In this paper, we present a numerical analysis of natural convection and the effects of collector radius variation on the velocity and temperature field. After transforming the conservation equations of mass, momentum and energy, we compare the results of our calculation code with those of Comsol. On the one hand, the comparative study of the temperatures in the collector reveals a slight difference at the entrance to the chimney, on the other hand we note that there is a perfect agreement with the general appearance of the evolution curves temperatures in the chimney. In addition, the evolution of speeds in the collector suggests the choice of a tighter mesh. We also note very low velocity values in the chimney. In addition we also present some velocity and temperature profiles in the flow as a function of the Rayleigh number. Finally, a variation in pressure during the flow was studied.
