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° are inserted into the tube with four relative ring-pitches (RP = P/D = 0.5, 1.0, 1.5 and 2.0) and three ring blockage ratios (RB = 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 RB 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 RB = 0.1 and RP = 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.