U.S. patent application number 12/615905 was filed with the patent office on 2010-05-13 for spatially distributed ventilation boundary using electrohydrodynamic fluid accelerators.
This patent application is currently assigned to TESSERA, INC.. Invention is credited to Kenneth A. Honer, Nels Jewell-Larsen, Hongyu Ran, Piyush Savalia, Matt Schwiebert, Yan Zhang.
Application Number | 20100116460 12/615905 |
Document ID | / |
Family ID | 42164120 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100116460 |
Kind Code |
A1 |
Jewell-Larsen; Nels ; et
al. |
May 13, 2010 |
SPATIALLY DISTRIBUTED VENTILATION BOUNDARY USING
ELECTROHYDRODYNAMIC FLUID ACCELERATORS
Abstract
In thermal management systems that employ EHD devices to
motivate flow of air through an enclosure, spatial distribution of
a ventilation boundary may facilitate reductions in flow resistance
by reducing average transit distance for cooling air from an inlet
portion of the ventilation boundary to an outlet portion. Some
thermal management systems described herein distribute a
ventilation boundary over opposing surfaces, adjacent surfaces or
even a single surface of an enclosure while providing a short, "U"
shaped, "L" shaped or generally straight through flow path. In some
cases, spatial distributions of the ventilation boundary facilitate
or enable enclosure geometries for which conventional fan or blower
ventilation would be impractical. In some cases, provision of
multiple portions of the ventilation boundary may allow the thermal
management system to tolerate blockage or occlusion of a subset of
the inlet and/or outlet portions and, when at least some of such
portions are non-contiguous spatially-distributed, tolerance to a
single cause of blockage or occlusion is enhanced.
Inventors: |
Jewell-Larsen; Nels;
(Campbell, CA) ; Honer; Kenneth A.; (Santa Clara,
CA) ; Schwiebert; Matt; (San Jose, CA) ; Ran;
Hongyu; (Mountain View, CA) ; Savalia; Piyush;
(San Jose, CA) ; Zhang; Yan; (San Jose,
CA) |
Correspondence
Address: |
ZAGORIN O'BRIEN GRAHAM LLP (149)
7600B N. CAPITAL OF TX HWY, SUITE 350
AUSTIN
TX
78731
US
|
Assignee: |
TESSERA, INC.
San Jose
CA
|
Family ID: |
42164120 |
Appl. No.: |
12/615905 |
Filed: |
November 10, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61113225 |
Nov 10, 2008 |
|
|
|
Current U.S.
Class: |
165/47 ;
165/104.31; 417/50 |
Current CPC
Class: |
F04B 19/006 20130101;
H02N 11/006 20130101; G06F 1/203 20130101; F28F 2250/08
20130101 |
Class at
Publication: |
165/47 ; 417/50;
165/104.31 |
International
Class: |
F24H 9/02 20060101
F24H009/02; H02K 44/02 20060101 H02K044/02; F28D 15/00 20060101
F28D015/00 |
Claims
1. An apparatus comprising: an enclosure; plural flow paths for
conveyance of air between ventilated boundary portions of the
enclosure, including a first outlet portion and at least two inlet
portions, the at least two inlet portions being non-contiguous and
spatially-distributed on the enclosure; and a first
electrohydrodynamic fluid accelerator disposed in at least a
respective one of the flow paths for ventilating the enclosure and
thereby cooling one or more devices disposed therein, the first
electrohydrodynamic fluid accelerator operable to motivate flow
between respective portions of the ventilated boundary.
2. The apparatus of claim 1, wherein the first outlet portion is
adjacent at least one of the inlet portions.
3. The apparatus of claim 1, wherein the first electrohydrodynamic
fluid accelerator is positioned to motivate an outflow of the air
toward the first outlet portion of the ventilated boundary and to
draw corresponding inflows from at least two of the non-contiguous,
spatially-distributed inlet portions.
4. The apparatus of claim 1, wherein the first electrohydrodynamic
fluid accelerator is positioned to motivate an outflow of the air
toward the first outlet portion of the ventilated boundary and to
draw corresponding inflows from at least a first one of the
non-contiguous, spatially-distributed inlet portions, and further
comprising at least a second electrohydrodynamic fluid accelerator
disposed in at least a respective one of the flow paths, the second
electrohydrodynamic fluid accelerator positioned to motivate an
outflow of the air toward a second outlet portion of the ventilated
boundary and to draw corresponding inflows from at least a second
one of the non-contiguous, spatially-distributed inlet
portions.
5. The apparatus of claim 4, wherein the first and second outlet
portions are non-contiguous and spatially-distributed on the
enclosure.
6. The apparatus of claim 1, wherein the first electrohydrodynamic
fluid accelerator is positioned to motivate an outflow of the air
toward the first outlet portion of the ventilated boundary and to
draw corresponding inflow from at least a first one of the
non-contiguous, spatially-distributed inlet portions, and further
comprising at least a second electrohydrodynamic fluid accelerator
disposed in at least a respective one of the flow paths, the second
electrohydrodynamic fluid accelerator positioned to motivate an
inflow of the air from second one of the non-contiguous,
spatially-distributed inlet portions toward at least a second
outlet portion of the ventilated boundary.
7. The apparatus of claim 6, wherein the first and second outlet
portions are non-contiguous and spatially-distributed on the
enclosure.
8. The apparatus of claim 1, the electrohydrodynamic fluid
accelerator including a spaced apart array of collector electrodes
and at least one corona discharge electrodes having a longitudinal
extent that spans a major dimension of the collector electrode
array.
9. The apparatus of claim 8, further comprising: a heat transfer
path from the one or more devices to the collector electrodes.
10. The apparatus of claim 8, further comprising: a additional heat
transfer surface disposed in at least one of the flow paths; and a
heat transfer path from the one or more devices to the additional
heat transfer surface.
11. The apparatus of claim 1, wherein the inlet portions and the
first outlet portion of the ventilated boundary are all formed in a
same surface of the enclosure; and wherein respective ones of the
flow paths include generally U-shaped trajectories between
respective inlet and outlet portions.
12. The apparatus of claim 1, wherein the inlet portions and the
first outlet portion of the ventilated boundary are formed in
respective generally opposing surfaces of the enclosure.
13. The apparatus of claim 1, wherein the inlet portions and the
first outlet portion of the ventilated boundary are formed in
generally adjacent surfaces of the enclosure.
14. A method comprising: ventilating an enclosure and thereby
cooling one or more devices disposed therein using a plurality of
EHD devices arranged to establish plural flow paths for conveyance
of air between ventilated boundary portions of the enclosure,
including a first outlet portion and at least two inlet portions,
the at least two inlet portions being non-contiguous and
spatially-distributed on the enclosure; and selectively enabling
and disabling a subset of the EHD devices to adapt the ventilating
to cooling requirements of the one or more devices.
15. The method of claim 14, further comprising: responsive to a
first cooling requirement, energizing a first subset of less than
all of the plural EHD devices and motivating air flow therethrough;
and responsive to a second cooling requirement, energizing a second
subset of the plural EHD devices and motivating air flow
therethrough, the second subset larger than the first subset.
16. An apparatus comprising: an enclosure; plural flow paths for
conveyance of air between ventilated boundary portions of the
enclosure, including plural outlet portions and plural inlet
portions, wherein respective ones of the inlet and outlet portions
are interspersed and spatially-distributed over a single boundary
surface; and plural electrohydrodynamic fluid accelerator instances
each disposed in at least a respective one of the flow paths for
ventilating the enclosure and thereby cooling one or more devices
disposed therein, the electrohydrodynamic fluid accelerators each
operable to motivate flow between respective portions of the
ventilated boundary.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present application claims the benefit of U.S.
Provisional Application No. 61/113,225, filed Nov. 10, 2008. The
present application is also related to commonly-owned, co-pending
U.S. patent application Ser. No. ______, entitled
"ELECTROHYDRODYNAMIC FLUID ACCELERATOR WITH HEAT TRANSFER SURFACES
OPERABLE AS COLLECTOR ELECTRODE," naming Jewell-Larsen, Honer,
Schwiebert, Ran, Savalia and Zhang as inventors, and to
commonly-owned, co-pending U.S. patent application Ser. No. ______,
entitled "REVERSIBLE FLOW ELECTROHYDRODYNAMIC FLUID ACCELERATOR,"
naming Jewell-Larsen, Honer, Schwiebert, Ran, Savalia and Zhang as
inventors, each filed on even date herewith.
BACKGROUND
[0002] 1. Field
[0003] The present application relates to thermal management, and
more particularly, to micro-scale cooling devices that use
electrohydrodynamic (EHD, also known as electro-fluid-dynamic, EFD)
technology to generate ions and electrical fields to control the
movement of fluids, such as air, as part of a thermal management
solution to dissipate heat.
[0004] 2. Related Art
[0005] In general, electrohydrodynamic (EHD) technology uses corona
discharge principles to move fluids (e.g., air molecules). Basic
principles of EHD fluid flow are reasonably well understood by
persons of skill in the art. Accordingly, a brief illustration of
corona discharge principles in a simple two electrode system sets
the stage for the more detailed description that follows.
[0006] With reference to the illustration in FIG. 1, corona
discharge principles include applying a high intensity electric
field between a first electrode 11 (often termed the "corona
electrode," the "corona discharge electrode," the "emitter
electrode" or just as the "emitter") and a second electrode 12.
Fluid molecules, such as surrounding air molecules, near the corona
discharge region 18 become ionized and form a stream 14 of ions 16
that accelerate toward second electrode 12, colliding with neutral
fluid molecules 22. During these collisions, momentum is imparted
from the stream 16 of ions 14 to the neutral fluid molecules 22,
inducing a corresponding movement of fluid molecules 22 in a
desired fluid flow direction, denoted by arrow 13, toward second
electrode 12. Second electrode 12 is variously referred to as the
"accelerating", "attracting", "collector" or "target" electrode.
While stream 14 of ions 16 are attracted to, and neutralized by,
second electrode 12, neutral fluid molecules 22 move past second
electrode 12 at a certain velocity. The movement of fluid produced
by corona discharge principles has been variously referred to as
"electric," "corona" or "ionic" wind and has been defined as the
movement of gas induced by the repulsion of ions from the vicinity
of a high voltage discharge electrode.
[0007] Devices built using the principle of the ionic movement of a
fluid are variously referred to in the literature as ionic wind
machines, electric wind machines, corona wind pumps, electrostatic
air accelerators, electro-fluid-dynamics (EFD) devices,
electrostatic fluid accelerators (EFA), electrohydrodynamic (EHD)
thrusters and EHD gas pumps. Some aspects of the technology have
also been exploited in devices referred to as electrostatic air
cleaners or electrostatic precipitators.
[0008] In the present application, embodiments of the devices
illustrated and described herein are referred to as
electrohydrodynamic fluid accelerator devices, also referred to in
an abbreviated manner herein as "EHD devices", and are utilized as
a component in a thermal management solution to dissipate heat
generated by an electronic circuit.
