2.1.3. Receiver thermal model
The receiver model was recently proposed by Fraser [15] and is obtained from the thermal analysis of a circular open cavity receiver with a flat absorber and thermal insulation in the walls. In this model, the receiver takes the energy from the reflector, and after being affected by heat loss, the fluid is transferred to a Stirling engine that works through a cylindrical tube absorber plane, as shown in Fig. 4. This model assumes that the solar energy distribution is uniform in the cavity, that the optical and thermal properties of the receptor remain constant and that the thermal losses that occur in the cavity are due to the temperature difference between the cavity and the environment. The radiation and convection losses are due to the receiver aperture area and conduction losses, which are transferred to the inner walls of the cavity, to the exterior walls and finally to the atmosphere by convection.