Design and Thermal Characteristics of a Synthetic Jet Ejector Heat Sink

2004 ◽  
Vol 127 (2) ◽  
pp. 172-177 ◽  
Author(s):  
Raghav Mahalingam ◽  
Ari Glezer
Keyword(s):  
Thermal Resistance ◽  
Steady Flow ◽  
Heat Sink ◽  
Power Dissipation ◽  
Ambient Air ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Electromagnetic Actuators ◽  
Air Jet

The design and thermal performance of a synthetic-air-jet-based heat sink for high-power dissipation electronics is discussed. Each fin of a plate-fin heat sink is straddled by a pair of two-dimensional synthetic jets, thereby creating a jet ejector system that entrains cool ambient air upstream of the heat sink and discharges it into the channels between the fins. The jets are created by periodic pressure variations induced in a plenum by electromagnetic actuators. The performance of the heat sink is assessed using a thermal test die encased in a heat spreader that is instrumented with a thermocouple. The case-to-ambient thermal resistance under natural convection with the heat sink is 3.15°C∕W. Forced convection with the synthetic jets enables a power dissipation of 59.2W at a case temperature of 70°C, resulting in a case-to-ambient thermal resistance of 0.76°C∕W. The synthetic-jet heat sink dissipates ∼40% more heat compared to steady flow from a ducted fan blowing air through the heat sink. The synthetic jets generate a flow rate of 4.48 CFM through the heat sink, resulting in 27.8 W/CFM and thermal effectiveness of 0.62. The effect of fin length on the thermal resistance of the heat sink is discussed. Detailed measurements on an instrumented heat sink estimate that the average heat transfer coefficients in the channel flow between the fins is 2.5 times that of a steady flow in the ducts at the same Reynolds Number.

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).

Experimental and numerical studies of synthetic jets driven by a dual-diaphragm piezoelectric actuator

2009 ◽  
Vol 223 (6) ◽  
pp. 1393-1400 ◽  
Author(s):  
A-S Yang ◽  
J-J Ro ◽  
W-H Chang
Keyword(s):  
Moving Boundary ◽  
Active Flow Control ◽  
Vortex Pair ◽  
Ambient Air ◽  
Lateral Spreading ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Visualization System ◽  
Air Jet ◽  
Centre Line

The applications of piezoelectric synthetic jet actuators have shown great potential as active flow control devices. The objective of this study is to investigate the flow phenomenon of a synthetic jet generated by a dual-diaphragm piezo-driven actuator. In this analysis, the computational approach adopted unsteady three-dimensional conservation equations of mass and momentum for examining the development process of synthetic jets. The moving boundary was also treated to represent the motion of the piezo diaphragm. Experimentally, a flow visualization system was employed to acquire the particle-streak images scattered from red fluorescent spheres for observing the synthetic jet flow. The jet velocity along the centre-line was also measured by using a hot-wire anemometer. The system test results demonstrated a satisfactory functioning of the actuator for producing synthetic jets. The predictions were then compared with the visualized particle-streak images and the measured centre-line velocity of the synthetic jet to validate the computer software. In the near-field, both simulation results and experimental observations revealed the time-cyclical formation and advection of a vortex pair in a full sinusoidal actuation cycle at an operating frequency of 4 Hz. When the vortex pair travelled well downstream, the ambient air from the vicinity of the slot was entrained into the cavity of the actuator. However, the overall far-field flow pattern, characterized by longitudinal decay of the centre-line velocity and lateral spreading, resembled a conventional continuous air-jet in essence.

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.

Cooling Performance Evaluation of Synthetic Jet Based Thermal Solution Module

2015 ◽  
Vol 7 (3) ◽  
Author(s):  
Ahmad Jalilvand ◽  
Masataka Mochizuki ◽  
Yuji Saito ◽  
Yoji Kawahara ◽  
Randeep Singh ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Sink ◽  
Electronic Devices ◽  
Heat Removal ◽  
Synthetic Jet ◽  
Air Jet ◽  
Convective Thermal ◽  
Thermal Solution ◽  
Pipe Heat

The convective thermal resistance which represents the heat removal from the heat sink surface of a heat pipe/heat sink module to mean coolant flow temperature is often a dominant contributor to the overall thermal resistance of a heat pipe/heat sink module or remote heat exchange (RHE). RHE is a thermal solution module composed of a heat spreader, thin flattened heat pipe with low profile heat sink which is widely used for the thermal management of compact portable electronic devices. Minimizing the convective thermal resistance at the heat sink of RHE as well as thickness reduction is often an important objective for the thermal designers. Recently, an alternate air mover system which operates based on piezoelectricity is developed. This device is called dual cooling jet (DCJ) in short which can be fabricated with very small thickness down to 1.0 mm. Thin DCJ as a synthetic jet generates air jet with more than 7 m/s air flow velocity which is promising for the increasing demands of thinner next generation portable electronic devices. DCJ is a promising device to dissipate the heat from the heat sink of a RHE. In this work, the performance of RHE is evaluated when heat is dissipated from its heat sink by DCJ. The results are compared with conventional rotary fan. The results show that more than 12 W of heat can be dissipated by DCJ which can easily compete with some commercialized rotary mini blowers while having much smaller thickness. Various configuration of heat sink–DCJ combinations as well as size and shape of both heat sink and DCJ are tested and based on thermal resistance data, cooling effectiveness of DCJ is studied.

