Numerical and Experimental Analysis of Impinging Synthetic Jets for Cooling a Point-Like Heat Source

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Robert Glowienko ◽  
Hans Derlien ◽  
Oezguer Ertunc ◽  
Antonio Delgado
Keyword(s):  
Heat Transfer ◽  
High Energy ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Heat Sinks ◽  
Light Emitting ◽  
Automotive Lighting ◽  
Axial Fans ◽  
Impact Plate ◽  
The Impact

High power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.

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%.

scholarly journals Comparing the Influence of Synthetic jets on Cooling the Angled Plates Versus Vertical and Horizontal Plates

2021 ◽  
Vol 5 (2) ◽  
pp. 23-35
Author(s):  
Miralireza Nabavi ◽  
Moharram Jafari
Keyword(s):  
Heat Transfer ◽  
Open Source Software ◽  
Flow Separation ◽  
Flight Control ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Weak Efficiency ◽  
Previous Decade ◽  
Jet Nozzle ◽  
The Impact

Synthetic jets besides being used in heat transfer, have also been used to control turbulence and flow separation. In the previous decade, research on the applications of a synthetic jet has indicated that by using these types of jets, flow separation can be reduced or even stopped altogether. In addition, these jets have been utilized in unmanned aerial vehicles (UAVs) (to control separation on airfoils) and flight control. In this study, the jet is located perpendicular to the flat plane with fixed heat flux and the effect of some geometric parameters including the ratio of the distance between the jet and the impact plane to the nozzle width, the ratio of the impact plane length to the jet nozzle width, the ratio of synthetic jet width to width of the nozzle, the ratio of the hole height to the nozzle width, the angle of the impact plate as well as the diaphragm characteristics such as amplitude and frequency of the jet diaphragm in heat transfer were evaluated numerically by using OpenFOAM open-source software. The findings indicate that synthetic jets have very weak efficiency for cooling vertical panels. However, they are extremely effective on angled plates. Synthetic jets have more influence on angled planes than horizontal planes.

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.

Assessment of Cooling Enhancement of Synthetic Jet in Conjunction With Forced Convection

2007 ◽  
Author(s):  
Yogen Utturkar ◽  
Mehmet Arik ◽  
Mustafa Gursoy
Keyword(s):  
Forced Convection ◽  
Cross Flow ◽  
Electronics Cooling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Channel Height ◽  
Large Area ◽  
Complete Replacement ◽  
Cooling Enhancement ◽  
The Impact

Synthetic jets are meso or micro fluidic devices, which operate on the “zero-net-mass-flux” principle. They impart a positive net momentum flux to the external environment, and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. As a result, recently their application as electronics cooling devices is gaining momentum. Traditionally, synthetic jets have been sought as a replacement to the fan in many electronic devices. However, in certain large applications, complete replacement of the fan is not feasible, because it is necessary to provide the basic level of cooling over a large area of a printed assembly board. Such applications often pose a question whether synthetic jet would be able to locally provide reasonable enhancement over the forced convection of the fan flow. In the present study, we present the cooling performance of synthetic jets complementing forced convection from a fan. Both experiments and CFD computations are performed to investigate the interaction of the jet flowfield with a cross flow from fan. The inlet velocity, jet disk amplitude, and channel height are varied in the computational simulations to evaluate the impact of these changes on the cooling properties. Overall, both studies show that a synthetic jet is able to pulse and disrupt the boundary layer caused from fan flow, and improve heat transfer up to 4× over forced convection.

The performance of round synthetic jets in quiescent flow

2006 ◽  
Vol 110 (1108) ◽  
pp. 385-393 ◽  
Author(s):  
M. Jabbal ◽  
J. Wu ◽  
S. Zhong
Keyword(s):  
Near Field ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Stroke Length ◽  
Synthetic Jet Actuators ◽  
Macro Scale ◽  
Jet Actuators ◽  
The Impact

