Heat exchangers are widely used for cooling or heating purposes in different industries, such as chemical plants, space heating, refrigeration, power plants, oil & gas processing plants \[1-4\]. This makes it important to enhance the performance of heat exchangers by increasing the heat transfer coefficient and or reducing the pressure drop so that the overall efficiency of heat exchangers could be optimized. Vortex generator (VG) refers to the components that can generate vortices to enhance the heat transfer performance of heat exchangers, especially those of compact type. Thus, the size of the heat exchanger can be reduced and more energy can be saved. Vortex generator (VG) is one of the passive techniques which could improve the heat transfer with relatively low pressure drop. Delta Winglets VG create streamwise longitudinal vortices which does not decay until far downstream that leads to have higher heat transfer with a lower pressure penalty. Consequently, longitudinal VGs are more efficient. Twisted or helical insert tapes, wire coils, turbulence rings and conical VGs are usually employed to increase the heat transfer performance of heat exchangers with circular tubes. VGs are widely used in compact heat exchangers, mixing biofuel, static mixtures, cooling of electrical devices, aero-engines and gas turbines etc. Torii et al. \[5\], experimentally, investigated the thermal performance and pressure drop of delta winglets VGs in a fin tube heat exchanger. Wu et al \[6\], numerically, investigated the thermal performance and flow structure of rectangular winglet VGs with different lengths, heights, attack angles, locations and shapes in a rectangular channel. In this research, heat transfer and pressure drop from a pipe with delta winglets insert are numerically investigated. CFD simulations, with and without VGs insert, are done for an air flow range (Reynolds numbers 6000 to 33000) and for a constant heat flux on the tube model surface. The Nusselt number and friction factor results show the influence of the VGs insert on thermal performance. We have investigated the thermal performance and flow structure with delta winglets insert in the circular tube.  Most of the previous research on VGs, experiments were conducted on the square duct or circular duct, but simulations were mostly based on the square duct or plain surface and barely in the circular tube. In our current research, we employed the SST k-omega model.  Firstly, the smooth tube was validated and, then, the Nusselt number and friction factor with VGs were calculated.  In addition the mechanism of generating vortices, flow structure and thermal enhancement are analyzed.

 

Reference:

\[1\] S. Tiggelbeck, N. Mitra, M. Fiebig, Flow structure and heat transfer in a channel

with multiple longitudinal vortex generators, Exp. Therm. Fluid Sci. 5 (4) (1992)

425–436.

\[2\] M.S. Aris, R. McGlen, I. Owen, C.J. Sutcliffe, An experimental investigation into the

deployment of 3-D, finned wing and shape memory alloy vortex generators in a

forced air convection heat pipe fin stack, Appl. Therm. Eng. 31 (14–15) (2011)

2230–2240.

\[3\] A. Akcayoglu, B. Sahin, C. Canpolat, H. Akilli, Experimental flow results in a noncircular

duct with heat transfer augmenting obstacles experimental flow results in a

non-circular duct with heat transfer augmenting obstacles, Proceedings of the

World Congress on Engineering, vol. II, 2010 WCE 2010, June 30 - July 2, 2010,

London, U.K.

\[4\] R. Vasudevan, V. Eswaran, G. Biswas, Winglet-type vortex generators for plate-fin

heat exchangers using triangular fins, Numer. Heat Tran. 38 (5) (2000) 533–555.

\[5\] K. Torii, K. Kwak, and K. Nishino, "Heat transfer enhancement accompanying pressure-loss reduction with winglet-type vortex generators for fin-tube heat exchangers," International Journal of Heat and Mass Transfer, vol. 45, pp. 3795-3801, 2002.

\[6\] J. Wu and W. Tao, "Numerical study on laminar convection heat transfer in a channel with longitudinal vortex generator. Part B: Parametric study of major influence factors," International Journal of Heat and Mass Transfer, vol. 51, pp. 3683-3692, 2008.


Heat Transfer Augmentation and Flow Visualization With Delta Winglets in a Tube - a Numerical Approach

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