An experimental investigation of the flow-field and thermal characteristics of synthetic jet impingement with different waveforms

Abstract

Present experimental investigation reports the flow and thermal behavior of electromagnetically actuated circular orifice synthetic jet involving sinusoidal and square waveforms. The effect of Reynolds number (1656–2218), dimensionless axial distance (1–25), and the excitation frequency (100–175 Hz) on the thermal performance is studied here. The flow field is investigated using the hot wire anemometry and particle image velocimetry technique to couple the thermal behavior with fluid dynamics. The surface temperature is measured using an infrared thermal imaging camera. The average Nusselt number for synthetic jet with sinusoidal waveform is found to be 20.86% higher compared to the synthetic jet with square waveform. However, in the stagnation region, the square waveform exhibits 18.94% higher heat transfer compared to the sinusoidal waveform. The flow dynamics reveal the underline flow physics for the variation in the heat transfer rate. The velocity contours show a smooth and wide top hat with the sinusoidal waveform. However, in the case of square waveform, the velocity profile is narrow, which results in a decrease in entrainment of fresh ambient fluid into the jet. The sine wave exhibits 73.68% higher mass flow rate compared to square wave pattern at its diaphragm resonance frequency (150 Hz). The power spectral density of the velocity signal, obtained from the hot wire anemometry, is analyzed to understand the formation and propagation of vortex rings. A unified correlation for average Nusselt number is developed for both sinusoidal and square waveforms. The results obtained from the present experimental investigation provide significant guidance for the efficient design of synthetic jets for space-constrained electronics cooling.