Performance investigation of integrated concentrating solar air heater with curved Fresnel lens as the cover

To obtain a tracking-free, economical medium-high temperature solar air collector, this paper presents an integrated concentrating solar air heater (ICSAH), which is compounded of a curved Fresnel lens, a V-groove secondary reflector, and an absorber placed inside a glass tube flow channel. The optical simulation to the ICSAH was carried out, and the maximum optical efficiency is found 0.77. And its acceptance angles are 9.6° in north-south and 42.5° in east-west. The heat transfer was analyzed in detail and a calculation model was established. Two ICSAHs with different length have been set up and tested to investigate the thermal performance and validate the simulation results. The thermal efficiency is found more sensitive to incident angle α than γ. Besides, an entire daytime test on the fixed full-scale ICSAH shows that the outlet air temperature remains above 100 °C for 4.5 h and the maximum temperature differential reached to 108 °C at air flow rate of 8.1 kg/min. With 6.5 working hours per day, its daily efficiency achieves 0.53. The curve of normalized thermal efficiency illustrates that the heat loss rate of the full-scale ICSAH is about 1.758 W·m⁻² K⁻¹. Finally, a techno-economics comparison was made between the ICSAH and other CSAHs.