Spatially-resolved-local flow structure, spatially-averaged flow structure, and surface Nusselt numbers are presented and compared for stationary channels with aspect ratios of 4 and rib turbulators inclined at 45degrees. Two different rib arrangements with perpendicular and parallel orientations on two opposite surfaces are investigated at Reynolds numbers (based on channel height), Re-H from 480 to 18,300. Comparisons show important local Nusselt number differences for the two rib arrangements, especially just upstream of the ribs, which are due to significant differences in global and local primary- and secondary-flow characteristics. (C) 2003 Elsevier Ltd. All rights reserved.