Steady and Unsteady Air Impingement Heat Transfer for Electronics Cooling Applications

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Mehmet Arik ◽  
Rajdeep Sharma ◽  
Jason Lustbader ◽  
Xin He
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Heat Removal ◽  
Synthetic Jets ◽  
Pulsating Flow ◽  
Coefficient Of Performance ◽  
Superior Performance ◽  
Number Range ◽  
Impingement Heat Transfer ◽  
Steady Jets

This paper focuses on two forced convection methods—steady jet flow and pulsating flow by synthetic jets—that can be used in applications requiring significant amounts of heat removal from electronics components. Given the dearth of available data, we have experimentally investigated steady jets and piezoelectrically driven synthetic jets that provide pulsating flow of air at a high coefficient of performance. To mimic a typical electronics component, a 25.4-mm × 25.4-mm vertical heated surface was used for heat removal. The impingement heat transfer, in the form of Nusselt number, is reported for both steady and unsteady jets over Reynolds numbers from 100 to 3000. The effect of jet-to-plate surface distance on the impingement heat transfer is also investigated. Our results show that synthetic jets can provide significantly higher cooling than steady jets in the Reynolds number range of 100 to 3000. We attribute the superior performance of synthetic jets to vortex shedding associated with the unsteady flow.

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.

Numerical Investigation of a Liquid Droplet Impinging on a Heated Surface

2009 ◽  
Author(s):  
Andres Diaz ◽  
Alfonso Ortega ◽  
Ryan Anderson
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Fundamental Problem ◽  
Water Drop ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Heat Removal ◽  
Droplet Spreading ◽  
Droplet Shape ◽  
Spreading Dynamics

Previous studies, most of them experimental, reveal that the cooling effectiveness of a water drop impinging on a heated surface depends on the wall temperature, droplet shape and velocity. All previous studies focus on the behavior of a droplet falling in a quiescent environment, such as still air. Evidence in the literature also shows that gas assisted droplet sprays, in which a gas phase propels the droplets, are more efficient in heat removal than sprays consisting of droplets alone. It is conjectured that this is due to an increase in the maximum droplet spreading diameter upon impact, a thinner film, and consequently an increase in the overall heat transfer coefficient. Recent experiments in the author’s group [1, 2] show that the carrier gas jet strongly influences droplet spreading dynamics by imposing normal and shear forces on the liquid surface. The heat transfer is greatly augmented in the process, compared to a free falling droplet. To date, there has been no fundamental investigation of the physics of gas assisted spray cooling. To begin to understand the complicated process, this paper reports on a fundamental problem of a single liquid droplet that impinges on a heated surface. This paper contributes a numerical investigation of the problem using the volume of fluid (VOF) technique to capture droplet spreading dynamics and heat transfer in a single drop event. The fluid mechanics is investigated and compared to the experimental data. The greatest uncertainty in the simulation is in the specification of the contact angle of the advancing or receding liquid front, and in capturing the onset of the three-dimensional fingering phenomena.

Numerical Investigation of Impingement Heat Transfer on a Flat and Square Pin-Fin Roughened Plates

2013 ◽  
Author(s):  
Chaoyi Wan ◽  
Yu Rao ◽  
Xiang Zhang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Investigation ◽  
Pressure Loss ◽  
Transfer Characteristic ◽  
Number Range ◽  
Pin Fin ◽  
Pressure Distributions ◽  
Impingement Heat Transfer

A numerical investigation of the heat transfer characteristics within an array of impingement jets on a flat and square pin-fin roughened plate with spent air in one direction has been conducted. Four types of optimized pin-fin configurations and the flat plate have been investigated in the Reynolds number range of 15000–35000. All the computation results have been validated well with the data of published literature. The effects of variation of jet Reynolds number and different configurations on the distribution of the average and local Nusselt number and the related pressure loss have been obtained. The highest total heat transfer rate increased up to 162% with barely any extra pressure loss compared with that of the flat plate. Pressure distributions and streamlines have also been captured to explain the heat transfer characteristic.

