Local Heat Transfer Coefficients of a High-Frequency Synthetic Jet during Impingement Cooling over Flat Surfaces

Abstract

It has been shown that synthetic jets can enhance heat transfer in air-cooling during natural convection heat transfer. Those meso scale devices are expected to be one of the methods of choice for cooling confined space, low heat-generating electronics. The present study focuses on the local and global heat transfer coefficients of a high-frequency meso scale synthetic jet. The experiments have been completed with synthetic jets, which are 12.5 mm in diameter and 2 mm thick with a square orifice of 1 mm. A synthetic jet has been driven at the resonance frequency of 4500 Hz, and voltage was between 30 V and 50 V. Earlier studies have focused on understanding the effect of voltage and driving frequency on the average heat transfer effect, while the current study aims for determining local heat transfer. A microscopic infrared thermal imaging technique was used to acquire local temperature distributions, and the data were analyzed for local convective and radiative heat transfer coefficients. Four square heaters (each with a different size) have been studied in the current study to determine the effect of the characteristic length as well. Heat transfer enhancements over the specific heater sizes are presented, and it is found to be between 4 and 10 times of natural convection.