###### Abstract  
A parabolic solar dish concentrator, as the heat source of an organic Rankine cycle (ORC), can be used for power generation. Different types of tubular cavity receivers with different nanofluids can be considered for use in the solar dish collector to improve its efficiency. In the current research, an ORC with three different cavity receivers including hemispherical, cubical, and cylindrical are investigated using three nanofluids: Al\({}_{2}\)O\({}_{3}\)/oil, CuO/oil, and SiO\({}_{2}\)/oil. A numerical model is validated using experimental data. The ORC analysis is done for a constant evaporator pressure of 2.5 MPa, and condenser temperature of 38 \({}^{\circ}\)C. Methanol is employed as the ORC's working fluid and a non-regenerative, ideal ORC system with different turbine inlet temperatures is considered. Furthermore, a fixed solar heat transfer fluid flow rate of 60 mL/s and dish diameter of 1.9 m is investigated. Results show that, compared to pure oil, the thermal efficiency of the cavity receivers increases slightly, and the pressure drop increases with the application of nanofluids. Furthermore, results show that the cubical cavity receiver, using oil/Al\({}_{2}\)O\({}_{3}\) nanofluid, is the most efficient choice for application as the investigated solar ORC's heat source. Keywords:thermal comparison; nanofluid; cavity receivers; solar dish concentrator +
Footnote †: journal: Applied Soft  
receivers under windy weather conditions. Various cavity receiver geometries for a dish concentrator were also investigated by [PERSON] and [PERSON] [3]. [PERSON] et al. [4] determined the thermal and optical properties of a parabolic dish concentrator numerically using cylindrical, spherical and conical cavity shapes. The highest optical and thermal performance was found for the conical cavity receiver, and the highest optical efficiency was found for the conical cavity receiver. The first and second law efficiencies of a solar dish collector were numerically and experimentally investigated in Ref. [5] with water as working fluid. The cylindrical cavity receiver had the highest first and second law efficiencies. A comprehensive review was presented by [PERSON] et al. [6] on convection heat loss from cavity receivers. [PERSON] et al. [7] investigated the effects of various parameters of a solar dish concentrator, such as incident solar irradiance, concentration ratio and optical error, on the solar heat flux distribution. It was concluded that the aspect ratio (receiver height vs. receiver diameter) and optical error has significant impact on the solar flux distribution. [PERSON] et al. [8] numerically investigated and simulated a rectangular cavity receiver as a dish collector absorber. They used air as the heat transfer fluid in the solar receiver and found that the thermal efficiency of the investigated solar system increased as the tube diameter of the cavity receiver decreased. Also, [PERSON] et al. [9] modeled a power system using dish concentrators and parabolic trough collectors for a cascade system. They concluded that higher efficiencies can be achieved with higher solar irradiance. [PERSON] et al. [10] investigated a dish concentrator, using a hemispherical cavity receiver, under windy conditions, both numerically and experimentally. An experimental model for the cavity heat losses due to wind was proposed. The thermal properties of a fluid can be improved by the addition of suspended ultra-fine solid particles. A suspension with added nano-sized (1-100 nm) particles in a pure conventional fluid is known as a nanofluid. Some of the advantages of nanofluid usage are increased thermal conductivity and minimal clogging of flow passages [11]. [PERSON] et al. [12] performed a first and second law analysis of a minichannel-based solar collector with different water-based nanofluids (Cu/water, Al\({}_{2}\)O\({}_{3}\)/water, TiO\({}_{2}\)/water and SiO\({}_{2}\)/water). Their results showed that the Cu/water nanofluid had the lowest entropy generation rate and the highest outlet temperature.