Effect of orifice shape in synthetic jet based impingement cooling

The effect of shape of the orifice of a synthetic jet assembly on impingement cooling of a heated surface is experimentally investigated in this study. The shapes considered are square, circular, and rectangular, of different aspect ratios (in the range of 1-20) and hydraulic diameters (3.8-8 mm). The average heat transfer coefficient as a function of the distance between the orifice and the heated surface is obtained. The Reynolds number (Re) is in the range of 950-4000 based on average velocity, while the normalized axial distance varies between 1 and 25. The heat transfer enhancement with a square orifice is found to be larger than that with rectangular and Circular shapes at larger axial distances z/d > 5, for the same set of boundary conditions. It is also found that rectangular orifice with aspect ratio between 3 and 5 gives best performance at smaller axial distances. An attempt is made to explain this behavior on phenomenological grounds. The effect of orifice shape on cooling with a synthetic jet is reported for the first time, and the present results are expected to have significant practical implications. (C) 2009 Elsevier Inc. All rights reserved.