In the present work, the numerical computations for three-dimensional laminar periodic duct flows over the 30° angled baffles mounted periodically on one duct wall are conducted with the main aim being to examine the changes in the flow structure and heat transfer behaviors. The application of the 30° angled baffles placed periodically on the lower wall of the tested duct is expected to generate a longitudinal vortex flow through the duct to better mixing of flows between the core and the wall leading to higher heat transfer rate in the duct.