The cross-sectional curvature effect of twisted tapes on heat transfer performance

This study reports the cross-sectional curvature effect resulted from a twisted tape fabrication or installation into an annular pipe on the enhancement of heat transfer to pay attention to the use of twisted tapes more efficiently. Six different twisted tapes having two twist ratios (3 and 4) and three curve ratios (1.761, 2.252 and 3.271) in the Reynolds number range from 5840 to 30,900 were numerically analyzed. The analysis method was validated with three different experimental results from loose-fit to tight-fit of a twisted tape. According to polyhedral mesh element analysis of curved cross-sectional twisted tapes, capable of having better compatibility with experimental results, Nusselt numbers increased with increasing curve ratio and decreasing Reynolds number and twist ratio. While the curved twisted tape is more efficient than the smooth tube, losses on heat transfer efficiency are observed compared to the classical twisted tape. Although the losses caused by the curvature on the twisted tape appear to be insignificant at high curve ratios, the effect of low curve ratios increases significantly. For the lowest CR and the highest TR under analysis conditions, it was observed that TT lost 28 % of its normal productivity increase due to this effect.