AbstractPIV measurements in the near-field region of a jet flow emanating from a round synthetic jet actuator into quiescent air were conducted over a range of operating conditions. The primary purpose of this work was to investigate the nature of synthetic jets at different operating conditions and to examine the jet flow parameters that dictate the behaviour of synthetic jet actuators. The effects of varying diaphragm displacement and oscillatory frequency for fixed actuator geometry were studied. It was observed that the characteristics of synthetic jets are largely determined by the Reynolds number and stroke length. An increase in the former is observed to increase the strength of consecutive vortex rings that compose a synthetic jet, whereas an increase in the latter results in an increase in relative vortex ring spacing and for further increases in stroke length, shedding of secondary vortices. Correlations were also made between the operating parameters and the performance parameters most effective for flow control and which therefore determine the impact of a synthetic jet on an external flow. Relations of time-averaged dimensionless mass flux, momentum flux and circulation with the jet flow conditions were established and found to widely support an analytical performance prediction model described in this paper. It is anticipated that the experimental data obtained in this study will also contribute towards providing a PIV database for macro-scale synthetic jet actuators.

Large-Eddy Simulations of Heat Transfer Within a Multi-Perforation Synthetic Jets Configuration

2019 ◽  
Author(s):  
Soizic Esnault ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Heat Transfer ◽  
Flow Behavior ◽  
Synthetic Jets ◽  
Large Eddy Simulations ◽  
Heated Plate ◽  
Piston Displacement ◽  
Large Eddy ◽  
Grazing Flow ◽  
The Impact ◽  
Ejection Phase

Abstract Synthetic jets are produced by devices that enable a suction phase followed by an ejection phase. The resulting mean mass budget is hence null and no addition of mass in the system is required. These particular jets have especially been considered for some years for flow control applications. They also display features that can become of interest to enhance heat exchanges, for example for wall cooling issues. Synthetic jets can be generated through different mechanisms, such as acoustics by making use of a Helmholtz resonator or through the motion of a piston as in an experience mounted at Institut Pprime in France. The objective of this specific experiment is to understand how synthetic jets can enhance heat transfer in a multi-perforated configuration. As a complement to this experimental set up, Large-Eddy Simulations are produced and analysed in the present document to investigate the flow behavior as well as the impact of the synthetic jets on wall heat transfer. The experimental system considered here consists in a perforated heated plate, each perforation being above a cavity where a piston is used to control the synthetic jets. Placed in a wind tunnel test section, the device can be studied with a grazing flow and multiple operating points are available. The one considered here implies a grazing flow velocity of 12.8 m.s−1, corresponding to a Mach number around 0.04, and a piston displacement of 22 mm peak-to-peak at a frequency of 12.8 Hz. These two latter parameters lead to a jet Reynolds number of about 830. A good agreement is found between numerical results and experimental data. The simulations are then used to provide a detailed understanding of the flow. Two main behaviours are found, depending on the considered mid-period. During the ejection phase, the flow transitions to turbulence and the formation of characteristic structures is observed; the plate is efficiently cooled. During the suction phase the main flow is stabilised; the heat enhancement is particularly efficient in the hole wakes but not between them, leading to a heterogeneous temperature field.

A Heat Transfer Comparison Between a Synthetic Jet and a Steady Jet at Low Reynolds Numbers

2008 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Stroke Length ◽  
Low Reynolds Numbers ◽  
Nusselt Numbers ◽  
Significant Difference ◽  
Low Reynolds ◽  
Surrounding Fluid

A study has been carried out to compare steady jet and synthetic jet heat transfer distributions at low Reynolds numbers. Both jets issued from a 5mm diameter orifice plate with air for the steady jet being supplied by a compressor via a plenum chamber. Tests were conducted for Reynolds numbers ranging from 1000 to 4000, and for non-dimensional surface to jet exit spacings (H/D) from 1 to 6. Dimensionless stroke length (Lo/D) for the synthetic jet was held constant at 8. A significant difference was observed between the steady and synthetic jet Nusselt numbers at low Reynolds numbers and low H/D. In comparison to steady jets, the stronger entrainment of surrounding fluid and the vigorous mixing near the impingement surface are characteristics of synthetic jets that are beneficial to heat transfer. Nonetheless, the steady jet yields higher Nusselt numbers for all test conditions.

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).

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

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