U.S. patent application number 12/642561 was filed with the patent office on 2010-06-24 for collector electrodes and ion collecting surfaces for 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 | 20100155025 12/642561 |
Document ID | / |
Family ID | 42264368 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100155025 |
Kind Code |
A1 |
Jewell-Larsen; Nels ; et
al. |
June 24, 2010 |
COLLECTOR ELECTRODES AND ION COLLECTING SURFACES FOR
ELECTROHYDRODYNAMIC FLUID ACCELERATORS
Abstract
Embodiments of electrohydrodynamic (EHD) fluid accelerator
devices utilize collector electrode structures that promote
efficient fluid flow and reduce the probability of arcing by
managing the strength of the electric field produced at the forward
edges of the collector electrodes. In one application, the EHD
devices dissipate heat generated by a thermal source in a thermal
management system.
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: |
42264368 |
Appl. No.: |
12/642561 |
Filed: |
December 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61139518 |
Dec 19, 2008 |
|
|
|
Current U.S.
Class: |
165/96 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/0002 20130101; F28F 2250/08 20130101; F28F 13/16
20130101; F04B 19/006 20130101; H01L 23/467 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
165/96 |
International
Class: |
F28F 13/16 20060101
F28F013/16 |
Claims
1. An apparatus comprising: an emitter electrode; and a
collector-radiator assembly including a fluid permeable ion
collection surface and an array of heat transfer surfaces extending
downstream of the emitter electrode, the fluid permeable ion
collection surface spanning a major dimension of the heat transfer
surface array, the emitter electrode and the collector-radiator
assembly energizable to motivate fluid along a flow path through
the fluid permeable ion collection surface and over the heat
transfer surfaces of the collector-radiator assembly.
2. An apparatus comprising: an array of generally planar collector
electrodes wherein at least a substantial subset thereof include
respective hollows defined therein; and an emitter electrode having
a longitudinal extent spanning a major dimension of the collector
electrode array and positioned relative to individual ones of the
collector electrodes such that the emitter electrode passes through
the respective hollows and such that, when the emitter and
collector electrodes are energized, generated ions motivate fluid
flow in a generally downstream direction toward and past dominant
ion collecting surfaces of the collector electrodes that are
nearest the emitter electrode, wherein for at least the substantial
subset of collector electrodes that include respective hollows, at
least some ion collecting surfaces extend upstream of the emitter
electrode.
3. An apparatus comprising: an array of collector electrodes; and
an emitter electrode having a longitudinal extent spanning a major
dimension of the collector electrode array and positioned relative
to the collector electrodes such that, when the emitter and
collector electrodes are energized, generated ions motivate fluid
flow in a generally downstream direction toward and past leading
surfaces of the collector electrodes that are proximate the emitter
electrode, wherein the leading surfaces of the collector
electrodes, but not further surfaces downstream of the leading
surfaces, are conditioned with a resistive material.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] The present application claims the benefit of U.S.
Provisional Application No. 61/139,518, filed Dec. 19, 2008.
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. 14, 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 when 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.
Fluid Permeable Ion Collection Surfaces
[0010] It has been discovered that, in some EHD device
configurations, a fluid-permeable ion collection surface may be
provided to promote development of a generally uniform electric
field distributed over downstream ion collection surfaces.
Accordingly, in some embodiments of the present invention, an
apparatus includes an emitter electrode and a collector-radiator
assembly including a fluid permeable ion collection surface and an
array of heat transfer surfaces extending downstream of the emitter
electrode. The fluid permeable ion collection surface spans a major
dimension of the heat transfer surface array. The emitter electrode
and the collector-radiator assembly are energizable to motivate
fluid along a flow path through the fluid permeable ion collection
surface and over the heat transfer surfaces of the
collector-radiator assembly.
[0011] In some embodiments, the fluid permeable ion collection
surface is conformal with leading portions of the heat transfer
surfaces. In some cases, the fluid permeable ion collection surface
is electrically and thermally coupled to the heat transfer
surfaces. In some cases, the fluid permeable ion collection surface
is electrically isolated from the heat transfer surfaces. In some
cases, the fluid permeable ion collection surface is conformal with
leading surfaces of a support structure mated with the heat
transfer surface array to define the collector-radiator assembly.
In some cases, such a support structure includes additional ion
collection surfaces downstream of the fluid permeable ion
collection surface. In some cases, the fluid permeable ion
collection surface presents a curved leading profile displaced from
the emitter electrode.
[0012] In some embodiments, the fluid permeable ion collection
surface includes a mesh or grid, a generally smooth perforated
surface, or a spaced apart array of strips or surface portions. In
some embodiments, the fluid permeable ion collection surface is at
least partially formed of an at least partially conductive
material, a metal or a carbon fiber or carbon fiber containing
material.
[0013] In some embodiments, a fluid permeable ion collection
surface presents, at least on surfaces exposed to substantial ion
bombardment, a surface comprised of gold (Au) over nickel (Ni),
NiPd over Ni or silver (Ag), silver oxide (Ag.sub.2O), an oxide of
manganese or an ozone catalytic or reactive material. In some
embodiments, a fluid permeable ion collection surface includes, at
least on surfaces exposed to substantial ion bombardment, a surface
coating that includes an electroplate over injection-molded UL94-VO
compliant thermoplastic; an electroplate over die-cast zinc (Zn) or
zinc alloy; an electroplated, anodized or alodized die-cast
aluminum (Al), aluminum alloy or magnesium (Mg) alloy; or an
electroplate over powder injection-molded metal.
[0014] In some embodiments, the heat transfer surfaces of the
collector-radiator assembly include spaced apart, generally planar
portions extending in a direction generally parallel to the flow
path. In some embodiments, the emitter electrode has a longitudinal
extent than spans a major dimension of the collector-radiator
assembly and the generally planar portions of the heat transfer
surfaces are oriented generally orthogonally to the longitudinal
extent of the emitter electrode. In some embodiments, the planar
portions of the heat transfer surfaces are oriented such that the
leading portions thereof are generally parallel to a longitudinal
extent of the emitter electrode.
[0015] In some embodiments, the fluid permeable ion collection
surface includes at least a portion positioned upstream of the
emitter electrode. In some embodiments, the emitter electrode and
the collector-radiator assembly are operatively coupled between
terminals of a high voltage source to establish a corona discharge
therebetween and to thereby motivate the fluid along the flow path.
