindrical cavities as a new result. In this section, performance of a solar ORC system with different shapes of the cavity receivers is considered including the hemispherical, cylindrical, and cubical cavity receivers. Thermal oil and  
Figure 11: Variation of the outlet temperature along the cavity receiver tube length, with pure thermal oil using weather conditions of 20 October 2016, Tehran, Iran. Figure 10: Variation of available solar power along the cavity tubes with pure thermal oil, when the solar beam irradiance is 1000 W/m\({}^{2}\) (for \(\eta_{mfl}\) = 100%). methanol were used as the solar working fluid, and ORC working fluid. Inlet temperature of the solar heat transfer fluid was assumed to be equal to 40 \({}^{\circ}\)C, and 632.97 W/m\({}^{2}\), respectively. Figure 12 shows variation of the total irreversibility versus turbine inlet temperature (TIT) for different shapes of the cavity receivers as the ORC heat source. Note that the total irreversibility rate of the cubical cavity receiver is the highest. This is because of a higher ORC mass flow rate required, for a specific inlet temperature, when using the cubical cavity receiver (Figure 13). The ORC mass flow rate for the cubical cavity receiver is the highest because it gains the most heat, based on Table 10. It is also concluded from Table 10 that the thermal efficiency and the pressure drop of the cubical cavity receiver is the highest. Furthermore, Figure 12 shows that the total irreversibility rate of the three investigated cavity receivers increases with increasing TIT of the ORC system. For all three cavity receivers, the mass flow rate of the investigated solar ORC decreases with increasing TIT of the ORC system. Similar results were concluded by Ref. [36] for a cubical cavity receiver as heat source of an ORC system. In the current study a performance comparison of different shapes of cavity receiver including hemispherical, cylindrical, and cubical cavity receivers is presented as heat source of the ORC system for selecting the best system for power generation. Figure 6:0 Variation of the total irreversibility rate versus turbine inlet temperature (TIT) with pure thermal oil using the weather conditions of 20 October 2016, Tehran, Iran. Figure 6:1 Variation of the ORC mass flow rate versus turbine inlet temperature (TIT) with pure thermal oil using the weather conditions of 20 October 2016, Tehran, Iran. In this part, the results for the different nanofluid applications in the investigated solar ORC are also presented. The influence of the application of different cavity receiver as the ORC's heat source is studied using application of different nanofluid as the solar working fluid.