Experimental Study of the Convective Heat Transfer From a Geometrically Scaled Up 2D Impinging Synthetic Jet

2013 ◽  
Author(s):  
Luis Silva ◽  
Alfonso Ortega ◽  
Isaac Rose
Keyword(s):  
Laboratory Experiments ◽  
Heated Surface ◽  
Target Surface ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Local Data ◽  
Low Frequencies ◽  
Cooling Air Flow ◽  
Cooling Air

Synthetic jets are created by periodically ejecting and injecting fluid from an orifice or channel. Despite delivering no net mass flow per cycle, a synthetic jet delivers flow with net positive momentum. Small, compact synthetic jet actuators can be fabricated to operate in the subaudible acoustic range and can be packaged in orientations that allow them to deliver cooling air flow to electronic devices. The most promising orientation is one that delivers the jet flow in a direction normal to the heated surface such that it impinges on the surface as a periodic jet. In previous studies, numerical simulations have been performed by the authors, utilizing a canonical geometry, with the purpose of eliminating actuator artifacts from the fundamental physics that drive the problem. The present paper reports on laboratory experiments that have been performed in order to nearly replicate the idealized synthetic jet geometry and thus allow comparison to the previous numerical investigations. The periodic volume change in an upstream plenum required to produce the synthetic jet is accomplished with an acoustic speaker operated at low frequencies. The amplitude and the frequency at which the jet is actuated determine the Reynolds and Strouhal numbers, which are the dominant non-dimensional groups that control the behavior of the impinging synthetic jet. By maintaining the Re and the St in the laboratory experiments to match those of the small scale actuators, the laboratory experiments have been geometrically scaled up to allow highly resolved measurements of the unsteady velocity field and the local time-dependent Nusselt number on the target heated surface. Experiments were performed at variable jet Re, frequencies, and height from the target surface. The dependence of the surface averaged Nu to jet parameters generally agrees with the computational results. However, discrepancies found between numerical and empirical local data are under revision.

Experiments and Simulation of an Impinging Synthetic Jet Designed to Eliminate Actuator Artifacts

2012 ◽  
Author(s):  
Luis Silva ◽  
Alfonso Ortega ◽  
Mahsa Ebrahim
Keyword(s):  
Laboratory Experiments ◽  
Heated Surface ◽  
Target Surface ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Local Data ◽  
Low Frequencies ◽  
Cooling Air Flow ◽  
Cooling Air

Synthetic jets are created by periodically ejecting and injecting fluid from an orifice or channel. Despite delivering no net mass flow per cycle, a synthetic jet delivers flow with net positive momentum. Small, compact synthetic jet actuators can be fabricated to operate in the subaudible acoustic range and can be packaged in orientations that allow them to deliver cooling air flow to electronic devices. The most promising orientation is one that delivers the jet flow in a direction normal to the heated surface such that it impinges on the surface as a periodic jet. In previous studies, numerical simulations have been performed by the authors, utilizing a canonical geometry, with the purpose of eliminating actuator artifacts from the fundamental physics that drive the problem. The present paper reports on laboratory experiments that have been performed in order to nearly replicate the idealized synthetic jet geometry and thus allow comparison to the previous numerical investigations. The periodic volume change in an upstream plenum required to produce the synthetic jet is accomplished with an acoustic speaker operated at low frequencies. The amplitude and the frequency at which the jet is actuated determine the Reynolds and Strouhal numbers, which are the dominant non-dimensional groups that control the behavior of the impinging synthetic jet. By maintaining the Re and the St in the laboratory experiments to match those of the small scale actuators, the laboratory experiments have been geometrically scaled up to allow highly resolved measurements of the unsteady velocity field and the local time-dependent Nusselt number on the target heated surface. Experiments were performed at variable jet Re, frequencies, and height from the target surface. The dependence of the surface averaged Nu to jet parameters generally agrees with the computational results. However, discrepancies found between numerical and empirical local data are under revision.

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.

Low Frequency Piezoelectric Synthetic Jets

2010 ◽  
Author(s):  
Charles E. Seeley ◽  
Mehmet Arik ◽  
Yogen Uttukar ◽  
Tunc Icoz
Keyword(s):  
Low Cost ◽  
Heated Surface ◽  
Fluid Structure Interaction ◽  
Low Frequency ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Active Cooling ◽  
Compact Size

Active cooling is often required for circuit boards with high heat generation densities. Synthetic jets driven with piezoelectric actuators offer interesting capabilities for localized active cooling of electronics due to their compact size, low cost and substantial cooling effectiveness. The design of synthetic jets for specific applications requires practical design tools that capture the strong fluid structure interaction without long run times. There is particular interest in synthetic jets that have a low operating frequency to reduce noise levels. This paper describes how common finite element (FE) and computational fluid dynamics (CFD) codes can be used to calculate parameters for a synthetic jet fluid structure interaction (FSI) model that only requires a limited number of degrees of freedom and is solved using a direct approach for low frequency synthetic jets. Tests are performed based on impinging on a heated surface to measure heat transfer enhancement. The test results are compared to the FSI model results for validation and agreement is found to be good in the frequency range of interest from 200 to 500 Hz.

