An experimental and numerical study on the laminar heat transfer and flow characteristics of a circular tube fitted with multiple conical strips inserts

In this work, numerical simulations on the flow structures and heat transfer enhancement of laminar flow in a heat exchanger tube fitted with multiple conical strips inserts have been carried out. And stereoscopic particle image velocimetry (SPIV) measurements on the flow structures have been conducted to verify the numerical results. Both the experimental and numerical results show that multiple longitudinal vortexes are generated in tube, and the flow structures obtained by simulations agreed well with those of the PIV measurements. Numerical results show that heat transfer and friction factor were respectively enhanced by approximately 2.54-7.63 and 2.40-28.74 times compared to the plain tube, and the overall heat transfer performance (performance ratio R3) was located in the range of 1.23-6.05. Moreover, effects of the number of conical strips (n), central angle (alpha), slant angle (theta) and the pitch (p) have been investigated. It is found that both the heat transfer rate and flow resistance increase with the increasing number of conical strips, central angle and the decreasing pitch, and they both increase first and then decrease with the increase of slant angle. Compared with the previous published works, the tube with multiple conical strips inserts can obtain a moderate heat transfer and low flow resistance, and thus achieve a high overall heat transfer performance. (C) 2017 Elsevier Ltd. All rights reserved.