In some embodiments, the apparatus is disposed in a flow path for
ventilating an enclosure and thereby cooling one or more devices
within the enclosure, wherein at least the heat transfer surfaces
of the collector-radiator assembly are thermally coupled into a
heat transfer path from the devices.
Ion Collection Surfaces Extending Upstream of an Emitter
Electrode
[0016] It has been further discovered that, in some EHD device
configurations, ion collection surfaces may extend upstream of an
emitter electrode so as to at least partially surround the emitter.
In some cases, such a configuration may protect the emitter from
mechanical intrusions and/or human contact with a high voltage
emitter. In some cases, such a configuration may tend to shield
other electrical components from unwanted electric fields and ion
bombardment. In some cases, surface conditioning or coating of
upstream surfaces may facilitate accumulation and retention of a
surface charge that tends to repel ions from the upstream
surfaces.
[0017] Accordingly, in some embodiments of the present invention,
an apparatus includes an array of generally planar collector
electrodes wherein at least a substantial subset thereof include
respective hollows defined therein. The apparatus further includes
an emitter electrode having a longitudinal extent spanning a major
dimension of the collector electrode array and positioned relative
to individual ones of the collector electrodes such that the
emitter electrode passes through the respective hollows and such
that, when the emitter and collector electrodes are energized,
generated ions motivate fluid flow in a generally downstream
direction toward and past dominant ion collecting surfaces of the
collector electrodes that are nearest the emitter electrode. For at
least the substantial subset of collector electrodes that include
respective hollows, at least some ion collecting surfaces extend
upstream of the emitter electrode.
[0018] In some embodiments, at least some of the hollows are holes
defining ion collecting surfaces that fully surround the emitter
electrode. In some embodiments, the hollows define at least a
partial Faraday cage around the emitter electrode. In some
embodiments, the apparatus is configured as a thermal management
assembly wherein collector electrodes constitute convective heat
transfer surfaces. In some embodiments, the apparatus is configured
as a thermal management assembly, wherein the motivated fluid flow
is over at least some convective heat transfer surfaces distinct
from the collector electrodes. In some embodiments, the emitter
electrode and the collector electrodes operatively coupled between
terminals of a high voltage source to establish a corona discharge
therebetween and to thereby motivate the fluid in the downstream
direction.
[0019] In some embodiments, the apparatus further includes at least
one additional emitter electrode that also passes through the
respective hollows. In some embodiments, the apparatus further
includes an additional hollow defined in the respective ones of the
collector electrodes and an additional emitter electrode that
passes through the additional hollows.
[0020] In some embodiments, dominant ion collecting surfaces of the
collector electrodes present the emitter electrode with generally
curved profiles proximate thereto. In some embodiments, at least
the dominant ion collecting surfaces present a surface comprised of
gold (Au) over nickel (Ni), NiPd over Ni or silver (Ag), silver
oxide (Ag.sub.2O), an oxide of manganese or an ozone catalytic or
reactive material. In some embodiments, at least some portions of
the collector electrodes other than the dominant ion collecting
surfaces are coated with MnO.sub.2 or another ozone catalytic or
reactive material. In some embodiments, the collector electrodes
are formed as an electroplate over injection-molded UL94-VO
compliant thermoplastic, an electroplate over die-cast zinc (Zn) or
zinc alloy, an electroplated, anodized or alodized die-cast
aluminum (Al), aluminum alloy or magnesium (Mg) alloy; or an
electroplate over powder injection-molded metal.
[0021] In some embodiments, the apparatus is disposed in a flow
path for ventilating an enclosure and thereby cooling one or more
devices within the enclosure, wherein convective heat transfer
surfaces are thermally coupled into a heat transfer path from the
devices and wherein the motivated fluid flow is over the convective
heat transfer surfaces. In some cases, the convective heat transfer
surfaces include surfaces of the collector electrodes.
Resistive Material Conditioning of Selected Ion Collection
Surfaces
[0022] It has been further discovered that, in some EHD device
configurations, ion collection surfaces most closely proximate to
an emitter electrode may be preferentially conditioned or coated
with a highly-resistive surface. In this way, electrical fields may
be advantageously shaped and spark limiting or quenching mechanisms
may be provided while still facilitating efficient heat transfer at
other downstream surfaces. In some cases, surface conditioning or
coating of upstream surfaces may be insulative so as to facilitate
accumulation and retention of a surface charge that tends to repel
ions from the upstream surfaces.
[0023] Accordingly, in some embodiments of the present invention,
an apparatus includes an array of collector electrodes and an
emitter electrode having a longitudinal extent spanning a major
dimension of the collector electrode array and positioned relative
to the collector electrodes such that, when the emitter and
collector electrodes are energized, generated ions motivate fluid
flow in a generally downstream direction toward and past leading
surfaces of the collector electrodes that are proximate the emitter
electrode. Leading surfaces of the collector electrodes, but not
further surfaces downstream of the leading surfaces, are
conditioned with a resistive material. In some cases, the resistive
material conditioning includes a coating applied to the leading
surfaces of the collector electrodes.
[0024] In some embodiments, the collector electrodes include spaced
apart, generally planar portions that include the downstream
surfaces not conditioned with the resistive material, the generally
planar portions extending in the downstream direction. In some
embodiments, the generally planar portions are oriented such that
the leading surfaces thereof are generally parallel to the
longitudinal extent of the emitter electrode. In some embodiments,
the resistive material conditioned leading surfaces of respective
of the collector electrodes are positioned, relative to one
another, to present the emitter electrode with a generally curved
array of the leading surfaces. In some embodiments, the generally
planar portions are oriented generally orthogonally to the
longitudinal extent of the emitter electrode. In some embodiments,
the resistive material conditioned leading surfaces of individual
ones of the collector electrodes present the emitter electrode with
a generally curved profile.
[0025] In some embodiments, individual ones of the collector
electrodes include respective hollows defined in the generally
planar portions thereof and the emitter electrode passes through
the respective hollows such that, when the emitter and collector
electrodes are energized, a dominant portion of ion flow is toward
downstream portions of the resistive material conditioned leading
surfaces that are closest the emitter electrode. In some cases, the
resistive material conditioned leading surfaces of individual ones
of the collector electrodes substantially surround the emitter
electrode. In some cases, the apparatus includes an additional
emitter electrode that also passes through the respective hollows.