Electronic Cooling Using Synthetic Jets

2005 ◽  
Author(s):  
Anna A. Pavlova ◽  
Michael Amitay
Keyword(s):  
Reynolds Number ◽  
Heated Surface ◽  
Low Frequency ◽  
Heat Removal ◽  
Jet Impingement ◽  
Constant Heat Flux ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Impingement Cooling ◽  
Jet Cooling

Efficiency of synthetic jet impingement cooling and the mechanisms of heat removal from a constant heat flux surface were investigated experimentally. The effects of jet’s formation frequency and Reynolds number at different nozzle-to-surface distances were investigated and compared to steady jet cooling. It was found that synthetic jets are up to three times more effective than steady jets at the same Reynolds number. For smaller distances, high formation frequency (f = 1200 Hz) synthetic jets remove heat better than low frequency (f = 420 Hz) jets, whereas low frequency jets are more effective at larger distances, with an overlapping region. Using PIV, it was shown that at small distances between the synthetic jet and the heated surface, the higher formation frequency jet is associated with accumulation of vortices before they impinge on the surface. For the lower frequency jet, the wavelength between coherent structures is so large that vortex rings impinge on the surface separately.

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.

Forced Air Cooling With Synthetic Jet Ejectors

2005 ◽  
Author(s):  
Raghav Mahalingam ◽  
Ari Glezer
Keyword(s):  
Mass Flux ◽  
Heated Surface ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Low Flow ◽  
Air Cooling ◽  
Zero Mass ◽  
High Heat Transfer ◽  
Forced Air

This paper discusses the concept of synthetic jet ejectors for forced air cooling and some practical implementations of the same. Synthetic or “zero-mass-flux” jets, unlike conventional jets, require no mass addition to the system, and thus provide means of efficiently directing airflow across a heated surface. Because these jets are zero net mass flux in nature and are comprised entirely of the ambient fluid, they can be conveniently integrated with the surfaces that require cooling without the need for complex plumbing. A synthetic jet ejector mechanism for obtaining high heat transfer rates at low flow rates is discussed. Synthetic jet ejectors consist of a primary “zero-mass-flux” unsteady jet driving a secondary airflow through a channel. Several practical implementations of synthetic jets are introduced from low form factor, low power spot cooling applications to high heat dissipation applications and flow bypass control where synthetic jets are used to enhance fan performance.

Meso Scale Pulsating Jets for Electronics Cooling

2005 ◽  
Vol 127 (4) ◽  
pp. 503-511 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Todd Wetzel ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Coefficient Of Performance ◽  
Small Scale ◽  
Driving Voltage ◽  
Driving Frequency ◽  
Air Velocity ◽  
Maximum Heat ◽  
Meso Scale

Microfluid devices are conventionally used for boundary layer control in many aerospace applications. Synthetic jets are intense small-scale turbulent jets formed from periodic entrainment and expulsion of the fluid in which they are embedded. The jets can be made to impinge upon electronic components thereby providing forced convection impingement cooling. The small size of these devices accompanied by the high exit air velocity provides an exciting opportunity to significantly reduce the size of thermal management hardware in electronics. A proprietary meso scale synthetic jet designed at GE Global Research is able to provide a maximum air velocity of 90m∕s from a 0.85 mm hydraulic diameter rectangular orifice. An experimental study for determining the cooling performance of synthetic jets was carried out by using a single jet to cool a thin foil heater. The heat transfer augmentation caused by the jets depends on several parameters, such as, driving frequency, driving voltage, jet axial distance, heater size, and heat flux. During the experiments, the operating frequency for the jets was varied between 3.4 and 5.4 kHz, while the driving voltage was varied between 50 and 90VRMS. Two different heater powers, corresponding to approximately 50 and 80 °C, were tested. A square heater with a surface area of 156mm2 was used to mimic the hot component and detailed temperature measurements were obtained with a microscopic infrared thermal imaging technique. A maximum heat transfer enhancement of approximately 10 times over natural convection was measured. The maximum measured coefficient of performance was approximately 3.25 due to the low power consumption of the synthetic jets.

scholarly journals Effects of Frequency and Jet to Surface Spacing on Synthetic Jet Impingement Heat Transfer

