Photo-thermal design and analysis of a novel CPC coupled solar air evacuated tube collector

The conventional evacuated tube solar air collector can't reach a higher temperature due to poor heat transfer between absorber and air. To maintain a low heat loss at medium temperature and enhance heat transfer, a novel evacuated tube solar air collector coupled with a compound parabolic concentrator is proposed. The matching shape is designed and optimized for the concentrator reflecting surface using non-imaging optics, and by ray tracing, the optical performance is obtained. The corresponding photothermal conversion and heat transfer models are established, and numerical simulation is conducted for thermal performance analysis. The results show that the thermal performance is mainly affected by the air flow rate, the inlet temperature, and the heat source energy density. Compared with the existing single-pass evacuated tube collector, the novel collector has advantages in heat output temperature, thermal efficiency, adaptability to flow rate changes, and potential for series temperature rise under most conditions. When concentrated solar power density is 800-1600 W/m2, the maximum outlet temperature of a novel collecting evacuated tube can reach to a limiting value of 181.17 degrees C, representing its thermal insulation performance, while that of the contrast one is 153.25 degrees C. Under normal inlet temperature of 25 degrees C, the maximum output temperature of a single tube of the novel collector is 146.05 degrees C at a flow rate of 1.02 m3/h, and the maximum thermal efficiency of 59.21% can be achieved at a flow rate of 3.58 m3/h.