Studies on the heat/mass transfer characteristics and fluid structure in a square internal cooling channel with dimpled surfaces

Experimental and numerical studies of heat/mass transfer on the dimpled surfaces in square channels are performed. The naphthalene sublimation method is employed in the experimental study. First, in a two-passage rotating channel, circle dimple matrices are cast on the leading and trailing walls in both the inlet and outlet of the serpentine channel. The experiments are carried out with Reynolds number of 7,000 and 21,000, and with Rotation number of 0 and 0.2. The dimpled walls lead to heat/mass transfer enhancements over smooth surfaces both in the stationary case and in the rotating case. In the stationary case, the dimple enhancement factor for Re=7,000 is about 2, but is less than 2 for Re=21,000. In the rotation case at Ro=0.2, the dimple enhancement factor is also at the order of 2. Secondly, four single dimples with printed shape on the wall of square, triangle, circle, and teardrop are studied experimentally in the same test section at stationary with Reynolds number of 21,000. The four dimples are also studied numerically using FLUENT. The heat transfer distributions on the wall and flow structures inside the dimples and in the regions adjacent to the dimples are identified. Vortex rolls caused by dimples are observed. Heat transfer enhancement is found in all of the four cases, and the teardrop dimple shows the most promising heat transfer characteristics