Performance evaluation of a double-pipe heat exchanger fitted with self-rotating twisted tapes

This study presents heat transfer and frication factor characteristics of heat exchanger tube with self-rotating twisted tapes (SRTTs). A comparison of SRTTs and stationary twisted tapes (STTs) as well as an examination of the effects of SRTTs with different twist ratios (Y = 2.2, 3, 4, and 6) on the thermal characteristics were experimentally investigated under turbulence flows (12000 < Re < 45000). The experimental results showed that SRTTs under rotating conditions could enhance the thermal performance of heat exchanger as compared with STTs. The twist ratios were found to have less effect on the initial stages of the rotating behavior, and the SRTTs with lower twisted ratios rotated faster under the same operating conditions. In addition, it was observed that the Nusselt number, pressure drop, and thermal performance factor increased with decreasing twist ratios. The maximum thermal performance factors of 1.03, 0.9444, 0.924, and 0.898 could be achieved at the start of rotating behavior for Y = 2.2, 3, 4, and 6, respectively. Finally, some correlations of the Nusselt number and frication factor were established within 10% deviation of the experimental data.