SUMMARY
[0009] EHD devices may be employed to motivate flow of air in a
thermal management system, such as employed to exhaust heat
dissipated by integrated circuits in computing devices and
electronics. For example, in devices such as laptop computers,
compact scale, flexible form factor and absence of moving parts can
provide design and user advantages over conventional forced air
cooling technologies that rely exclusively on fans or blowers. EHD
device solutions can operate silently (or at least comparatively
so) with reduced volume and mass. In some cases, products
incorporating EHD device solutions may be thinner and lighter than
those employing conventional forced air cooling technologies.
Flexible form factors of EHD devices can facilitate compelling
product designs and, in some cases, may provide functional
benefits.
[0010] It has been discovered that in thermal management systems
that employ EHD devices to motivate flow of air through an
enclosure, spatial distribution of a ventilation boundary may
facilitate reductions in flow resistance by reducing average
transit distance for cooling air from an inlet portion of the
ventilation boundary to an outlet portion. In some cases, spatial
distributions of the ventilation boundary facilitate or enable
enclosure geometries for which conventional fan or blower
ventilation would be impractical. In some cases, the provision of
multiple portions of the ventilation boundary may allow the thermal
management system to tolerate blockage or occlusion of a subset of
the inlet and/or outlet portions and, when at least some of such
portions are non-contiguous spatially-distributed, tolerance to a
single cause of blockage or occlusion is enhanced.
[0011] In some embodiments in accordance with the present
invention, an apparatus includes an enclosure, plural flow paths
for conveyance of air between ventilated boundary portions of the
enclosure, and a first electrohydrodynamic fluid accelerator
disposed in at least a respective one of the flow paths for
ventilating the enclosure and thereby cooling one or more devices
disposed therein. The ventilated boundary portions of the enclosure
include a first outlet portion and at least two inlet portions. The
at least two inlet portions are non-contiguous and
spatially-distributed on the enclosure. The first
electrohydrodynamic fluid accelerator is operable to motivate flow
between respective portions of the ventilated boundary.
[0012] In some embodiments, the first outlet portion is adjacent at
least one of the inlet portions. In some embodiments, the first
electrohydrodynamic fluid accelerator is positioned to motivate an
outflow of the air toward the first outlet portion of the
ventilated boundary and to draw corresponding inflows from at least
two of the non-contiguous, spatially-distributed inlet
portions.
[0013] In some embodiments, the first electrohydrodynamic fluid
accelerator is positioned to motivate an outflow of the air toward
the first outlet portion of the ventilated boundary and to draw
corresponding inflows from at least a first one of the
non-contiguous, spatially-distributed inlet portions, and the
apparatus further includes at least a second electrohydrodynamic
fluid accelerator. The second electrohydrodynamic fluid accelerator
is disposed in at least a respective one of the flow paths and
positioned to motivate an outflow of the air toward a second outlet
portion of the ventilated boundary and to draw corresponding
inflows from at least a second one of the non-contiguous,
spatially-distributed inlet portions. In some variations, the first
and second outlet portions are non-contiguous and
spatially-distributed on the enclosure.
[0014] In some embodiments, the first electrohydrodynamic fluid
accelerator is positioned to motivate an outflow of the air toward
the first outlet portion of the ventilated boundary and to draw
corresponding inflow from at least a first one of the
non-contiguous, spatially-distributed inlet portions, and the
apparatus further includes at least a second electrohydrodynamic
fluid accelerator. The second electrohydrodynamic fluid accelerator
is disposed in at least a respective one of the flow paths and
positioned to motivate an inflow of the air from second one of the
non-contiguous, spatially-distributed inlet portions toward at
least a second outlet portion of the ventilated boundary. In some
variations, the first and second outlet portions are non-contiguous
and spatially-distributed on the enclosure.
[0015] In some embodiments, the electrohydrodynamic fluid
accelerator includes a spaced apart array of collector electrodes
and at least one corona discharge electrodes having a longitudinal
extent that spans a major dimension of the collector electrode
array. In some embodiments, the apparatus further includes a heat
transfer path from the one or more devices to the collector
electrodes. In some embodiments, the apparatus further includes an
additional heat transfer surface disposed in at least one of the
flow paths and a heat transfer path from the one or more devices to
the additional heat transfer surface.
[0016] In some embodiments, the inlet portions and the first outlet
portion of the ventilated boundary are all formed in a same surface
of the enclosure, and respective ones of the flow paths include
generally U-shaped trajectories between respective inlet and outlet
portions. In some embodiments, the inlet portions and the first
outlet portion of the ventilated boundary are formed in respective
generally opposing surfaces of the enclosure. In some embodiments,
the inlet portions and the first outlet portion of the ventilated
boundary are formed in generally adjacent surfaces of the
enclosure.
[0017] In some method embodiments of the present invention, a
method includes (i) ventilating an enclosure and thereby cooling
one or more devices disposed therein using a plurality of EHD
devices arranged to establish plural flow paths for conveyance of
air between ventilated boundary portions of the enclosure,
including a first outlet portion and at least two inlet portions,
the at least two inlet portions being non-contiguous and
spatially-distributed on the enclosure; and (ii) selectively
enabling and disabling a subset of the EHD devices to adapt the
ventilating to cooling requirements of the one or more devices.
[0018] In some embodiments, the method further includes (i)
responsive to a first cooling requirement, energizing a first
subset of less than all of the plural EHD devices and motivating
air flow therethrough, and (ii) responsive to a second cooling
requirement, energizing a second subset of the plural EHD devices
and motivating air flow therethrough, the second subset larger than
the first subset.
[0019] In some embodiments in accordance with the present
invention, an apparatus includes an enclosure, plural flow paths,
and plural electrohydrodynamic fluid accelerator instances. The
plural flow paths are configured for conveyance of air between
ventilated boundary portions of the enclosure, including plural
outlet portions and plural inlet portions, wherein respective ones
of the inlet and outlet portions are interspersed and
spatially-distributed over a single boundary surface. The
electrohydrodynamic fluid accelerator instances are each disposed
in at least a respective one of the flow paths for ventilating the
enclosure and thereby cooling one or more devices disposed therein,
and are each operable to motivate flow between respective portions
of the ventilated boundary.
[0020] Building on the foregoing, we present a variety of
embodiments. In some embodiments, collector electrodes of the EHD
device are themselves thermally coupled to a heat source such that
at least some surfaces thereof act as fins of a heat exchanger. In
some embodiments, the EHD device motivates flow of a fluid
(typically air) past a heat exchanger that is thermally integrated
with the collector electrodes. In some embodiments, multiple EHD
device instances are ganged and/or staged so as to increase volume
of flow, pressure or both. These and other embodiments will be
understood with reference to the description that follows and with
respect to the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The description of illustrative embodiments will be
understood when read in connection with the accompanying drawings.
Drawings are not necessarily to scale; emphasis has instead been
placed upon illustrating the structural and fabrication principles
of the described embodiments.
[0022] FIG. 1 is a graphical depiction of certain basic principles
of corona-induced electrohydrodynamic (EHD) fluid flow.
[0023] FIG. 2A is a simplified perspective view of a corona
discharge electrode assembly. FIG. 2B is a simplified perspective
view of a collector electrode assembly. FIG. 2C depicts fluid flow
relative to inlet and outlet portions of a ventilated boundary for
an EHD device that establishes a corona discharge between corona
discharge and collector electrodes of assemblies such as
illustrated in FIGS. 2A and 2B.
[0024] FIG. 3 depicts fluid flow relative to inlet and outlet
portions of a ventilated boundary formed on adjacent surfaces of an
enclosure for an EHD device that establishes a corona discharge
between corona discharge and collector electrodes.
[0025] FIG. 4 depicts fluid flow relative to inlet and outlet
portions of a ventilated boundary formed on opposing surfaces of an
enclosure for an EHD device that establishes a corona discharge
between corona discharge and collector electrodes.
[0026] FIGS. 5, 6 and 7 depict several illustrative end-on views of
EHD device configurations in which one or more corona discharge
electrodes have longitudinal extent that is oriented orthogonally
to respective generally planar surfaces of collector electrodes.
FIG. 5 depicts an illustrative single corona electrode
configuration. FIG. 6 depicts an illustrative multiple corona
electrode configuration. FIG. 7 depicts an illustrative ganged
configuration.
[0027] FIG. 8A depicts a simplified perspective view, consistent
with certain of the preceding EHD device configurations, of a
corona discharge electrode and several orthogonally-oriented
generally planar collector electrodes with curved leading surface
profiles. FIG. 8B depicts a side cross-sectional view consistent
with FIG. 8A. FIG. 8C depicts a side cross-sectional view for an
alternative collector electrode geometry.
[0028] FIG. 9A depicts a side cross-sectional view, consistent with
certain alternative EHD device configurations, of a corona
discharge electrode and several generally planar collector
electrodes that are arranged to present a curved array of leading
surfaces, where each of the leading surfaces is oriented generally
parallel to the longitudinal extent of the corona discharge
electrode. FIG. 9B depicts a perspective view of a collector
electrode assembly consistent with the arrangement of FIG. 9A. FIG.
9C depicts a perspective view of a corona discharge electrode and
collector electrode assemblies consistent with the arrangement.
[0029] FIG. 10A is a perspective view of a first EHD device
configuration illustrating a generally "U" shaped fluid flow path
between inlet and outlet portions of a ventilated boundary surface.
FIG. 10B is a corresponding plan view illustration.
[0030] FIG. 11A is a perspective view of a second EHD device
configuration in which additional heat transfer surfaces are
provided and illustrating a generally "U" shaped fluid flow path
between inlet and outlet portions of a ventilated boundary surface.
FIG. 11B is a corresponding plan view illustration. FIG. 11C is a
plan view illustration for an alternative configuration in which
flow ordering over collector electrodes and additional heat
transfer surfaces is reversed. FIG. 11D is a plan view illustration
of a further alternative configuration in which additional heat
transfer surfaces are extended. FIG. 11E shows a top plan view of
still another alternative configuration.
[0031] FIG. 12A is a perspective view of an EHD device
configuration in which additional heat transfer surfaces are
provided and illustrating a comingled pair of generally "U" shaped
fluid flow path between plural inlet portions and a single outlet
portion of a ventilated boundary surface. FIG. 12B is a
corresponding plan view illustration.
[0032] FIG. 13 is a plan view illustration an EHD device
configuration in which of EHD devices are staged proximate to
respective inlet and outlet portions of a ventilated boundary
surface to motivate flow along a generally "U" shaped fluid flow
path.
[0033] FIGS. 14A and 14B are respective plan view illustrations an
EHD device configuration in which two separately energizable corona
discharge components are positioned at opposing leading surfaces of
an array of collector electrodes to facilitate reversible flow.
FIG. 14C depicts a variation in which opposing leading surfaces are
of respective collector electrodes (or collector electrode
portions) separated by additional heat transfer surfaces.
