Reduced-Order Investigation of Synthetic Jet Cooling for Electronic Applications

2009 ◽  
Author(s):  
Rao G. Dhananjaya ◽  
Ajay Rao ◽  
Yogen Utturkar ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
System Level ◽  
Heat Transfer Analysis ◽  
Time Saving ◽  
Reduced Order ◽  
Jet Cooling ◽  
Zero Net Mass Flux

Synthetic jets are meso-scale devices operating at zero-net-mass-flux principle. These devices produce periodic jet-like streams, which have local velocities 10–20 times greater than the average fan velocities. As a result, positioning one or more of these jets close to a heat sink causes high-velocity air currents in tightly spaced fin gaps and enhances the surface heat transfer. A reduced-order modeling (ROM) approach was followed in simulating the heat transfer analysis of commercial heat sink with synthetic jet. Unsteady state results are matched with steady state results as part of the ROM approach. The methodology is implemented on two problems (i.e canonical problem of jet impinging perpendicularly on a flat plate and jet blowing on a commercial heat sink). Results from ROM for two cases are validated against experimental results. It is found that, this approach provides 90% time saving within ±5% accuracy. Modeling via ROM is much faster and cheaper computationally; hence this approach can be used for studying the system-level convective heat transfer enhancement of heat sinks using synthetic jets.

An Active Radial Countercurrent Heat Sink Driven by a Synthetic Jet Actuator

2001 ◽  
Author(s):  
Jelena Vukasinovic ◽  
Ari Glezer
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Jet Impingement ◽  
Ambient Air ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Heat Transfer Analysis ◽  
Orifice Diameter ◽  
Synthetic Jet Actuator ◽  
Extended Surface

Abstract The performance of a low-profile radial countercurrent heat sink driven by an integrated synthetic jet actuator is investigated experimentally. A packaged thermal test die is cooled using an array of synthetic jets normally impinging on the extended surface. A power dissipation of 50 W is accomplished at the nominal case temperature of Tc = 70 °C. The heat sink design is driven by the flow and heat transfer analysis of normal jet impingement in a confined flow geometry consisting of two parallel circular plates having a diameter that is typically an order of magnitude larger than the spacing between the plates. The velocity and temperature distributions are measured using particle image velocimetry and arrays of thermocouple sensors. A jet actuator is integrated into one of the plates and cools a test heater attached to the opposite surface. The jet draws its makeup air from ambient, impinges on the heater, and ultimately rejects the heat to ambient. This introduces a radial countercurrent flow in the gap between the plates that includes a layer of hot air dispensed along the top plate and a layer of cooler ambient air entrained along the jet exit plane. When the jet is activated the heater temperature drops substantially. Although the global heat transfer coefficient decreases with decreasing gap height, flow pathlines show that the jet can still entrain cool air from ambient and effect substantial cooling even when the spacing between the plates is of the order of the jet orifice diameter.

Heat Transfer Enhancement by Synthetic Jet Arrays in Air-Cooled Heat Sinks for Use in Electronics Cooling

2012 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Min Zhang ◽  
Youmin Yu ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Sink ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A synthetic jet is an intermittent jet which issues through an orifice from a closed cavity over half of an oscillation cycle. Over the other half, the flow is drawn back through the same orifice into the cavity as a sink flow. The flow is driven by an oscillating diaphragm, which is one wall of the cavity. Synthetic jets are widely used for heat transfer enhancement since they are effective in disturbing and thinning thermal boundary layers on surfaces being cooled. They do so by creating an intermittently-impinging flow and by carrying to the hot surface turbulence generated by breakdown of the shear layer at the jet edge. The present study documents experimentally and computationally heat transfer performance of an array of synthetic jets used in a heat sink designed for cooling of electronics. This heat sink is comprised of a series of longitudinal fins which constitute walls of parallel channels. In the present design, the synthetic jet flow impinges on the tips of the fins. In the experiment, one channel of a 20-channel heat sink is tested. A second flow, perpendicular to the jet flow, passes through the channel, drawn by a vacuum system. Surface- and time-averaged heat transfer coefficients for the channel are measured, first with just the channel flow active then with the synthetic jets added. The purpose is to assess heat transfer enhancement realized by the synthetic jets. The multiple synthetic jets are driven by a single diaphragm which, in turn, is activated by a piezoelectrically-driven mechanism. The operating frequency of the jets is 1250 Hz with a cycle-maximum jet velocity of 50 m/s, as measured with a miniature hot-film anemometer probe. In the computational portion of the present paper, diaphragm movement is driven by a piston, simulating the experimental conditions. The flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. Computed heat transfer coefficients show a good match with experimental values giving a maximum difference of less than 10%. The effects of amplitude and frequency of the diaphragm motion are documented. Changes in heat transfer due to interactions between the synthetic jet flow and the channel flow are documented in cases of differing channel flow velocities as well as differing jet operating conditions. Heat transfer enhancement obtained by activating the synthetic jets can be as large as 300% when the channel flow is of a low velocity compared to the synthetic jet peak velocity (as low as 4 m/s in the present study).

