Transcript Development of Synthetic Air Jet Technology for Applications in Electronics Cooling

Development of Synthetic Air Jet
Technology for Applications in
Electronics Cooling
Dr. Tadhg S. O’Donovan
School of Engineering and Physical Sciences
Heriot-Watt University
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
What is a Synthetic Air Jet?
•
A flexible membrane or diaphragm
forms one end of a partially
enclosed chamber
•
Opposite to the membrane is an
opening, such as a jet nozzle or
orifice plate
•
A mechanical actuator or a
piezoelectric diaphragm causes the
membrane
to
oscillate
and
periodically forces air into and out
of the opening
•
Thus creating a pulsating jet that
can be directed at a heated
surface, such as an electronic
device
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Characteristics of a Jet Impingement Cooling
• Instabilities in the flow at a jet nozzle develop into
vortices that impinge on the heated surface
• The breakdown of vortices along the impingement
surface increases velocity fluctuations normal to the
impingement surface (O’Donovan and Murray [1], [2])
• These fluctuations result in enhanced heat transfer or
secondary peaks in the heat transfer distribution
• Synthetic air jets are comprised entirely of successive
vortex rings
• Introduce a stronger entrainment of surrounding air than
conventional, steady jets
• These factors combine to give superior heat transfer
characteristics
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
•
Current technologies to cool state of the art circuit chips and multi-chip
modules (MCMs) rely on global forced air cooling which can dissipate
0.5 to 1 W/cm2.
•
It is anticipated that in the next five to ten years this requirement will
increase up to 10 to 40 W/cm2
•
In a cooling performance benchmark test by Kercher et al. [3], it has
been shown that synthetic microjets outperform conventional CPU fan
coolers
Cooling
Device
Cooling Efficiency
[W/m2K]
2.4 mm Synthetic Jet
96.90
NMB CPU Fan
61.52
Shicoh CPU Fan
44.30
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Characterisation of a Synthetic Air Jet
• Stroke Length
• Reynolds Number
• Strouhal Number

L0   U t dt
0
U0 
2
L0

2
U 0 D
Re 

fD
 L0 
Sr 
 0.5 
U0
D
1
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Synthetic Air Jet Electronics Cooling
Experimental Set-up No. 1
Nusselt Number
Particle Image Velocimetry (PIV)
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Synthetic Air Jet Electronics Cooling
Phase Locked Particle Image Velocimetry
Re = 2670
L0 = 15 d
Re = 2670
L0 = 7.7 d
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Experimental Set-up No. 2
Flush Mounted Heat Flux Sensors on a UWT Impingement Surface
•
RdF MicroFoil Heat Flux Sensor
•
Senflex Hot Film Sensor
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Synthetic Air Jet Electronics Cooling
Heat Transfer Distributions, H/D = 2
At this height above the surface
the plate lies in the vortex
formation region; this results in a
high velocity flow occurring
between the vortex and the plate
at a radial distance of r/D = 0.7.
It can be seen that the mean heat
transfer distribution has a local
minimum at the stagnation point
for Reynolds numbers of 2300
and above.
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Synthetic Air Jet Electronics Cooling
Heat Transfer Distributions, H/D = 4
At this height above the surface
the plate lies in the vortex are fully
formed before impingement
Resulting in a high velocity
fluctuations overall and a peak at
the geometric centre.
Some increase in surface heat
transfer fluctuations can be seen
in the wall jet flow region
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Phase Locked Vorticity Plot, H/D = 1, Re = 3700, L0/D = 17
Φ = 120°
Φ = 180°
Φ = 240°
Φ = 300°
Φ = 0°
Φ = 60°
1  V U 

  

2  x y 
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Phase Locked Vorticity Plot, H/D = 2, Re = 3700, L0/D = 17
Φ = 120°
Φ = 180°
Φ = 240°
Φ = 300°
Φ = 0°
Φ = 60°
1  V U 

  

2  x y 
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Development of an SAJ Electronics Cooler
• Design a synthetic jet array where jets interact constructively
jet diameters, array geometries, frequency of oscillation,
amplitude etc.
• Encourage the introduction of fresh cold air into the confined region
by control of the pulsation characteristics of the individual jets
aligned in a channel
phase, frequency, and amplitude
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
Conclusions
• Synthetic Air Jet Cooling can outperform standard fan-fin CPU
coolers and are more effective than similar steady impinging air jets
• The current research addresses the limitations of conventional
synthetic jet impingement cooling systems.
• Recycling of the air in a synthetic jet array causes its temperature to
continually increase which adversely affects the heat removal
capacity of the jets.
• To ensure that the air being forced over the heated surface is
sufficiently cool, fresh ambient air must be brought in. This is
typically achieved by introducing a secondary cross-flow of air over
the heated device via a fan.
• Preliminary results show that synthetic jets can operate in clusters or
arrays to achieve enhanced cooling of surfaces such as electronic
devices.
27th HEXAG Meeting, Heriot-Watt University, Edinburgh
Synthetic Air Jet Electronics Cooling
References
1.
T. S. O'Donovan and D. B. Murray, "Jet impingement heat transfer - Part I:
Mean and root-mean-square heat transfer and velocity distributions,"
International Journal of Heat and Mass Transfer, vol. 50, pp. 3291-3301,
2007.
2.
T. S. O'Donovan and D. B. Murray, "Jet impingement heat transfer - Part
II: A temporal investigation of heat transfer and local fluid velocities,"
International Journal of Heat and Mass Transfer, vol. 50, pp. 3302-3314,
2007.
3.
D. S. Kercher, J. B. Lee, O. Brand, M. G. Allen, and A. Glezer, "Microjet
cooling devices for thermal management of electronics," IEEE
Transactions on Components and Packaging Technologies, vol. 26, pp.
359 - 366, 2003.
4.
T. Persoons and T. S. O'Donovan, "A pressure-based estimate of synthetic
jet velocity," Physics of Fluids, vol. 19, pp. 128104-4, 2007.
27th HEXAG Meeting, Heriot-Watt University, Edinburgh