HEAT TRANSFER ENHANCEMENT IN TURBULENT FLOW THROUGH A CIRCULAR TUBE WITH VARIOUS ARRANGEMENTS OF A DELTA WINGLET VORTEX GENERATOR

An experimental investigation was carried out to study heat transfer enhancement in turbulent flow through a circular tube with various arrangements of delta winglet vortex generator. Delta winglets of double row, double delta, and two pair 'V' array configurations were tested for their advantage over a single pair of delta winglet. For all configurations investigated, the projection area was 10.4% of the flow area. The test section was heated electrically at a constant wall heat flux. The frontal air velocity varied in the range from 5 m/s to 14 m/s corresponding the Reynolds number range based on the hydraulic diameter of 22,000 to 58,000. The air velocity, air inlet and outlet temperature, wall temperature, and pressure drops along the axial length of the test section were measured to analyze the friction factor, Nusselt number, and the heat transfer coefficient. Rearrangement of the projection area by these configurations of delta winglets provided a distinguishable increase in the Nusselt number and required lower pumping power. At comparable Reynolds numbers, using delta winglet vortex generators in two pair 'V' array, double delta, and double row configurations, the Nusselt number was increased up to 131.2%, 125.4%, and 118.4%, at 7%, 16%, and 15% less pumping power, respectively, compared to that of a single pair of delta winglet vortex generators.