EXPERIMENTAL RESULTS BY IR-THERMOGRAPHY ON CONVECTIVE HEAT TRANSFER OVER ENHANCED SURFACES

This paper presents experimental results on convective heat transfer of air flows over a not-thin aluminum plate with transverse, straight ribs for different pitch-to-rib-side ratio values. Data over a flat plate are also reported for comparisons. The plate is 200 mm long and 150 mm wide, and it is heated by a thin foil heater; ribs have a square cross-section of 3-mm side. The paper first reviews the experimental setup and the data processing to recover heat transfer characteristics from IR-thermographic images; then, thermal performances of tested configurations, namely, pitch-to-rib-side ratio ranging from 10 to 40, are presented and discussed. Air flows at room temperature with speed from 2.3 to 11.6 m/s, corresponding to Reynolds numbers at the end of the heated-length between 50000 and 250000, and for a heat flux of near 550 W/m2. For the considered ribbed surfaces, the average Nusselt number shows an increase with respect to the flat plate varying from 45 to 130% as Re increases but with slight differences between them.