Enhancing convective heat transfer in laminar and turbulent flow regions using multi-channel twisted tape inserts

Abstract

Numerical analysis of the thermal and fluid behaviors of the tubes with multi-channel twisted tapes has been investigated under constant wall temperature condition. The multi-channel twisted tapes were arranged periodically in the tubes. Twist ratio (y/w) of tape was varied from 2.0 to 4.0 and channel number (N) of tape number of channel was varied from 2 to 8. The study was carried out in both laminar and turbulent flow regions (800 ≤ Re ≤ 2000 and 5000 ≤ Re ≤ 15,000) using water as the working fluid. The finite volume method with the laminar model was applied for a laminar flow while the RNG k-ε turbulence model was applied for a turbulent flow. The numerical results show that the multi-channel twisted tapes induce multi-swirling flows which help to improve fluid mixing and enhance heat transfer rate in the tubes with the tapes as compared to those in a plain tube. For the laminar flow, the maximum thermal performance factor of 7.28 is obtained by using the tube with the multi-channel twisted-tape with N = 2 and y/w = 2.5 at Reynolds number of 2000. For turbulent flow, the maximum thermal performance factor of 1.04 is obtained by using the tube with multi-channel twisted tapes with N = 2 and y/w = 3.0 at the lowest Reynolds number of 5000. These results provide evidence that the use of multi-channel twisted tape is a promising technique for laminar convection heat transfer enhancement. It is possible to gain promising tradeoff between enhanced heat transfer and increased friction by selecting the multi-channel twisted tape with proper geometries.