U.S. patent application number 11/494913 was filed with the patent office on 2007-02-01 for synthetic jet ejector for augmentation of pumped liquid loop cooling and enhancement of pool and flow boiling.
This patent application is currently assigned to Innovative Fluidics, Inc.. Invention is credited to Ari Glezer, Samuel Neil Heffington, Raghavendran Mahalingam.
Application Number | 20070023169 11/494913 |
Document ID | / |
Family ID | 37693025 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070023169 |
Kind Code |
A1 |
Mahalingam; Raghavendran ;
et al. |
February 1, 2007 |
Synthetic jet ejector for augmentation of pumped liquid loop
cooling and enhancement of pool and flow boiling
Abstract
A thermal management system (201) is disclosed which comprises
(a) a liquid medium (207), (b) a heat generating device (203)
disposed in said medium, (c) a heat transfer device (205) in
thermal contact with said heat generating device, said heat
transfer device comprising a thermally conductive material and
having a channel (213) defined on a surface thereof, and (d) a
synthetic jet ejector (223) adapted to direct a jet of the liquid
medium along said channel.
Inventors: |
Mahalingam; Raghavendran;
(Austin, TX) ; Heffington; Samuel Neil; (Austin,
TX) ; Glezer; Ari; (Atlanta, GA) |
Correspondence
Address: |
FORTKORT & HOUSTON P.C.
9442 N. CAPITAL OF TEXAS HIGHWAY
ARBORETUM PLAZA ONE, SUITE 500
AUSTIN
TX
78759
US
|
Assignee: |
Innovative Fluidics, Inc.
|
Family ID: |
37693025 |
Appl. No.: |
11/494913 |
Filed: |
July 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60704049 |
Jul 29, 2005 |
|
|
|
Current U.S.
Class: |
165/104.28 ;
62/259.2 |
Current CPC
Class: |
F28D 15/0266 20130101;
F28F 13/02 20130101; F25D 17/02 20130101; F28D 15/00 20130101; F28F
3/12 20130101; H05K 7/20172 20130101 |
Class at
Publication: |
165/104.28 ;
062/259.2 |
International
Class: |
F28D 15/00 20060101
F28D015/00; F25D 23/12 20060101 F25D023/12 |
Claims
1. A thermal management system, comprising: a liquid medium; a heat
generating device disposed in said medium; a heat exchanger in
thermal contact with said heat generating element, said heat
transfer element comprising a thermally conductive material and
having a channel defined on a surface thereof; and a synthetic jet
ejector adapted to direct a jet of the liquid medium along said
channel.
2. The thermal management system of claim 1, wherein said heat
exchanger has a plurality of channels defined in a surface
thereof.
3. The thermal management system of claim 2, further comprising a
plurality of synthetic jet ejectors, each being adapted to direct a
jet of the liquid medium along one of said plurality of
channels.
4. The thermal management system of claim 1, wherein said synthetic
jet ejector is disposed adjacent to an opening of said channel.
5. The thermal management system of claim 1, wherein said synthetic
jet ejector is disposed within said channel.
6. The thermal management system of claim 1, further comprising a
pump adapted to create a flow of the liquid medium across the
surface of said heat exchanger.
7. The thermal management system of claim 6, wherein said pump is a
closed loop pump.
8. The thermal management system of claim 6, wherein said actuator
is positioned such that it does not disrupt the flow of the liquid
medium across the heat exchanger.
9. The thermal management system of claim 1, wherein said heat
exchanger comprises a plurality of ridges which define a plurality
of channels.
10. The thermal management system of claim 1, wherein the heat
generating device is a die.
11. The thermal management system of claim 10, wherein said
synthetic jet ejector comprises a diaphragm equipped with an
actuator.
12. The thermal management system of claim 11, wherein said
actuator is a piezoelectric actuator.
13. The thermal management system of claim 1, wherein said heat
exchanger comprises a plurality of levels, and wherein each level
has a plurality of channels defined therein.