[0034] FIG. 15 is a top plan view of a first illustrative pair of
EHD devices configured to operate in a cooperative configuration
relative to adjacent inlet and outlet portions of a distributed
ventilation boundary.
[0035] FIG. 16 is a top plan view of a second illustrative pair of
EHD devices configured to operate in a cooperative configuration
relative to adjacent inlet and outlet portions of a distributed
ventilation boundary.
[0036] FIGS. 17 and 18 are respective top plan views of additional
plural configurations of EHD devices configured to operate in a
cooperative configuration with comingled flow paths
illustrated.
[0037] FIGS. 19A, 19B and 19C illustrate representative EHD device
configurations in a thermal management solution context. In
particular, FIG. 19A is a schematic drawing of a corona discharge
electrode component and FIG. 19B is a schematic drawing of a first
embodiment of a convective heat transfer component that includes
collector electrodes. FIG. 19C illustrates an EHD device
configuration that includes corona discharge electrode and
convective heat transfer components of FIGS. 19A and 19B positioned
proximate to a ventilated boundary portion of an enclosure.
[0038] FIG. 19D is a schematic drawing of an alternative design for
a convective heat transfer component.
[0039] FIG. 19E illustrates an EHD device configuration that
includes corona discharge electrode and convective heat transfer
components of FIGS. 19A and 19D and employs convective heat
transfer structures along an extension surface for dissipating heat
from a thermal source.
[0040] FIG. 20 is a volumetric illustration of an EHD device having
a certain geometry expressed as a ratio of length to height, or
length to depth.
[0041] FIG. 21 is table of design parameters for representative
implementations of various EHD device embodiments described and
illustrated herein.
[0042] The use of the same reference symbols in different drawings
indicates similar or identical items.
DETAILED DESCRIPTION
[0043] Thermal management systems described herein employ EHD
devices to motivate flow of air between ventilated boundary
portions of an enclosure. In this way, heat dissipated by
electronics (e.g., microprocessors, graphics units, etc.) and other
components may be transferred to the air flow and exhausted.
Typically, the thermal management system includes heat transfer
paths (often implemented as heat pipes or using other technologies)
to transfer heat from where it is dissipated (or generated) to a
location (or locations) within the enclosure where air flow
motivated by an EHD device (or devices) flows over heat transfer
surfaces.
[0044] As described herein relative to certain illustrative
embodiments, some heat transfer surfaces may act as collector
electrodes and participate in EHD acceleration of fluid flow
(typically air flow), while additional heat transfer surfaces are
provided that do not substantially contribute to motivation of
fluid flow. Those heat transfer surfaces that act as collector
electrodes and those that do not substantially contribute to
motivation of fluid flow are introduced at different positions
along a flow path. In some embodiments, heat transfer surfaces that
act as collector electrodes and those that do not are nonetheless
integrated, either physically, thermally or both. For example, in
some embodiments, additional heat transfer surfaces may be
implemented as an extension structure that replicates unit
structures of a collector electrode assembly, but for which no
proximate corona discharge electrode establish a corona discharge.
In such a configurations, some heat transfer structures of an
integrated assembly participate in EHD acceleration of fluid flow,
while others do not.
[0045] As described herein relative to certain illustrative
embodiments, reversible flows may be provided in EHD device
configurations that selectively energize corona discharge
electrodes arranged to motivate flows in generally opposing
directions. In some embodiments, a first set of one or more corona
discharge electrodes is positioned, relative to a first array of
collector electrode surfaces, to when energized, motivate flow in a
first direction, while second set of one or more corona discharge
electrodes is positioned, relative to a second array of collector
electrode surfaces, to when energized, motivate flow in a second
direction that opposes the first. In some embodiments, the first
and second arrays of collector electrode surfaces are opposing
surfaces of individual collector electrodes. In some embodiments,
the first and second arrays of collector electrode surfaces are
opposing surfaces of respective collector electrodes. The
alternative sets of corona discharge electrodes are typically
energized at different times consistent with a flow reversal
objective or scheme.
[0046] As described herein relative to certain illustrative
embodiments, in thermal management systems that employ EHD devices
to motivate flow of air through an enclosure, spatial distribution
of a ventilation boundary may facilitate reductions in flow
resistance by reducing average transit distance for cooling air
from an inlet portion of the ventilation boundary to an outlet
portion. Some thermal management systems described herein
distribute a ventilation boundary over opposing surfaces, adjacent
surfaces or even a single surface of an enclosure while providing a
short, "U" shaped, "L" shaped or generally straight-through flow
path. In some cases, spatial distributions of the ventilation
boundary facilitate or enable enclosure geometries for which
conventional fan or blower ventilation would be impractical. In
some cases, the provision of multiple portions of the ventilation
boundary may allow the thermal management system to tolerate
blockage or occlusion of a subset of the inlet and/or outlet
portions and, when at least some of such portions are
non-contiguous spatially-distributed, tolerance to a single cause
of blockage or occlusion is enhanced. In some cases, thermal
management solutions that distribute multiple EHD devices along a
ventilation boundary with multiple, spatially distributed, input
and output portions facilitate ventilation strategies that
selectively energize individual ones of the EHD devices in a manner
consistent with, and responsive to, cooling requirements.
[0047] In general, a variety of scales, geometries and other design
variations are envisioned for collector electrodes, together with a
variety of positional interrelationships between corona discharge
and collector electrodes of a given EHD device. For concreteness of
description, we focus on certain illustrative embodiments and
certain illustrative surface profiles and positional
interrelationships with other components. For example, in much of
the description herein, plural planar collector electrodes are
arranged in a parallel, spaced-apart array proximate to a corona
discharge wire that is displaced from leading surfaces of the
respective collector electrodes. In some embodiments, planar
portions of the collector electrodes are oriented generally
orthogonally to the longitudinal extent of a corona discharge wire.
In other embodiments, orientation of collector electrodes is such
that leading surfaces thereof are generally parallel to the
longitudinal extent of a corona discharge wire. In some
embodiments, other corona discharge electrode configurations are
provided.
[0048] In some embodiments, leading surfaces present a curved
arrangement or profile to a corona discharge electrode (or
electrodes). In some embodiments, leading surfaces present other
(e.g., non-curved) arrangements or profiles to a corona discharge
electrode (or electrodes). In some thermal management system
embodiments, collector electrodes provide significant heat transfer
to fluid flows motivated therethrough or thereover. In some thermal
management system embodiments, heat transfer surfaces that do not
participate substantially in EHD fluid acceleration may provide the
substantial, even dominant, heat transfer.
[0049] It will be understood that particular EHD design variations
are included for purposes of illustration and, persons of ordinary
skill in the art will appreciate a broad range of design variations
consistent with the description herein. In some cases, and
particularly in the illustration of flow paths, EHD designs are
illustrated simply as a corona discharge electrode assembly and a
collector electrode assembly proximate each other; nonetheless,
such illustrations within the broad context of a full range of EHD
design variations are described herein.
[0050] Although embodiments of the present invention are not
limited thereto, much of the description herein builds upon
enclosure geometries, air flows, and heat transfer paths typical of
laptop-type computer electronics and will be understood in view of
that descriptive context. Of course, the described embodiments are
merely illustrative and, notwithstanding the particular context in
which any particular embodiment is introduced, persons of ordinary
skill in the art having benefit of the present description will
appreciate a wide range of design variations and exploitations for
the developed techniques and configurations. Indeed, EHD device
technologies present significant opportunities for adapting
structures, geometries, scale, flow paths, controls and placement
to meet thermal management challenges in a wide range of
applications and systems. Moreover, reference to particular
materials; dimensions, electrical field strengths; exciting
voltages, currents and/or waveforms; packaging or form factors,
thermal conditions, loads or heat transfer conditions and/or system
designs or applications is merely illustrative. In view of the
foregoing and without limitation on the range of designs
encompassed within the scope of the appended claims, we now
describe certain illustrative embodiments.
Electrohydrodynamic (EHD) Fluid Acceleration, Generally
[0051] Basic principals of electrohydrodynamic (EHD) fluid flow are
well understood in the art and, in this regard, an article by
Jewell-Larsen, N. et al., entitled "Modeling of corona-induced
electrohydrodynamic flow with COMSOL multiphysics" (in the
Proceedings of the ESA Annual Meeting on Electrostatics 2008)
(hereafter, "the Jewell-Larsen Modeling article"), provides a
useful summary. Likewise, U.S. Pat. No. 6,504,308, filed Oct. 14,
1999, naming Krichtafovitch et al. and entitled "Electrostatic
Fluid Accellerator" describes certain electrode and high voltage
power supply configurations useful in some EHD devices. U.S. Pat.
No. 6,504,308, together with sections I (Introduction), II
(Background), and III (Numerical Modeling) of the Jewell-Larsen
Modeling article are hereby incorporated by reference herein for
all that they teach.
[0052] Note that the simple illustration of corona-induced
electrohydrodynamic fluid flow shown in FIG. 1 (which has been
adapted from the Jewell-Larsen Modeling article and discussed
above) includes shapes for first electrode 10 and second electrode
12 that are particular to the simple illustration thereof.
Likewise, the electrode configurations illustrated in U.S. Pat. No.
6,504,308 and aspects of the power supply design are particular
thereto. Accordingly, such illustrations, while generally useful
for context, are not intended to limit the range of possible
electrode or high voltage power supply designs in any particular
embodiment of the present invention.
[0053] FIGS. 2A and 2B are simplified perspective views of corona
discharge electrode and collector electrode assemblies that may be
positioned and energized to induce EHD fluid flow. The corona
discharge electrode assembly includes multiple corona discharge
electrodes 110 supported by a frame fabricated from dielectric
material(s) to provide electrical isolation from other components
(including collector electrodes 120) of an EHD device. Corona
discharge electrodes 110 have small radii of curvature and, in some
embodiments, may take the form of wires or rods. Other shapes are
also possible; for example, corona discharge electrode 110 may take
the shape of barbed wire, a band, blade or place that, in some
embodiments, may present a knife- or serrated-edge. In some
embodiments, a cross-section such as illustrated in FIG. 1 for
electrode 10 may be employed. Typically, a small radius of
curvature or sharp point tends to facilitate ion production at an
appropriate point when high voltage is applied.
[0054] In general, corona discharge electrodes 110 may be
fabricated in a wide range of materials. For example, in some
embodiments, compositions such as described in U.S. Pat. No.
7,157,704, filed Dec. 2, 2003, entitled "Corona Discharge Electrode
and Method of Operating the Same" and naming Krichtafovitch et al.
as inventors may be employed. U.S. Pat. No. 7,157,704 is
incorporated herein for the limited purpose of describing materials
for some corona discharge electrodes that may be employed in some
embodiments. In general, a high voltage power supply (not
specifically shown) creates the electric field between corona
discharge electrodes 110 and collector electrodes 120.
