A new mini-CPC with a U-type evacuated tube under thermal and optical investigation

In this study a mini-CPC with a U-type evacuated tube and a cylindrical absorber is analyzed optically and thermally. The operation of the collector was simulated in horizontal position for ten different inlet water temperatures (10-100 °C per 10 °C) while the heat from the sun was considered to be perpendicular to the aperture plane of the reflector for the thermal analysis part. The thermal efficiency and the overall heat loss coefficient of the collector were calculated and the temperature fields of the absorber, the cover and the water were determined. Moreover, the convection between the water and the tube was examined and compared to a specific model of heat transfer theory. Particularly, the heat transfer coefficient values resulted from the simulation were found to diverge about 6% from the theoretical solution. In addition, the optical efficiency was investigated for several transversal and longitudinal incident angles of the sun rays while a similar collector with a flat absorber was used in order to compare its optical performance to the examined collector. It was found that the longitudinal incident angle modification did not diversify the collectors' performances significantly while the transversal one revealed that the circular absorber configuration appears greater optical performance compared to the flat one. Moreover, the optical performance of the specific collector was compared with the respective of two other CPCs from literature studies and found to exceed them. Also, the secondary flows inside the bend of the U-pipe were determined and explained. The design and the simulation of the collector have been done with Solidworks.