Computational fluid dynamics (CFD) has been used to study fully developed laminar flow and heat transfer behaviour in periodic serpentine channels with a semi-circular cross-section. The serpentine elements are characterised by their wavelength (2L), channel diameter (d) and radius of curvature of bends (R-c), with results reported for Reynolds numbers (Re) up to 450, as well as for a range of geometric configurations (3 < L/d < 12.5, 0.525 < R-c/d < 2.25) at Re = 110. The flow in these channels is characterised by the formation of Dean vortices following each bend. As the Reynolds number is increased, more complex vortical flow patterns emerge and the flow domain becomes increasingly dominated by these vortices. Alignment of flow with vorticity leads to efficient fluid mixing and high rates of heat transfer. Constant wall heat flux (H2) and constant wall temperature (T) boundary conditions and a range of fluid Prandtl numbers (0.7 < Pr < 100) have been examined. High rates of heat transfer and low pressure loss are found relative to fully-developed flow in a straight pipe, with heat transfer enhancements greater than 10 for a Prandd number of 100. As part of this work, we also obtain an accurate value for the Nusselt number for fully-developed flows in straight semi-circular passages with constant wall temperature. Nu(T) = 3.323(+/- 0.001). (c) 2006 Elsevier Ltd. All rights reserved.