Ventilated Boundary Variations
[0055] FIG. 2C is a perspective view that illustrates fluid flow
relative to inlet and outlet portions of a ventilated boundary for
an EHD device that establishes a corona discharge between corona
discharge and collector electrodes of assemblies such as
illustrated in FIGS. 2A and 2B. The illustrated EHD device
configuration provides a useful context in which to describe
certain aspects of certain illustrative embodiments. As detailed
herein, a wide variety of EHD device configurations may be employed
and the particular configuration and component geometries depicted
in the present illustration should not be taken as limiting.
[0056] As described above with reference to FIG. 1, when a high
intensity electric field is established between corona discharge
collector electrodes (here, corona discharge electrodes 110 and
collector electrodes 120), air molecules near a corona discharge
region become ionized and are accelerated in the electric field
toward collector electrodes. Collisions with neutral molecules
impart momentum, thereby inducing a corresponding movement of fluid
molecules in a fluid flow direction.
[0057] Thus, in the illustration of FIG. 2C, flow 29 is induced by
operation of the EHD device (EHD device 2) defined by placement of
corona discharge electrodes 110 closely proximate to collector
electrodes 120. In the illustrated embodiment, a partial surface 10
of an enclosure (e.g., a partial side or back side surface of a
laptop computer enclosure) includes ventilated boundary portions
103 and 104 that respectively admit ambient air from outside the
enclosure and allow air from inside the enclosure to exit. A
generally "U" shaped flow path is illustrated. In the illustrated
embodiment, both collector electrodes 120 and additional heat
transfer surfaces 122 may be employed to transfer heat generated at
a thermal source disposed in the interior of the enclosure to the
air flow. Thermal pathways from the thermal source (e.g., from a
processor or graphics unit) are omitted for simplicity of
illustration.
[0058] FIGS. 3 and 4 illustrate ventilated boundary configurations
in which air flow is motivated between respective portions of the
ventilated boundary formed on different surfaces of an enclosure.
For simplicity of illustration, corona discharge components and
collector electrode components are each illustrated as a general
volume separated by a small air gap 102 across which corona
discharge voltages may be established. The generalized volumetric
presentation of corona discharge and collector electrode components
will be understood to be representative of various EHD device
configurations, including the substantial range of alternative EHD
device configurations and geometries specifically described and/or
illustrated herein.
[0059] In particular, FIG. 3 is a perspective view of EHD device 3
illustrated as being positioned proximate to adjoining partial
boundary surfaces 10 and 20 of an enclosure large enough to contain
EHD device 3. Partial boundary surface 10 includes a ventilated
portion 104, and partial boundary surface 20 includes a ventilated
portion 105. When EHD device 3 is operational in this position
within an enclosure, EHD forces generated in air gap 102 between
one or more corona discharge electrodes 110 and collector
electrodes 120 motivate the fluid in the direction of flow 39
through or over collector electrodes 120 to exit the enclosure
through ventilated portion 104 of partial boundary surface 10.
Fluid enters the enclosure through ventilated portion 105 of
partial boundary surface 20 and is generally drawn in the direction
of flow 39 toward corona discharge component 110. The position and
configuration of EHD device 3 thus provides a relatively compact
and short path for the flow of fluid through the enclosure.
[0060] In FIG. 3, EHD device 3 is situated in a three-dimensional
coordinate system 101 in which the x-y plane respectively
designates the width and depth of EHD device 3 and the z direction
designates the height of EHD device 3. When coordinate system 101
also represents the coordinate system of the enclosure, boundary
surface 10 may be a "side" of the enclosure and boundary surface 20
may be the "bottom" of the enclosure. A person of skill in the art
will recognize that coordinate system 101 is only an exemplary
representation of the position EHD device may occupy in the
enclosure, and that EHD device 3 could be positioned as shown
between any two adjoining boundary surfaces of the enclosure. So,
for example, when the enclosure has a coordinate system 111 in
which the c direction designates the height of the enclosure and
the a-b plane designates the width and depth of the enclosure,
respectively, when EHD device is situated in the enclosure
according to coordinate system 111, boundary surface 10 would be
considered to be the "top" of the enclosure and boundary surface 20
would be considered to be a "side" of the enclosure.
[0061] FIG. 4 is a perspective view of EHD device 4 illustrated as
being positioned proximate to opposing partial boundary surfaces 10
and 30 of an enclosure large enough to contain EHD device 4.
Partial boundary surface 10 includes a ventilated portion 104, and
partial boundary surface 30 includes a ventilated portion 106. When
EHD device 4 is operational in this position within an enclosure,
EHD forces generated in air gap 102 between one or more corona
discharge electrodes 110 and collector electrodes 120 motivate the
fluid in the direction of flow 49 through or over collector
electrodes 120 to exit the enclosure through ventilated portion 104
of partial boundary surface 10. Fluid enters the enclosure through
ventilated portion 106 of partial boundary surface 30 and is
generally drawn in the direction of flow 49 toward discharge
electrodes 110. When the distance 108 between opposing partial
boundary surfaces 10 and 30 of the enclosure is small, the position
of EHD device 4 thus provides a relatively compact and short path
for the flow of fluid through the enclosure.
[0062] When coordinate system 101 also represents the coordinate
system of the enclosure, boundary surface 10 may be a first "side"
of the enclosure and boundary surface 30 may be a second, opposing
"side" of the enclosure. However, it is understood that, when the
enclosure has a coordinate system 111 in which the c direction
designates the height of the enclosure and the a-b plane designates
the width and depth of the enclosure, respectively, when EHD device
is situated in the enclosure according to coordinate system 111,
boundary surface 10 would be considered to be the "top" of the
enclosure and boundary surface 30 would be considered to be a
"bottom" of the enclosure.
Illustrative EHD Device Variations
[0063] Although EHD device configurations are simplified for some
depictions and descriptions herein to emphasize other aspects
(particularly flows and placements with respect to ventilated
boundary portions of an enclosure), it should be understood that a
broad range of EHD design variations is envisioned. To this end,
several more detailed illustrations of EHD device configurations
follow. Based on the illustrations and descriptions thereof,
persons of ordinary skill in the art will appreciate a range of EHD
device variations suitable for inclusion as corona discharge
electrode and collector electrode assemblies illustrated more
generally herein.
[0064] FIGS. 5, 6 and 7 depict several illustrative end-on views of
EHD device configurations in which one or more corona discharge
electrodes have longitudinal extent that is oriented orthogonally
to respective generally planar surfaces of collector electrodes.
FIG. 5 depicts an illustrative single corona electrode
configuration. FIG. 6 depicts an illustrative multiple corona
electrode configuration. FIG. 7 depicts an illustrative ganged
configuration.
[0065] More specifically, FIG. 5 is a front, side view of an EHD
device in accordance with some embodiments of the present
invention. EHD device 5 will be understood relative to a
three-dimensional coordinate system 101 in which the x-y plane
respectively designates the width and depth of device 5 and the z
direction (into the page) designates the height, h, of device 5. In
FIG. 5, device 5 motivates flow of a fluid in the y direction; that
is, fluid is drawn into a first, or front, surface of device 5
shown in FIG. 5 and typically exits a surface, opposite the first
surface, not shown in FIG. 5.
[0066] In the configuration illustrated, EHD device 5 includes
first and second opposing frame members 504 and 506 that function
to hold, or support, corona discharge electrode 110 and collector
electrode array 120. Frame members 504 and 506 may be fabricated of
a dielectric material in order to provide electrical isolation from
other components of EHD device 5. Corona discharge electrode 110 in
EHD device 5 has a small radius of curvature and, in some
embodiments, may take the form of a wire or rod. Other shapes for
corona discharge electrode 110 are also possible; for example,
corona discharge electrode 110 may take the shape of barbed wire, a
band, blade or place that, in some embodiments, may present a
knife- or serrated-edge. In some embodiments, a cross-section such
as illustrated in FIG. 1 for electrode 10 may be employed.
Typically, a small radius of curvature or sharp point tends to
facilitate ion production at an appropriate point when high voltage
is applied.
[0067] In general, corona discharge electrode 110 may be fabricated
in a wide range of materials. For example, in some embodiments,
compositions such as described in U.S. Pat. No. 7,157,704, filed
Dec. 2, 2003, entitled "Corona Discharge Electrode and Method of
Operating the Same" and naming Krichtafovitch et al. as inventors
may be employed. U.S. Pat. No. 7,157,704 is incorporated herein for
the limited purpose of describing materials for some corona
discharge electrodes that may be employed in some embodiments. In
general, a high voltage power supply (not specifically shown)
creates the electric field between corona discharge electrode 110
and collector electrode array 120.
[0068] In the embodiment of FIG. 5, frame members 504 and 506
include a pair of curved recesses 108, generally conformal with an
end portion of corona discharge electrode 110. Each opposing end of
corona discharge electrode 110 passes through a respective recess
108 and is attached to an interior portion (not shown) of a
respective frame member. Recess 108 provides a transition region
for corona discharge electrode 110 to pass through from its
positioning proximate to collector electrode array 120 and one of
frame members 504 and 506. The transition region eliminates the
sharp points that may occur at an abrupt junction between corona
discharge electrode 110 and its respective frame member, thereby
reducing arcing and other undesirable effects in the surrounding
high electric field created during operation of EHD device 5.
[0069] With continued reference to FIG. 5, collector electrode
array 120 includes a plurality of substantially parallel unit
structures 121 attached to a pair of parallel and substantially
flat, spaced apart support members 132. Each unit structure 121
functions as a collector electrode and may generally have greater
depth (in the y direction) than width (in the x direction). Unit
structures 121 may be fabricated of any suitable metal material,
such as aluminum or copper. The number of, and distance between,
unit structures 121 in collector array 120 may vary according to
device specifications. Unit structures 121 are generally planar
and, in some embodiments, present a curved leading surface exposed
toward corona discharge electrode 110. In some embodiments, unit
structures 121 include a generally rectangular extent in the
direction of fluid flow (the y direction), although, more
generally, may be formed in other shapes.
[0070] FIG. 6 depicts an illustrative multiple corona electrode
configuration of EHD device 6 akin to that just described. Multiple
corona discharge electrodes 110 are included. Unit structures 121
of collector electrode array 120 are generally planar and present a
leading surface exposed toward corona discharge electrodes 110.
[0071] FIG. 7 is a side view of an EHD device configuration in
which multiple assemblies are ganged to increase total volume of
fluid flow. A first, or front, surface of EHD device 7 is situated
in a three-dimensional coordinate system 101 in which the x-y plane
respectively designates the width and depth of EHD device 7 and the
z direction designates the height, h, of EHD device 7. As before,
EHD device 7 motivates flow of a fluid in the y direction; that is,
fluid is drawn into the first, or front, surface of EHD device 7
and exits a rear surface, opposite the first surface.
[0072] EHD device 7 includes a plurality of corona discharge
electrodes and associated collector electrode arrays of the type
described with respect to EHD device 5 of FIG. 5, assembled in a
single housing or frame. The presentation in FIG. 5 of EHD device 7
as having three EHD device assemblies is solely for the sake of
illustration, and is not intended to be limiting in any way. EHD
device 7 includes opposing frame members that function to hold, or
support, corona discharge electrodes 110 and associated collector
electrode arrays 120. Each frame member includes a plurality of
recesses 108 as previously described.