Electronic Cooling Using Synthetic Jets

2005 ◽  
Author(s):  
Anna A. Pavlova ◽  
Michael Amitay
Keyword(s):  
Reynolds Number ◽  
Heated Surface ◽  
Low Frequency ◽  
Heat Removal ◽  
Jet Impingement ◽  
Constant Heat Flux ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Impingement Cooling ◽  
Jet Cooling

Efficiency of synthetic jet impingement cooling and the mechanisms of heat removal from a constant heat flux surface were investigated experimentally. The effects of jet’s formation frequency and Reynolds number at different nozzle-to-surface distances were investigated and compared to steady jet cooling. It was found that synthetic jets are up to three times more effective than steady jets at the same Reynolds number. For smaller distances, high formation frequency (f = 1200 Hz) synthetic jets remove heat better than low frequency (f = 420 Hz) jets, whereas low frequency jets are more effective at larger distances, with an overlapping region. Using PIV, it was shown that at small distances between the synthetic jet and the heated surface, the higher formation frequency jet is associated with accumulation of vortices before they impinge on the surface. For the lower frequency jet, the wavelength between coherent structures is so large that vortex rings impinge on the surface separately.

Numerical Investigation of Heat Transfer Enhancement in a Microchannel With Offset Micro Pin-Fins

2010 ◽  
Author(s):  
Haleh Shafeie ◽  
Omid Abouali ◽  
Khosrow Jafarpour
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Numerical Study ◽  
Removal Rate ◽  
Heat Removal ◽  
Coefficient Of Performance ◽  
Navier Stokes ◽  
Liquid Region ◽  
Noticeable Effect ◽  
Pin Fins

This paper presents a numerical study of laminar forced convection in microchannels network heat sinks with fabricated offset pin-fins. A 3-dimensional mathematical model, for conjugate heat transfer in both solid and liquid is presented. For this aim the Navier-Stokes and energy equations for the liquid region and the energy equation for the solid region are solved simultaneously and the pressure drop together heat transfer characteristics of a single-phase microchannel heat sink were investigated. A typical microchannel was selected and it was shown that using offset pin-fins has a noticeable effect and heat removal rate can be increased using this technique. However the pressure drop is also highly increasing which leads to a low coefficient of performance for microchannel with this type of micro-structure.

Heat transfer augmentation in a radial curved microchannel

2021 ◽  
pp. 095440892110412
Author(s):  
Nitin Kumar Mamidi ◽  
Karthik Balasubramanian ◽  
Kiran Kumar Kupireddi ◽  
V P Chandramohan ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Characteristics ◽  
Heat Removal ◽  
Heat Transfer Analysis ◽  
Cooling Systems ◽  
Number Range ◽  
Cooling Performance ◽  
Curvature Ratio ◽  
Reynolds Number Range

Rapid advancement toward miniaturization has emerged with confront for superior heat dissipation techniques. Of all the available cooling systems, microchannel-based cooling systems stand out to provide better cooling performance through superior heat removal abilities. In the present study, the cooling performance and hydraulic flow characteristics of a radial curved microchannel with three curvature ratios were numerically investigated and compared with a radial straight microchannel. Unlike the conventional straight microchannels, curved channels possess better fluid mixing as a result of the centrifugal force caused due to curvature. This phenomenon has a significant effect on heat transfer and fluid flow characteristics. Work on radial curved microchannels has been scarce and there is a lot of potential to augment the heat transfer with lower pumping power particularly with a central inlet. A three-dimensional conjugate heat transfer analysis was carried out for three radial curved microchannels and a radial straight microchannel using the ANSYS Fluent commercial software with the Reynolds number range of 125–275. The results showed a Nusselt number increment of 36.38% for radial curved microchannels when compared to the radial straight microchannel. Further, the lowest average wall temperature was noted for the radial curved microchannel with a curvature ratio of 0.17 which was 15.63 °C lower when compared to that in a radial straight microchannel for the same Reynolds number. Contours of velocity and temperature are presented at various locations along the stream to aid the results. The overall performance of all three radial curved microchannels was found to be higher than that of the radial straight microchannel in the Reynolds number range considered, out of which the maximum performance factor of 1.245 was obtained for the radial curved microchannel with a curvature ratio of 0.17 as compared to the radial straight microchannel.

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.