14. The thermal management system of claim 13, wherein each of a
plurality of channels within each of said plurality of levels has a
synthetic jet ejector disposed therein.
15. The thermal management system of claim 13, wherein said heat
exchanger is in fluidic communication with a heat sink.
16. The thermal management system of claim 15, wherein said heat
sink is adapted to transfer heat from the liquid medium to the
ambient atmosphere.
17. The thermal management system of claim 16, further comprising a
pump which is adapted to maintain a flow of the liquid medium
between said heat exchanger and said heat sink.
18. A method for cooling a heat generating device, comprising:
providing a heat generating device which is to be cooled, the heat
generating device being in thermal contact with a heat exchanger
which is immersed in a liquid medium and which has a channel
defined in a surface thereof; providing a synthetic jet ejector
which is positioned to direct a jet of the liquid into said
channel; and activating the synthetic jet ejector.
19. The method of claim 18, wherein the synthetic jet ejector is
activated when the device reaches a predetermined temperature
threshold.
20. The method of claim 18, wherein the synthetic jet ejector is
activated when the liquid medium reaches a predetermined
temperature threshold.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority from U.S.
Provisional Application No. 60/704,049, filed Jul. 29, 2005, having
the same title, and having the same inventors, and which is
incorporated herein by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates generally to synthetic jet
ejectors, and more specifically to the use of synthetic jet
ejectors to augment the flow of liquid in a pumped liquid loop
cooling system.
BACKGROUND OF THE DISCLOSURE
[0003] As the size of semiconductor devices has continued to shrink
and circuit densities have increased accordingly, thermal
management of these devices has become more challenging. This
problem is expected to worsen in the foreseeable future. Thus,
within the next decade, spatially averaged heat fluxes in
microprocessor devices are projected to increase by a factor of
two, to well over 100 W/cm.sup.2, with core regions of these
devices experiencing local heat fluxes that are several times
higher.
[0004] In the past, thermal management in semiconductor devices was
often addressed through the use of forced convective air cooling,
either alone or in conjunction with various heat sink devices, and
was accomplished through the use of fans. However, fan-based
cooling systems were found to be undesirable due to the
electromagnetic interference and noise attendant to their use.
Moreover, the use of fans also requires relatively large moving
parts, and corresponding high power inputs, in order to achieve the
desired level of heat transfer.
[0005] More recently, thermal management systems have been
developed which utilize synthetic jet ejectors. These systems are
more energy efficient than comparable fan-based systems, and also
offer reduced levels of noise and electromagnetic interference. One
such system is depicted in FIG. 1. Systems of this type are
described in greater detail in U.S. Pat. No. 6,588,497 (Glezer et
al.).
[0006] The system shown in FIG. 1 utilizes an air-cooled heat
transfer module 101 which is based on a ducted heat ejector (DHE)
concept. The module utilizes a thermally conductive, high aspect
ratio duct 103 that is thermally coupled to one or more IC packages
105. Heat is removed from the IC packages 105 by thermal conduction
into the duct shell 107, where it is subsequently transferred to
the air moving through the duct. The air flow within the duct 103
is induced through internal forced convection by a pair of low form
factor synthetic jet ejectors 109 which are integrated into the
duct shell 107. In addition to inducing air flow, the turbulent jet
produced by the synthetic jet ejector 109 enables highly-efficient
convective heat transfer and heat transport at low volume flow
rates through small-scale motions near the heated surfaces, while
also inducing vigorous mixing of the core flow within the duct.
[0007] While the system disclosed in Glezer et al. represents a
very notable improvement in the art of thermal management systems,
in light of the aforementioned challenges in the art, a need exists
for thermal management systems with even greater heat transfer
efficiencies, and which can handle even greater heat flux loads.
