Heat Transfer Intensification in a Heat Exchanger by Means of Twisted Tapes in Rib and Sawtooth Forms

This experimental study aimed to intensify the aerothermal performance index (API) in a round tube heat exchanger employing twisted tapes in rib and sawtooth forms (TTRSs) as swirl/vortex flow generators. The TTRSs have a constant twist ratio of 3.0, a constant rib pitch ratio (p/e) of 1.0, and six different sawtooth angles (alpha = 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, and 70 degrees). Experiments were carried out in an open flow using air as the working fluid for Reynolds numbers between 6000 and 20,000 in the current study, which was conducted in a heated tube under conditions of uniform wall heat flux. A typical twisted tape (TT) was also tested for comparison. The experimental results suggest that TTRSs yield Nusselt numbers ranging from 1.42 to 2.10 times of those of a plain tube. TTRSs with larger sawtooth angles (alpha) offer superior heat transfer. The TTRSs with alpha = 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, and 70 degrees respectively, enhance average Nusselt numbers by 158%, 162%, 166%, 172%, 180%, and 187% with average friction factors of 3.51, 3.55, 3.60, 3.67, 3.75 and 3.82 times higher than a plain tube. Additionally, TTRSs with sawtooth angles (alpha) of 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, and 70 degrees offer APIs in the ranges of 0.99 to 1.19, 1.01 to 1.21, 1.03 to 1.26, 1.05 to 1.31, 1.07 to 1.42, and 1.09 to 1.48, respectively, which are higher than those of the typical twisted tape (TT) by around 5%, 7%, 11%, 16%, 25%, and 31%, respectively. This demonstrates that twisted tapes in rib and sawtooth form (TTRSs), with appropriate geometries, give a promising trade-off between enhanced heat transfer and an increased friction loss penalty.

Automated summary

This experimental study focuses on improving the aerothermal performance index (API) of a round tube heat exchanger using twisted tapes in rib and sawtooth forms (TTRSs) as vortex flow generators. The results show that TTRSs with larger sawtooth angles offer better heat transfer, with Nusselt numbers increasing by 1.42 to 2.10 times compared to a plain tube. The TTRSs also have higher API values, ranging from 0.99 to 1.48, which are 5% to 31% higher than a typical twisted tape.