Numerical and Experimental Studies on Heat Transfer Enhancement in a Circular Tube Inserted with Twisted Tape Inserts

Haoxu Liu,Xiaogang Lv,Guowei Zheng,Changzhong Man,Ke Jiang

doi:10.11648/j.ajee.20210902.12

Abstract

Numerical simulations and experiments are carried out in this paper to research about characteristics of heat transfer, frictional resistance and comprehensive performance of turbulent water flow (3000 < Re < 10,000) in a circular tube with twisted tape inserts. A new type of twisted tape is proposed and it shows excellent performance on heat transfer enhancement. Effects of three parameters including twist ratio (p/w=3, 4, 5), geometrical structure of alternation of clockwise and counterclockwise, existence of semicircular cuts are researched in simulations. The results show that lower twist ratio and the geometrical structure of alternation of clockwise and counterclockwise can enhance heat transfer while the existence of semicircular cuts can significantly reduce flow resistance. Experiments are conducted to validate the actual effect of the twisted tapes and the experimental results are basically consistent with the simulation results. Nusselt number and friction factor with the new type of twisted tape inserts are respectively 1.66-2.42 times and 4.36-4.97 times to that of plain tube while the maximum value of PEC (performance evaluation criteria) reaches 1.42 in experiments. The results of simulations and experiments indicate that the new type of twisted tape has a distinct advantage on heat transfer enhancement. Verification between simulations and experiments are carried out. The result shows that all deviations of corresponding values between simulations and experiments are within 15%, which reflects that the numerical predications are basically in agreement with the experiment results. Finally, a comparative analysis was carried out with the new type of twisted tape in this paper and the different twisted tapes in the previous research. The new type of twisted tape proposed in this paper has higher Nusselt number and friction coefficient.

Highlights

Since heat exchangers were applied in various industries such as oil industry, chemical industry, vehicle and aerospace, the efficiency of heat exchange has been an important factor affecting profits of enterprises
The main methods of heat transfer enhancement could be divided into three aspects: active methods, passive methods and compound methods
The different geometric model used are plain twisted tape (PTT), circular cut twisted tape (CCTT), elliptical cut twisted tape (ECTT), alternate-axis elliptical cut twisted tape (AECTT), triangular cut twisted tape (TCTT) et al The results indicated that the type of cuts on the twisted tapes has effects on heat transfer characteristics

Summary

Introduction

Since heat exchangers were applied in various industries such as oil industry, chemical industry, vehicle and aerospace, the efficiency of heat exchange has been an important factor affecting profits of enterprises. To improve the efficiency of heat exchange, a large number of researches about heat transfer enhancement were made [1,2,3,4]. The main methods of heat transfer enhancement could be divided into three aspects: active methods, passive methods and compound methods. Twisted tape is one type of passive methods and has a distinct advantage on heat transfer enhancement than other methods. Inserting twisted tapes can enhance disturbance of fluid in the tube and produce swirl flow to increase heat transfer coefficient without big changes on structure of heat exchangers. Various experiments have been made to improve the efficiency of twisted tapes on heat transfer enhancement [6,7,8]

Methods

Results

Conclusion