Improvement in the Performance of a Solar Hot Air Generator Using a Circular Cone

Abstract

In this work the design and the study of a solar hot air generator, using concentrated solar radiation are proposed. This generator consists of a circular disc heated by the radiation reflected by a parabolic collector. The disc is placed at the entrance of an opened vertical cone. Under the thermal radiation effect emitted by the hot source, the internal wall of the generator is heated. The heating of the air at the generator-inlet generates a thermosiphon flow that is added to the one created by the hot source. In order to determine the critical parameters, the local convective transfer along the generator wall as well as the thermal and dynamic fields of the hot air at the cone exit for different angles and ratios of the rays are studied. It has been found out that the critical parameters of the conical generator, from which the thermal and dynamic characteristics of the hot air produced are R*=0.5; C=0.65; α=8°, have significantly improved. A comparative study of the hot air characteristics at the exit of the optimal conical generator, with two cylindrical and rectangular generators of the same geometrical characteristics is realized. The obtained results reveal relative increases of the mass flow rate of 78% and the heat flux absorbed by the air of 116% at the exit of the optimal cone compared to the cylinder. The results show also relative increases of the air temperature and the thermal flux absorbed by the air respectively of 400% and 129% at the exit of the optimal cone compared to the channel. A correlation between the hot source temperature and the air temperature at the exit of the optimal conical generator has been determined.