The effect of vortex generator base length on thermal hydraulic performance across fin-and-tube heat exchanger

Abstract

Heat transfer enhancement is believed can be achieved by using vortex generator. In the past decades, many researches have been performed to investigate the effect of various vortex generator geometry and parameters including vortex generator angle of attack and height. However, less study has been conducted to investigate the influence of vortex generator length at different arrangement towards the heat transfer performance across the fin-and-tube heat exchanger (FTHE). Therefore, the effects of different strategy on the rectangular winglet vortex generator (RWVG) base length towards the thermal hydraulic performance across the FTHE were numerically investigated in this study. Two types of RWVG arrangement known as common flow down (CFD) or common flow up (CFU) arrangement were used and placed behind four rows of tube in inline arrangement. Total of 7 cases were investigated including the default RWVG, extended front and extended back for both RWVG in CFD and CFU arrangement together with FTHE without vortex generator which was set as the baseline case. The Reynolds number ranged from 500 to 900. It was found that the size of the wake region behind the RWVG contributed to the additional pressure drop penalty across the FTHE. Meanwhile, different thermal characteristics were found for different base length strategy in CFD and CFU arrangement. For RWVG arranged in CFD and CFU arrangement, the extended back case shows the highest heat transfer enhancement with 5 - 25 % and 5 - 15 % increment compared to the baseline case respectively. Based on JF factor evaluation, default RWVG in CFU arrangement provide better heat transfer enhancement than the pressure drop penalty compared to other RWVG cases with average JF factor value is 0.8. Nonetheless, none of the tested cases shows higher JF factor value than the baseline case.