Heat transfer of impinging jet-array onto concave- and convex-dimpled surfaces with effusion

Abstract

Heat transfer measurements for an impinging jet-array onto two enhanced surfaces using concave and convex dimples with effusion are performed to acquire the detailed Nusselt number (Nu) distributions. The study focuses on the effects of effusion on local and area-averaged heat transfer performances with jet Reynolds number (Re) and separation distance (S/Dj) varying in the ranges of 5000⩽Re⩽15,000 and 0.5⩽S/Dj⩽10. For each Re and S/Dj tested, three sets of heat transfer data are acquired from each effused impinging surface at three eccentricities (E) between jet-center and dimple-center of 0, 1/4 and 1/2 dimple-pitch (H). Effects of effusions on heat transfer performances are revealed by comparing the Nu measurements obtained from each dimpled surface with and without effusion. A set of selected experimental data illustrates the influences of effusion on the interdependent impacts of surface topology, Re, S/Dj and E/H on the detailed Nu distributions and the area-averaged Nu over the central jet region (Nu¯C). Relative enhancement in heat transfer convected by each dimpled surface with and without effusion from the reference Nu¯C obtained from the smooth-walled impinging surface without effusion is examined for each Re, S/Dj and E/H tested. To assist the engineering applications, six Nu¯C correlations for two effused surfaces with concave and convex dimples at E/H=0, 1/4 and 1/2 are individually obtained using Re and S/Dj as the controlling parameters.