In some cases, the apparatus includes an additional hollow defined
in the generally planar portions of the collector electrodes and an
additional emitter electrode that passes through the additional
hollows.
[0026] In some embodiments, the apparatus is configured as a
thermal management assembly, wherein the collector electrodes
constitute convective heat transfer surfaces. In some embodiments,
the apparatus is configured as a thermal management assembly,
wherein the motivated fluid flow is over at least some convective
heat transfer surfaces distinct from the collector electrodes. In
some embodiments, the emitter electrode and the collector
electrodes are operatively coupled between terminals of a high
voltage source to establish a corona discharge therebetween and to
thereby motivate the fluid in the downstream direction.
[0027] In some embodiments, the apparatus is disposed in a flow
path for ventilating an enclosure and thereby cooling one or more
devices within the enclosure, wherein convective heat transfer
surfaces are thermally coupled into a heat transfer path from the
devices, and wherein the motivated fluid flow is over the
convective heat transfer surfaces. In some embodiments, the
convective heat transfer surfaces include surfaces of the collector
electrodes downstream from the resistive material conditioned
leading surfaces thereof.
[0028] 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
[0029] 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.
[0030] FIG. 1A depicts a side cross-sectional view, consistent with
certain 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. 1B depicts a
perspective view of a collector electrode assembly consistent with
the arrangement of FIG. 1A. FIG. 1C depicts a perspective view of a
corona discharge electrode and collector electrode assemblies
consistent with the arrangement.
[0031] FIG. 2A depicts a side cross-sectional view, consistent with
certain EHD device configurations in which a collector electrode
assembly includes a fluid permeable ion collection surface
electrically coupled to and conformal with an arrangement of
collector electrodes. In the illustrated configuration, a curved
array of leading surfaces are provided, each oriented generally
parallel to the longitudinal extent of a corona discharge
electrode. FIG. 2B depicts a perspective view of a collector
electrode assembly consistent with the arrangement of FIG. 2A. FIG.
2C depicts a perspective view of a corona discharge electrode and
collector electrode assemblies consistent with the arrangement.
FIG. 2D depicts a side cross-sectional view of a variation in which
fluid permeable ion collection surfaces extend upstream of, and
fully surround the corona discharge electrode.
[0032] FIG. 3 is a side cross-sectional view of still another
variation in which several instances of the EHD device
configuration illustrated with reference to FIGS. 2A, 2B and 2C are
integrated into a ganged structure.
[0033] FIG. 4A is a perspective view of a variation in which a pair
of collector electrode assemblies such as illustrated with
reference to FIG. 1B integrated into a ganged structure for use in
an EHD device configuration. FIGS. 4B, 4C, 4D and 4E illustrate
thermal pathways consistent with several design variations in which
collector electrode surfaces are thermally coupled (via a thermal
conduit) to a heat source and dissipate heat into a fluid flow
motivated by operation of the EHD device.
[0034] FIG. 5A depicts a side cross-sectional view, consistent with
certain EHD device configurations, of a corona discharge electrode
and several columnar or rod-shaped collector electrodes positioned
between generally planar collector electrodes. Leading surfaces of
collector electrodes are arranged to present a curved array, where
each of the leading surfaces is oriented generally parallel to the
longitudinal extent of the corona discharge electrode. FIG. 5B
depicts a perspective view of a collector electrode assembly
consistent with the arrangement of FIG. 5A. FIG. 5C depicts a
perspective view of a corona discharge electrode and collector
electrode assemblies consistent with the arrangement.
[0035] FIGS. 6A, 6B and 6C are side cross-sectional views of
several generally planar collector electrode surfaces suitable for
use in certain EHD device configurations in which ion collection
surfaces of the collector electrode extend upstream and define a
hollow that fully surrounds the corona discharge electrode. FIG. 6D
is a perspective view of one such EHD device configuration
utilizing the collector electrode structure of FIG. 6C and
illustrated as a component of a thermal management system in which
a thermal conduit acts as a heat transfer path to collector
electrode surfaces which, in turn, dissipate heat into a motivated
fluid flow.
[0036] FIG. 7A is an end-on view of an EHD device configuration in
which an array of generally planar collector electrodes present
generally curved profiles of leading surfaces to a corresponding
corona discharge electrodes. FIG. 7B is a cross-sectional view of
the EHD device of FIG. 7A.
[0037] FIG. 8A is a side cross-sectional view of another generally
planar collector electrode configuration in which an array of such
surfaces are oriented orthogonally to a longitudinal extent of a
corona discharge electrode and in which the generally planar
collector electrode present the corona discharge electrode with a
generally curved leading surface profile. FIG. 8C is a perspective
view of a collector electrode assembly consistent with geometries
illustrated in FIG. 8A, in which a fluid permeable ion collection
surface is electrically coupled to and conformal with the generally
curved leading surfaces. FIG. 8B is an enlarged perspective view of
a portion of the generally planar collector electrode illustrated
in FIG. 8A.
[0038] FIGS. 9A and 9B are perspective views of representative EHD
device deployments relative to a pair of ventilated boundary
surfaces of representative enclosures, illustrating respective
fluid flow paths therethrough.
[0039] FIGS. 10A, 10B and 10C illustrate representative variations
on certain previously illustrated collector electrodes or
assemblies in which semi-conductive or resistive coating (or
surface conditioning) is provided at surfaces substantially exposed
to ion impingement during EHD device operation. FIG. 10A is a
perspective view of the collector electrode array of FIG. 1B,
illustrating the use of a semi-conductive or resistive coating or
surface treatment at leading surfaces thereof. FIG. 10B is a
partial cross-sectional view of a representative portion of a
generally planar collector electrode, illustrating the disposition
of a resistive coating thereon. FIG. 10C is a cross-sectional view
of the collector electrode of FIG. 6B, illustrating the use of a
resistive coating or surface treatment at ion collection surfaces
of a hollow that fully surrounds a corona discharge electrode.
[0040] FIG. 11 is a perspective view of an EHD device having a
certain geometry expressed as a ratio of length to height, or
length to depth.
[0041] FIG. 12 is a table of design parameters for implementing the
various embodiments of EHD devices described and illustrated
herein.
