An investigation of performance of synthetic jets emanating from circular, elliptical and rectangular nozzles

Abstract

Impinging synthetic jets have been considered as a future solution for cooling miniature structures. Synthetic jet performance is sensitive to a number of parameters such as orifice size, orifice shape and nozzle-to-target spacing. For the former, it has been shown that synthetic jet performance is sensitive to the distance between the jet nozzle and the target surface where enhancement of heat transfer usually decreases with a reduction in nozzle-to-target plate distance. For the latter, different nozzle shapes are responsible for generating different vortex fields which affect the temperature distribution over the target plate. However, no detailed information about the momentum and temperature fields has been shown, therefore further investigation is needed. In this study, three different meso scale synthetic jets were fabricated with three different nozzle shapes, namely, circular, elliptical and rectangular with each having an identical hydraulic diameter. A wave form generator was used to create a sine wave on the enclosure's diaphragm to form the jet action. Deflection on the diaphragm and local heat transfer coefficients on the heated target plate were determined as a function of the jet frequency and relevant discussions were made. It was found that the nozzle shape significantly affects the heat removal rates on the target plate. In addition, it was shown that the conventional hydraulic diameter definition used to compare synthetic jets with non-circular orifices may not be the correct length scale to evaluate the thermal/hydraulic performance of such devices. A short discussion on the jet fabrication techniques was also included.