The flow and heat transfer characteristics of zigzag channels with a semi-circular cross-section are studied numerically in the steady, laminar flow regime for different Reynolds numbers (50 < Re < 320) and Prandtl numbers (0.7 < Pr < 20). The computational domain consists of 10 repeating zigzag units with smoothly joined inlet and outlet sections to investigate the effect of chaotic advection. The simulation results show that chaotic advection can occur for Reynolds numbers above 200 with the zigzag unit geometrical parameters of R-c/d = 0.51, L-z/d = 1.75 and theta = 45 degrees and this leads to the disappearance of the spatial periodicity of the flow pattern. The pressure drop and heat transfer coefficient fluctuate from one unit to the next in the chaotic flow regime. The results show that the mean heat transfer rate increases smoothly with increasing Reynolds number, even as the flow changes from being periodic to chaotic. In the regime of chaotic advection, the local characteristics vary from unit to unit and are very sensitive to small changes of the inlet conditions; a proportional relation is found between the mean Nusselt number and Pr-1/3. The geometric parameter ranges of 1.75 < L-z/d < 3.5, 0.51 < R-c/d < 1.0 and 5 degrees < theta < 45 degrees are studied numerically with chaotic advection present in much of the parameter range. (C) 2013 Elsevier Ltd. All rights reserved.