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.

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.

Wing tip vortex control using synthetic jets

2006 ◽  
Vol 110 (1112) ◽  
pp. 673-681 ◽  
Author(s):  
P. Margaris ◽  
I. Gursul
Keyword(s):  
Synthetic Jet ◽  
Synthetic Jets ◽  
Tip Vortex ◽  
Particle Image Velocimetry System ◽  
Driving Frequency ◽  
Velocity Measurements ◽  
Vortex Control ◽  
Image Velocimetry ◽  
Wing Tip ◽  
Jet Blowing

AbstractAn experimental investigation was conducted to study the effect of synthetic jet (oscillatory, zero net mass flow jet) blowing near the wing tip, as a means of diffusing the trailing vortex. Velocity measurements were taken, using a Particle Image Velocimetry system, around the tip and in the near wake of a rectangular wing, which was equipped with several blowing slots. The effect of the synthetic jet was compared to that of a continuous jet blowing from the same configurations. The results show that the use of synthetic jet blowing is generally beneficial in diffusing the trailing vortex and comparable to the use of continuous jet. The effect was more pronounced for the highest blowing coefficient used. The driving frequency of the jet did not generally prove to be a significant parameter. Finally, the instantaneous and the phase-locked velocity measurements helped explain the different mechanisms employed by the continuous and synthetic jets in diffusing the trailing vortex.

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.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

scholarly journals A Numerical and Experimental Investigation of Dimple Effects on Heat Transfer Enhancement with Impinging Jets

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 813 ◽  
Author(s):  
Parkpoom Sriromreun ◽  
Paranee Sriromreun
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Transfer Enhancement ◽  
Air Flow ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Transfer Enhancement ◽  
Test Plate ◽  
Hot Surface

This research was aimed at studying the numerical and experimental characteristics of the air flow impinging on a dimpled surface. Heat transfer enhancement between a hot surface and the air is supposed to be obtained from a dimple effect. In the experiment, 15 types of test plate were investigated at different distances between the jet and test plate (B), dimple diameter (d) and dimple distance (Er and Eθ). The testing fluid was air presented in an impinging jet flowing at Re = 1500 to 14,600. A comparison of the heat transfer coefficient was performed between the jet impingement on the dimpled surface and the flat plate. The velocity vector and the temperature contour showed the different air flow characteristics from different test plates. The highest thermal enhancement factor (TEF) was observed under the conditions of B = 2 d, d = 1 cm, Er= 2 d, Eθ = 1.5 d and Re = 1500. This TEF was obtained from the dimpled surface and was 5.5 times higher than that observed in the flat plate.

Numerical Evaluation of the Effectiveness of Micro Pulsating Water Jets for Cooling of Microchips

2009 ◽  
Author(s):  
F. L. Hew ◽  
V. Timchenko ◽  
J. A. Reizes ◽  
E. Leonardi
Keyword(s):  
Heat Transfer ◽  
Minimum Temperature ◽  
Impinging Jets ◽  
Synthetic Jet ◽  
Maximum Temperature ◽  
Distinct Advantage ◽  
Synthetic Jet Actuator ◽  
Synthetic Jet Actuators ◽  
Micro Channels ◽  
Jet Actuators

In this study the effects of having multiple synthetic jet actuators and multiple orifices in a single jet actuator on creating better flow mixing and improving heat transfer in micro-channels have been investigated numerically. Unsteady computations of laminar flow have been performed for two dimensional configurations of micro-channel open at either end. A constant heat flux of 1 MWm−2 at the top of the silicon wafer represented the heat generated by the microchip. Synthetic jet actuators were attached to the bottom wall of the channel, with the 50 μm wide orifice. It is shown that by using double orifices single synthetic jet actuator, the heat transfer enhancement in micro-channels can be greatly improved. At the end of 30 cycles of actuation, the maximum temperature in the wafer has been reduced by approximately 27 K and the minimum temperature on the bottom of the wafer has been reduced by approximately 19 K in comparison with the steady flow values. In comparison with a single orifice synthetic jet actuator, double orifices synthetic jet actuator led to an additional 10 K reduction of the maximum temperature in wafer and 4 K reduction of minimum temperature on the interface of the wafer and water. It was demonstrated that the number of synthetic jet actuators is not the main factor influencing the thermal performance. The crucial factor is the number of impinging jets generated from the orifice which encourages better mixing in the flow. However, there is a distinct advantage associated with having multiple jet actuators in that out of phase flow could be generated which led to even lower temperatures than the in-phase jets.

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.

Study on the Flow Characteristics of Synthetic Jets Near a Rigid Plane Boundary

2011 ◽  
Author(s):  
Ryota Tsunoda ◽  
Koichi Nishibe ◽  
Yuki Fujita ◽  
Kotaro Sato ◽  
Kazuhiko Yokota ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Maximum Velocity ◽  
Stokes Number ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Plane Boundary ◽  
Jet Flows ◽  
Rigid Boundary ◽  
Wire Method ◽  
Rigid Plane

The jet flows have been applied to various fields to control the flow separation. Over the last decade, several studies have investigated synthetic jets. However, there are still many clarifications needed, including details of the structure and Coanda effect of synthetic jets. The present study clarifies some fundamental flow characteristics of free synthetic jets and synthetic jets near a rigid boundary by conducting an experiment and numerical simulations. As the main results, it is found that the velocity distribution of free synthetic jets depends on K = Re/S2 (the ratio of the Reynolds number to the square of the Stokes number) and can be identified by the maximum velocity at the centerline and the jet half-width. Flow visualization is carried out applying the smoke wire method. In addition, it is confirmed that the flow characteristics of the synthetic jet near a rigid boundary and re-attachment length of the synthetic jet are determined not only by H1/b0 (normalized step heights) but also K.

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