Interaction of Synthetic Jet Cooling Performance With Gravity and Buoyancy Driven Flows

2007 ◽  
Author(s):  
Mehmet Arik ◽  
Yogen Utturkar ◽  
Mustafa Gursoy
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Jet Cooling ◽  
Impingement Heat Transfer ◽  
Buoyancy Driven Flows ◽  
Experimental Findings ◽  
Meso Scale

Meso scale cooling devices have been of interest for low form factor, tight space, and high COP thermal management problems. A candidate meso scale device, known as synthetic jets, operates with micro fluidic principles and disturbs the boundary layer causing significant heat transfer over conventional free convective heat transfer in air. Previous papers have dealt with the impingement and cross flow, but did not study mixed convection for synthetic jet with natural convection. In the present study, we discuss the results of an experimental study to investigate the interplay between jet orientations with respect to gravity, elevated temperature conditions, and synthetic jet heat dissipation capacity. Experiments were performed by placing synthetic at different positions around a square, 25.4mm heated flat surface. The flow physics behind the experimental findings is discussed. It is found that impingement heat transfer outperformed more than 30% compared to other orientations. The jet showed about 15% sensitivity to angular orientations.

scholarly journals NUMERICAL STUDY OF COOLING BY TANGENTIAL SYNTHETIC JET

2015 ◽  
Vol 14 (1) ◽  
pp. 47
Author(s):  
F. Munhoz ◽  
C. Y. Y. Lee ◽  
F. L. D. Alves
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Conventional Technique ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Jet Cooling ◽  
Processing Power ◽  
Equivalent Mass ◽  
Heated Element

Modern electronics are becoming more compact and with higher processing power, which translates into a demand for higher heat dissipation. Current electronic "coolers," which are based on the combination of fans and heat sinks, are becoming unable to provide sufficient heat dissipation since they rely primarily on generating large volumetric flowrates of air to achieve their results. As an alternative, synthetic jets are under consideration due to their known property to enhance turbulence and heat transfer. Synthetic jets are produced by the oscillation of a membrane in a sealed cavity equipped with an orifice. For this study, a numerical model of channel mounted with a heating element on one surface and a synthetic jet directed to blow along the wall was constructed on ANSYS CFX. Heat dissipation provided by the synthetic jet was analyzed with respect to changes in Reynolds number, pulsing frequency and placement of the heated element. Results were compared to a conventional technique represented by a steady channel flow of equivalent mass flow rate to the average flow induced by the synthetic jet. Results showed that the synthetic jet formed a thin layer of intense vorticity along the targeted surface with cooling greatly outperforming conventional techniques. Synthetic jet cooling was also determined to be most affected by jet velocity and Reynolds number while pulsing frequency and placement of the heated element were not as influential.

Flow Field and Heat Transfer of an Impinging Synthetic Jet in the Presence of Cross-Flow: Application of SAS and DES Approaches

2021 ◽  
pp. 095440892110644
Author(s):  
Farzad Bazdidi–Tehrani ◽  
Ali Saadniya ◽  
Soroush Rashidzadeh
Keyword(s):  
Heat Transfer ◽  
Flow Velocity ◽  
Active Flow Control ◽  
Experimental Studies ◽  
Cross Flow ◽  
Numerical Data ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Detached Eddy Simulation ◽  
Cross Flow Velocity

Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

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.

An Experimental Study of a Synthetic Jet in Cross Flow in a Microchannel

2010 ◽  
Author(s):  
Alexander Sinclair ◽  
John Reizes ◽  
Victoria Timchenko ◽  
Gary Rosengarten
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Cross Flow ◽  
Oscillatory Solution ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Square Duct ◽  
Transfer Rates ◽  
Mixing Performance ◽  
Jet In Cross Flow

Laminar flow limits the mixing performance and heat transfer rates that occurs within microdevices. Synthetic jets in the microscale could disrupt laminar flow and improve the performance of such devices. In this paper a synthetic microjet integrated in a microchannel was designed and fabricated using micromachining techniques. The channel flow was driven by a syringe pump at a rate of 1.39μL/s and the device was actuated using a piezoceramic disc at a frequency of 600Hz. Flow fields were measured phase locked to the actuation cycle using the MicroPIV technique in the mid plane of the jet. The resultant fields revealed a jet with a largest velocity of 2.3m/s. The average velocity during expulsion was estimated to be 0.73m/s using a comparison to the oscillatory solution to flow in a square duct. Measurements at different phases in the cycle revealed a jet strong enough to impinge on the opposing wall and the growth and decay of a pair of vortices formed at the edge of the orifice. It was also shown that the synthetic jet significantly altered the flow patterns showing promising signs for enhancing mixing and heat transfer in microchannels.

