Louvered fin and round tube heat exchangers are widely used in air conditioning devices and heat pumps. In this study the effect of punching delta winglet vortex generators into the louvered fin surface in the near wake region of each tube was numerically investigated using computational fluid dynamics (CFD). The delta winglets serve to reduce the size of the tube wakes. They cause three important mechanisms of heat transfer enhancement. First, due to the swirling motion of the generated vortices, hot air is removed from the tube wake to the mainstream regions and vice versa. Second, the induced wall-normal flow locally thins the boundary layer, which also enhances the heat transfer. Third, the size of the wake zones is reduced because the flow separation from the tube surface is delayed. This also results in a reduced form drag of the tube surface. The net core pressure drop, however, increases when adding delta winglets to the louvered fins because of increased friction and flow blockage. For the same heat duty and pumping power, the louvered fin heat exchanger with delta winglets is more compact than when no delta winglets are present. (C) 2012 Elsevier Ltd. All rights reserved.