[0073] In one exemplary implementation of EHD device 7, frame
sections 704 and 706 may have a height, h, of approximately 9 mm,
and a distance 712 between adjacent corona discharge electrodes 110
may be approximately 4 mm. In some embodiments, unit structures 121
present a curved leading surface exposed toward respected corona
discharge electrodes 110.
[0074] FIG. 8A depicts a simplified perspective view, consistent
with certain of the preceding EHD device configurations, of a
corona discharge electrode and several orthogonally-oriented
generally planar collector electrodes with curved leading surface
profiles. FIG. 8B depicts a side cross-sectional view consistent
with FIG. 8A. FIG. 8C depicts a side cross-sectional view for an
alternative collector electrode geometry.
[0075] More specifically, FIG. 8A illustrates several adjacent unit
structures 121 of collector electrode array 120. For simplicity of
description (and generality with respect to alternative EHD device
configurations), such unit structures 121 are hereafter referred to
as collector electrodes 120, although persons of ordinary skill in
the art will immediately recognize that, in some configurations,
additional structures (such as support members 132) may be
electrically conductive and act as part of an overall "collector
electrode." In view of the foregoing, we now turn to the leading
surface(s) 136 of collector electrodes 121.
[0076] Fluid flow through collector electrode array 120 is
generally in the direction of flow 89. In the embodiment shown in
FIG. 8A, collector electrodes 121 are substantially rectangular in
shape, having a leading edge disposed closest to corona discharge
electrode 110 and a trailing edge opposite to leading edge 138. The
leading edge includes a contoured or curved surface 136. As will be
understood by persons of ordinary skill in the art, consistent with
principles of high voltage design, curved leading surface 136 is
intended to present generally curvaceous surface contours toward
corona discharge electrode 110 and any sharp exposed edges are
merely an artifact of the illustration and cross section of FIG.
8A. Corona electrode 110 is shown positioned a distance, d, above
collector electrodes 121. Distance d may sometimes be referred to
as the "gas gap" or "air gap."
[0077] The illustrated EHD device may be constructed in a variety
of sizes, and thus is suitable for a variety of thermal management
applications involving the cooling of electronic circuits. In one
exemplary implementation, corona discharge electrode 110 may be a
bare or coated tungsten wire having a diameter of about 12.5 .mu.m;
collector electrodes 121 of collector array 120 have a height of
approximately 3 mm, a width (thickness) of about 0.25 mm and are
spaced approximately 3 mm apart on center; and the distance, d,
between corona discharge electrode 110 and collector electrodes 121
is approximately 1.6 mm. The voltage applied across the air gap
between corona discharge electrode 110 and collector electrodes 121
may be in the range of 1.5 kV to 4 kV.
[0078] FIG. 8B is a simplified cross-sectional view of corona
discharge electrode 110 and a single collector electrode 121
instance in accord with the curved leading surface profiles
illustrated FIG. 8A. In particular, FIG. 8B illustrates a side view
of collector electrode 121. In operation, when an electric field is
created between corona discharge electrode 110 and collector
electrode 121, ions generally flow in the directions of the
electric field lines. Curved leading surface 136 may provide
certain enhancements to the operation of EHD device 100. For
example, utilizing a generally curved leading surface 136 for
instances of collector electrode 120 may allow for a shorter
distance, d, between corona electrode 110 and collector electrode
121, while at the same time increasing ion production and assisting
in preventing sparks and arcing. In addition, utilizing curved
surface 136 for collector electrode 121 may provide electrical
separation between adjacent corona discharge electrodes in some
embodiment described elsewhere herein that gang multiple EHD device
instances.
[0079] FIG. 8C is a simplified cross-sectional view of corona
discharge electrode 110 and a single collector electrode 121
instance in accord with an alternative leading surface profile. In
some embodiments, such as that illustrated in FIG. 6, multiple
corona discharge electrodes 110 may be provided.
[0080] FIG. 9A depicts a side cross-sectional view, consistent with
certain alternative EHD device configurations, of a corona
discharge electrode and several generally planar collector
electrodes that are arranged to present a curved array of leading
surfaces, where each of the leading surfaces is oriented generally
parallel to the longitudinal extent of the corona discharge
electrode. FIG. 9B depicts a perspective view of a collector
electrode assembly consistent with the arrangement of FIG. 9A. FIG.
9C depicts perspective view of a corona discharge electrode and
collector electrode assemblies consistent with the arrangement.
Note that perspective views are situated in a three-dimensional
coordinate system 101 (FIGS. 9B and 9C) in which the x-y plane
respectively designates width and depth of the illustrated EHD
device. Flow 99 is in generally the y direction and the z direction
indicates the height of the device.
[0081] Referring to FIG. 9A, EHD device 9 includes an array 120 of
collector electrodes 121. Collector electrodes disposed between top
and bottom collector electrodes are recessed away from corona
discharge electrode 110 in a manner such that the leading surfaces
thereof form a curved leading surface array 906. When EHD device 9
is operational, the EHD forces generated between corona discharge
electrode 110 and collector electrode array 120 motivate fluid in
the direction of flows 99 between the collector electrodes. FIG. 9B
is a front perspective view of collector electrode array 120 of
FIG. 9A showing individual collector electrodes 121 attached to
support members. FIG. 9C is a front perspective view of EHD device
9 showing corona discharge electrode 110 supported by a frame
positioning corona discharge electrode 110 a distance 102 from
collector electrode array 120, and illustrating the fluid flow
direction produced when EHD device 9 is operational.
[0082] Assemblies for corona discharge electrode 110 and for
collector electrode array 120 are shown as discrete structures
purely for purposes of illustration relative to the more general
depictions that follow. As before, persons of ordinary skill in the
art will recognize that EHD device 9 may be constructed using a
unitary dielectric support structure. Also, while a single corona
discharge electrode and generally curved arrangement of collector
electrode leading surfaces is illustrated, persons of ordinary
skill in the art will appreciate (based on the description herein)
that multiple corona electrode variations, and variations in which
other (e.g., uncurved) arrangements of leading surfaces present,
may be provided in other embodiments.
Flow Paths
[0083] Each of the EHD device embodiments described herein includes
at least one corona discharge electrode. As previously explained,
corona discharge electrodes generally have a small radius of
curvature and may take the form of a wire or rod or edge. Other
shapes for the corona discharge electrode are also possible; for
example, the corona discharge electrode may take the shape of
barbed wire, wide metallic strips, and serrated plates or
non-serrated plates having sharp or thin parts that facilitate ion
production at the portion of the electrode with a high radius of
curvature when high voltage is applied. Corona discharge electrodes
may be fabricated in a wide range of materials.
[0084] Likewise, each of the EHD device embodiments described
herein includes at least one collector electrode. In general,
collector electrodes may be fabricated of any suitable metal
material, such as aluminum or copper, and may have the shape of a
bar or plate. Collector electrodes (referred to therein as
"accelerating" electrodes) may be formed in aerodynamically
"friendly" shapes that provide a low coefficient of drag for the
fluid (air) in the range of 0.01 to no greater than 1. Furthermore,
as known in the art, collector electrodes may be fabricated with
high resistivity material (often as a coating) that acts to quench
arcing. Examples of such relatively high resistance materials
include carbon filled plastic, silicon, gallium arsenide, indium
phosphide, boron nitride, silicon carbide, and cadmium selenide.
Typically, many of the EHD devices described and illustrated herein
will comprise an array of collector electrodes. The number of, and
distance between, the collector electrodes, and the shape of the
collector electrodes comprising a collector electrode array may
vary according to device specifications and the type of fluid being
moved.
[0085] In order to simplify description of flows illustrated in
FIGS. 10A-18 that follow, one or more corona discharge electrodes
of any suitable design or configuration are illustrated simply as
corona discharge electrode component 110. Likewise, one or more
collector electrodes of any suitable design or configuration are
illustrated simply as collector electrode component 120. In
general, the distance between a corona discharge electrode and a
collector electrode is referred to as the "gap" or "air gap" and is
determined by the particular shapes of the corona discharge
electrode(s) and the collector electrode(s). Such gaps are
illustrated (at a high-level) as air gap 102 in the some of
simplified flow illustrations of FIGS. 10A-18. Finally, although
terminals of a high voltage power supply are typically electrically
connected to and create the electric field between corona discharge
and collector electrodes which in turn generates an ion stream that
accelerates ambient fluid toward the collector electrode, power
supply connections are omitted for simplicity.
[0086] Several of the embodiments of the EHD devices described
herein are illustrated as being proximate to a single boundary
surface, or single partial boundary surface (see, for example,
partial boundary surface 10 in FIG. 1) that forms one of the
boundary sides, top or bottom of an enclosure (e.g., housing or
container or case) large enough to contain the EHD device. The
boundary surface of the enclosure has at least one ventilated
portion (for example, ventilated portion 104 in FIG. 10A) that both
admits fluid from outside into the enclosure and allows for fluid
inside the enclosure to exit. Each such embodiment is illustrated
to show the path of fluid flow into and out of the enclosure
through the single boundary surface when the EHD device is
operational, and is thus described below as producing a
"single-surface fluid flow path" into and out of the enclosure that
contains the device. Each of the embodiments of an EHD device
illustrated herein that is illustrated to show a single-surface
fluid flow path is preferably housed in an enclosure in which the
single boundary surface is the predominant boundary surface of the
enclosure that is ventilated to permit a fluid to enter or exit the
enclosure. However, this is not a requirement for implementing
these EHD device embodiments; the enclosure that contains the
device may have more than one ventilated boundary surface to permit
a fluid to enter or exit the enclosure. Moreover, the single
ventilated boundary surface is not limited to being a flat or
linear surface as illustrated in several of the figures; it may be
a curved surface with sufficient curvature to surround the EHD
device such that fluid is drawn in from one portion of the curved
boundary surface and is forced out of the enclosure by the
operation of the EHD device through another portion of the curved
boundary surface.
[0087] Several other embodiments of EHD devices described herein
are illustrated as being proximate to at least two boundary
surfaces, or partial boundary surfaces (for example, partial
boundary surfaces 104 and 105 in FIG. 10) of an enclosure large
enough to contain the EHD device. Each of the at least two boundary
surfaces of the enclosure has a ventilated portion that both admits
ambient air from outside into the enclosure and allows for air
inside the enclosure to exit. The figures that illustrate these
embodiments show the path of fluid flow that is created when the
EHD device is operational into and out of the enclosure through the
at least two boundary surfaces.
[0088] While not illustrated and described herein, it is understood
that any one of the embodiments of the EHD devices described herein
may be implemented in a plural configuration in which two or more
individual EHD devices of the type described herein are
sequentially disposed relative to a desired fluid flow direction.