There is also a need in the art for such a system that is scalable
and compact, and that does not contribute significantly to the
overall size of the device. These and other needs are met by the
devices and methodologies described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an illustration of a prior art thermal management
system based on the use of synthetic jet ejectors;
[0009] FIG. 2 is an illustration of a first embodiment of a liquid
loop cooling system made in accordance with the teachings
herein;
[0010] FIG. 3 is an illustration of a synthetic jet ejector
suitable for use in the thermal management systems described
herein;
[0011] FIG. 4 is an illustration of a synthetic jet ejector
suitable for use in the thermal management systems described
herein;
[0012] FIG. 5 is an illustration of a synthetic jet ejector
suitable for use in the thermal management systems described
herein;
[0013] FIG. 6 is an illustration of a second embodiment of a liquid
loop cooling system made in accordance with the teachings herein;
and
[0014] FIG. 7 is a perspective view of a first embodiment of the
heat exchanger of the liquid loop cooling system of FIG. 6; and
[0015] FIG. 8 is a top view of a second embodiment of a heat
exchanger suitable for use in the liquid loop cooling system of
FIG. 6, and with synthetic jet actuators mounted in the channel of
the heat exchanger.
SUMMARY OF THE DISCLOSURE
[0016] In one aspect, a thermal management system is provided which
comprises (a) a liquid medium, (b) a heat generating device
disposed in said medium, (c) a heat exchanger in thermal contact
with said heat generating element, said heat exchanger comprising a
thermally conductive material and having a channel defined on a
surface thereof, and (d) an actuator adapted to direct a jet of the
liquid medium along said channel.
[0017] In another aspect, a method for dissipating heat from a heat
generating device is provided. In accordance with the method, a
heat generating device is provided which is to be cooled, the heat
generating device being in thermal contact with a heat exchanger
which is immersed in a liquid medium and which has a channel
defined in a surface thereof. A synthetic jet ejector is also
provided which is positioned to direct a jet of the liquid into
said channel, and the synthetic jet ejector is activated.
[0018] These and other aspects of the present disclosure are
described in greater detail below.
DETAILED DESCRIPTION
[0019] It has now been found that the aforementioned needs can be
addressed through the provision of a pumped liquid loop cooling
system which utilizes one or more synthetic jet ejectors, in
combination with vibration induced boiling enhancement (VIBE), to
cool semiconductor die and other heat generating devices by
augmenting the flow of liquid coolant through the system. In such a
system, the heat generating device may be thermally coupled with a
heat exchanger which comprises a plurality of channels, and each of
the synthetic jet ejectors may be positioned to direct a jet of the
liquid coolant along one of the channels. When energized, each of
the synthetic jet ejectors provides one or more high momentum
synthetic jets directed in the same direction as the pumped coolant
flow, and along the longitudinal axis of one of the channels.
[0020] The use of focused jets in liquid loop cooling systems is
found to have several advantages. First of all, while the pumps
utilized in these systems can provide a suitable global flow of the
liquid coolant through the system, the flow rate of the liquid
coolant within the channels of the heat exchanger is typically much
slower, due to the pressure drop created by the channel walls. This
problem worsens as the system becomes smaller. Indeed, such a
pressure drop is one of the biggest obstacles to the
miniaturization of pumped liquid loop cooling systems. The use of
focused jets to direct a stream of liquid into the channels
overcomes this problem by reducing this pressure drop, and hence
facilitates increased entrainment of the flow of the liquid coolant
into the channels.
[0021] The use of focused jets in the thermal management systems
described herein also significantly improves the efficiency of the
heat transfer process. Under conditions in which the liquid coolant
is in a non-boiling state, the flow augmentation provided by the
use of synthetic jet ejectors increases the rate of local heat
transfer in the channel structure, thus resulting in higher heat
removal. Under conditions in which the coolant is in a boiling
state, these jets induce the rapid ejection of vapor bubbles formed
during the boiling process. This dissipates the insulating vapor
layer that would otherwise form, and hence delays the onset of
critical heat flux. In some applications, as explained in greater
detail below, the synthetic jets may also be utilized to create
beneficial nucleation sites to enhance the boiling process.
