Experimental Investigation by IR-Thermography of Heat Transfer Over Rib-Roughened Surfaces

This paper presents experimental results on convective heat transfer of air flows over a not-thin plate with different rib-roughness patterns; data over a flat plate are also reported for comparisons. The paper first reviews the technique principles, the experimental setup, and the data processing to recover heat transfer characteristics from IR-thermographic images. Then, thermal performances of three differently ribbed surfaces, namely, with ribs tilted of 90° and 60° angles over flow direction, as well as with 60° V-shape ones are presented and discussed. In all the configurations, the plate is 200 mm long and 150 mm wide, whereas ribs have a square cross-section with 3-mm side, and a corrugation-pitch to rib-side ratio of 13.3. Air flows at room temperature with speed ranging 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 650 W/m². For all three enhanced surfaces, the average Nusselt number over the plate horizontal midline shows the same dependence on the Reynolds number as the flat plate, but its values are from 50% to 130% higher with slight differences between the different tested configurations.