[0042] FIG. 13A is an elevated cross-sectional side view of an EHD
device disposed within an enclosure and illustrating several
dimensions that may be useful in designing a device with improved
fluid flow performance. FIG. 13B is a top plan view of a portion of
the collector electrode array of the EHD device of FIG. 13A
illustrating additional dimensions that may be useful in designing
a device with improved fluid flow performance.
[0043] FIG. 14 is a graphical depiction of certain basic principles
of corona-induced electrohydrodynamic (EHD) fluid flow.
[0044] Use of the same reference symbols in different drawings
indicates similar or identical items.
DETAILED DESCRIPTION
[0045] Some embodiments of thermal management systems described
herein employ EHD devices to motivate flow of a fluid, typically
air, based on acceleration of ions generated as a result of corona
discharge. Other embodiments may employ other ion generation
techniques and will nonetheless be understood in the descriptive
context provided herein. Using heat transfer surfaces that may or
may not be monolithic or integrated with collector electrodes, heat
dissipated by electronics (e.g., microprocessors, graphics units,
etc.) and/or other components can be transferred to the fluid flow
and exhausted. Typically, when a thermal management system is
integrated into an operational environment, heat transfer paths
(often implemented as heat pipes or using other technologies) are
provided 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. Of course, while some embodiments may be fully
integrated in an operational system such as a laptop or desktop
computer, a projector or video display device, etc., other
embodiments may take the form of subassemblies.
[0046] Often, heat transfer surfaces and dominant ion collecting
surfaces of a collector electrode can present differing design
challenges and, relative to some embodiments, may be provided using
different structures or with different surface conditioning. In
some embodiments, a monolithic structure may act as a collector
electrode and provide heat transfer surfaces. In some embodiments,
collector electrodes and dominant heat transfer surfaces are
provided (or at least fabricated) as separate structures that may
be mated, integrate or more generally proximate each other in
operational configurations. These and other variations will be
understood even with respect to embodiments described, for
simplicity, with collector electrode assemblies that include
portions that operate as ion collection surfaces and as heat
transfer surfaces.
[0047] In general, a variety of scales, geometries and other design
variations are envisioned for collector electrodes and/or the
dominant ion collection surfaces that functionally constitute a
collector electrode, 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.
[0048] In some embodiments, a fluid permeable ion collection
surface is provided that is conformal with and electrically coupled
to leading surfaces of an array of collector electrodes. In some
embodiments, such a fluid permeable ion collection surface is
conformal with leading surfaces of support structure that need not
participate substantially in ion collection. In some embodiments,
such a fluid permeable ion collection surface may be electrically
isolated from downstream heat transfer surfaces.
[0049] In some embodiments, leading surfaces (whether of collector
electrodes of an array or fluid permeable ion collection 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 substantial, even dominant, heat
transfer.
[0050] 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.
[0051] Although embodiments of the present invention are not
limited thereto, much of the description herein is consistent with
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
[0052] 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 Accelerator" 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.
[0053] Note that the simple illustration of corona-induced
electrohydrodynamic fluid flow shown in FIG. 14 (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.
[0054] EHD device embodiments described herein include one or more
corona discharge electrodes. In general, such corona discharge
electrodes include a portion that exhibits 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 the small radius of
curvature when high voltage is applied. In general, corona
discharge electrodes 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 creates the electric field between corona discharge
electrodes and collector electrodes.
[0055] EHD device embodiments described herein include ion
collection surfaces positioned downstream of one or more corona
discharge electrodes. Often such ion collection surfaces include
leading surfaces of generally planar collector electrodes extending
downstream of the corona discharge electrode(s). In some cases, a
fluid permeable ion collection surface is provided. In some cases,
such a fluid permeable ion collection surface is disposed at
leading edges of, and electrically connected to, generally planar
collector electrodes that extend downstream of the corona discharge
electrode. In general, a collector electrode (and/or fluid
permeable ion collection surfaces described herein) may be
fabricated of any suitable metal material, such as aluminum or
copper.
[0056] As disclosed in U.S. Pat. No. 6,919,698 to Krichtafovitch,
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). As further
disclosed in the '698 patent, collector electrodes may be made of a
body of high resistivity material that readily conducts a corona
current, but for which a result voltage drop along current paths
through the body of high resistivity collector electrode material
provides a reduction of surface potential, thereby damping or
limiting an incipient sparking event. Examples of such relatively
high resistance materials include carbon filled plastic, silicon,
gallium arsenide, indium phosphide, boron nitride, silicon carbide,
and cadmium selenide. U.S. Pat. No. 6,919,698 is incorporated
herein for the limited purpose of describing materials for some
collector electrodes that may be employed in some embodiments. Note
that in some embodiments described herein, a surface conditioning
or coating of high resistivity material (as contrasted with bulk
high resistivity) may be employed.
[0057] Typically, configurations described and illustrated herein
include an array of collector electrodes (and/or fluid permeable
surfaces) that constitute the dominant ion collection surfaces
during EHD device operations. The number of, and distances between,
such collector electrodes and surfaces shown (as shown in the
Figures) is merely exemplary and generally not to scale. Indeed,
numbers and distances may vary from what is shown according to
device specifications and the type of fluid being moved. The
distance between a corona discharge electrode and a collector
electrode is referred to as the "gap" or "air gap" (see, e.g., gap
102 in FIG. 1C) and is determined by the particular shapes of the
corona discharge electrode(s) and the collector electrode(s).
[0058] Although not shown in the Figures that illustrate the
embodiments herein, a high voltage power supply is electrically
connected to, and creates the electric field between, the corona
discharge electrode and the collector electrode, generating an ion
stream that moves ambient fluid toward the collector electrode.
[0059] EHD device embodiments described herein may be implemented
in a repeated adjacent plural configuration in order, for example,
to improve fluid flow efficiency, or to fit into a specific space
within an enclosure. Likewise, embodiments of EHD devices described
herein may also be implemented in combination with a different
embodiment of an EHD device in a plural adjacent configuration. In
addition, while not illustrated and described herein, it is
understood that any one of the embodiments of the EHD devices
described herein may also be implemented in a plural configuration
in which two or more individual EHD devices of the type described
herein are sequentially disposed along a desired fluid flow
direction. Each individual EHD device may then be 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.
[0060] Embodiments of EHD devices illustrated herein may be used to
dissipate heat from a thermal source housed in an enclosure, as
part of a thermal management system. The thermal management system
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
that houses the thermal source to generally follow along a fluid
flow path through or over the heated collector electrode component
and then 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.
