U.S. patent application number 12/470553 was filed with the patent office on 2010-11-25 for high performance heat transfer device, methods of manufacture thereof and articles comprising the same.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Hendrik Pieter Jacobus de Bock, Tao Deng, Brian Magann Rush, Boris Alexander Russ, Kripa Kiran Varanasi, Stanton Earl Weaver, JR..
Application Number | 20100294475 12/470553 |
Document ID | / |
Family ID | 42537954 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100294475 |
Kind Code |
A1 |
Rush; Brian Magann ; et
al. |
November 25, 2010 |
HIGH PERFORMANCE HEAT TRANSFER DEVICE, METHODS OF MANUFACTURE
THEREOF AND ARTICLES COMPRISING THE SAME
Abstract
Disclosed herein is an heat transfer device comprising a shell;
the shell being an enclosure that prevents matter from within the
shell from being exchanged with matter outside the shell; the shell
having an outer surface and an inner surface; and a porous layer
disposed on the inner surface of the shell; the porous layer having
a thickness effective to enclose a region between opposing faces;
the region providing a passage for the transport of a fluid; the
porous layer having a thermal conductivity of about 0.1 to about
2000 watts per meter-Kelvin and a mass flow rate of about 10.sup.-9
to about 10.sup.-4 kilograms per second.
Inventors: |
Rush; Brian Magann;
(Niskayuna, NY) ; de Bock; Hendrik Pieter Jacobus;
(Clifton Park, NY) ; Deng; Tao; (Clifton Park,
NY) ; Russ; Boris Alexander; (Niskayuna, NY) ;
Varanasi; Kripa Kiran; (Cambridge, MA) ; Weaver, JR.;
Stanton Earl; (Northville, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, BLDG. K1-3A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
42537954 |
Appl. No.: |
12/470553 |
Filed: |
May 22, 2009 |
Current U.S.
Class: |
165/185 |
Current CPC
Class: |
F28F 2245/02 20130101;
F28D 15/046 20130101; F28F 2245/04 20130101; B22F 3/1121 20130101;
B22F 7/004 20130101; H01L 23/427 20130101; H01L 2924/0002 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/185 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Goverment Interests
STATEMENT OF FEDERAL SUPPORT
[0001] The present invention was developed in part with funding
from the U.S. Government Defense Advanced Projects Research Agency
under Grant #N66001-08-C-2008. The United States Government has
certain rights in this invention.
Claims
1. A heat transfer device comprising: a shell; the shell being an
enclosure that prevents matter from within the shell from being
exchanged with matter outside the shell; the shell having an outer
surface and an inner surface; and a porous layer disposed on the
inner surface of the shell; the porous layer having a thickness
effective to enclose a region between opposing faces; the region
providing a passage for the transport of a fluid; the porous layer
having a thermal conductivity of about 0.1 to about 2000 watts per
meter-Kelvin and a mass flow rate of about 10.sup.-9 to about
10.sup.-4 kilograms per second.
2. The heat transfer device of claim 1, having a plurality of
different cross-sectional designs along its length; the length
being the dimension along the direction in which both heat and mass
flow are predominantly directed.
3. The heat transfer device of claim 1, where the heat transfer
device has a first section having a first cross-sectional design
proximately disposed to a first end of the heat transfer device
where heat is introduced into the heat transfer device, a second
section having a second cross-sectional design proximately disposed
to the first section and a third section having a third
cross-sectional design proximately disposed to the second section;
where the third section is proximately disposed to the second end
of the heat transfer device; the heat being removed from the second
end of the heat transfer device.
4. The heat transfer device of claim 3, where the first
cross-sectional design is different from the second cross-sectional
design or the third cross-sectional design.
5. The heat transfer device of claim 3, where the second
cross-sectional design is different from the third cross-sectional
design.
6. The heat transfer device of claim 1, where the shell has a
height of about 100 nanometers to about 20 centimeters.
7. The heat transfer device of claim 3, where the heat transfer
device contacts a heat source at its first end and a heat sink at
its second end.
8. The heat transfer device of claim 1, where the fluid is in a
saturated form.
9. The heat transfer device of claim 1, where the heat transfer
device recirculates the fluid.
10. The heat transfer device of claim 1, where the shell comprises
a metal, a ceramic, a polymer, or a combination thereof.
