Influence of co/counter arrangements of multiple twisted-tape bundles on heat transfer intensification

Heat transfer intensification in tubes containing multiple twisted-tape bundle inserts was experimentally investigated. The experimental parameters included the tape numbers (N) of 2, 4 and 6 pieces, tape twist ratios (y/w) of 4.0, 5.0 and 6.0) and two different tape arrangements: co-swirl tapes (CoT) and counter-swirl tapes (CT). The tests were carried out using air as the working fluid under a constant heat flux. The experimental results showed that all multiple twisted tape bundles caused higher heat transfer rates, pressure losses and thermal hydraulic performance than a typical twisted tape. The heat transfer rate (Nu) and friction factor (f) increased with the number of tapes (N) and decreased with the twist ratio (y/w). At similar operating conditions, the counter-swirl flow twisted tape sets (CT) provided higher heat transfer (Nu) and friction factors (f) than the co swirl flow sets (CoT). The highest thermal hydraulic performance (eta) of 1.33, was offered by the twisted tapes having y/w = 4.0 and N = 6 at Re = 6000.

Automated summary

The experimental study showed that heat transfer intensification can be achieved by inserting multiple twisted-tape bundles into tubes, with increasing number of tapes leading to higher heat transfer rates and friction factors, while increasing twist ratio leading to decreased heat transfer performance. Counter-swirl flow twisted tape sets provided higher thermal hydraulic performance compared to co-swirl flow sets under similar operating conditions.