Effect of Synthetic Jets Over Natural Convection Heat Sinks

2008 ◽  
Author(s):  
Mehmet Arik ◽  
Yogen Utturkar ◽  
Murat Ozmusul
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Heat Sinks ◽  
Junction Temperature ◽  
Allowable Limit

In moderate power electronics applications, the most preferred way of thermal management is natural convection to air with or without heat sinks. Though the use of heat sinks is fairly adequate for modest heat dissipation needs, it suffers from some serious performance limitations. Firstly, a large volume of the heat sink is required to keep the junction temperature at an allowable limit. This need arises because of the low convective film coefficients due to close spacing. In the present computational and experimental study, we propose a synthetic jet embedded heat sink to enhance the performance levels beyond two times within the same volume of a regular passive heat sink. Synthetic jets are meso-scale devices producing high velocity periodic jet streams at high velocities. As a result, by carefully positioning of these jets in the thermal real estate, the heat transfer over the surfaces can be dramatically augmented. This increase in the heat transfer rate is able to compensate for the loss of fin area happening due to the embedding of the jet within the heat sink volume, thus causing an overall increase in the heat dissipation. Heat transfer enhancements of 2.2 times over baseline natural convection cooled heat sinks are measured. Thermal resistances are compared for a range of jet operating conditions and found to be less than 0.9 K/W. Local temperatures obtained from experimental and computational agreed within ± 5%.

Interaction of Synthetic Jet Cooling Performance With Gravity and Buoyancy Driven Flows

2007 ◽  
Author(s):  
Mehmet Arik ◽  
Yogen Utturkar ◽  
Mustafa Gursoy
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Jet Cooling ◽  
Impingement Heat Transfer ◽  
Buoyancy Driven Flows ◽  
Experimental Findings ◽  
Meso Scale

Meso scale cooling devices have been of interest for low form factor, tight space, and high COP thermal management problems. A candidate meso scale device, known as synthetic jets, operates with micro fluidic principles and disturbs the boundary layer causing significant heat transfer over conventional free convective heat transfer in air. Previous papers have dealt with the impingement and cross flow, but did not study mixed convection for synthetic jet with natural convection. In the present study, we discuss the results of an experimental study to investigate the interplay between jet orientations with respect to gravity, elevated temperature conditions, and synthetic jet heat dissipation capacity. Experiments were performed by placing synthetic at different positions around a square, 25.4mm heated flat surface. The flow physics behind the experimental findings is discussed. It is found that impingement heat transfer outperformed more than 30% compared to other orientations. The jet showed about 15% sensitivity to angular orientations.

Heat Transfer Enhancement of a Heat Sink by Inclined Synthetic Jets for Electronics Cooling

2013 ◽  
Author(s):  
Arya Ayaskanta ◽  
Longzhong Huang ◽  
Terrence Simon ◽  
Taiho Yeom ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Thermal Dissipation ◽  
Transfer Enhancement ◽  
Resonance Frequencies ◽  
Jet Array

