HEAT TRANSFER ENHANCEMENT MECHANIMS OF HEAT EXCHANGER TUBES WITH ROTATING
TWISTED TAPE INSERT

ZHANG Lin^{1, 3} QIAN Hongwei^{1, 3} YU Xiumin² XUAN Yimin³

3. School of Power Engineering, Nanjing University of Science & Technology, Nanjing 210094 )

Abstract: The question of the low efficiency and fouling deposit for heat exchangers is a worldwide difficult problem all the time. The technology of a self-rotating cleaning twisted tape is developed, which has double functions of heat transfer enhancement and online cleaning fouling. Some heat transfer enhancement mechanisms of the rotating twisted tape are proposed, it can be attributed to the following four effects: ① The reduction of the equivalent diameter. ② The velocity increase near the tube wall due to the blockage of the twisted tape. ③ The velocity increase due to the helical flow following the twisted tape. ④ The velocity increase due to the second flow. Based on the theory analysis of the four heat transfer enhancement mechanisms, the prediction correlations of the heat transfer Nusselt number are put forward respectively. The results show that, for y≥10, the reduction effect of the equivalent diameter and the velocity increase effect near the tube wall area are the main contributing factor of heat transfer enhancement, for y＜10, the helical flow effect is the main contributing factor of heat transfer enhancement. The contribution to heat transfer enhancement of the second flow motion is smaller than other three ones, only for y≤1, it becomes the main contributing factor. The prediction results of the heat transfer Nusselt number for the tube with a self-rotating twisted tape insert are compared with the experimental results. They show reasonably good agreement.

Key words: Rotating twisted tape Swirl flow Heat transfer mechanism Preventing fouling

CLC No: TK124

国家教育部科学技术研究重点计划(00208)和江苏省高校自然科学研究计划(06KJB530046)资助项目. Received 20060212,  received in revised form 20060809