Heat transfer characterization in a tubular heat exchanger with V-shaped rings

This article presents the influence of V-shaped rings (or V-ring) placed in a uniform heat-fluxed tube on heat transfer and flow resistance characteristics. In the current experiment, the V-ring elements with attack angle of 30 degrees are inserted into the tube with four relative ring-pitches (R-p = P/D = 0.5, 1.0, 1.5 and 2.0) and three ring blockage ratios (R-B = e/D = 0.1, 0.15 and 0.2). Air as the test fluid flows through the tube for Reynolds number of about 5000-25,000. The experimental results reveal that the V-ring can considerably enhance the heat transfer rate up to 5.8 times above the plain tube whereas the friction factor is up to 82 times. The increase in R-B leads to higher heat transfer and friction loss while the increment in Rp provides the reversing trend. The thermal enhancement factor of the V-ring is in the range of 1.36-1.63 where its maximum regarded as the optimum point is at R-B = 0.1 and R-p = 1.0. In comparison with other vortex-flow devices, the V-ring yields much higher thermal performance than the published inclined rings, wire-coils and twisted tapes. Nusselt number and friction factor correlations for the V ring are also determined. (C) 2016 Elsevier Ltd. All rights reserved.