[0022] The systems and methodologies described herein further
increase the efficiency of the heat transfer process by permitting
this process to be augmented locally in accordance with localized
thermal loads. For example, the current trend in the semiconductor
industry is toward semiconductor devices that generate heat in an
increasingly non-uniform manner. This results in the creation of
hotspots in these devices which, in many cases, is the first point
of thermal failure of the device. Through the provision of
directed, localized synthetic jets, these hot spots can be
effectively eliminated, thereby reducing the global power
requirements of the thermal management system. The reduction in
power requirement attendant to the flow augmentation provided by
the synthetic jet ejectors also reduces the noise of the system,
and improves the reliability of the main pump (or pumps) used to
circulate the liquid coolant.
[0023] The principles described herein can be further understood
with reference to FIG. 2, which illustrates a first, non-limiting
embodiment of a liquid loop cooling system 201 made in accordance
with the teachings herein. The system 201 comprises a heat
generating device 203 which, in this particular embodiment, is a
die, and which is in thermal contact with a heat exchanger 205. The
heat generating device 203 and the heat exchanger 205 are disposed
in a liquid coolant 207. The heat exchanger 205 comprises a planar,
thermally conductive plate 209 with a series of ridges 211 disposed
thereon that define a plurality of channels 213. A pump 215 and a
conduit 217 are provided that operate to maintain a flow of the
liquid coolant in a direction generally parallel to the
longitudinal axes of the channels 213.
[0024] Referring again to FIG. 2, a synthetic jet ejector (SJE)
apparatus 219 is provided adjacent to the heat exchanger 205. The
synthetic jet ejector 219 comprises a base plate 221 which is
equipped with a plurality of nozzles 223. The nozzles 223 are each
adapted to produce synthetic jets, and are positioned so that the
synthetic jet produced is directed along the longitudinal axis of
the channel 213. The nozzles 223 operate to create air bubbles 225
in the fluid flow, which augments the cooling of the heat
generating device 203.
[0025] While the cooling of a semiconductor die has been
specifically illustrated herein, one skilled in the art will
appreciate that the devices and methodologies described herein may
be applied to the thermal management of a wide variety of heat
generating devices. These include, without limitation, printed
circuit boards and the components thereof, memory devices,
processors, and the like.
[0026] FIGS. 3-5 illustrate one possible, non-limiting embodiment
of a synthetic jet ejector 301 suitable for use in the devices and
methodologies disclosed herein. The synthetic jet ejector 301
illustrated therein comprises a body 303 that terminates on one end
in a wall 305 having an orifice 307 defined therein, and which
terminates on the other end in a diaphragm 309. In the particular
embodiment depicted, the diaphragm 309 is equipped with a plurality
of piezoelectric actuators 311. The actuators 311 are in electrical
communication with a driver 313 by way of suitable connectors 315.
The driver 313, which may be a wave generator, microcomputer, or
other controllable voltage source, operates to create oscillations
of a suitable frequency in the diaphragm 309 by causing the
actuators 311 to vibrate. During the inward phase of the
oscillation, as shown in FIG. 4, a synthetic jet of the liquid
coolant is emitted from the orifice 307. During the outward phase
of the oscillation, as shown in FIG. 5, the flow is reversed, and
liquid coolant is drawn into the synthetic jet ejector 301 through
the orifice 307.
[0027] It will be appreciated that the shape of the synthetic jet
ejector 301, as well as its overall dimensions and the relative
size of its components, can vary considerably. For example, any of
the various synthetic jet ejector designs disclosed in U.S. Pat.
No. 6,588,497 (Glezer et al.), which is incorporated herein by
reference, may be incorporated into the thermal management systems
described herein.
