Impingement heat transfer enhancement by focusing the jet from synthetic jet array

In the present study, jet impingement experiments are conducted to analyze the influence of focusing the jets originating from a synthetic jet array (SJ array) on enhancing heat transfer from a heated plate. After characterizing the synthetic jet actuators (SJAs) using a hot wire anemometry, all heat transfer experiments were conducted with the SJ array operating at a Reynolds number (Re=600) and Strouhal number (St=0.1). For the SJ array having fixed geometric and operating parameters, the focusing of the jets is achieved by providing a non-linear phase delay (∅) between the actuators. For the SJ array operated at Re=600 and St=0.1, due to maximum focusing ∅=120^°, the enhancement of maximum heat transfer area (stagnation region) is approximately 65% compared to ∅=0^°. Interestingly, for ∅=180^°, although vortices of the leading actuator feel strong suction from their adjacent lagging actuators, but due to focusing, the maximum heat transfer area is enhanced by approximately 18% compared to ∅=0^°. Likewise, the enhancement in overall heat transfer was calculated using the area average Nusselt number (Nu_avg) due to maximizing focusing (∅=120^°) in the intermediate field is ∼ 21% higher compared to the ∅=0^°. Most importantly, while a single actuator SJ experiences a substantial 45% reduction in Nu_avgbetween the intermediate and far field, this investigation reveals that, with maximum focusing (∅=120^°), the reduction in Nu_avg between these zones is approximately 17%. This study of enhancing heat transfer in the far field through jet focusing addresses a fundamental issue observed in single actuator SJs, where the drastic reduction in vortex coherence results in inefficient heat transfer in the far field.