2020 ◽  
Vol 9 (5) ◽  
pp. 655-660
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heated Surface ◽  
Low Frequency ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Nozzle Geometry ◽  
Ansys Fluent ◽  
Piston Cylinder

Synthetic jet is a new technique for electronic chip cooling, which combines stagnant air to form a jet resulting from periodic diaphragm oscillations in a cavity. In this work, the heat transfer characteristics of a synthetic jet are investigated experimentally and numerically. A Piston-cylinder arrangement powers the synthetic jet through a circular orifice for the impingement of jet on the heated surface. Air is considered as the cooling medium. The major parameters identified to describe the impinging jet heat transfer are Reynolds number, frequency, ratio of jet spacing to diameter(Z/D) and nozzle geometry. Numerical studies have been carried out using the finite volume based commercial software ANSYS Fluent. The turbulent model used is k-ω model. The dimensionless distance between the nozzle and plate surface is in the range 2 to 16. Numerical results are in fair agreement with experimental results. As the frequency increases the average Nusselt number increases. High frequency synthetic jets were found to remove more heat than low frequency jets for small Z/D ratio, while low frequency jets are more effective at larger Z/D ratio. Nusselt number is maximum at the stagnation point and there occurs a secondary peak at lower Z/D ratios. Synthetic jet with rectangular orifice is more effective as compared to circular and square geometries.

A Computational Study on the Momentum and Heat Transfer Distribution of a Low Frequency Round Impinging Synthetic Jet

2015 ◽  
Author(s):  
Muhammad Ikhlaq ◽  
Baris Dogruoz ◽  
Omidreza Ghaffari ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Computational Study ◽  
Low Frequency ◽  
Target Surface ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Temperature Fields ◽  
Momentum And Heat Transfer ◽  
Prior Literature

Impinging synthetic jets have been considered as a possible solution for cooling miniature structures. 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 decreases with a reduction in nozzle-to-target plate distance. At low nozzle-to-target spacing, no detailed information about the momentum and temperature fields have been shown in prior literature, therefore further investigation is needed. In this study, a 3-D computational fluid dynamics model was constructed to determine the flow and temperature fields of a meso-scale synthetic jet at a nozzle-to-target surface spacing of H/D = 2, ReD,j= 1400 and f = 500 Hz. Unlike the majority of previous computational studies, rather than specifying the boundary conditions at the nozzle, the flow inside the synthetic jet device was solved by specifying the time dependent boundary conditions on the vibrating diaphragm and utilizing the moving mesh technique. Local surface pressure and heat transfer coefficient distributions were determined and discussed. It was found that the pulsating flow at the nozzle exit for a round jet generates vortex rings and these rings seem to have some considerable effects on the target surface profiles.

Convective Heat Transfer in an Impinging Synthetic Jet: A Numerical Investigation of a Canonical Geometry

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Luis A. Silva ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Stokes Equations ◽  
Heated Surface ◽  
Vortex Pair ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Scaling Analysis ◽  
Dependent Flow

Synthetic jets are generated by an equivalent inflow and outflow of fluid into a system. Even though such a jet creates no net mass flux, net positive momentum can be produced because the outflow momentum during the first half of the cycle is contained primarily in a vigorous vortex pair created at the orifice edges; whereas in the backstroke, the backflow momentum is weaker, despite the fact that mass is conserved. As a consequence of this, the approach can be potentially utilized for the impingement of a cooling fluid onto a heated surface. In previous studies, little attention has been given to the influence of the jet's origins; hence it has been difficult to find reproducible results that are independent of the jet apparatus or actuators utilized to create the jet. Furthermore, because of restrictions of the resonators used in typical actuators, previous investigations have not been able to independently isolate effects of jet frequency, amplitude, and Reynolds number. In the present study, a canonical geometry is presented, in order to study the flow and heat transfer of a purely oscillatory jet that is not influenced by the manner in which it is produced. The unsteady Navier–Stokes equations and the convection–diffusion equation were solved using a fully unsteady, two-dimensional finite volume approach in order to capture the complex time dependent flow field. A detailed analysis was performed on the correlation between the complex velocity field and the observed wall heat transfer. Scaling analysis of the governing equations was utilized to identify nondimensional groups and propose a correlation for the space-averaged and time-averaged Nusselt number. A fundamental frequency, in addition to the jet forcing frequency, was found, and was attributed to the coalescence of consecutive vortex pairs. In terms of time-averaged data, the merging of vortices led to lower heat transfer. Point to point correlations showed that the instantaneous local Nusselt number strongly correlates with the vertical velocity v although the spatial-temporal dependencies are not yet fully understood.

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