Heat transfer analysis of a solar absorber tube using 3D-printed swirl generators

In this study, novel 3D-printed short-length swirlers with various twist angles in the range of 0°-450° were inserted in a solar absorber tube heat exchanger to induce decaying swirl flow and investigate their thermo-hydraulic effects. Laminar air flow with Reynolds number in the range of 513 and 2054 was used. First, computational fluid dynamics (CFD) simulations were carried out by using the Finite Volume Method (FVM). Next, experimental analysis was conducted to validate numerical results. The results demonstrated that increasing the twist angle resulted in augmented thermal performance and increased friction factor. Similarly, the increase in Reynolds number caused an increase in Nusselt number. According to numerical results, the swirler with the highest twist angle of 450° employed together with the flow at Reynolds number of 2054 lead to the highest Nusselt number and friction factor enhancement ratios as 3.17 and 17.3, respectively. The highest Performance Evaluation Criteria (PEC) of 1.15 was observed at Reynolds 1031 using a swirler with 150° twist angle. Finally, the local analysis findings highlighted that flow near the swirler locations has higher tangential velocities indicating swirl-dominant flow and hence contributing to heat transfer enhancement remarkably.