The effects of short length and full length swirl generators on heat transfer and flow fields in a solar air heater tube

The effects of short length (SL) and full length (FL) swirl generators on heat transfer and flow fields in a solar air heater tube have been investigated experimentally. Thermal energy transport coefficient performance for different values of the spring ratio, twist ratio, tape thickness ratio and diameter ratio (DR) was studied for Reynolds numbers (Re) ranging between 6000 and 20,000. The tube with swirl generator inserts augments the thermal energy transport coefficient mostly, which is accompanied by a larger pressure penalty. The twisted and spring tape (FL) leads to larger thermal energy transport coefficient than spring and twisted tape (SL). It was found that by using spring and twisted tape (FL) at constant pumping power, heat duty increases up to 22% and 27% in comparison with spring and twisted tape (SL), respectively. Similarly, by using spring and twisted tape (FL) at constant heat duty, pumping power rises up to 27% and 33% in comparison with spring and twisted tape (SL), respectively. A large database has been generated for the thermal energy transport coefficient and thermal–hydraulic performance which is beneficial for the design of solar thermal heaters and heat exchangers.