Investigation of effect of the circular ring turbulators on heat transfer augmentation and fluid flow characteristic of solar air heater

• Heat transfer augmentation of SAH with different PR and N were performed.
• The best heat transfer augmentation was obtained with the decrement of PR and N.
• The correlation for Nu, f and η was compared with experimental results.

This study presented effects of the circular ring turbulators (CRTs) having different pitch ratio and hole number on heat transfer augmentation in a new type solar air heater (SAH). The experiments have been performed by varying the parameters, pitch ratio (PR), hole number (N) and Reynolds number (Re) in a range of between 3000 and 7500 under solar radiation heat flux (I). The results obtained using CRTs compared with conventional plain tube. The experimental results have shown a significant enhancement in heat transfer on SAHs with CTRs. According to the experimental results, the higher heat transfer augmentation with CRTs inserted inside the tube in SAHs have been obtained for PR = 2 and N = 2. The best experimental results were found with ∼229% heat transfer enhancement, ∼5.8 times friction factor compared to a conventional plain tube and the thermal performance factor (η) was computed as ∼1.83. In addition, statistical correlations for Nu, f and η were developed. These correlation results illustrated a good agreement with experimental results with ±10% deviation.