Each individual EHD device is then referred to as a stage, and the
entire configuration is referred to as a multi-stage EHD device. In
operation, each individual EHD device stage may be operated
simultaneously and synchronously with the others in order to
produce increased volume and pressure of fluid flow in the desired
direction, thereby sequentially accelerating a fluid through the
multiple stages. Synchronous operation of a multi-stage EHD device
is defined herein to mean that a single power supply, or multiple
synchronized and phase-controlled power supplies, provide high
voltage power to each EHD device stage such that both the phase and
amplitude of the electric power applied to the same type of
electrodes in each stage (i.e., the corona discharge electrodes or
the collector electrodes) are aligned in time. U.S. Pat. No.
6,727,657, entitled "Electrostatic Fluid Accelerator for and a
Method of Controlling a Fluid Flow" provides a discussion of the
configuration and operation of several embodiments of a multi-stage
EHD device, including computing an effective inter-stage distance
and exemplary designs for a high voltage power supply for powering
neighboring EHD device stages with respective synchronous and
syn-phased voltages. U.S. Pat. No. 6,727,657 is incorporated by
reference herein in its entirety for all that it teaches.
[0089] The EHD devices described and illustrated herein may be
operated to dissipate heat generated by a thermal source disposed
in the enclosure using principles of forced convective heat
transfer. Forced convective heat transfer is a mechanism of heat
transfer in which the movement of the fluid that dissipates the
heat is induced by an external source such as a pump or fan or an
EHD device of the type described herein. The ability to attain
efficient heat dissipation depends in part on both the volumetric
flow rate and the velocity of the air flow that can be achieved by
the fluid movement source, as well as on the total surface area of
the convective surfaces from which the heat is transferred.
Improvements in heat dissipation efficiency of a thermal management
solution may be achieved, in part, by design choices that (1)
minimize fluid flow resistance caused by obstacles and flow
restrictions in the path of the fluid flow, (2) minimize the length
of the path through which the fluid flows as it is forced over or
around the heated convective surfaces, (3) maximize the total
surface area of the convective surfaces from which the heat is
transferred, and (4) minimize the speed of fluids in the system
while maintaining a desired, or target, fluid flow rate. The
embodiments of the EHD devices described herein achieve
improvements in heat dissipation efficiency using one or more of
these three design choices, alone or in combination.
[0090] When an embodiment of an EHD device illustrated herein is
used to dissipate heat from a thermal source, it may be part of a
thermal management system that may further comprise one or more
additional elements that efficiently transports heat generated by
the thermal source to the collector electrode component of the EHD
device, thereby heating the collector electrode component. The
operational EHD device causes a substantial amount of the fluid
entering the enclosure to generally follow the fluid flow path
shown by the arrows in each figure through or over the heated
collector electrode component to exit the enclosure, thereby
dissipating heat accumulating in the air above and in the vicinity
of the EHD device, and in particular, the collector electrode
component.
Fluid Flow Paths Involving Ventilated Portions of a Single Boundary
Surface
[0091] FIG. 10A is a perspective view that illustrates flows
relative to an EHD device 100 situated in a three-dimensional
coordinate system 101 in which the x-y plane respectively
designates the width and depth of device 100 and the z direction
designates the height of device 100. EHD device 100 comprises
corona discharge component 110 and collector electrode component
120. These components are shown as generally rectangular structures
for purposes of illustration only, and their relative sizes and
shapes in FIG. 10A are not intended to convey any specific
relationships between the two components. Corona discharge
component 110 includes at least one corona discharge electrode, and
collector electrode component 120 includes at least one collector
electrode, neither of which is individually shown in FIG. 10A. EHD
device 100 is illustrated as being positioned proximate to partial
boundary surface 10 of an enclosure large enough to contain EHD
device 100. Partial boundary surface 10 includes a ventilated
portion 104.
[0092] In the embodiment of FIG. 10A, when EHD device 100 is
operational, a substantial amount of the fluid entering the
enclosure through a first portion of partial boundary surface 10 is
drawn generally in the direction of arrow 140 and follows air flow
path 150 toward corona discharge component 110 of EHD device 100.
The EHD forces generated in air gap 102 between corona discharge
component 110 and collector electrode component 120 force fluid in
the direction of arrow 130 through or over collector electrode
component 120 to exit the enclosure through a second portion of
partial boundary surface 10. The configuration of EHD device 100
thus provides a relatively compact and short "U" shaped path, as
defined by arrow 140, arrow 150 and arrow 130, for the flow of
fluid through the enclosure.
[0093] FIG. 11A is a perspective view that illustrates flows
relative to an EHD device 200 which is a variation of EHD device
100 (previously described) in which both collector electrode
component 120 and additional heat transfer surfaces 122 are
employed to transfer heat to the fluid flow. In some embodiments in
accord with FIG. 11A, additional heat transfer surfaces 122 are an
electrically and thermal conductive extension of collector
electrode component 120 whose surfaces are not sufficiently
proximate to a corona discharge electrode to contribute to EHD
motivated fluid flow. In some embodiments, heat transfer surfaces
122 are structurally distinct from collector electrode component
120, though each is coupled into a heat transfer pathway. In some
embodiments, heat transfer surfaces 122 may be the dominant heat
transfer surfaces. As before, partial boundary surface 10 has a
ventilated portion (not specifically shown in FIG. 11A) that
permits a fluid to flow into and out of the enclosure. Fluid flow
follows the same path as illustrated in FIG. 10A, except that the
fluid passes through or over additional heat transfer surfaces
122.
[0094] In some embodiments, heat transfer surfaces of EHD device
100 (and of other EHD devices described herein) whether operating
as collector electrodes or otherwise are at least partially coated
with ozone reducing catalyst material. Although a variety of ozone
reducing catalysts may be employed, for collector electrode
surfaces a generally non-conductive catalyst may be preferred. U.S.
Pat. No. 6,603,268 to Lee, entitled "Method and Apparatus for
Reducing Ozone Output from an Ion Wind Device" described catalyst
materials (including certain manganese dioxide coatings) suitable
for use in some embodiments and is incorporated herein by
reference.
[0095] FIG. 12A is a perspective view that illustrates flows
relative to an EHD device 300 which is a further variation of EHD
device 200 (previously described) in which both collector electrode
component 120 and additional heat transfer surfaces 122 are
employed to transfer heat to the fluid flow. As before, in some
embodiments, both collector electrode component 120 and additional
heat transfer surfaces 122 are employed to transfer heat to the
fluid flow and partial boundary surface 10 has a ventilated portion
(not specifically shown in FIG. 12A) that permits a fluid to flow
into and out of the enclosure. The configuration of EHD device 300
provides two paths for fluid flow through the electronic apparatus:
the first is defined by the combination of the arrow 340, arrow 350
and arrow 330, and the second is defined by the combination of the
arrow 360, arrow 370 and arrow 330.
[0096] In some embodiments in accord with FIG. 12A, additional heat
transfer surfaces 122 are implemented as electrically and thermally
conductive extensions of collector electrode component 120 whose
surfaces are not sufficiently proximate to a corona discharge
electrode to contribute to EHD motivated fluid flow. In such
embodiments, corona discharge component 110 may be positioned at
various points along the illustrated x-axis 326 such that portions
sufficiently proximate to corona discharge electrodes constitute
the collector electrode array 122 and remaining portions constitute
the additional heat transfer surfaces 122. In some embodiments,
additional heat transfer surfaces 122 are structurally distinct
from collector electrode component 120, though each is coupled into
a heat transfer pathway. In some embodiments, heat transfer
surfaces 122 may be the dominant heat transfer surfaces.
[0097] FIGS. 10B, 11B-D, 12B and 13-19 are top plan views of
various embodiments of EHD devices situated in a three-dimensional
coordinate system 103 in which the x-y plane respectively
designates the width and depth of the embodiment of the EHD device
illustrated in the respective figure. The z direction indicates the
height of the device.
[0098] FIG. 10B is a top plan view of EHD device 100 of FIG. 10A,
showing EHD device 100 positioned proximate to partial boundary
surface 10 of an enclosure that houses EHD device 100, and further
showing the fluid flow path defined by arrows 140, 150 and 130 into
and out of the enclosure when EHD device is operational. Similarly,
FIG. 11B shows a top plan view of EHD device 200 and FIG. 12B shows
a top plan view of EHD device 300.
[0099] FIG. 11C shows a top plan view of a variation on EHD device
200 in which corona discharge component 110 and collector electrode
component 120 are oriented to motivate flow into (rather that out
of) the enclosure through partial boundary surface 10. The
illustrated EHD device 210 provides the same relatively compact and
short path, as defined by arrow 140, arrow 150 and arrow 130, for
the flow of fluid through the enclosure as provided by the EHD
devices of FIGS. 10A, 10B, 11A and 11B, but achieves fluid flow in
a different manner. In the illustration of FIG. 11C, when EHD
device 210 is operational, the high voltage power supply (not
shown) energizes corona discharge component 110 and collector
electrode component 220 so as to generate EHD forces in the
direction of arrow 140, thereby pulling fluid from outside of the
enclosure through an inlet portion of ventilated partial side
boundary 10 into the enclosure and then along the fluid flow path
defined by arrows 150 and 130 over or through additional heat
transfer surfaces 122 to exit the enclosure through an outlet
portion of ventilated partial side boundary 10.
[0100] FIG. 11D shows a top plan view of another variation on EHD
device 200 (illustrated as EHD device 400) in which additional heat
transfer surfaces 122 are extended in the y-axis direction to
facilitate greater transfer heat to the fluid flow. As before,
additional heat transfer surfaces 122 may be an electrically and
thermal conductive extension of collector electrode component 120
whose surfaces are not sufficiently proximate to a corona discharge
electrode to contribute to EHD motivated fluid flow or, in some
embodiments, heat transfer surfaces 122 may be structurally
distinct from collector electrode component 120.
[0101] FIG. 11E shows a top plan view of still another variation on
EHD device 200 (illustrated as EHD device 410) in which heat
transfer surfaces 122 are extended such that fluid flow motivated
by corona discharge between one or more electrodes of corona
discharge component 110 and collector electrodes of collector
electrode component 120 motivates fluid flow over heat transfer
surfaces 122. In some embodiments, heat transfer surfaces 122 may
be structurally distinct, though appurtenant to, collector
electrode component 120.
[0102] FIG. 13 is a top plan view of a configuration 500 that
includes two EHD devices 530 and 540 staged adjacent to one
another. EHD device 530 includes corona discharge component 530a
and collector electrode component 530b oriented to motivate flow
into the enclosure through an inlet portion of partial boundary
surface 10. EHD device 540 includes corona discharge component 540a
and collector electrode component 540b oriented to motivate flow
out of the enclosure through an outlet portion of partial boundary
surface 10. EHD devices 530 and 540 proximate to partial boundary
surface 10 of an enclosure large enough to contain EHD device 500.
The configuration provides the same relatively compact and short
path, as defined by arrow 140, arrow 150 and arrow 130, for the
flow of fluid through the enclosure as provided by the EHD devices
of FIGS. 10A, 10B, 11A and 11B, but achieves the fluid flow path in
a different manner.
