LAUSR

Abstract This study investigated the thermal-hydraulic characteristic of a circular tube equipped with self-rotating twisted tapes (SRTTs) at different length ratios (LR = 0.3, 0.45, 0.6, and 1) when the Reynolds number is in the range of 12,000 to 45,000. The experimental outcomes revealed that full-length SRTTs can start rotating at a lower Reynolds number (Re = 18,700), and larger length ratios significantly increase the rotational speed. Moreover, the tube equipped with full-length SRTTs was found to provide a higher friction factor, thermal performance factor and Nussle number compared with those with shorter length ratios. The thermal performance factor was considerably increased from 0.91 to 0.95, 0.95 to 1.05, 1.04 to 1.08, and 1.09 to 1.27 owing to the operating condition of SRTTs switching from a stationary to a rotating condition. Finally, this study also derived associated correlations regarding the length ratio to predict the thermal performance in formulas of the Nussle number and friction factor.