Spatially-resolved, local flow structure and surface Nusselt numbers are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45degrees with perpendicular orientations on two opposite surfaces. Instantaneous flow visualizations and time-averaged flow structural data show a variety of flow phenomena, including: (i) the development of increased numbers of multiple, smaller vortex pairs as the Reynolds number increases, and (ii) strong spanwise secondary flow components, which move in opposite directions in the top and bottom halves of the channel, and result in the formation of other secondary flows and vortical motions. The resulting increases in three-dimensional turbulence transport, as well as other flow phenomena, are then related to local Nusselt numbers, which vary significantly over the surface of the ribbed channel. (C) 2003 Elsevier Science Ltd. All rights reserved.