Augmented heat transfer in tubular heat exchanger fitted with V-baffled tapes

Effects of insertion of a straight tape mounted with double-sided V-baffles used as a longitudinal vortex generator (LVG) on turbulent convection heat transfer behaviors in a constant heat-fluxed tube in the Reynolds number (Re) range of 4120 to 25,800 are experimentally and numerically investigated. In the present experiment, the V-baffles at a fixed attack angle (alpha = 30 degrees) were placed on the tape with two arrangements: V-apex pointing downstream and upstream (hereinafter called V-down and V-up). The V-down and up tapes with three baffle height ratios, (R-B = b/D = 0.20, 0.15, 0.10) and pitch ratios, (R-P = P/D = 1.5, 1.0, 0.5) were tested. Data of the current smooth or plain tube were also examined for comparison. The experimental results have shown that the employ of the V-down tape generally yields higher heat transfer, friction loss and thermal performance than that of the V-up one. A new derived thermal-performance enhancement factor (TEF) is proposed. The maximum TEF of the V-down tape is around 2.07 at R-B = 0.15, R-P = 1.0 and is, in average, about 1.4% higher than the V-up one having its peak of 2.04. A 3D numerical V-baffled-tube flow model was also simulated to examine the fluid flow and heat transfer patterns. The numerical validation was seen in close agreement with available experimental data. Numerical heat transfer contours and flow structures were also reported.