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>5z/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.