The flow structure and heat transfer in a plane channel with periodically placed vortex generators of different forms have been investigated in the Reynolds number range corresponding to unsteady laminar and transitional flow. Numerical results from four different configurations are reported: a pair of square bars, a rectangular bar, and two different baffle arrangements. The heat transfer and pressure drop are strongly dependent on the geometry used. A wide range of geometric parameters have been computed to cover the different possibilities. The unsteady Navier-Stokes equations and the energy equation have been solved by a finite-volume code with staggered grids combined with SIMPLEC pressure correction. The velocity and temperature fields were computed. Results for the same pumping power show heat transfer enhancement by a factor larger than 3.5 in the best cases. (C) 2003 Elsevier Science Ltd. All rights reserved.