Experimental and numerical study on the heat transfer and flow performance for the circular tube fitted with drainage inserts

In the present study, the heat transfer and flow performance in turbulent flow of the tube fitted with the drainage inserts are investigated. The results show that the new-type insert can lead the fluid at the core to the tube wall, strengthening the mixing of cold and hot fluid. And the insert also generates the vortex to make perturbation in the fluid domain. The experiment investigates the influence of pitch ratio on the Nusselt number and friction factor. The Nusselt number and friction factor both increase with the decrease of pitch ratio. And the pitch ratio of 3.3 is recommended for the insert. Some numerical results validated by the experimental results are also shown in the study to analyze the influence of slant angle on heat transfer and flow performance. The results indicate that 45 is suggested as the best slant angle for the insert. The numerical results of Nu/Nu(0), f/f(0) and PEC range from 1.82 to 1.94, 6.70 to 7.15 and 0.95 to 1.04, respectively, for the insert with the slant angle of 45 degrees and the pitch ratio of 3.3. The results show that the insert is of good performance and the correlations of Nu and f are developed in the study. (C) 2016 Elsevier Ltd. All rights reserved.