1 Heat Transfer Enhancement in a Diffuser using Vortex Generators Placed on the Side Wall Ghobad Shafiei Sabet a ,S. Pavithran b* , R.R. Kulkarni c a Department of Mechanical Engineering, Shahrood Branch,Islamic Azad University, Shahrood, Iran. b * Department of Mechanical Engineering,Vishwakarma Institute of Technology, Pune, India. c Department of Mechanical Engineering,Vishwakarma Institute of Technology, Pune, India. a ghobad_sh@yahoo.com b vspavitra@gmail.com c ratnakarkulkarni36@gmail.com Abstract The experimental investigation of heat transfer enhancement and flow analysis in a diffuser using vortex generators is carried out. Two diffuser angles are looked into. One and two vortex pairs are considered. The velocity profile at the diffuser inlet is uniform and the flow is a developing one. The vortex generators are placed on the side vertical side wall, near the diffuser inlet. It is observed that the heat transfer enhancement is more with the two pair case. The Reynolds number is in the range 2.5-3.6 5 10  . The maximum enhancement is 62% at constant Reynolds Number and 40% at constant dissipation. The diffuser efficiency is lower for the rough cases, with the two pair case yielding a lower value. The enhancement increases with the angle of attack of the vortex generator. Keywords: heat transfer enhancement, diffuser, vortex generator 1. Introduction The effect of vortex generators (VGs) and protrusions has been looked into in the recent past. The main mechanism is the transfer of momentum to the boundary layer leading to heat transfer enhancement .This is achieved through swirl and vortices causing flow destabilization. Fiebig et al. [1] reported results for VGs for one delta wing and one delta winglet pair in a rectangular channel for the Reynolds number ranges 1360-2270. It was shown that the delta wing geometry was the most effective, with local enhancements up to 200%. Teoman et al. [2] reported experimental results for a channel flow with longitudinal VGs in the form of winglet type for Reynolds number between 3000 and 30000.Wings were aligned at various angles. It was reported that each winglet pair induces longitudinal vortices behind it and strong mixing effects occur in the buffer region between divergent and convergent channel arrangements. It was found that the enhancement of heat transfer caused the increment of the friction coefficient. Edwards and Alker [3] reported enhancement for VGs in the form of cubes and delta winglets at a constant Reynolds number of 61000. The enhancement evaluation showed that the heat transfer increases by up to 76% for cubes and 42% for a counter-rotating vortex generators pair. Rassell et al. [4] reported the use of longitudinal vortices to enhance finned tube heat exchanger performance and they showed rectangular winglets placed in two staggered row gave the best result. Gentry et al. [5] showed that heat transfer and mass transfer enhancements are 50% and