Transient liquid crystal technique was employed for experimental investigation of heat transfer distribution in high aspect ratio rectangular ducts featuring different dimple configurations. Four different dimple configuration shapes, viz. diamond, square, triangular and cylindrical, have been studied. This study also attempts to understand the dimple side wall heat transfer and correlate to the mechanisms of the flow inside the dimple. A brief numerical simulation study was also conducted to understand the vortex formation inside the dimples and how they affect the heat transfer on the dimple walls. Experiments were carried out at three different Reynolds number of 10,000, 16,000 and 21,000. Detailed normalized Nusselt number plots for different configurations has been presented. Pressure drop across each geometry was also recorded and a comparison of thermal–hydraulic performance is given. It was observed that heat transfer enhancement due to dimples was maximum for Re =10,000 case when compared to a flat plate scenario at the same Reynolds number. Thermal–hydraulic performance comparison showed that diamond and triangular dimples performed better due to lower pressure drop penalty.

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