[0061] As a preliminary matter, the front perspective views of the
embodiments of EHD devices and collector electrode arrays
illustrated herein are situated in a three-dimensional coordinate
system 101 (FIG. 1B) in which the x-y plane respectively designates
the width and depth of the embodiment of the EHD device illustrated
in the Figure. The z direction indicates the height of the device.
The coordinate system 101 is shown with the embodiment of the
collector electrode array illustrated in FIG. 1B and is not
repeated in the other Figures.
[0062] FIG. 1A is a cross-sectional view of a first embodiment of
an EHD device 100 comprising corona discharge electrode 110 and
collector electrode array 120. Collector electrode array 120
comprises several collector electrodes 122, 124, 126 and 128 in the
shape of substantially flat plates of any desirable length and
thickness. Collector electrodes 124 and 126, disposed between top
and bottom collector electrodes 122 and 128, are recessed away from
corona discharge electrode 110 in a manner such that the ends of
the collector electrodes form a generally curved shape 106. Each
collector electrode is illustrated as having a rounded end 123,
which may reduce the strength of the electric field in this area of
the collector electrode and beneficially promote fluid flow past
collector electrode structure. It is understood, however, that the
ends may have sharp edges as well. When EHD device 100 is
operational, the EHD forces generated between corona discharge
electrode 110 and collector electrode array 120 force fluid in the
direction of arrow 130 between the collector electrodes. FIG. 1B is
a perspective view of collector electrode array 120 of FIG. 1A
showing individual collector electrodes 122, 124, 126 and 128
attached to support members 142. FIG. 1C is a perspective view of
EHD device 100 showing corona discharge electrode 110 supported by
frame 112 positioned a distance 102 from collector electrode array
120, and illustrating the fluid flow direction produced by the
device 100 when it is operational. Although corona discharge
electrode 110 and collector electrode array 120 are shown as
discrete structures, a person of skill in the art will recognize
that EHD device 100 may be constructed as a unitary structure by,
for example, extending frame 112 to include support members
142.
[0063] FIGS. 2A, 2B and 2C illustrate various views of EHD device
200 which is a variation of EHD device 100 of FIGS. 1A, 1B and 1C.
In EHD device 200, a fluid-permeable, electrically conductive
element 240 is disposed as a dominant ion collection surface in
front of the forward end portions 215 of the collector electrodes.
Element 240 comprises pores or openings of sufficient size to
permit the fluid being moved to pass minimally impeded through
collector electrode array 120 in fluid flow direction 130. Suitable
fluid-permeable elements include a metal mesh structure made of
metal, a carbon fiber material or any at least partially conductive
materials such as a plastic with carbon fiber elements or the
like.
[0064] When EHD device 200 is operational, the EHD forces generated
between corona discharge electrode 110 and collector electrode
array 120 force fluid in the direction of arrow 130, through
fluid-permeable element 240 and between the collector electrodes.
The presence of fluid-permeable element 240 promotes the
development of a uniform electric field at the forward leading
edges 215 of the collector electrode structure, which in turn
reduces the electric field strength at these leading edges 215. The
reduced electric field strength in this portion of the collector
electrode structure may reduce the probability of back corona or
arcing originating from leading edges 215. The presence of a
uniform electric field at the collector electrodes may in turn
cause a more uniform discharge of ions from all portions of corona
discharge electrode 110 resulting in improved fluid flow in the
direction of arrow 130.
[0065] FIG. 2D is a cross-sectional view of EHD device 210 which is
a variation of EHD device 200 of FIGS. 2A, 2B and 2C. In EHD device
210, a fluid permeable, electrically conductive element 250 defines
a dominant ion collection surface disposed in front of the forward
end portions 215 of collector electrodes 120 and extends in such a
manner as to surround corona discharge electrode 110. Element 250
comprises pores or openings of sufficient size to permit the fluid
being moved to pass unimpeded through collector electrode array 120
in fluid flow direction 130. While element 250 may have any
suitable shape and length, L, it may be preferable for element 250
to have a shape that permits corona discharge electrode 110 to be
positioned a greater distance away from inner surface 251 than from
inner surface 252 in order to promote fluid flow in the direction
of arrow 130. Element 250 may function as a type of EMI shield and
as protection against damage or handling of corona discharge
electrode 110.
[0066] FIG. 3 is a cross-sectional view of an EHD device 300
comprised of several EHD devices 200a, 200b and 200c of the type
illustrated in FIG. 2A having fluid-permeable electrically
conductive element 240 disposed in front of collector electrode
array 120. Note that in FIG. 3, EHD device 200a shares collector
electrode 128 with EHD device 200b. It is understood by those of
skill in the art that the EHD device 100 illustrated in FIG. 1A may
also be ganged in a similar manner. In one embodiment, it may be
preferable to form blunted edge 351 at the junction of any two
ganged EHD devices.
[0067] In addition to ganged collector electrode arrays that
together form a collector electrode array such as that shown in
FIG. 3, collector electrode arrays may also be ganged as
illustrated in FIG. 4A. FIG. 4A is a perspective view of a pair of
collector electrode arrays 120 positioned adjacent to one another
and sharing a center support member 143 to form one collector
electrode array 420.
[0068] FIGS. 4B through 4E are perspective views of various
embodiments of collector electrode array 420 of FIG. 4A when
collector electrode array 420 is used as heat dissipation component
in an EHD device that is part of a thermal management system for
dissipating heat generated by one or more thermal sources. In each
of FIGS. 4B through 4E, the corona discharge electrode(s) are
omitted from the Figure. FIG. 4B illustrates heat dissipation
component 440 which comprises collector electrode arrays 446.
Collector electrode arrays 446 are made of both a
thermally-conductive and electrically conductive material and
function both as collector electrodes and as a heat sink. As
defined herein, a heat sink is an object that absorbs and
dissipates heat from another object using conductive, convective or
radiant thermal contact. Heat dissipation component 440 further
comprises thermally conductive vertical support members 442 and
thermal conduit 445. Vertical support members 442 support collector
electrode arrays 446 and are in thermal contact with thermal
conduit 445. Thermal conduit 445 transports heat from a thermal
source disposed in the interior of the enclosure to vertical
support members 442 which, in turn, transfers heat to the collector
electrodes. In each of FIGS. 4B through 4E, the extent of the path
and configuration of thermal conduit 445 from the thermal source
within the enclosure are omitted. Small horizontal and vertical
arrows 447 in FIG. 4B indicate the direction of heat movement and
heat transfer from thermal conduit 445 to vertical support members
442 and the individual horizontal collector electrodes that
comprise heat dissipation component 440. In operation, the EHD
device generates EHD forces in the direction of arrow 441 to move
ambient air within the enclosure over the collector electrodes of
heat dissipation component 440.