[0103] In the configuration of FIG. 13, when EHD devices are
operational, a high voltage power supply (not shown) energizes
corona discharge component 530a and collector electrode component
530b of EHD device 530 so as to generate EHD forces in the
direction of arrow 140, thereby pulling fluid from outside of the
enclosure through an inlet portion of ventilated partial side
boundary surface 10 into the enclosure. The high voltage power
supply also energizes corona discharge component 540a and collector
electrode component 540b of EHD device 540 so as to generate EHD
forces in the direction of arrow 130 to force the fluid to exit the
enclosure through an outlet portion of ventilated partial side
boundary surface 10. The configuration is constructed so as to have
an electrical boundary 523 between the EHD devices 530 and 540.
Reversible Flow Configurations
[0104] FIGS. 14A and 14B are top plan views of a reversible flow
EHD device 600 in accordance with some embodiments of the present
invention. Reversible flow EHD device 600 includes corona discharge
electrodes 610a and 610b and collector electrodes 620. EHD device
600 is illustrated proximate to a ventilated portion of partial
boundary surface 10 of an enclosure large enough to contain EHD
device 600. EHD device 600 may be operated in at least two
modes.
[0105] In one mode of operation, illustrated in FIG. 14A, EHD
device 600 is operated to motivate fluid flow along a relatively
compact and short path, as defined by arrow 140, arrow 150 and
arrow 130, such as that previously illustrated for flow of fluid
through an enclosure relative EHD devices 100 and 200 (recall FIGS.
10A and 11A). In this first mode of operation, fluid passes through
or over heat transfer surfaces 622 as it enters the enclosure
through a first inlet portion 11 of ventilated partial boundary
surface 10. A high voltage power supply (not specifically shown)
provides a voltage differential between collector electrodes 620
and corona discharge electrodes 610a so as to generate EHD forces
in the direction of arrow 130, thereby pulling fluid from inside of
the enclosure, including a substantial amount of the fluid entering
the enclosure in the direction of arrows 140 and 150 and forcing
the fluid through a second outlet portion 12 of ventilated partial
boundary surface 10 to exit the enclosure.
[0106] With reference to FIG. 14B, in a second mode of operation
EHD device 600 motivates fluid flow along a path that is generally
opposite that illustrated in FIG. 14A. The high voltage power
supply (not specifically shown) provides a voltage differential
between collector electrodes 620 and corona discharge electrodes
610b so as to generate EHD forces in the direction of arrow 140,
thereby pulling fluid from outside of the enclosure through (now)
inlet portion 12 of ventilated partial boundary 10 into the
enclosure and then along the fluid flow path defined by arrows 150
and 130 over or through heat transfer surfaces 622 to exit the
enclosure through (now) outlet portion 11 of ventilated partial
boundary surface 10.
[0107] In some embodiments, both collector electrodes 620 and
additional heat transfer surfaces 622 are thermally coupled to
transfer heat to the EHD motivated fluid flow. In some embodiments,
heat transfer surfaces 622 are the dominant heat transfer
structures. As with previous configurations, additional heat
transfer surfaces 622 may be implemented as an extension of
structures that provide collector electrodes 620. Alternatively, in
some embodiments, heat transfer surfaces 622 and collector
electrodes 620 are implemented as distinct structures that both
thermally coupled into heat transfer paths from heat dissipating
devices within the enclosure.
[0108] FIG. 14C depicts a further variation in which an array of
collector electrodes 620 is at least partially bifurcated by a
portion of heat transfer surfaces 622. In the embodiment of FIG.
14C, corona discharge electrodes 610a are positioned proximate to a
first array of leading surfaces of respective collector electrodes,
such that when energized, fluid flow is motivated in the first flow
direction 140. Corona discharge electrodes 610B are correspondingly
positioned proximate to a second array of leading surfaces, such
that when energized, fluid flow is motivated in second flow
direction 130. In each case, motivated fluid flow includes flow
through or over the interposed portion of heat transfer surfaces
622. In some embodiments, the illustrated extension of heat
transfer surfaces 622 proximate ventilated boundary portion 11 may
be omitted or extended consistent with design objectives for a
given thermal management solution.
[0109] As before, any of a variety of variations on corona
discharge and collector electrode geometries and positional
interrelationships are envisioned. Based on the description herein,
persons of ordinary skill in the art will appreciate variations
consistent with alternatives described herein, including
alternatives illustrated and described with respect to FIGS. 5-9C,
above. Also as before, any of a variety of heat transfer paths may
be provided from heat dissipating devices or electronics to heat
transfer surfaces 622 and/or to collector electrodes 620, including
heat pipes not specifically shown.
Repeated or Plural Configurations
[0110] Each of EHD device configurations described herein may be
implemented in a repeated plural configuration in order, for
example, to improve fluid flow efficiency, to fit into a specific
space within an enclosure, or to take advantage of a particular
portion of an available ventilated boundary surface. FIG. 15 is a
top plan view of an embodiment of EHD device 700 that illustrates
one such plural configuration. EHD device 700 includes two EHD
device instances (400a and 400b) such as previously illustrated and
described with reference to FIGS. 11A-11D. Other embodiments may
include additional instances in accord with cooling requirements,
space constraints or other design factors. In the illustrated
configuration, EHD devices 400a and 400b are positioned proximate
to partial boundary surface 10 of an enclosure large enough to
contain EHD device 700 and with collector electrodes in a spaced
apart configuration. Inlet portions and outlet portions of the
ventilation boundary are interspersed in the illustrated
configuration. In other configurations, EHD devices 400a and 400b
may be positioned with collector electrodes adjacent to each other
with corresponding changes to the spatial distribution of inlet
portions and outlet portions of the ventilation boundary. Each EHD
device (400a and 400b) may be operated by a respective, dedicated
high voltage power supply, or both devices may be operated by the
same high voltage power supply.
[0111] Operation of each EHD device 400a and 400b and the fluid
flow paths produced will be understood as described herein (for
individual instances) relative to FIGS. 11A, 11B and 11D. In
general, EHD devices 400a and 400b may be operated simultaneously
or independently, according to the needs of the application or
function they perform. Additional heat transfer surfaces 422a and
422b which are respectively associated with EHD devices 400a and
400b will also be understood as previously described. As before,
heat transfer surfaces 422a and 422b may be implemented as an
extension of collector electrode structures or may be distinct,
though thermally coupled structures. In some thermal management
system embodiments, heat transfer surfaces 422a and 422b may be the
dominant heat transfer surfaces. Although, heat transfer surfaces
422a and 422b are illustrated as being of substantially the uniform
size, such uniformity is not an implementation requirement. In some
embodiments, either or both heat transfer surfaces 422a and 422b
may be omitted entirely.
[0112] Repeated plural configurations may also be implemented as
combinations of dissimilar EHD devices. For example, FIG. 16 is a
top plan view of an embodiment of EHD device 800 that illustrates
one such plural configuration. EHD device 800 includes an instance
of EHD device 400 (recall FIGS. 11A, 11B and 11D) and an instance
of EHD device 210 (recall FIG. 11C). Other embodiments may include
additional instances in accord with cooling requirements, space
constraints or other design factors. In the illustrated
configuration, EHD device instances 400 and 210 are positioned
proximate to partial boundary surface 10 of an enclosure large
enough to contain EHD device 800 and with additional heat transfer
surfaces adjacent each other. Inlet portions and outlet portions of
the ventilation boundary are interspersed in the illustrated
configuration. In other configurations, EHD devices 400 and 210 may
be positioned differently with corresponding changes to the spatial
distribution of inlet portions and outlet portions of the
ventilation boundary. As before, each EHD device (400 and 210) may
be operated by a respective, dedicated high voltage power supply,
or both devices may be operated by the same high voltage power
supply.
[0113] As before, additional heat transfer surfaces associated with
the EHD device instances (here EHD device 400 and EHD device 210)
will be understood as previously described. As before, heat
transfer surfaces may be implemented as an extension of collector
electrode structures or may be distinct, though thermally coupled
structures. In some thermal management system embodiments, heat
transfer surfaces other than the collector electrodes may be the
dominant heat transfer surfaces and, as before, while heat transfer
surfaces are illustrated as substantially uniform in size, such
uniformity is not an implementation requirement. Either or both
heat transfer surfaces may be omitted entirely in embodiments in
which collector electrodes provide substantial heat transfer to
motivated fluid flows.
[0114] FIG. 17 is a top plan view of an embodiment of EHD device
900 that illustrates yet another plural configuration. The
illustrated configuration includes an EHD device instance 400
(recall FIGS. 11A, 11B and 11D) together with an additional EHD
device 530. EHD device 900 is positioned proximate to partial
boundary surface 10 of an enclosure large enough to contain EHD
device 900. Although a central heat transfer surface is illustrated
in association with EHD device instance 400, in some embodiments,
heat transfer surfaces may be thermally coupled to collector
electrodes of both constituent devices.
[0115] As before, each EHD device may be operated by a respective,
dedicated high voltage power supply, or both devices may be
operated by the same high voltage power supply. The operation of
EHD device instances 400 and 530 and the fluid flow paths produced
are described above in the description of FIGS. 11A, 11B, 110 and
13. Inlet portions and outlet portions of the ventilation boundary
are again interspersed in the illustrated configuration. Note that
some amount of the fluid drawn in from the exterior of the
enclosure by EHD device instance 530 may also travel along fluid
path 950 toward corona discharge electrode 110 of EHD device 400
which will then operate to force the fluid to exit the
enclosure.
[0116] EHD device 900 may itself be replicated in a further plural
configuration as illustrated in FIG. 18 as EHD device instance 910.
EHD device 910 includes two instances of EHD devices 900 positioned
as shown together with additional heat transfer surfaces 924
inserted therebetween. EHD device 910 is positioned proximate to
partial boundary surface 10 of an enclosure large enough to contain
EHD device 910. Inlet portions and outlet portions of the
ventilation boundary are distributed with adjacent inflows and
outflows in the illustrated configuration. As before, each of the
individual EHD devices of EHD device 910 may be operated
independently by a respective dedicated high voltage power supply.
Alternatively, some or all of the devices may be operated by the
same high voltage power supply. The operation of constituent
devices of EHD device 900 and the fluid flow paths produced are as
described above relative to respective ones of FIGS. 11A, 11B, 11D,
13 and 17.
[0117] As before, some amount of the fluid drawn in from the
exterior of the enclosure by EHD device 530 may travel along both
fluid paths 950 and 960 toward a neighboring corona discharge
electrode (e.g., 110a or 110b) which will then operate to force the
fluid to exit the enclosure. The individual EHD devices may be
operated simultaneously or independently, according to the needs of
the application or function they perform. As before, uniformity of
heat transfer surfaces is not an implementation requirement.
Likewise, certain heat transfer surfaces may be omitted entirely
and thermal coupling amongst heat transfer surfaces and collector
electrodes may be adapted in accord with design goals of a
particular thermal management system.