[0028] Moreover, the actuators in these devices may be adapted to
operate at ultrasonic or non-ultrasonic frequencies. In some
applications, the use of actuators operating at non-ultrasonic
frequencies may be preferred, due to the additional nucleation
sites, in the form of vapor bubbles, which may be generated at such
frequencies. The formation of these vapor bubbles is induced by
local accelerations of the liquid coolant in the vicinity of the
transducer. These accelerations result in extremely high local
velocities in the coolant, and a corresponding reduction in
pressure. When the reduction in pressure is sufficiently high, the
coolant undergoes localized phase changes at ambient temperatures,
thus resulting in cavitation of the coolant. As the transducer
oscillates, the cavitation bubbles alternately form and collapse,
thereby entraining the surrounding fluid and generating a synthetic
jet. As depicted in FIG. 2, some of these tiny cavitation bubbles
become entrained in the jet and are directed toward the hot
surfaces of the heat exchanger, where they provide excellent
nucleation sites for the boiling process.
[0029] FIG. 6 illustrates a second particular, non-limiting
embodiment of a liquid loop cooling system made in accordance with
the teachings herein. In the system 401 depicted therein, a printed
circuit board 403 is provided which is flip-chip bonded to a die
405 by way of a plurality of solder joints 407. The die 405 has a
heat exchanger 409 mounted on a surface thereof.
[0030] The details of the heat exchanger 409 may be appreciated
with reference to FIG. 7. As seen therein, the heat exchanger 409
comprises a stack of individual heat exchanger elements 411. Each
of these heat exchanger elements 411 comprises a base portion 413
with a series of parallel ridges 415 thereon that define a
plurality of microchannels 417.
[0031] Referring again to FIG. 6, the die 405 and the heat
exchanger 409 are encapsulated within a chamber 419 having an inlet
421 and an outlet 423. The inlet 421 and outlet 423 are in fluidic
communication with a cooling loop 425 through which a cooling
liquid flows under the control of an in-line pump 427. A heat sink
429, which acts as a heat exchanger between the liquid coolant and
the ambient atmosphere, is also incorporated into the cooling loop
425.
[0032] In use, cooled liquid coolant flows into the chamber 419 by
way of inlet 421. After entering the chamber 419, the coolant flows
through the microchannels 417 (see FIG. 7) of the heat exchanger
409. In so doing, the liquid coolant withdraws heat from the
surfaces of the microchannels 417, thereby cooling the die 405. The
warmed coolant then exits the chamber 419 through the outlet 423,
where it traverses the cooling loop 425 to the heat sink 429. The
heat sink 429, which may be fashioned as a liquid-to-air heat
exchanger, operates to withdraw heat from the liquid coolant and
reject it to the ambient atmosphere. The cooled liquid coolant then
exits the heat sink 429 and is routed back to the chamber 419 by
the pump 427.
[0033] As seen in FIG. 6, the flow of the liquid coolant through
the microchannels 417 (see FIG. 7) of the heat exchanger 409 is
augmented by a series of synthetic jet actuators 431 that are
mounted on an interior wall of the chamber 419 adjacent to the
openings of the microchannels 417. As in the previous embodiment
described herein, the synthetic jet actuators 431 operate to direct
a jet of the liquid coolant along the longitudinal axis of the
microchannels 417. The jets so produced have the effect of reducing
or eliminating the pressure drop in the microchannels 417, with all
of the attendant advantages as have been previously discussed.
[0034] The use of a stacked heat exchanger 409 of the type shown in
FIG. 7 is particularly advantageous in the cooling system 401 of
FIG. 6 in that this type of heat exchanger has the capability to
handle on-chip non-uniformities in power. The manifolding and
three-dimensional stacking employed in the heat exchanger 409
allows the liquid coolant to be brought into proximity with the
heated regions thereof, where the heat can be evenly distributed
and discharged without increasing the footprint of the system 401.