11. The heat transfer device of claim 1, where the shell is a
cylinder, a pyramid, a cube, an ellipsoid, a sphere, a rectangular
cuboid, a geodesic dome, an n-sided antiprism, a cupola, a
rhombohedron or a prism.
12. The heat transfer device of claim 1, where the shell has an
aspect ratio of about 5 to about 10,000.
13. The heat transfer device of claim 1, where one or more porous
layers comprise particles having average particle sizes of about 10
nanometers to about 10,000,000 nanometers.
14. The heat transfer device of claim 1, where the porous layer
comprises particles arranged in a plurality of layers.
15. The heat transfer device of claim 1, where the porous layer
comprises a first layer having particles of a first particle size
distribution and a second layer having particles of a second
particle size distribution; the second layer being disposed upon
the first layer.
16. The heat transfer device of claim 15, where the second layer
has particles that have a larger particle size larger than those of
the first layer; and where the first layer has a unimodal particle
size distribution.
17. The heat transfer device of claim 15, where the second layer
has particles that have a larger particle size smaller than those
of the first layer.
18. The heat transfer device of claim 15, where the porous layer
further comprises a third layer having particles of a third
particle size distribution; the third layer being disposed upon the
second layer; third particle size distribution being different from
the second particle size distribution and the first particle size
distribution.
19. The heat transfer device of claim 15, where the porous layer is
bounded on its sides by particles having the first particle size
distribution.
20. The heat transfer device of claim 19, where the first particle
size distribution comprises particles having an average particle
size of about 10 to about 10,000 nanometers; the second particle
size distribution has particles having an average particle size of
about 10,001 nanometers to about 100,000 nanometers and the third
particle size distribution has particles having an average particle
size of about 100,001 to about 10,000,000 nanometers.
21. The heat transfer device of claim 1, where a particle of the
porous layer has a contact angle with water of about zero degrees
to about 120 degrees.
22. The heat transfer device of claim 1, where the fluid is water,
alcohol, ketones, or a combination comprising at least one of the
foregoing fluids.
23. The heat transfer device of claim 1, where the fluid is
saturated water.
24. The heat transfer device of claim 1, where the porous layer has
pore sizes of about 10 to about 10,000,000 nanometers and where the
porous layer has a porosity of about 10 to about 90 volume percent,
based on the total volume of the layer.
25. The heat transfer device of claim 1, where the particles
comprise copper.
26. The heat transfer device of claim 1, where the particles are
coated with silica.
27. The heat transfer device of claim 1, where the particles are
coated with a metal oxide.
28. The heat transfer device of claim 1, wherein the region
enclosed between the opposing surfaces of the porous layer is
filled with large particles having an average particle size of
about 10,000 nanometers to about 10,000,000 nanometers.
29. A method comprising: disposing a slurry upon a substrate; the
slurry comprising a liquid and about 0.0001 to about 60 volume
percent of nanoparticles, based upon the total volume of the
slurry; evaporating the liquid from the substrate to form a porous
layer having a thickness of about 10 nanometers to about 10,000,000
nanometers upon the substrate; and forming the substrate into a
shell; the shell being an enclosure that prevents matter from
within the shell from being exchanged with matter outside the
shell; the porous layer being disposed upon an inner surface of the
shell.
30. The method of claim 29, where the evaporating is brought about
by heating the liquid.
31. The method of claim 29, where the disposing of the slurry upon
the substrate is accomplished by spin coating, dip coating, spray
painting, electrostatic spray painting or dip coating.
32. An article manufactured by the method of claim 29.
33. The article of claim 29, where the article is a pipe, a power
electronic module, a magnetic resonance imaging gradient driver or
a nuclear fuel rod.
34. A method comprising: contacting a first end of an heat transfer
device with a source of heat; the heat transfer device comprising:
a shell; the shell being an enclosure that prevents matter from
within the shell from being exchanged with matter outside the
shell; the shell having an outer surface and an inner surface; and
a porous layer disposed on the inner surface of the shell; the
porous layer having a thickness effective to enclose a region
between opposing faces; the region providing a passage for the
transport of a fluid; the porous layer having a thermal
conductivity of about 0.1 to about 2000 watts per meter-Kelvin and
a mass flow rate of about 10.sup.-9 to about 10.sup.-4 kilograms
per second; evaporating a fluid that is disposed in the porous
layer; and promoting a flow of the fluid to a second end of the
heat transfer device; the second end of the heat transfer device
contacting a heat sink.
