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.

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).

Development of Synthetic Jet Arrays for Heat Transfer Enhancement in Air-Cooled Heat Sinks for Electronics Cooling

2012 ◽  
Author(s):  
Min Zhang ◽  
Taiho Yeom ◽  
Youmin Yu ◽  
Longzhong Huang ◽  
Terrence W. Simon ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Power Consumption ◽  
Flow Velocity ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Sink ◽  
Synthetic Jet ◽  
Total Power ◽  
Transfer Enhancement ◽  
Jet Array

Synthetic jet arrays driven by a piston-diaphragm structure with a translational motion were fabricated. A piezo-bow actuator generating large translational displacements at a high working frequency was used to drive the jets. Vibration analysis with a laser vibrometer shows the peak-to-peak displacement of the piston inside the jet cavity of about 0.5 mm at the second resonant vibrational frequency of 1,240 Hz. In this driving condition, the peak velocity of a 20-orifice jet array reaches 45 m/s for each orifice with a total power consumption of 1.6 W. Heat transfer performance of the jet array was tested on a 100-mm-long single channel of a 26-channel heat sink. The synthetic jet flow impinges on the tips of the fins. A cross flow through the channel enters from the two ends of the channel, and exits from the middle. Results show that the activation of jets generates a unit-average heat transfer enhancement of 9.3% when operating with a channel flow velocity of 14.7 m/s, and 23.1% when operating with a channel flow velocity of 8 m/s. The effects of various choices for orifice configuration and different dimensionless distances from the fin tips, z/d, on jet performance were evaluated. By decreasing the length of the fin channel from 100 mm to 89 mm and reducing the orifice number of the jet array from 20 to 18, jet peak velocities of about 54 m/s can be obtained with the same power consumption, and a heat transfer enhancement of 31.0% from the jets can be achieved on the 89-mm-long heat sink channel with a flow velocity of 8 m/s.

Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets

2011 ◽  
Author(s):  
Youmin Yu ◽  
Terrence Simon ◽  
Min Zhang ◽  
Taiho Yeom ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Single Channel ◽  
Synthetic Jets ◽  
Heat Sinks ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Enhancing Heat Transfer

Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.

Recent Developments on Synthetic Jets (Review Paper)

2016 ◽  
Vol 66 (5) ◽  
pp. 489 ◽  
Author(s):  
T. Murugan ◽  
Monami Deyashi ◽  
Santanu Dey ◽  
Subhas Chandra Rana ◽  
P.K. Chatterjee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Review Paper ◽  
Ambient Air ◽  
External Source ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Enhancement ◽  
Aerospace Applications ◽  
Recent Developments

<p>Synthetic jet is a form of pulsatile jet where the flow is synthesised from the ambient air and it does not need any external source as the flow is induced from the fluid existing around orifice/nozzle. This property makes synthetic jet unique compared to pulsatile and continuous jets. Recently, the synthetic jet is being widely used for flow control, mixing and heat transfer enhancement in aerospace applications. Focused on reviewing the recent developments on synthetic jet characterization and their applications resulting from the development of advanced diagnosing tools.</p>

Active Heat Transfer Enhancement in Single-Phase Microchannels by Using Synthetic Jets

2013 ◽  
Vol 5 (1) ◽  
Author(s):  
Ruixian Fang ◽  
Jamil A. Khan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Synthetic Jets ◽  
Transfer Performance ◽  
Microchannel Flow ◽  
Transfer Enhancement ◽  
Pressure Dynamics ◽  
A Minor

The present work experimentally investigates the effect of synthetic jets on the heat transfer performance in a microchannel heat sink. The heat sink consists of five parallel rectangular microchannels measuring 500 μm wide, 500 μm deep, and 26 mm long each. An array of synthetic jets with 100 μm diameter orifices is placed right above the microchannel with a total of eight jet orifices per channel. Microjets are synthesized from the fluid flowing through the microchannel. Periodic disturbances are generated when the synthetic jets interact with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and penetrates the thermal boundary layer near heated channel wall. The effects of synthetic jets on microchannels heat transfer performance are studied for several parameters including the channel stream flow rate, the synthetic jets strength and operating frequency. It shows that the synthetic jets have higher heat transfer enhancement for microchannel flow at lower channel flow rates. A maximum of 130% heat transfer enhancement is achieved for some test cases. The pressure dynamics introduced by the synthetic jets are also investigated. The synthetic jets cause a minor increase in the pressure drop.

Synthetic jet cross-flow interaction with orifice obstruction

2015 ◽  
Vol 25 (4) ◽  
pp. 749-761 ◽  
Author(s):  
Samir Laouedj ◽  
Juan P. Solano ◽  
Abdelylah Benazza
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Stokes Equations ◽  
Cross Flow ◽  
Electronics Cooling ◽  
Limited Range ◽  
Synthetic Jet ◽  
Operating Conditions ◽  
Transfer Enhancement ◽  
Content Type

Purpose – The purpose of this paper is to describe the flow structure and the time-resolved and time-mean heat transfer characteristics in the interaction between a synthetic jet and a cross flow, when an obstruction reduces the cross-section of the orifice where the jet is formed. Design/methodology/approach – The microchannel flow interacted by the pulsed jet is modeled using a two-dimensional finite volume simulation with unsteady Reynolds-averaged Navier-Stokes equations while using the Shear-Stress-Transport (SST) k-ω turbulence model to account for fluid turbulence. Findings – The computational results show a good and rapid increase of the synthetic jet influence on heat transfer enhancement when the obstruction of the orifice is superior to 30 per cent and the synthetic jet oscillating amplitudes are below 50 µm. It is found that when the obstruction is close to the exit orifice, the heat transfer enhancement is significant. The obstruction has proved to accelerate the jet and change the formation of large vortical structures. Additional windward vortices appear, which influence the flow field and enhance the heat transfer. Research limitations/implications – The work proposes the use of a compound enhancement technique for electronics cooling. A limited range of operating conditions and geometrical configurations is presented. A further analysis of the performance evaluation, based on the increased energy consumption of the device, would complement the study. Originality/value – The authors provide a compound technique to enhance heat transfer in synthetic-jet electronic cooling devices.

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