Numerical and experimental investigation of solar air collector with internal swirling flow

Swirling flow was introduced into the solar air collector (SAC) with the purpose of thermal performance improvement. Numerical simulation was carried out to analyze the parameters that affect the thermal performance. The internal flow and heat transfer characteristics were compared between the basic and swirling-flow collectors in order to explain their difference in performance. The sensitivity study shows that the parameters of the swirling type, the swirling state and the swirling intensity all have significant influence on thermal performance of SAC. The numerical results show that the active swirling flow can yield better improvement than passive swirling flow. The maximum thermal efficiency growth rate (TEGR) of active swirling flow and passive swirling flow are 23.83% and 16.03%, respectively, compared with the basic model in the calculation. An experimental model was built to verify the effectiveness of swirling flow in thermal performance enhancement of SAC. The TEGR can be increased by up to 13.24% under small flow rate in the experiment. However, the improvement is not significant when the flow state is turbulent and the Reynolds number is high. This paper provides a new idea for the performance improvement of flat-plate solar air collectors.