[0069] FIGS. 4C, 4D and 4E illustrate variations of heat
dissipation component 440 of FIG. 4B in which the thermal conduit
that transports heat from the thermal source to the vertical
support members is disposed in different positions within the heat
dissipation component, with small horizontal and vertical arrows
indicating the direction of heat movement and heat transfer from a
thermal conduit to vertical support members, and the larger arrows
indicating fluid flow direction. In all other respects, the
description of heat dissipation component 440 of FIG. 4B above is
equally applicable to the heat dissipation components in these
Figures. FIG. 4C is a front perspective view of heat dissipation
component 450 which comprises collector electrode arrays 456,
thermally conductive vertical support members 452 and thermal
conduit 455. In FIG. 4C, thermal conduit 455 is disposed at the top
of heat dissipation component 450 and heat transfer to vertical
support members 452 is in the downward direction, as indicated by
small vertical arrows 457. FIG. 4D is a front perspective view of
heat dissipation component 460 which comprises collector electrode
arrays 466, thermally conductive vertical support members 462 and
thermal conduit 465. In FIG. 4D, thermal conduit 465 is disposed in
an interior position of heat dissipation component 450 between
individual collector electrodes. Heat transfer to vertical support
members 462 is both in the upward and downward direction, as
indicated by small vertical arrows 467. FIG. 4E is a front
perspective view of heat dissipation component 470 which comprises
collector electrode arrays 476, thermally conductive vertical
support members 472 and thermal conduit 475. In FIG. 4E, thermal
conduit 475 is disposed at the bottom of heat dissipation component
470, as in heat dissipation component 440 of FIG. 4B. Thermal
conduit 475 includes a portion that is perpendicularly oriented to
heat dissipation component 470. Heat transfer to vertical support
members 472 is in the upward direction, as indicated by small
vertical arrows 477.
[0070] FIG. 5A is a cross-sectional view of another embodiment of
an EHD device 500 comprising corona discharge electrode 110 and
collector electrode array 520. Collector electrode array 520
comprises a pair of horizontally disposed collector electrodes 522
and 524 in the shape of substantially flat plates of any suitable
length and thickness, and several wire- or rod-shaped collector
electrodes 526, 528 and 530. Collector electrodes 526, 528 and 530,
disposed between collector electrodes 522 and 524, are recessed
away from corona discharge electrode 110 in a manner such that the
edges of the collector electrodes closest to corona discharge
electrode 110 form a parabolic shape 106. Collector electrodes 522
and 524 are illustrated as having a rounded end 523, but it is
understood that the ends may be flat as well. When EHD device 500
is operational, the EHD forces generated between corona discharge
electrode 110 and collector electrode array 520 force fluid in the
direction of arrow 130 between the collector electrodes. FIG. 5B is
a front perspective view of collector electrode array 520 of FIG.
5A showing individual collector electrodes 522, 524, 526, 528 and
538 attached to support members 542. FIG. 5C is a front perspective
view of EHD device 500 showing corona discharge electrode 110
supported by frame 112 positioned a distance 502 from collector
electrode array 520, and illustrating the fluid flow direction 130
produced by the device 500 when it is operational. Although corona
discharge electrode 110 and collector electrode array 520 are shown
as discrete structures, a person of skill in the art will recognize
that EHD device 500 may be constructed as a unitary structure by,
for example, extending frame 112 to include support members
542.
[0071] FIGS. 6A, 6B and 6C are cross-sectional views of variations
of a collector electrode structure which may be constructed of a
thermally- and electrically-conductive material in any suitable
length and thickness. Each of the collector electrode structures
622, 624 and 626 of FIGS. 6A, 6B and 6C comprises at least one
opening through which a corona discharge electrode (not shown) will
pass. In operation, an EHD device comprising any one of the
collector electrode structures 622, 624 or 626 will force fluid in
the direction of arrow 630. Collector electrode structure 622 of
FIG. 6A comprises at least one substantially round opening 612,
while collector electrode structures 624 and 626 comprise at least
one substantially oblong opening 614. Collector electrode structure
626 of FIG. 6C further comprises cutout portion 616 which may
accommodate a support member or other structure not shown in the
Figure.
[0072] FIG. 6D is a front perspective view of a fourth embodiment
of an EHD device using the collector electrode structure of FIG. 6C
and illustrated as a component of a thermal management system for
dissipating heat generated by one or more thermal sources. EHD
device 600 comprises corona discharge electrodes 110 and collector
electrode array 620 of plural collector electrodes 626 of FIG. 6C.
Collector electrodes 626 are made of both a thermally-conductive
and electrically conductive material and function both as collector
electrodes and as a heat sink. EHD device 600 further comprises
thermal conduit 645 which is in thermal contact with collector
electrodes 626. Thermal conduit 645 transports heat from a thermal
source in the general direction or small arrows 647 to collector
electrodes 626 of array 620. The extent of the path and
configuration of thermal conduit 645 from the thermal source are
omitted. In operation, EHD device 600 generates EHD forces in the
direction of arrow 630 to move ambient air in the vicinity of the
EHD device between collector electrodes 626.
[0073] FIG. 7A is a top plan view of a fifth embodiment of an EHD
device comprising an array of corona discharge electrodes 710 and
an array 720 of collector electrodes. Individual collector
electrodes 721 are supported by at least one support member 714.
Frame members 712 support corona discharge electrodes disposed in
parallel with the collector electrodes 720. While EHD device 700 is
illustrated as having a relatively shallow depth (in the y
direction), it is understood that EHD device 700 may be configured
in a variety of aspect ratios (width-to-height relationships) to
suit a particular purpose. In operation, EHD device 700 generates
EHD forces in the downward z direction to move a fluid in the
vicinity of the EHD device between collector electrodes 720. FIG.
