Thermal performance of an open thermosyphon using nanofluid for evacuated tubular high temperature air solar collector

• A novel solar air collector with simplified CPC and open thermosyphon is designed and tested.
• Simplified CPC has a much lower cost at the expense of slight efficiency loss.
• Nanofluid effectively improves thermal performance of the above solar air collector.
• Solar air collector with open thermosyphon is better than that with concentric tube.

A novel evacuated tubular solar air collector integrated with simplified CPC (compound parabolic concentrator) and special open thermosyphon using water based CuO nanofluid as the working fluid is designed to provide air with high and moderate temperature. The experimental system has two linked panels and each panel includes an evacuated tube, a simplified CPC and an open thermosyphon. Outdoor experimental study has been carried out to investigate the actual solar collecting performance of the designed system. Experimental results show that air outlet temperature and system collecting efficiency of the solar air collector using nanofluid as the open thermosyphon’s working fluid are both higher than that using water. Its maximum air outlet temperature exceeds 170 °C at the air volume rate of 7.6 m3/h in winter, even though the experimental system consists of only two collecting panels. The solar collecting performance of the solar collector integrated with open thermosyphon is also compared with that integrated with common concentric tube. Experimental results show that the solar collector integrated with open thermosyphon has a much better collecting performance.