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 depend¬ence on the Reynolds number as the flat plate, but its values are from 50% to 130% higher with slight differ-ences between the different tested configurations.