This experimental study explores the heat transfer characteristics over a horizontal heating plate cooled by the separated vortical flows downstream the trailing edges of two counteracting cantilever flapping fins. The cantilever fins are stimulated by piezoelectric ceramic discs (twin-fin piezofan) at five frequencies (f) of 135, 145, 150, 160 and 180 Hz with three oscillating amplitudes (lambda) of 0.51, 0.62 and 0.85 mm for each f. Smoke detection method is used to visualize the vortical flow structures downstream the flapping fins; while the full-field Nusselt number (Nu) distributions over the horizontal plate are measured by the steady-state infrared thermography method with the flapping fins orientated at five attack angles (alpha) of 0 degrees, 15 degrees, 30 degrees, 60 degrees and 90 degrees. At each alpha-f-lambda test condition, heat transfer tests are performed with four ascending heat fluxes to vary the buoyancy level. As a increases from 0 to 90, the near-wall flows above the horizontal plate are considerably modified, leading to the corresponding shrinkage of effective cooling region and the elevated local Nu. Area-averaged Nusselt numbers (Nu) over bar over the horizontal plate at all the alpha-f-lambda test conditions are favorably correlative with modified Strouhal number (St) defined as 2 pi f lambda/ root gWp. The typical isolated/interdependent St and buoyancy effects on (Nu) over bar are illustrated using a set of selective heat transfer results. While (Nu) over bar is increased by raising St at present test conditions, the increase of buoyancy level simultaneously extends the effective heat transfer region on the horizontal plate with local Nu and (Nu) over bar elevated. Empirical (Nu) over bar correlation using alpha, St and buoyancy parameter (beta Delta T) as the determining variables is devised to permit the evaluation of isolated/interdependent alpha, f, lambda and beta Delta T effect on (Nu) over bar for electronic cooling applications. (C) 2014 Elsevier Ltd. All rights reserved.