Enhanced thermal performance in tubular heat exchanger contained with V-shaped baffles

Abstract

The vortex-flow device is a promising streamwise vortex generator employed to produce the counter-rotating vortices along a heated tube to augment the heat transfer rate with comparatively smaller friction loss penalty. Thus, the influences of V-shaped baffle vortex generator (hereafter called “V-baffle”) insert in a heated tube on thermal-performance enhancement were experimentally examined in the current work. The geometric characteristics of the V-baffles mounted repeatedly on the edges of a flat plate/tape were three ratios of relative baffle blockages, (b/D = BR = 0.1, 0.15 and 0.2), and four ratios of baffle pitches, (P/D = PR = 0.5, 1.0, 1.5 and 2.0) at a fixed angle of attack (α = 30°). The present V-baffle placed on the tape edge was aimed to lessen the pressure loss from disturbing the central core flow for the case of placing it on the double sides of a tape as found in the literature. The experiment was conducted by letting air flow through the test tube with Reynolds number (Re) in the range of 4192 to 25,750. The current study indicated that the friction factor and heat transfer using the V-baffle inserts increase considerably with rising BR but reducing PR. The V-baffle with BR = 0.2, PR = 0.5 provides the highest friction factor and rate of heat transfer at about 18.25 and 4.46 times above the plain tube, respectively. A new modified thermal enhancement factor (TEF) is offered and found that its peak for each case appearing at the lowest Re, is in a range of 2.14–2.34 where the optimum TEF of 2.34 is visible at PR = 1.0, BR = 0.15. Furthermore, correlations of Nusselt number and friction factor for the present V-baffles are determined. TEF of the current device is found to be superior to that of other enhanced devices in comparison.