7B is a cross-sectional view of the EHD device of FIG. 7A taken at
dashed line 702 of FIG. 7A, and illustrating fluid flow direction
730. It can be seen from this view that the height of the collector
electrodes varies in a pattern. For example, collector electrodes
722 are shorter than collector electrodes 721 and form parabolic
shape 706 near each corona discharge electrode 710.
[0074] FIG. 8A is a cross-sectional view of a collector electrode
structure 822 which may be constructed of a thermally- and
electrically-conductive material in any suitable length and
thickness. Collector electrode structure 822 is shown relative to a
corona discharge electrode 810 and comprises a curved forward
surface 804 at leading edge 815. In operation, an EHD device
comprising collector electrode structure 822 will force fluid in
the direction of arrow 830. In the embodiment of collector
electrode structure 822 shown in FIG. 8A, the lower and upper
leading ends of collector electrode 822 as called out by leading
end 816 are illustrated as having sharp edges. FIG. 8B is an
enlarged partial perspective view of collector electrode 823, which
is a variation of the collector electrode structure 822 of FIG. 8A
in which the leading end 817 of collector electrode structure 823
is blunted or curved in shape, which may reduce the strength of the
electric field in this area of the collector electrode and
beneficially promote fluid flow past collector electrode structure
823 in direction 830.
[0075] FIG. 8C is a top perspective view of an array 820 of
collector electrode structures 822 which may be attached to or
formed integrally with a base support member not shown in the
Figure. Array 820 of collector electrode structures 822 further
comprises a fluid-permeable, electrically conductive element 840
disposed (as a dominant ion collection surface) in front of the
leading edge portions 815 of collector electrodes 822. Element 840
comprises pores or openings of sufficient size to permit the fluid
being moved to pass minimally impeded through collector electrode
array 820 in fluid flow direction 830. Suitable fluid-permeable
elements include a metal mesh material.
[0076] FIGS. 9A and 9B illustrate exemplary enclosures and
positions of EHD devices disposed therein. FIG. 9A is a perspective
view of EHD device 900 disposed within enclosure 915 between
opposing boundary surfaces with ventilated portions 904 and 906. In
operation, EHD device 900 moves ambient air both within enclosure
915 as well as air drawn from outside of the enclosure, and
produces a flow path in the direction of arrow 960. If enclosure
915 is typically used in the orientation as shown in FIG. 9A while
supported on a flat surface, then enclosure 915 may have support
structures (not shown) on its bottom surface to raise enclosure 915
up and away from the supporting flat surface in order to allow air
to circulate under enclosure 915. EHD device 900 may be any one of
the embodiments of EHD devices described above, oriented within
enclosure 915 in a manner that produces air flow in the direction
of arrow 960.
[0077] By way of another example, FIG. 9B is a perspective view of
EHD device 1400 disposed within enclosure 1415 between adjoining
boundary surfaces with ventilated portions 1404 and 1405. In the
orientation of enclosure 1415 illustrated in FIG. 9B, ventilated
portion 1404 is part of a rear side boundary and ventilated portion
1404 is part of a bottom boundary of enclosure 1415. Top boundary
1418 opens from the rest of enclosure 1415 by way of hinge 1416.
Enclosure 1415 may also have an interior fixed or movable boundary
surface, not shown in the Figure, which is disposed between EHD
device 1400 and top boundary surface 1418. In operation, EHD device
1400 produces an air flow path in the direction of the arrows shown
in the interior of enclosure 1415. If enclosure 1415 is typically
used in the orientation as shown in FIG. 9B while supported by flat
surface 1420, then enclosure 1415 may have support structures (not
shown) on its bottom surface to raise enclosure 1415 up and away
from supporting flat surface 1420 in order to allow air to
circulate under enclosure 1415, for example, in the direction of
arrow 1440. EHD device 1400 may be any one of the embodiments of
EHD devices described above, oriented within enclosure 1415 in a
manner that produces air flow in the direction of the arrows as
shown in the Figure.
[0078] FIGS. 10A, 10B and 10C illustrate the use of a
semi-conductive or resistive coating on the edges of a collector
electrode. FIG. 10A is a front perspective view of collector
electrode array 120 of FIG. 1B with semi-conductive or resistive
coating 1012 applied to the edges of individual collector
electrodes 128. Area 1022 of collector electrodes 128 is enlarged
to show that semi-conductive or resistive coating 1012 may extend
to the front and side edges 1014 of electrode 128. FIG. 10B
illustrates one embodiment in which semi-conductive or resistive
coating 1012 may extend to the bottom surface 1024 of electrode
128. FIG. 10C is a side elevation view of collector electrode 626
of collector electrode array 620 of FIG. 6D and illustrating
semi-conductive or resistive coating 1032 applied on the
front-facing visible surface 625 of collector electrode 626 around
the edges of openings 614. While not shown in the Figure,
semi-conductive or resistive coating 1032 is also applied on the
rear-facing surface of collector electrode 626 in the same
manner.
[0079] The presence of the resistive coating on the leading edges
of the collector electrodes is one mechanism for managing the
electric field strength of the portion of the collector electrodes
closest to the corona discharge electrode. The presence of the
resistive coating serves to physically dull the edges of the
collector electrodes that are proximate to the corona discharge
electrode and eliminate sharp edges at the collector electrode ends
that could cause ions attracted to the collector electrodes to tend
to collect only at the collector electrode ends which would
adversely affect the performance of the fluid movement through the
collector electrode array. One benefit of having ions and fluid
move through collector electrode array 120 is that charged
particles, such as dust, in the fluid may accumulate in areas of
the collector electrodes that are more distant from the corona
discharge electrode. The presence of the resistive coating in
certain areas of the collector electrodes thus reduces the electric
field strength in these areas. The presence of the resistive
coating may also prevent arcing between the corona discharge
electrode and the ends of the collector electrodes.
[0080] While many of the collector electrode structures illustrated
in the Figures herein are illustrated as having substantially
smooth and uniformly even surfaces, a person of skill in the art
will recognize that they need not be so limited. It may be
advantageous in some implementations of EHD devices for the sides
of the collector electrodes that are parallel to the fluid flow
direction to have non-planar, bumpy or uneven surfaces. By way of
one example, FIG. 10D illustrates a partial top plan view of
collector electrode 1050 with side surfaces 1052a and 1052b
parallel to fluid flow direction 1030 each having a wave-like
shape. Other side surface configurations that depart from a
uniformly planar surface are also possible.
