An Experimental and Computational Sensitivity Analysis of Synthetic Jet Cooling Performance

2006 ◽  
Author(s):  
Yogen Utturkar ◽  
Mehmet Arik ◽  
Mustafa Gursoy
Keyword(s):  
Numerical Models ◽  
Heated Surface ◽  
Cross Flow ◽  
Heat Removal ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Thermal Source ◽  
Cooling Performance ◽  
Jet Cooling ◽  
The Impact

Synthetic jets are meso or micro scale fluidic devices, which operate on the "zero-net-mass-flux" principle. However, they impart a positive net momentum flux to the external environment, and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. The rate of heat removal from the thermal source is expected to depend on the location, orientation, strength, and shape of the jet. In the current study, we investigate the impact of jet location and orientation on the cooling performance via time-dependent numerical simulations, and verify the same with experimental results. We firstly present the experimental study along with the findings. Secondly, we present the numerical models/results, which are compared with the experiments to gain the confidence in the computational methodology. Finally, a sensitivity evaluation has been performed by altering the position and alignment of the jet with respect to the heated surface. Two prime orientations of the jet have been considered, namely, perpendicular and cross jet impingement on the heater. It is found that if jet is placed at an optimum location in either impingement or cross flow position, it can provide similar enhancement.

An Experimental and Computational Heat Transfer Study of Pulsating Jets

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Yogen Utturkar ◽  
Mehmet Arik ◽  
Charles E. Seeley ◽  
Mustafa Gursoy
Keyword(s):  
Numerical Models ◽  
Heated Surface ◽  
Cross Flow ◽  
Heat Removal ◽  
Jet Impingement ◽  
Synthetic Jets ◽  
Thermal Source ◽  
Zero Net Mass Flux ◽  
Pulsating Jets ◽  
The Impact

Synthetic jets are meso or microscale fluidic devices, which operate on the “zero-net-mass-flux” principle. However, they impart a positive net momentum flux to the external environment and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. The rate of heat removal from the thermal source is expected to depend on the location, orientation, strength, and shape of the jet. In the current study, we investigate the impact of jet location and orientation on the cooling performance via time-dependent numerical simulations and verify the same with experimental results. We firstly present the experimental study along with the findings. Secondly, we present the numerical models/results, which are compared with the experiments to gain the confidence in the computational methodology. Finally, a sensitivity evaluation has been performed by altering the position and alignment of the jet with respect to the heated surface. Two prime orientations of the jet have been considered, namely, perpendicular and cross jet impingement on the heater. It is found that if jet is placed at an optimum location in either impingement or cross flow position, it can provide similar enhancements.

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.

Assessment of Cooling Enhancement of Synthetic Jet in Conjunction With Forced Convection

2007 ◽  
Author(s):  
Yogen Utturkar ◽  
Mehmet Arik ◽  
Mustafa Gursoy
Keyword(s):  
Forced Convection ◽  
Cross Flow ◽  
Electronics Cooling ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Channel Height ◽  
Large Area ◽  
Complete Replacement ◽  
Cooling Enhancement ◽  
The Impact

Synthetic jets are meso or micro fluidic devices, which operate on the “zero-net-mass-flux” principle. They impart a positive net momentum flux to the external environment, and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. As a result, recently their application as electronics cooling devices is gaining momentum. Traditionally, synthetic jets have been sought as a replacement to the fan in many electronic devices. However, in certain large applications, complete replacement of the fan is not feasible, because it is necessary to provide the basic level of cooling over a large area of a printed assembly board. Such applications often pose a question whether synthetic jet would be able to locally provide reasonable enhancement over the forced convection of the fan flow. In the present study, we present the cooling performance of synthetic jets complementing forced convection from a fan. Both experiments and CFD computations are performed to investigate the interaction of the jet flowfield with a cross flow from fan. The inlet velocity, jet disk amplitude, and channel height are varied in the computational simulations to evaluate the impact of these changes on the cooling properties. Overall, both studies show that a synthetic jet is able to pulse and disrupt the boundary layer caused from fan flow, and improve heat transfer up to 4× over forced convection.