EHD Device as Part of a Thermal Management Solution
[0118] FIGS. 19A, 19B and 19C illustrate EHD device configurations
akin to those previously introduced (e.g., with respect to FIGS.
2A, 2B and 2C) in a thermal management solution context. As before,
designs for corona discharge electrode and collector electrode
assemblies are illustrative and will be understood as but one
example amongst the wide range of variations on electrode designs,
geometry and positional interrelationships described herein.
Accordingly, based on the description herein, persons of ordinary
skill in the art will appreciate adaptations of the illustrated
thermal management configurations to alternative corona and
collector electrode configurations. Indeed, based on the
description of FIGS. 19A, 19B and 19C, it will be understood that
each of the EHD device configurations described herein may be
including as part of a similar thermal management system for
dissipating heat generated by one or more thermal sources.
[0119] FIG. 19A is a schematic drawing of corona discharge
electrode component 1210 including a plurality of corona wires 1216
supported by a frame 1214. FIG. 19B is a schematic drawing of a
first embodiment of a convective heat transfer component.
Convective heat transfer component 1220 includes collector
electrode array 1222 and sub-component 1224 having a convective
surface 1226. Collector electrode array 1222 includes a plurality
of vertically disposed unit structures each of which may function
as a collector electrode. Sub-component 1224 may also serve as a
support for the vertical collector electrodes of collector
electrode array 1222, as shown in FIG. 12B, or it may be a separate
structure. In general, there is no requirement that the
sub-components that comprise convective heat transfer component
1220 be either distinct physical entities from one another, or that
they be constructed as a single integral structure. For example, in
some embodiments, collector electrode array 1222 and sub-component
1224 may be electrically isolated from each other during operation
of the EHD device, but are constructed to be thermally
connected.
[0120] In some embodiments, collector electrode array 1222 may
function both as a collector electrode array and as a heat sink,
and sub-component 1224 may function as a thermal conduit such as a
heat pipe. As defined herein, a heat sink is an object that absorbs
and dissipates heat from another object using either direct or
radiant thermal contact. When sub-component 1224 functions as a
thermal conduit, it is preferable, but not necessary, to
electrically isolate it from the thermal source using a thermal
interface material and to maintain a thermal connection between
sub-component 1224 and collector electrode array 1222. Further,
when sub-component 1224 functions as a thermal conduit, it need not
also function as a support for the unit structures of collector
electrode array 1222; it is sufficient that thermal conduit 1224
come in contact with each of the unit structures of collector
electrode array 1222 such that collector electrode array 1222
absorbs heat from thermal conduit 1224.
[0121] FIG. 19C illustrates EHD device 1250 configured for
dissipating heat from a thermal source. EHD device 1250 includes
corona discharge electrode component 1210 and convective heat
transfer component 1220 (as previously described with reference to
FIGS. 19A and 19B) positioned proximate to a ventilated boundary
portion 1204 of partial boundary surface 1201 of an enclosure
containing the thermal source. In EHD device 1200, collector
electrode array 1222 functions both as a collector electrode array
and as a heat sink. Sub-component 1224 is constructed as a
convective heat transfer surface and functions as a heat spreader.
Thermal conduit 1254 transports heat from a thermal source disposed
in the interior of the enclosure to both collector electrode array
1222 and convective heat transfer surfaces of sub-component 1224.
The extent of the path and configuration of thermal conduit 1254
from the thermal source within the enclosure are not shown. In the
illustrated embodiment, ventilated portion 1204 of partial boundary
surface 1201 includes an inlet portion that admits ambient air from
outside of the apparatus into the enclosure that houses EHD device
1250 and an outlet portion that allows for heated air inside the
enclosure to exit the enclosure. In operation, EHD device 1250
produces an air flow path from the inlet portion to the outlet
portion along the arrows as shown.
[0122] FIG. 19D is a schematic drawing of an alternative design for
the previously described convective heat transfer component.
Alternative convective heat transfer component 1230 includes
collector electrode array 1222 (as illustrated in FIG. 19C)
together with an extension 1234 of the vertically disposed unit
structures having the same or similar design as corresponding
structures of collector electrode array 1222. The individual unit
structures in sub-components 1222 and 1234 each have convective
surfaces such as surface 1236 and increase the surface area for
heat transfer when compared with the embodiment of FIG. 19B. In
some embodiments, structure and/or spacing of the vertically
disposed convective heat transfer structures along extension 1234
may differ from those that constitute collector electrode array
1222. For example, in some embodiments, a more widely spacing is
provided for convective heat transfer structures along extension
1234. In any case, although extension 1234 has the same or similar
design as collector electrode array 1222, without closely spaced
corona discharge electrodes extension 1234 does not function as a
collector electrode array.
[0123] FIG. 19E illustrates an EHD device 1200 configuration that
employs convective heat transfer structures along extension 1234
for dissipating heat from a thermal source. EHD device 1200 is a
variation of EHD device 1250 of FIG. 19C in which collector
electrode array 1222 functions as a both collector electrode array
and as a heat sink, but in which additional convective heat
transfer structures along extension 1234 contribute to heat
transfer. EHD device 1200 further comprises thermal conduit 1254,
which directs heat from a thermal source disposed in the interior
of the enclosure to collector electrode array 1222. The extent of
the path and the configuration of thermal conduit 1254 from the
thermal source within the enclosure are not shown. In operation,
EHD device 1200 produces substantially the same air flow path into
and out of the enclosure of the apparatus as produced by EHD device
1250.
[0124] While FIGS. 19C and 19E illustrate EHD devices 1250 and 1200
proximate a single boundary surface of the enclosure, it is
understood that either EHD device 1250 or 1200 may also be disposed
in an enclosure in the positions illustrated in FIG. 3 or 4 so as
to produce an air flow path between two ventilated boundary
surfaces of the enclosure. While vertical unit structures in FIGS.
19A-19E are shown for illustrative purposes as resembling the
protrusions commonly found as part of a conventional heat sink, it
is to be understood that other designs and configurations of
conductive surfaces and collector electrodes may be used in the
convective components of the embodiments of the EHD devices
described herein.
Design Adaptations for Particular Thermal Management Systems
[0125] EHD devices illustrated herein may be constructed in a wide
range of sizes in order to meet the requirements of a particular
thermal heat management solution. By way of one example, when EHD
device 1250 of FIG. 19C is configured for dissipating heat from an
electronic circuit in an electronic apparatus, corona discharge
electrode assembly 1210 (see FIG. 19A) may have a height, H, in the
range of 0.5 mm to 30 mm, and a length, L, chosen to meet the needs
of the particular enclosure within which the EHD device will
operate. When the corona discharge electrode component comprises
multiple corona discharge electrodes such as in corona discharge
electrode assembly 1210 (see FIG. 19A), the distance between
adjacent corona discharge electrodes 1216 may be approximately 2-4
mm. Such a device may be suitable for use in an electronic device
having a thin form factor. Note that the scale of the individual
components shown in the Figures herein is solely for illustration
purposes; each component may have height, width and depth
dimensions that are different from the relative dimensions shown in
a particular Figure.
[0126] Many discussions of the performance of an EHD device focus
on techniques and electrode configurations (e.g., device
geometries) that attempt to improve the velocity or pressure at
which fluid moves through the device, or through the enclosure
within which the device operates, in order to achieve an improved
fluid flow rate. Various EHD device designs illustrated herein,
when used as a component in a thermal management system, may be
adapted to achieve a target fluid flow rate that is sufficient to
dissipate a target heat quantity generated by a particular one or
more thermal sources contained within an enclosure, while operating
the EHD device under the constraint of a given pressure head range.
Once the target fluid flow rate and target heat quantity are known,
the design of such an EHD device begins with determining the
geometry and fluid flow resistance of the device that will permit
the operation of an EHD device within the desired pressure head
range. In some embodiments, an EHD device may be configured to
operate with a pressure head in the range of 1-20 Pa. For some
thermal management applications, the desired, or target, pressure
head range may be a range of 3-7 Pa.
[0127] In general, EHD devices described herein may be configured
to have a high aspect ratio and positioned within the enclosure
proximate to one or more ventilated surface boundaries in order to
minimize resistance along the fluid flow path, according to one of
the illustrated embodiments. With reference to FIG. 20, assume that
structure 1700 is an EHD device of the type illustrated in FIG. 19C
including collector electrodes (e.g., collector electrode assembly
1230 that also functions as a heat sink) and additional heat
transfer surfaces (e.g., as provided by sub-component 1224) that
function as a heat spreader to direct heat from a thermal source to
the array of collector electrodes. A high-aspect ratio EHD device
is defined herein as having at least one of the following
relationships:
5<L/H<300 or (1)
5<L/D<150, (2)
where L is the length of the device, H is the height of the device,
and D is the depth of the device, where the depth of the device is
along the fluid flow path. In some embodiments of an EHD device,
these relationships may preferably be stated as:
10<L/H<40 or (3)
10<L/D<30. (4)
[0128] When the EHD device is configured according to the
relationships of any one of Equations (1)-(4), and the EHD device
is positioned proximate to one or more ventilated boundary surfaces
as illustrated herein to produce a substantially compact fluid flow
path, the EHD device should operate within the desired pressure
head range. The operational pressure head of the EHD device will
produce a fluid flow velocity through the collector electrode array
component and at the output of the device sufficient to achieve the
target fluid flow rate that is needed to dissipate the target heat
quantity. Given the pressure head ranges and EHD device aspect
ratios recited above, the fluid flow velocity is expected to be in
the range of 0.1-3 m/s in some embodiments, and preferably in the
range of 0.2-1.5 m/s in other embodiments.
[0129] FIG. 21 summarizes the ranges of the several factors
discussed above. In addition, in some configurations of an EHD
device according to these designs, the device operation will
maximize the dissipation of heat from the thermal source while
maintaining a substantial equilibrium of the fluid flow velocity
through the enclosure within which the EHD device operates. That
is, the device will maintain a fluid flow velocity at the intake
ventilated boundary surface that is substantially equal to the
fluid flow velocity at the outgoing ventilated boundary surface.
Note that EHD device 1700 of FIG. 20 is represented in a
substantially rectangular form. It is understood that this is for
illustration purposes only; the actual shape of the EHD device is
dependent on the configuration of the collector electrodes and the
position of any associated thermal management components such as a
heat pipe. It is sufficient that the EHD device have a length,
height and depth by which the ratios of Equations (1) through (4)
may be satisfied.
Other Embodiments
[0130] While the techniques and implementations of the EHD devices
discussed herein have been described with reference to exemplary
embodiments, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted for
elements thereof without departing from the scope of the appended
claims. In addition, many modifications may be made to adapt a
particular situation or material to the teachings without departing
from the essential scope thereof. Therefore, the particular
embodiments, implementations and techniques disclosed herein, some
of which indicate the best mode contemplated for carrying out these
embodiments, implementations and techniques, are not intended to
limit the scope of the appended claims.
* * * * *