Effect of actuator deflection on heat transfer for low and high frequency synthetic jets

Abstract

Due to copyright restrictions, the access to the full text of this article is only available via subscription.Synthetic jets are being investigated over the last four decades. Researchers have been interested in its unique applications for a wide range of flow control to thermal management of electronics applications. Synthetic jets are made up of actuators such as piezoelectric, magnetic, or linear piston technology etc. In this study, we performed an experimental and numerical investigation of a piezoelectric disk deflection over a range of frequencies in order to understand the performance for low and high frequency synthetic jets. First, we performed a numerical analysis of a piezoelectric based synthetic jet and, validated computational result with experimental findings. Numerical models are performed by using commercial finite element software. To understand the size effect on the operating frequency, three jets with different sizes are manufactured and examined. Two different low frequency synthetic jets manufactured in our laboratory and a commercially available high frequency jet are included in the present study. Heat transfer performance is given as an enhancement over natural convection heat transfer. The heat transfer enhancement factor of each of these jets with respect to natural convection is measured over a 25.4×25.4 (mm) vertical heater. Finally, power consumption of the low and high frequency synthetic jets were measured and compared. It is found that disk deflection and operating frequency are directly related to heat transfer enhancement factor, if the Helmholtz frequency of a cavity has no effect on the performance of a jet. The Helmholtz frequency of each jet was calculated to ensure that it has no effect on the synthetic jet, but we found that the commercial synthetic jet took partial advantage of Helmholtz phenomena to enhance the performances at high frequencies.TÜBİTA

An investigation into flow and heat transfer of an ultrasonic micro-blower device for electronics cooling applications

“…The natural convective loss from step 1 is subtracted from the total, leaving the conductive losses to the substrate, Q loss . Computational simulations [10] verified the magnitude of these losses, agreeing to within 5% of the experimental measurements. In step 3, the heater is operated with the micro-blower active, and the total heat transfer, Q tot , is measured.…”

“…Fig. 3 shows the test fixture, which is described in detail in previous publications [2,10]. The jet is placed on a traverse, which is used to fix its position to micron-scale accuracy.…”

“…We use a series of experimental and computational analyses to determine the conduction, natural convection, and radiation losses, using methods explained in detail earlier [2,6,10]. Conduction and natural convection losses are examined using a three-step process, initially developed by Garg et al [6].…”

“…For this ultrasonic blower, the unique multi-orifice structure results in a more complex frequency response. The micro-blower has a Helmholtz resonant frequency around 21 kHz when using the exhaust nozzle [10], and it has a resonance at 15.5 kHz for its inner cavity alone [9]. In principle, the design could match the diaphragm resonant frequency and the cavity Helmholtz resonance for the best performance, but that might lead to noise at frequencies below the audible limit of 20 kHz.…”

“…Piezoelectric designs generate rapid diaphragm motion, producing a high velocity jet stream that mixes with the ambient air. Unfortunately, effective synthetic jets often require operation at the actuator resonant frequency to maximize jet exit velocity, coinciding with the highest noise output [8][9][10]. For example, Arik [11] observed that a synthetic jet with a 1-mm orifice achieved its peak jet velocity of 90 m/s at a resonant frequency of 3.6 kHz.…”