Impact of Sweeping Jet on Area-Averaged Impingement Heat Transfer

2019 ◽  
Author(s):  
Andrea Osorio ◽  
Justin Hodges ◽  
Husam Zawati ◽  
Erik J. Fernandez ◽  
Jayanta S. Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Thermal Inertia ◽  
Jet Impingement ◽  
Target Surface ◽  
Bottom Surface ◽  
Fluidic Oscillator ◽  
Surface Temperatures ◽  
Sweeping Motion ◽  
The Impact

Abstract A series of sweeping jet-impingement experiments are conducted over a circular heated surface, with a main objective of understanding the impact of the unique flow field on the resulting heat transfer. The sweeping motion of the fluidic oscillator is influenced by the sweeping frequency and sweeping angle where each is directly dependent on the geometric design (i.e. internal feedback loops, mixing chamber, etc.). The target surface consists of a heated copper disk, where heater power is supplied to the bottom surface of the disk and adjusted until a differential of 30°C is obtained between the jet and target surface temperatures. An energy balance over the target surface temperatures provides a means for calculating area-averaged heat transfer rate, hence Nusselt number. An increase in the sweeping jet’s thermal inertia initiates an augmentation in heat transfer due to sweeping motion of the jet across the target surface. PIV data was acquired for two jet configurations, confined and unconfined, so that the recirculation behavior can be determined. The fluidic oscillator is found to improve only at a low z/d. At large z/d (greater than 4 in this study), the fluidic oscillator adversely affects the heat transfer.

Unsteady CFD Analysis of Turbulent Flow and Heat Transfer in a Gas Turbine Blade Trailing Edge Subjected to Rotation

2012 ◽  
Author(s):  
Domenico Borello ◽  
Giovanni Delibra ◽  
Cosimo Bianchini ◽  
Antonio Andreini
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Heated Surface ◽  
Heat Removal ◽  
Gas Turbine Blade ◽  
Trailing Edge ◽  
Flow And Heat Transfer ◽  
The Impact

Internal cooling of gas turbine blade represents a challenging task involving several different phenomena as, among others, highly three-dimensional unsteady fluid flow, efficient heat transfer and structural design. This paper focuses on the analysis of the turbulent flow and heat transfer inside a typical wedge–shaped trailing edge cooling duct of a gas turbine blade. In the configuration under scrutiny the coolant flows inside the duct in radial direction and it leaves the blade through the trailing edge after a 90 deg turning. At first an analysis of the flow and thermal fields in stationary conditions was carried out. Then the effects of rotational motion were investigated for a rotation number of 0.275. The rotation axis here considered is normal to the inflow and outflow bulk velocity, representing schematically a highly loaded blade configuration. The work aimed to i) analyse the dynamic of the vortical structures under the influence of strong body forces and the constraints induced by the internal geometry and ii) to study the impact of such motions on the mechanisms of heat removal. The final aim was to verify the design of the equipment and to detect the possible presence of regions subjected to high thermal loads. The analysis is carried out using the well assessed open source code OpenFOAM written in C++ and widely validated by several scientists and researchers around the world. The unsteadiness of the flow inside the trailing edge required to adopt models that accurately reconstructed the flow field. As the computational costs associated to LES (especially in the near wall regions) largely exceed the available resources, we chose for the simulation the SAS model of Menter, that was validated in a series of benchmark and industrially relevant test cases and allowed to reconstruct a part of the turbulence spectra through a scale-adaptive mechanism. Assessment of the obtained results with steady-state k-ω SST computations and available experimental results was carried out. The present analysis demonstrated that a strong unsteadiness develops inside the trailing edge and that the rotation generated strong secondary motions that enhanced the dynamic of heat removal, leading to a less severe temperature distribution on the heated surface w.r.t the non rotating case.

Heat Transfer due to the Impingement of an Axisymmetric Synthetic Jet Emanating From a Circular Orifice: A Numerical Investigation of a Canonical Geometry

2013 ◽  
Author(s):  
M. Ebrahim ◽  
L. Silva ◽  
A. Ortega
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stokes Equations ◽  
Heated Surface ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Heated Wall ◽  
Driving Frequency ◽  
Surface Distance

Synthetic jets are produced by periodically injecting and ejecting fluid from an orifice. The mass flow rate is conserved in such a jet but net momentum flux is created due to the difference in the fluid dynamics at the orifice between the ejection and suction parts of each cycle. When pointed towards a heated surface, the synthetic jet can be used for cooling using the well-known advantages of jet impingement. In the present work, we have created a “canonical” jet in order to investigate the flow and heat transfer of a purely periodic synthetic jet which is not influenced by the manner in which it is generated. As such the “canonical” jet and the resulting heat transfer, can be considered to be dependent solely on the driving suction/ejection mechanisms at the orifice and thus can be examined independently of the actuator. The unsteady Navier-Stokes equations and the convection-diffusion equation were solved using a fully unsteady, laminar, three-dimensional axisymmetric finite volume approach in order to capture the complex time-dependent flow field created by different frequencies. The influence of jet-to-surface distance, Reynolds number, and driving frequency on heat transfer were investigated. Both stagnation and averaged Nusselt numbers were observed to be less dependent on frequency. Heat transfer was found to be higher at high Re numbers and low jet-to-surface distance. Results were compared with the steady continuous jet, experimental data of previous studies and the canonical slot synthetic jet at the same Reynolds number. A circular jet was found to be less efficient in removing heat over the heated wall than a slot synthetic jet.

