Heat transfer enhancement of a heated flat surface via a flexible strip pair

A pair of 12.7 mm wide (W) and 25.4 mm tall rectangular flexible strips made of 0.1 mm thick aluminum sheet was employed to enhance convective heat transfer from a flat surface in a closed-loop wind tunnel. The strip pair was placed side-by-side with a spacing of 1W, 2W and 3W. The incoming wind velocity was fixed at 10 m/s, resulting in a Reynolds number based on the strip width (ReW) of 8.5 × 103. The heat transfer enhancement was represented in terms of the Nusselt number with respect to the reference Nusselt number in the absence of the strip pair (Nu/Nuo). A triple-sensor hotwire probe was employed to characterize the flow characteristics when the plate was unheated. Particularly strong vortex-vortex interactions, a large downwash velocity and intense flow fluctuations were obtained behind the 1W-spaced strip pair. These contributed to better mixing and transport of the thermal energy. The 1W-spaced strip pair generated the highest Nu/Nu0 values. Nu/Nu0 of approximately 1.50 was achieved at the middle of the strip pair at X=9W. At this location, the pairs separated by 2W and 3W resulted in Nu/Nu0 value of around 1.26 and 1.17, respectively. The 1W-spaced strip pair also produced the largest span-averaged Nu/Nu0