[0081] The EHD devices illustrated herein are suitable for
dissipating heat generated by a thermal source, as a component in a
thermal management system for an electronic circuit in an
electronic apparatus. As defined herein, an electronic circuit is
defined as one or more electronic components. When there is more
than one electronic component, the electronic components are in
mutual electromechanical contact, usually by being soldered to a
printed circuit board (PCB). An electronic component is any
physical entity in an electronic system whose intention is to
affect the electrons or their associated fields in a desired manner
consistent with the intended function of the electronic system.
Electronic components may be packaged singly or in more complex
groups as integrated circuits. Some common electronic components
are capacitors, resistors, diodes and transistors. As used herein,
an "electronic apparatus" is an apparatus that comprises one or
more electronic circuits.
[0082] The 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 100 of FIG. 1C is configured for dissipating heat
from an electronic circuit in an electronic apparatus, corona
discharge electrode 110 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 shown in FIG. 3, the distance between
adjacent corona discharge electrodes 110 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.
[0083] The various embodiments of EHD devices illustrated herein,
when used as a component in a thermal management system, may be
designed 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 the EHD device within the desired pressure head
range. In one embodiment, the EHD device may be configured to
operate with a pressure head in the range of 1-50 Pa. For some
thermal management applications, the desired, or target, pressure
head range may be a range of 3-20 Pa.
[0084] Each of the various embodiments of EHD devices illustrated
herein may be configured to have a high aspect ratio and positioned
within an enclosure proximate to one or more ventilated surface
boundaries in order to minimize resistance along the fluid flow
path. With reference to FIG. 11, assume that structure 1100 is an
EHD device of the type illustrated in FIG. 6D comprising collector
electrode array 620 that also functions as a heat sink and a
sub-component 645 that functions as a thermal conduit (e.g., a heat
pipe) that directs heat from a thermal source to array 620 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 Equation (1), or
5<L/D<150 Equation (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 Equation (3), or
10<L/D<30 Equation (4).
[0085] 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
in an enclosure, as illustrated, for example, in FIGS. 8 and 9
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. FIG. 12 summarizes the ranges of
the several factors discussed above.
[0086] 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 an intake ventilated
boundary surface that is substantially equal to the fluid flow
velocity at an outgoing ventilated boundary surface. Note that EHD
device 1100 of FIG. 11 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.
[0087] The discussion above in conjunction with FIGS. 11 and 12
relates to achieving improved fluid flow performance by optimizing
the aspect ratio of the entire EHD device. Fluid flow performance
improvements may also be achieved by optimizing characteristics of
the relationship of a corona discharge electrode to one or more
collector electrodes. Assume, for example, that EHD device 1400 of
FIG. 9B disposed in enclosure 1415 is configured to have one or
more corona discharge electrodes in the shape of a thin wire and
the collector electrode structure illustrated in FIGS. 8A and 8B.
FIGS. 13A and 13B illustrate some exemplary dimensions of such an
EHD device. These are referenced and described in Table 1
below:
TABLE-US-00001 TABLE 1 Ref. No or Symbol Dimension Dimension
description 1302 d.sub.1 Diameter of corona discharge wire 1304 d2
Distance from corona discharge wire to leading edge of collector
electrode, also referred to as the air gap H Height Height of
collector electrode L Length Length of collector electrode 1306 d3
The center-to-center distance between collector electrodes, or
pitch 1308 T The thickness of the collector electrode 1310 d4 A
portion of the length, L, of the collector electrode closest to the
corona discharge electrode, referred to as the leading edge length.
Henc Height Height of the enclosure in which the EHD device
operates
[0088] FIG. 13A is a cross-sectional side elevation view of an EHD
device. In FIG. 13A, corona discharge electrode 810 has a diameter,
d.sub.1, and collector electrode 823 has a length, L, and a width,
W. The air gap distance 1304 between corona discharge electrode 810
and collector electrode structure 823 is denoted as d.sub.2. When
the EHD device of FIG. 13A is operational, fluid travels in the
direction of arrow 830. FIG. 13B is a top plan view of collector
electrode array 1320 which is a portion of the collector electrode
array of the EHD device illustrated in FIG. 13A. In FIG. 13B, fluid
flow is along the length of collector electrode 823 in the
direction of arrow 830. The center-to-center distance 1306 between
collector electrodes, or pitch, is denoted as d.sub.3, and the
thickness 1308 of each collector electrode 823 is denoted as T.
[0089] Designing an EHD device using the dimensions referenced in
Table 1 and illustrated in FIGS. 13A and 13B and consistent with
the relationships stated in the following equations may improve
fluid flow performance:
L/d3<20 Equation (5),
0.1<T/d3<0.5 Equation (6), and
1.25<d2/d3<10 Equation (7).
The ratio of the length, L, of the collector electrode to the
pitch, d.sub.3, should preferably be less than 20. The ratio of the
thickness, T, of each collector electrode to the pitch, d.sub.3,
should preferably be between 0.1 and 0.5. The ratio of the air gap
distance, d.sub.2, to the pitch, d.sub.3, should preferably be
between 1.25 and 10. In addition, as a general principle, an EHD
device will achieve efficient fluid flow performance in a thermal
management system when the pitch of the collector electrodes is
greater than or equal to 0.5 mm and less than or equal to 2 mm.
Boundary layer disruption is another characteristic to be
considered. More significant boundary layer disruption along the
side surface of collector electrode is likely to be achieved in the
distance d.sub.4 of the electrode (i.e., the portion of the length,
L, of the collector electrode closest to the corona discharge
electrode, referred to as the leading edge length). The extent of
distance d.sub.4 is affected by the length, L, of a collector
electrode as well as the pitch, d.sub.3. Decreasing the pitch of
the collector electrodes may affect the electric field strength at
the leading edges of the collector electrodes.
[0090] Some of the embodiments of electrohydrodynamic fluid
accelerator devices illustrated and described herein are discussed
in the context of a thermal management solution to dissipate heat
generated by a thermal source. However, the devices are not limited
in their use to that context. Embodiments of the devices
illustrated and described herein may be suitable for use in any
type of device that requires the movement of a fluid, such as, for
example, electrostatic precipitators, and electrostatic air
cleaners and purifiers.
Other Embodiments
[0091] 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.
* * * * *