The periodicity of convection heat transfer in channels with periodically grooved parts is studied numerically using ail unsteady-state model. The governing equations are discretized using SIMPLE algorithm with a QUICK scheme. The computational results show that there exists a critical Reynolds number, above which the fluid flow and heat transfer will exhibit time-dependent behavior and will oscillate more frequently at higher Reynolds number. When the oscillation takes place, the instantaneous phenomenon of the convection is not periodically fully developed, but the average behaviors of the convective heat transfer show the characteristics of periodically fully-developed flow and heat transfer. (c) 2007 Elsevier Ltd. All rights reserved.