Stacked heat exchangers of the type shown in FIG. 7 have been
fabricated which can handle average heat fluxes of more than 200
W/cm.sup.2.
[0035] Various modifications are possible to the liquid loop
cooling system depicted in FIG. 6. For example, a number of
different heat exchangers can be used in place the heat exchanger
depicted in FIG. 7. One such heat exchanger is shown in FIG. 8. In
the heat exchanger 410 depicted therein, the synthetic jet
actuators 431 are mounted within the microchannels 417, rather than
being mounted on a wall of the chamber adjacent to the heat
exchanger as shown in FIG. 6. In embodiments of this type, the
synthetic jet actuators 431 preferably have a low profile so that
their presence in the microchannel 417 will not significantly
interfere with the egress of liquid coolant through the
microchannels 417.
[0036] The systems and methodologies described herein, and the
synthetic jet ejectors utilized in these systems and methodologies,
can be implemented in various sizes and dimensions. Thus, for
example, at the millimeter scale, synthetic jet ejectors can be
integrated into liquid loops using commercially available
piezoelectric transducers. At the micron scale, synthetic jet
ejectors can be incorporated into the system utilizing conventional
semiconductor fabrication techniques. At the nanometer scale,
synthetic jet ejectors can be created using nano-scale
lithography.
[0037] The synthetic jet ejectors utilized in the systems and
methodologies described herein may operate on a continuous basis,
or on a non-continuous basis. For example, the synthetic jet
ejectors may be utilized on an on-demand basis, where they are
activated when a temperature sensing probe disposed on a die or
other heat-generating device reaches a prescribed temperature
limit. The use of the synthetic jet ejectors on an on-demand basis
may be advantageous in some applications from the standpoint of
improving the reliability of the synthetic jet ejector, while
maintaining the heat generating device within prescribed
temperature limits.
[0038] The synthetic jet ejectors may also be configured to be
driven at various frequencies, and the frequency at which a
particular synthetic jet ejector is driven in a device of the type
described herein may differ from the frequencies at which other
synthetic jet ejectors in the device are driven. However,
ultrasonic driving frequencies are preferred in many applications,
since they reduce acoustic emissions in the audible region of the
spectrum. Since actuator frequencies increase with decreasing size,
ultrasonic operation becomes easier to implement as device sizes
decrease. Hence, the systems and methodologies described herein are
favored by Moore's law.
[0039] Various liquids may be utilized as the liquid coolant or
medium in the devices and methodologies described herein. These
include, without limitation, water and various organic liquids,
such as, for example, polyethylene glycol, polypropylene glycol,
and other polyols, partially fluorinated or perfluorinated ethers,
and various dielectric materials. Liquid metals may also be
advantageously used in the devices and methodologies described
herein. Such materials are generally metal alloys with an amorphous
atomic structure.
[0040] The systems and methodologies described herein may be used
advantageously in a wide variety of applications where thermal
management or boiling enhancement is desired. Such applications
include, but are not limited to, single phase cooling enhancement
applications (such as pool boiling applications), multiphase forced
flow boiling applications, heat pipe applications, and thermosyphon
applications.
[0041] One skilled in the art will also appreciate that the systems
and methodologies described herein may be readily adapted for use
in refrigeration applications. In such applications, the synthetic
jet actuators described herein may be used, for example, to augment
the flow of a refrigerant through the coils or surfaces of a heat
exchanger. The use of synthetic jet actuators in these applications
is especially suitable for use in miniaturized refrigeration
systems, due to their ability to compensate for the pressure drop
of refrigerant as it flows through the channels of a heat
exchanger.
[0042] The above description of the present invention is
illustrative, and is not intended to be limiting. It will thus be
appreciated that various additions, substitutions and modifications
may be made to the above described embodiments without departing
from the scope of the present invention. Accordingly, the scope of
the present invention should be construed in reference to the
appended claims.
* * * * *