The effect of different nanofluids with temperature dependent properties on the thermal efficiency of the solar receiver

Cavity receivers are the most common design in solar dish concentrators in order to achieve high thermal performance. In the current research, in order to design the solar receiver optimally to increase the output fluid temperature, the variables of diameter and pitch of a specific type of receiver, fluid type and velocity and the flow regime have been investigated. The most suitable dimensions of the receiver and flow Reynolds are according to the parameters that lead to the highest fluid outlet temperature. In this study, a spherical concentrator with a spherical cavity receiver is considered. The results show, the most suitable diameter of the receiver tube and its corresponding pitch is 5 mm and 17 rings, the maximum temperature of the outlet fluid is obtained at Reynolds 200 and slow flow regime. Also, the temperature of the outlet fluid with the working fluid of oil and nanofluid oil with nanoparticles have been compared with each other on different days of the year. Therminol with temperature function properties has been used. Nanoparticles of copper, copper oxide and alumina in volume percentages of 0 to 5 % have been added to the oil and the temperature of the nanofluid outlet has been calculated. The results of this comparison show that by adding nanoparticles to the oil, the temperature of the output fluid will increase. The most suitable nanoparticle is copper with a concentration of 5%, which leads to an increase in the temperature of the output fluid by 118 Kelvin degrees.