Numerical investigation of thermal and flow characteristics of impinging synthetic jet with different nozzle geometries at low nozzle-to-plate distances

Synthetic impinging jets are potentially useful techniques in electronic cooling. In this paper, the fluid and heat transfer characteristics of impinging synthetic jets were analyzed numerically by using circular, square, and rectangular shaped nozzles under short nozzle-to-plate spacing and actuation frequencies. A three-dimensional model was built to investigate dimensionless nozzle-to-plate distance (H/D = 0.10 - 1.00), Reynolds number (Re = 1810-4140), and excitation frequency (f = 250 - 500 Hz) effects on flow and heat transfer for a single jet. Firstly, the results were compared with experimental results from the literature, and a fair agreement has been obtained. Afterwards, instantaneous images of velocity contours and streamlines were presented to show the flow characteristics. By using simulation results, time-averaged Nu number and time and area-averaged Nu number (Nuavg) values were presented. Finally, a correlation was proposed for different cases to describe the variation in Nuavg. It was observed that a more homogenous temperature distribution on the impingement surface could be obtained by decreasing H/D and increasing Re number, whereas by increasing the nozzle-to-plate distance, lower temperature values could be obtained at the impingement region. Nuavg is almost unaffected from the nozzle geometry under the present investigated conditions. Higher local Nu number values were obtained for 0.50 = H/D around the impingement region. On the other hand, for 0.10 & LE; H/D < 0.50, a more uniform temperature distribution was obtained which leads to higher Nuavg. This study provides significant knowledge about the flow and heat transfer characteristics of synthetic impinging jets at low nozzle-to-plate distances, which could provide guidance in the thermal design procedure of electronic components.