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.

Numerical Simulation of a Novel Jet-Impingement Micro Heat Sink With Cross Flow Under Non Uniform Heating Condition

2011 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flat Plate ◽  
Heat Sink ◽  
Cross Flow ◽  
Jet Impingement ◽  
Jet Flow ◽  
Maximum Temperature ◽  
Cooling Performance

A novel micro heat sink applying the jet-impingement and cross flow is proposed to dissipate the heat from the electrical devices. Six hotspots of 2 mm × 2 mm are positioned on a flat plate of 25.4 mm × 25.4 mm. The area of flat plate except the hotspots is provided a constant heat flux of 20 W/cm2 as background heating source among cases. Four heat fluxes from 40 to 100 W/cm2 on the hotspots are tested to simulate the different operation conditions. The cross flow is used to remove the background heat flux and jet flow is supplied into the swirl microchannel, located at the right top of hotspot, to dissipate the large heat flux from hotspots. The channel depth is 0.5 mm and the width of swirl microchannel is 0.38 mm. The cross flow and jet flow velocity vary from 0.1 m/s to 0.5 m/s and from 0.5 m/s to 2 m/s, respectively. The effects of cross flow and jet flow on the cooling performance are investigated by numerical simulation. The local heat transfer coefficient and Nusselt number are calculated to evaluate the cooling performance of proposed micro heat sink for the targets of low maximum temperature, temperature gradient and pressure drop. The results show that the maximum temperature of the proposed design occurred at the outlet is approximately 65 °C among tested cases. The corresponding pressure drop is 5.5 kPa. The overall thermal resistance reaches as small as 0.23 K/W.

scholarly journals Effects of Frequency and Jet to Surface Spacing on Synthetic Jet Impingement Heat Transfer

2020 ◽  
Vol 9 (5) ◽  
pp. 655-660
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heated Surface ◽  
Low Frequency ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Nozzle Geometry ◽  
Ansys Fluent ◽  
Piston Cylinder

Synthetic jet is a new technique for electronic chip cooling, which combines stagnant air to form a jet resulting from periodic diaphragm oscillations in a cavity. In this work, the heat transfer characteristics of a synthetic jet are investigated experimentally and numerically. A Piston-cylinder arrangement powers the synthetic jet through a circular orifice for the impingement of jet on the heated surface. Air is considered as the cooling medium. The major parameters identified to describe the impinging jet heat transfer are Reynolds number, frequency, ratio of jet spacing to diameter(Z/D) and nozzle geometry. Numerical studies have been carried out using the finite volume based commercial software ANSYS Fluent. The turbulent model used is k-ω model. The dimensionless distance between the nozzle and plate surface is in the range 2 to 16. Numerical results are in fair agreement with experimental results. As the frequency increases the average Nusselt number increases. High frequency synthetic jets were found to remove more heat than low frequency jets for small Z/D ratio, while low frequency jets are more effective at larger Z/D ratio. Nusselt number is maximum at the stagnation point and there occurs a secondary peak at lower Z/D ratios. Synthetic jet with rectangular orifice is more effective as compared to circular and square geometries.

scholarly journals Heat Transfer Enhancement from a Heated Plate with Hemispherical Convex Dimples by Forced Convection Along with a Cross Flow Jet Impingement

2020 ◽  
Vol 25 (1) ◽  
pp. 127-141
Author(s):  
P. Patro ◽  
S. Garnayak
Keyword(s):  
Heat Transfer ◽  
Plane Surface ◽  
Heated Surface ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Cross Flow ◽  
Jet Impingement ◽  
Axial Direction ◽  
Bottom Plate ◽  
Heated Plate

AbstractIn the present study, heat transfer from a small three dimensional rectangular channel due to turbulent jet impinging from a nozzle normal to the main flow at the inlet has been investigated. Hemispherical convex dimples are attached to the bottom plate from where heat transfer calculations are to be performed. Numerical simulations were performed using the finite volume method with SST k– ω turbulence model. The duct and nozzle Reynolds number are varied in the range of 10000 ≤ ReD ≤ 50000 and 6000 ≤ Red ≤ 12000, respectively. Different nozzle positions (X/D = 10.57, 12.88, 15.19) along the axial direction of the rectangular duct have been considered. It has been found that higher heat transfer is observed at X/D = 10.57 as compared to the other positions. The heat transfer enhancements with and without cross-flow effects have also been compared. It has been shown that the heat transfer rate with cross-flow is found to be much higher than that without cross-flow. Also, the effect of dimples on the heated surface on heat transfer was investigated. The heat transfer is found to be greater in the presence of a dimpled surface than a plane surface.

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