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.

scholarly journals Experimental Investigations of Different Loudspeakers Applied as Synthetic Jet Actuators

Actuators ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 224
Author(s):  
Paweł Gil ◽  
Joanna Wilk
Keyword(s):  
Thermal Resistance ◽  
Resonance Frequency ◽  
Sound Pressure Level ◽  
Heat Sink ◽  
Sound Pressure ◽  
Pressure Level ◽  
Synthetic Jet ◽  
Experimental Investigations ◽  
Driving Frequency ◽  
Jet Velocity

The paper presents the preliminary results of the experimental investigation of four various loudspeakers used for driving the synthetic jet actuator. The parameters, characteristic synthetic jet velocity, pressure inside the cavity, device sound pressure level (SPL), and the heat sink thermal resistance, were presented for various input power and driving frequency. The resonance frequency was determined based on electrical impedance. The highest synthetic jet momentum velocity was achieved at diaphragm resonance frequency. The maximum sound pressure level was observed, also at resonant frequency. For the same real power delivered to the actuator and for its resonance frequency, the heat sink thermal resistance had the lowest value for the specific loudspeaker. In turn, the synthetic jet velocity reached maximum for this actuator. For all actuators tested, the sound pressure level was dependent on momentum velocity.

scholarly journals Heat Transfer From a Finned Surface in Ducted Air Jet Suction and Impingement

1999 ◽  
Vol 122 (3) ◽  
pp. 282-285 ◽  
Author(s):  
Luis A. Brignoni ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Jet Impingement ◽  
Target Distance ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Air Jet ◽  
Finned Surface ◽  
Different Diameters

Experimental measurements were obtained to characterize the thermal performance of ducted air suction in conjunction with a pin-fin heat sink. Four single nozzles of different diameters and two multiple-nozzle arrays were studied at a fixed nozzle-to-target distance, for different turbulent Reynolds numbers 5000⩽Re⩽20,000. Variations of nozzle-to-target distance, i.e., open area, in ducted suction were found to have a strong effect on heat transfer especially with the larger diameter single nozzle and both multiple-nozzle arrays. Enhancement factors were computed with the heat sink in suction flow, relative to a bare surface, and were in the range of 8.3 to 17.7, with the largest value being obtained for the nine-nozzle array. Results from the present study on air jet suction are compared with previous experiments with air jet impingement on the pin-fin heat sink. Average heat transfer coefficients and thermal resistance values are reported for the heat sink as a function of Reynolds number, air flow rate, and pumping power. [S1043-7398(00)00903-8]

Heat Transfer Measurements of Impinging Synthetic Air Jet

2007 ◽  
Author(s):  
Alan McGuinn ◽  
Tadhg S. O’Donovan ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Impinging Jets ◽  
Copper Plate ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Driving Frequency ◽  
Promising Alternative ◽  
Air Jet ◽  
Cooling Effects

The implementation of synthetic jets for use in the cooling of electronics is a relatively new technology. It is well established that effective rates of cooling can be achieved using conventional steady flow impinging jets. However it has been shown that synthetic jets can deliver similar cooling effects without the need for an air supply system and therefore represent an extremely promising alternative for thermal management applications. A study has been undertaken of the heat transfer distribution to an impinging synthetic jet flow. The jet is directed at a heated copper plate, which approximates a uniform wall temperature. Nusselt number profiles generated by the synthetic jet for various Reynolds numbers and heights above the plate were obtained. Time varying velocity measurements were also carried out to provide information about the flow characteristics of the synthetic jet and to aid with evaluation of the heat transfer data. For continuous jets mean heat transfer distributions have been shown to have a direct relation to jet velocity profiles, however, for synthetic jets fluctuations in local heat flux illustrate a significant dependence on the driving frequency.

Experimental Study on the Effect of Synthetic Jets on Flow Boiling Heat Transfer in Microchannels

2012 ◽  
Author(s):  
Ruixian Fang ◽  
Jamil Khan
Keyword(s):  
Heat Sink ◽  
Flow Boiling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Driving Voltage ◽  
Micro Channel ◽  
Two Phase ◽  
Synthetic Jet Actuator ◽  
Micro Channels ◽  
Boiling Flow

Two-phase flow instabilities in micro-channel exhibit pressure and temperature fluctuations with different frequencies and amplitudes. An active way to suppress the dynamic instabilities in the boiling micro-channels is to introduce synthetic jets into the channel fluid. Thus the bubbles can be condensed before they clog the channel and expand upstream causing flow reversal. The present work experimentally investigated the effect of synthetic jets on the suppression of flow boiling instabilities exhibited in a micro-channel heat sink. The heat sink is consisted of five parallel rectangular microchannels measured 500 μm wide, 500 μm deep each. An array of synthetic jets was placed right above the micro-channels with each channel corresponds to 8 jet orifices. The strength and frequency of the jets are controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. Tests were performed with synthetic jets operating at 80 Hz and 150 Hz respectively. It is found that the bubbles were effectively condensed inside the jet cavity. The boiling flow reversals were notably delayed by the synthetic jets. Meanwhile, the pressure fluctuation amplitudes were substantially reduced. Test results were analyzed and discussed in detail.

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