Heat transfer characteristics and flow structure in laminar and turbulent flows through a rectangular channel containing built-in-vortex generators have been analyzed by means of solutions of the full Navier-Stokes and energy equations. The geometrical configuration of interest is representative of single,element of a plate-fin cross-flow heat exchanger. Each winglet-pair induces longitudinal vortices behind it. These vortices swirl the flow around the axis parallel to the mainstream direction and strongly enhance the exchange of fluid between the wall and the core region which causes high, heat transfer augmentation. A detailed evaluation of the performance parameters in the laminar flow regime with regard to the enhancement of heat transfer using winglet-type vortex generators has been accomplished in this study. It may be mentioned that for some special applications the fluid velocity becomes very high and one may encounter turbulent flows in plate-fin heat exchangers. In the present study, the predictions for turbulent flows have been made and an effort has been undertaken to compare the accuracy of the predictive procedure with well documented experiments of another research group. The computational results agree I reasonably well with their experimental counterpart.