Heat transfer enhancement in a channel with longitudinal vortex generators and field synergy principle analysis

3D numerical simulations are performed for laminar heat transfer and fluid flow characteristics of a flat-plate channel with longitudinal vortex generators. The effects of two different type longitudinal vortex generators (LVGs), rectangular winglet pairs (RWP) and delta winglet pairs (DWP), with two different configurations, common-flow-down and common-flow-up, are examined. The Reynolds number based on the height of the channel varies from 190 to 1125. The numerical results show that the applications of the LVGs obviously enhance the heat transfer of the channel, the maximum enhancement of average Nusselt number is 46%. Compared by the performance evaluation parameter, (Nu_m/Nu_m0)/(f/f0), the DWP shows a better overall performance than RWP, the common-flow-down and common-flow-up configurations of DWP have almost same overall performance, the common-flow-down configuration has a better overall performance than the common-flow-up configuration for RWP. The numerical results are also analyzed from the view point of field synergy principle, and it is found that the inherent mechanism of heat transfer augmentation by LVGs is that the secondary flow generated by LVGs results in the reduction of the intersection angle between velocity and temperature gradient.