35. The method of claim 32, where the first end is opposedly
disposed to the second end.
36. The method of claim 32, further comprising recycling the fluid
from the second end of the heat transfer device to the first end.
Description
BACKGROUND OF THE INVENTION
[0002] This disclosure relates to a high performance heat transfer
device, methods of manufacture thereof and to articles comprising
the same.
[0003] When a fluid is contained in a vessel under saturation
conditions, addition of heat leads to evaporation or boiling. This
evaporation causes an increase in vapor pressure, which drives the
flow of vapor to the cooler areas of the system, hereby referred to
as the condenser region. At the condenser region, heat is rejected
as vapor condenses to a liquid. Porous media capillaries or gravity
can be used to transport liquid back to the evaporation area. This
mechanism of two-phase heat transfer is often employed, as it is
very efficient at moving large amounts of heat at minimal
temperature gradient. A porous structure can also enhance heat
transfer in the evaporation region as it increases the effective
evaporation area and supplies nucleation sites for vapor bubbles to
generate from.
[0004] The capillary action of a porous medium relates to its
effective pore size distribution, which relates to its particle
size. Smaller pores enable structures with higher capillary action.
Permeability of a porous medium relates to the rate at which a
fluid can be transported through the medium given a pressure
difference across the system. In order to achieve high
permeability, large pore sizes are desired. In applications such
as, for example, evaporator sections for heat pipes, where both
heat transfer and capillary-driven mass transfer are simultaneously
desired, a trade-off is required to between capillary action and
permeability of the porous medium. This trade-off can be further
complicated when applications require that the transport section
function under increasing gravitational forces. This requires
decreased pore sizes, which then limit the heat transfer.
BRIEF DESCRIPTION OF THE INVENTION
[0005] Disclosed herein is a heat transfer device comprising a
shell; the shell being an enclosure that prevents matter from
within the shell from being exchanged with matter outside the
shell; the shell having an outer surface and an inner surface; and
a porous layer disposed on the inner surface of the shell; the
porous layer having a thickness effective to enclose a region
between opposing faces; the region providing a passage for the
transport of a fluid; the porous layer having a thermal
conductivity of about 0.1 to about 2000 watts per meter-Kelvin and
a mass flow rate of about 10.sup.-9 to about 10.sup.-4 kilograms
per second.
[0006] Disclosed herein too is a method comprising disposing a
slurry upon a substrate; the slurry comprising a liquid and about
0.0001 to about 60% volume percent of nanoparticles, based upon the
total volume of the slurry; evaporating the liquid from the
substrate to form a porous layer having a thickness of about 10
nanometers to about 10,000,000 nanometers upon the substrate; and
forming the substrate into a shell; the shell being an enclosure
that prevents matter from within the shell from being exchanged
with matter outside the shell; the porous layer being disposed upon
an inner surface of the shell.
[0007] Disclosed herein is a method comprising contacting a first
end of a heat transfer device with a source of heat; the heat
transfer device comprising a shell; the shell being an enclosure
that prevents matter from within the shell from being exchanged
with matter outside the shell; the shell having an outer surface
and an inner surface; and a porous layer disposed on the inner
surface of the shell; the porous layer having a thickness effective
to enclose a region between opposing faces; the region providing a
passage for the transport of a fluid; the porous layer having a
thermal conductivity of about 0.1 to about 2000 watts per
meter-Kelvin and a mass flow rate of about 10.sup.-9 to about
10.sup.-4 kilograms per second; evaporating a fluid that is
disposed in the porous layer; and promoting a flow of the fluid to
a second end of the heat transfer device; the second end of the
heat transfer device contacting a heat sink.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an exemplary schematic drawing depicting a heat
transfer device where heat is input at the first end and extracted
from the heat transfer device at the second end;
[0009] FIGS. 2(a), (b), (c), (d) and (e) depicts various
combinations of particles in the porous layer of the first section.
The exemplary views depicted in the FIGS. 2(a), (b), (c), (d) and
(e) are expanded views of the section C-C' taken from the FIG. 1.
