Experimental Study of Thermal Performance and Flow Behaviour With Winglets Vortex Generators in a Circular Tube

Abstract

Vortex generator (VG) is one of the passive techniques which could improve the heat transfer with relatively low pressure drop. Vortex generators create streamwise longitudinal vortices which does not decay until far downstream that leads to have higher heat transfer with a lower pressure drop. The objectives of this experiment were to study the heat transfer and flow characteristics of fully developed turbulent flow due to different arrangement of VGs in a tube. The experiments were performed by using delta winglet vortex generators in a 52 mm circular copper tube. The flow regime varied from 6000 to 27000 Reynolds number. Four vortex generators with 45° angle of attack were used inside the circular tube. Different parameters of the VGs studied in this experiment such as lengths (L = 10, 15, and 20 mm) and arrangements (R = 0° to −15°). The results indicate that the length affected friction factor (f) and Nusselt number (Nu) significantly. L20 reached the highest f and Nu. The staggered arrangement concludes a significant drop on friction factor and a significant increase on Nusselt number. Consequently, the thermal performance of all staggered arrangement cases could reach a significant rise compared to the inline arrangement. The oil flow visualization could track down the trace of vortex behind the VG. The inline arrangement showed a strong vortex formed as a result of VG which was related to higher f while the staggered arrangement indicated a weak vortex.