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.

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.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

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.

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.

Experimental Investigation on Heat Transfer and Pressure Drop of Nanodiamond-Engine Oil Nanofluid in a Microfin Tube

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
M. Ghazvini ◽  
E. Rasouli
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Engine Oil ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

In this study, the effect of adding nanodiamond powder as an additive to engine oil on laminar flow heat transfer enhancement and pressure drop increasing is experimentally investigated. The plain and microfin tubes were used as the test sections and were heated by an electrical coil heater to produce constant heat fluxes. Thermal conductivity and heat capacity of nanofluids were measured for different volume fractions and temperatures. Convection heat transfer coefficients and Nusselt numbers of nanofluids were obtained for different nanoparticle concentrations as well as various Peclet and Reynolds numbers. Experimental results show the enhancement of heat transfer due to the nanoparticles presence. Furthermore, the effect of particle concentration on pressure drop was studied for different heat fluxes. Finally, the performance evaluation of both nanofluid and microfin tube from the point view of heat transfer enhancement and pressure drop increasing is done.

Heat Transfer Enhancement by Delta-Wing-Generated Tip Vortices in Flat-Plate and Developing Channel Flows

2002 ◽  
Vol 124 (6) ◽  
pp. 1158-1168 ◽  
Author(s):  
M. C. Gentry ◽  
A. M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flat Plate ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Delta Wing ◽  
Leading Edge ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Vortex Strength

Using delta wings placed at the leading edge of a flat plate, streamwise vortices are generated that modify the flow; the same wings are also used to modify a developing channel flow. Local and average measurements of convection coefficients are obtained using naphthalene sublimation, and the structure of the vortices is studied using flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement of the channel flow is also investigated. In regions where a vortex induces a surface-normal inflow, the local heat transfer coefficients are found to increase by as much as 300 percent over the baseline flow, depending on vortex strength and location relative to the boundary layer. Vortex strength increases with Reynolds number, wing aspect ratio, and wing attack angle, and the vortex strength decays as the vortex is carried downstream. Considering the complete channel surface, the largest spatially averaged heat average heat transfer enhancement is 55 percent; it is accompanied by a 100 percent increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator.

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