A computational fluid dynamics methodology is developed to study steady laminar flow and heat transfer in periodic zigzag channels with square cross-sections, considering the effect of chaotic advection. The computational domain consists of up to 14 repeating zigzag units with smoothly joined inlet and outlet sections. The results show fully-developed periodic flow fields can be achieved for Re < 200; however, a spatially periodic flow field is no longer seen for higher Reynolds number due to the enhanced effect of chaotic advection with increasing Reynolds number; for Re > 400 the flow field becomes transient. The flow field shows that the secondary flow pattern varies significantly at different axial locations. Highly enhanced heat transfer appears in the regions where strong Dean vortices occur, as indicated by more pronounced twisting of flow streaklines. For Re > 200, the unit-averaged heat transfer enhancement and pressure-drop penalty (relative to straight passages) are no longer uniform from unit to unit but mean values of both of these performance metrics increase with increasing Reynolds number over the whole range of 50 < Re < 400. (C) 2012 Elsevier Ltd. All rights reserved.