Heat transfer in a dimpled channel: combined influences of aspect ratio, temperature ratio, Reynolds number, and flow structure

Experimental results, measured on and above a dimpled test surface placed on one wall of a channel, are given for Reynolds numbers from about 600 to about 11 000 and ratios of air inlet stagnation temperature to surface temperature ranging from 0.78 to 0.94. These include flow visualizations, and spatially resolved local Nusselt numbers. Ratios of channel height to dimple print diameter of 0.20, 0.25, 0.50, and 1.00 are employed. The ratio of dimple depth to dimple print diameter is 0.2. Visualized flow smoke patterns show that the vortex pairs, which are periodically shed from the dimples, becomes stronger as non-dimensional channel height H/D decreases. Such behavior is leads to local Nusselt number augmentations at these same locations, which also become larger as H/D decreases. Local Nusselt number ratios also increase substantially at same locations as T_oi/T_w decreases because of buoyancy and variable property influences.