Effect of Electric Fields on Two-Phase Impingement Heat Transfer

2007 ◽  
Author(s):  
Xin Feng ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Electric Fields ◽  
Capillary Flow ◽  
Heated Surface ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Two Phase ◽  
Transfer Rates ◽  
Impingement Heat Transfer

The effect of electric fields applied to two-phase impingement heat transfer is explored for the first time. The application of an electric field between a capillary and heated surface results in the ability to control the free boundary flow from discreet drops to jets to sprays. Through an experimental study, the impingement heat transfer was evaluated over a range of operating and geometrical parameters using subcooled ethanol as the working fluid. The ability to change the mode of impinging mass did change the surface heat transfer. The characteristics of the impinging mass on heat transfer was dependent on capillary flow rate, applied voltage, capillary to heated surface spacing, capillary geometry, and heat flux. Enhancement occurred primarily at low heat fluxes (below 30 W/cm2) under ramified spray conditions where the droplet momentum promoted thin films on the heated surface. Higher heat fluxes resulted in greater vapor momentum from the surface minimizing the effect of different modes. However, under ramified spray conditions less mass was impacting the heated surface showing that heat transfer rates at higher heat fluxes were achievable with less mass, resulting in greater evaporation efficiency.

Numerical Simulation of Local Heat Transfer and Scaling of a Synthetic Impinging Jet in a Canonical Geometry

2011 ◽  
Author(s):  
Luis Silva ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Heated Surface ◽  
Vortex Pair ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Synthetic Jets ◽  
Navier Stokes ◽  
Dependent Flow ◽  
Finite Volume Approach

Synthetic jets are generated by an equivalent inflow and outflow of fluid into a system. Even though such a jet creates no net mass flux, net positive momentum can be produced because the outflow momentum during the first half of the cycle is contained primarily in a vigorous vortex pair created at the orifice edges whereas in the backstroke, the backflow momentum is weaker, despite the fact that mass is conserved. As a consequence of this, the approach can be potentially utilized for the impingement of a cooling fluid over a heated surface. In the present study, a canonical geometry is presented, in order to study the flow and heat transfer of a purely oscillatory jet that is not influenced by the manner in which it is produced. The unsteady Navier-Stokes equations and the convection-diffusion equation were solved using a fully unsteady, two-dimensional finite volume approach in order to capture the complex time dependent flow field. A detailed analysis was performed on the correlation between the complex velocity field and the observed wall heat transfer. A fundamental frequency, in addition to the jet forcing frequency, was found, and was attributed to the coalescence of consecutive vortex pairs. In some instances, this vortex pairing can lead to zones of low heat transfer. Two point correlations showed that the Nusselt number Nu, showed stronger correlation with the vertical velocity v although the spatial-temporal dependencies are not yet fully understood. It was found that the Reynolds number and the Strouhal number, are sufficient to successfully scale the problem at larger dimensions and this is presently being exploited in order to design validation experiments using jets large enough to allow careful local measurements.

Electrohydrodynamic Microfabricated Ionic Wind Pumps for Thermal Management Applications

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Andojo Ongkodjojo Ong ◽  
Alexis R. Abramson ◽  
Norman C. Tien
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Management ◽  
High Reliability ◽  
Semiconductor Industry ◽  
Heat Removal ◽  
Coefficient Of Performance ◽  
Air Cooling ◽  
Ionic Wind

This work demonstrates an innovative microfabricated air-cooling technology that employs an electrohydrodynamic (EHD) corona discharge (i.e., ionic wind pump) for electronics cooling applications. A single, microfabricated ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. A grid structure on the collector electrodes can enhance the overall heat-transfer coefficient and facilitate an IC compatible batch process. The optimized devices studied exhibit an overall device area of 5.4 mm × 3.6 mm, an emitter-to-collector gap of ∼0.5 mm, and an emitter curvature radius of ∼12.5 μm. The manufacturing process developed for the device uses glass wafers, a single mask-based photolithography process, and a low-cost copper-based electroplating process. Various design configurations were explored and modeled computationally to investigate their influence on the cooling phenomenon. The single devices provide a high heat-transfer coefficient of up to ∼3200 W/m2 K and a coefficient of performance (COP) of up to ∼47. The COP was obtained by dividing the heat removal enhancement, ΔQ by the power consumed by the ionic wind pump device. A maximum applied voltage of 1.9 kV, which is equivalent to approximately 38 mW of power input, is required for operation, which is significantly lower than the power required for the previously reported devices. Furthermore, the microfabricated single device exhibits a flexible and small form factor, no noise generation, high efficiency, large heat removal over a small dimension and at low power, and high reliability (no moving parts); these are characteristics required by the semiconductor industry for next generation thermal management solutions.

Sign in / Sign up

Export Citation Format

Share Document