Rising thermal dissipation from modern electronics has increased the challenge of cooling using conventional heat sinks. In addition to fans and blowers, focus is turning to active cooling devices for augmenting performance. A piezoelectrically-actuated synthetic jet array is one under consideration. Synthetic jets are zero-net–mass-flow jets realized by a cavity with an oscillating diaphragm on one side and an orifice or multiple orifices on the other side. They generate highly unsteady jetting flows that can impinge upon heated surfaces and enhance cooling. However, the synthetic jet actuation components might interfere with other components of the electronics module, such as the fan, requiring a displacement of the cavity center from the jet array center. Herein, heat transfer enhancement by an inclined piezoelectrically-actuated synthetic jet arrangement in a heat sink for electronics cooling has been experimentally and numerically studied. A wedge-shaped platform is designed to introduce the jets with an inclined configuration into the finned channels of the heat sink. The unit is inclined to avoid interference with other components of the module. The penalty is described in terms of velocities of jets emerging from this wedge-shaped platform, compared to those from an aligned cavity-orifice design. Effects on heat transfer performance for the heat sink are documented. The jets are arranged as wall jets passing over heat sink fins. The experimental study is complemented with a numerical analysis of flow within the synthetic jet cavity. Optimization is done on the number of jets against the penalty on jet velocity for obtaining maximum cooling performance. The jets are driven by piezoelectric actuators operating at resonance frequencies of 700–800 Hz resulting in peak jet velocities of approximately 35m/s from 92, 0.9 mm × 0.9 mm orifices. The results give guidance to those who face a similar interference problem and are considering displacement of the synthetic jet assembly.

Piezoelectric Synthetic Jet Integrated With Heat Sink for Heat Transfer Enhancement

2013 ◽  
Author(s):  
Qiao Li ◽  
Longzhong Huang ◽  
Min Zhang ◽  
Mark T. North ◽  
Terrence Simon ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Carbon Fiber ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Ansys Fluent ◽  
Moving Wall ◽  
Enhancing Heat Transfer ◽  
Flow Through ◽  
Zero Net Mass Flux ◽  
Piezoelectric Stack Actuator

Synthetic jets, known as zero-net mass-flux (ZNMF) devices, have been widely used for cooling electronics. A synthetic jet is generally composed of a cavity with an orifice on one side and an oscillating diagram on the other side. The vibration of the diaphragm will generate a periodically impinging flow through the orifice which is found to be effective in enhancing heat transfer. The thermal performance of the synthetic jet is highly dependent on the peak velocity of the synthetic jet is able to generate. The orifice shape, orifice thickness, and the number of the orifices are the factors which affect the vibration condition of the diaphragm and thus to affect the performance of the synthetic jet. This study will use both experimental and computational methods to find out the optimal design of synthetic jet and how these factors affect synthetic jet performance. The synthetic jet arrays are driven by a piezoelectric stack actuator which is vibrating at around 720 Hz and the mean-to-peak amplitude is around 0.2 mm. The jet diaphragm (120 mm × 15 mm) is designed using a composite structure composed of a carbon fiber beam, a carbon fiber frame, and a jet frame fabricated by polymethyl methacrylate (PMMA). Four different orifice shapes (square, single slot, double slot, and triangle) with the same area have been designed and the square orifice has the highest velocity. The effect of the orifice thickness is also studied by testing four kinds of PMMA films with different thicknesses (1.5 mm, 2 mm, 3 mm, and 4.5 mm) and the case with 4.5 mm thick orifice has the best performance. The numerical simulation is conducted using the CFD software ANSYS Fluent to support the experimental results. The vibrating of the diaphragm is defined as a moving wall using a user defined function. The fluid power consumed by the diaphragm is used to determine the performances of different designs. The same trend with orifice thickness has been found and the reason has been demonstrated.

Micro Fluidic Jets for Thermal Management of Electronics

Volume 4 ◽  
2004 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heated Surface ◽  
Turbulent Jets ◽  
Harmonic Signal ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Air Cooling ◽  
Infrared Thermal Imaging

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.

Experimental Investigation of the Effect of Synthetic Jets in Minichannels With Subcooled Boiling Flow

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. The experimental range extends from transitional to turbulent flows. Local wall temperature measurements indicate that increases of heat transfer coefficient of over 20% can occur directly below the synthetic jet with low exit qualities. In this study, the heat transfer augmentation by using synthetic jets was dictated by the momentum ratio of the synthetic jet to the bulk fluid flow. As local quality was increased, the heat transfer augmentation dropped from 23% to 10%. Surface tension variations had a large effect on the Nusselt number, while variations in inertial forces had a small effect on Nusselt number in this operating region.

Sign in / Sign up

Export Citation Format

Share Document