Effect of Synthetic Jets Over Natural Convection Heat Sinks

2008 ◽  
Author(s):  
Mehmet Arik ◽  
Yogen Utturkar ◽  
Murat Ozmusul
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Heat Sinks ◽  
Junction Temperature ◽  
Allowable Limit

In moderate power electronics applications, the most preferred way of thermal management is natural convection to air with or without heat sinks. Though the use of heat sinks is fairly adequate for modest heat dissipation needs, it suffers from some serious performance limitations. Firstly, a large volume of the heat sink is required to keep the junction temperature at an allowable limit. This need arises because of the low convective film coefficients due to close spacing. In the present computational and experimental study, we propose a synthetic jet embedded heat sink to enhance the performance levels beyond two times within the same volume of a regular passive heat sink. Synthetic jets are meso-scale devices producing high velocity periodic jet streams at high velocities. As a result, by carefully positioning of these jets in the thermal real estate, the heat transfer over the surfaces can be dramatically augmented. This increase in the heat transfer rate is able to compensate for the loss of fin area happening due to the embedding of the jet within the heat sink volume, thus causing an overall increase in the heat dissipation. Heat transfer enhancements of 2.2 times over baseline natural convection cooled heat sinks are measured. Thermal resistances are compared for a range of jet operating conditions and found to be less than 0.9 K/W. Local temperatures obtained from experimental and computational agreed within ± 5%.

scholarly journals Heat Transfer in Adjacent Interacting Impinging Synthetic Jets

2009 ◽  
Author(s):  
Tim Persoons ◽  
Tadhg S. O’Donovan ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Normal Velocity ◽  
Mean Flow ◽  
Stroke Length ◽  
Cooling Performance ◽  
Single Jet

An impinging synthetic jet can attain heat transfer rates comparable to a continuous jet, without net mass input. However it needs a forced cross-flow to supply fresh cooling medium. The vectoring effect of adjacent synthetic jets allows directing the flow by changing the phase between the jets. This study uses the vectoring effect of two adjacent synthetic jets to draw in fresh air, while maintaining high impingement cooling performance. The experimental approach applies infrared thermography and particle image velocimetry to quantify the local convective heat transfer and flow field, respectively. The heat transfer profiles for various phase differences have been compared to the mean flow field and wall-normal velocity fluctuation intensity. For a fixed operating point (stroke length and Reynolds number) and geometry, the cooling performance has been optimised for phase and jet-to-surface spacing, resulting in about 90% enhancement of the maximum and overall cooling rate compared to a single jet, without the need for external cross-flow forcing.

Reduced-Order Investigation of Synthetic Jet Cooling for Electronic Applications

2009 ◽  
Author(s):  
Rao G. Dhananjaya ◽  
Ajay Rao ◽  
Yogen Utturkar ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
System Level ◽  
Heat Transfer Analysis ◽  
Time Saving ◽  
Reduced Order ◽  
Jet Cooling ◽  
Zero Net Mass Flux

Synthetic jets are meso-scale devices operating at zero-net-mass-flux principle. These devices produce periodic jet-like streams, which have local velocities 10–20 times greater than the average fan velocities. As a result, positioning one or more of these jets close to a heat sink causes high-velocity air currents in tightly spaced fin gaps and enhances the surface heat transfer. A reduced-order modeling (ROM) approach was followed in simulating the heat transfer analysis of commercial heat sink with synthetic jet. Unsteady state results are matched with steady state results as part of the ROM approach. The methodology is implemented on two problems (i.e canonical problem of jet impinging perpendicularly on a flat plate and jet blowing on a commercial heat sink). Results from ROM for two cases are validated against experimental results. It is found that, this approach provides 90% time saving within ±5% accuracy. Modeling via ROM is much faster and cheaper computationally; hence this approach can be used for studying the system-level convective heat transfer enhancement of heat sinks using synthetic jets.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

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