Experimental study of heat transfer enhancement with winglets inside a tube

Abstract

Various technologies have been developing to enhance heat transfer with a lower pressure penalty for an efficient compact heat exchanging devices. Vortex generator is an emerging technology which create longitudinal vortices that does not decay until further downstream and consequently enhance heat transfer rate with comparatively lower pressure penalty. In this research we have experimentally studied heat transfer enhancement and pressure drop inside a tube with winglets vortex generators (VG) insert. Winglets were inserted inside a tube in a circular pattern for different pitch ratios. For this experiment, a constant heat flux was maintained by supplying dc current and accuracy of the heat transfer surface was compared with empirical correlations. The effect of attack angles (0°- 45°), pitch ratios (1.6-4.8), winglet length (10mm-20 mm) on heat transfer enhancement pressure penalty were experimentally investigated. The experiments were conducted in a turbulent flow regime with a Reynolds numbers ranging from 6000 to 27000. The experimental results show a significant effect of winglets on the heat transfer and pressure loss over the smooth tube. Results show that increasing the length and the attack angle will intensify both heat transfer coefficient and friction factor. Higher Nusselt number and friction factor were achieved for lower pitch ratio. The contribution of pitch ratio was found more favorable than the length and attack angle on thermal enhancement. Maximum thermal enhancement of 1.17 was achieved for the case of l10 β45 PR4.8 combination at a lower Reynolds number. Flow structure was also investigated to understand the flow behavior which contributes heat transfer enhancement.