Heat transfer fins (110), and heat exchangers (100) incorporating such fins (110), enhancing heat transfer with acceptable pressure drop increase. The fins (110) include tabs or secondary fins bent upward and downward from the fin body at a selected bend angle. All or a majority of the tabs are aligned with a simple flow path or with local flow paths for cooling air adjacent the fins (110) to minimize turbulence and pressure drop. The tabs are planar and generally aligned parallel to the simple flow path or local flow paths and are arranged so as to serve as a plurality of sites for starting new boundary layers by offsetting the tabs such that downstream tabs are not shadowed by upstream tabs. The tabs have a height sufficiently large to extend the tabs out into boundary layers on the fin (110). The tabs provide more uniform flow over fins (110) and shrink wake size behind tubes (120).
CONTRACTURAL ORIGIN OF THE INVENTION
 The United States Government has rights in this invention under Contract No. DE-AC36-99GO-10337 between the United States Department of Energy and the National Renewable Energy Laboratory, a Division of the Midwest Research institute.