These views are cross-sectional views taken in a direction
perpendicular to the length "l" of the heat transfer device at
A-A';
[0010] FIG. 3 depicts a unit cell formed by the particles
comprising the porous layer;
[0011] FIG. 4 is a graph that depicts the thin film area per unit
cell at a contact angle of 10 degrees and a fill factor of 50%;
[0012] FIG. 5 is a graph that depicts the thin film area per unit
cell versus the contact angle for particles having a diameter of 16
micrometers and a fill factor 80%; and
[0013] FIG. 6 depicts the manufacturing of a porous layer comprised
of copper or silica particles.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The disclosure will be described more fully hereinafter with
reference to the accompanying drawings, in which exemplary
embodiments are shown. As one would realize, the described
embodiments may be modified in various different ways, all without
departing from the spirit or scope of the invention.
[0015] In the drawings, the thickness of layers, films, panels,
regions, and the like, are exaggerated for clarity. Like reference
numerals designate like elements throughout the specification. It
will be understood that when an element such as a layer, film,
region, or shell is referred to as being "on" another element, it
can be directly on the other element or intervening elements may
also be present. In contrast, when an element is referred to as
being "directly on" another element, there are no intervening
elements present.
[0016] It will be understood that, although the terms first,
second, third, and the like, may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are only used to distinguish
one element, component, region, layer or section from another
region, layer or section. Thus, a first element, component, region,
layer or section discussed below could be termed a second element,
component, region, layer or section without departing from the
teachings of the present invention.
[0017] Spatially relative terms, such as "lower," "under," "upper"
and the like, may be used herein for ease of description to
describe the relationship of one element or feature to another
element(s) or feature(s) as illustrated in the figures. It will be
understood that the spatially relative terms are intended to
encompass different orientations of the device in use or operation,
in addition to the orientation depicted in the figures. For
example, if the device in the figures is turned over, elements
described as "lower" or "under" relative to other elements or
features would then be oriented "upper" or "over" relative to the
other elements or features. Thus, the exemplary term "under" can
encompass both an orientation of above and below. The device may be
otherwise oriented (rotated 90 degrees or at other orientations)
and the spatially relative descriptors used herein interpreted
accordingly.
[0018] Furthermore, in describing the arrangement of components in
embodiments of the present disclosure, the terms "upstream" and
"downstream" are used. These terms have their ordinary meaning. For
example, an "upstream" device as used herein refers to a device
producing a fluid output stream that is fed to a "downstream"
device. Moreover, the "downstream" device is the device receiving
the output from the "upstream" device. However, it will be apparent
to those skilled in the art that a device may be both "upstream"
and "downstream" of the same device in certain configurations,
e.g., a system comprising a recycle loop.
[0019] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
[0020] Embodiments are described herein with reference to
cross-section illustrations that are schematic illustrations of
idealized embodiments (and intermediate structures) of the
invention. As such, variations from the shapes of the illustrations
as a result, for example, of manufacturing techniques and/or
tolerances, are to be expected. Thus, embodiments should not be
construed as limited to the particular shapes of regions
illustrated herein but are to include deviations in shapes that
result, for example, from manufacturing.
[0021] For example, an implanted region illustrated as a rectangle
will, typically, have rounded or curved features and/or a gradient
of implant concentration at its edges rather than a binary change
from implanted to non-implanted region. Likewise, a buried region
formed by implantation may result in some implantation in the
region between the buried region and the surface through which the
implantation takes place. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the actual shape of a region of a device and are not
intended to limit the scope of the invention.
[0022] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0023] The term "comprising" as used herein may be substituted by
"consisting of" or "consisting essentially of". In addition, the
use of the term "about" preceding a numeral is intended to include
that numeral. For example, the use of the phrase "about 0.1 to
about 1" is intended to mean that both 0.1 and 1 are included in
the range. In addition, all numbers and ranges disclosed herein are
interchangeable.
[0024] All methods described herein can be performed in a suitable
order unless otherwise indicated herein or otherwise clearly
contradicted by context. The use of any and all examples, or
exemplary language (e.g., "such as"), is intended merely to better
illustrate the invention and does not pose a limitation on the
scope of the invention unless otherwise claimed. No language in the
specification should be construed as indicating any non-claimed
element as essential to the practice of the invention as used
herein.
[0025] Disclosed herein is a heat transfer device (such as, for
example, an heat pipe, vapor chamber or thermal ground plane) for
thermal applications that have a plurality of different
cross-sectional designs along its length, the length being the
dimension along the direction in which both heat and mass flow are
predominantly directed. The different cross-sectional designs can
facilitate an efficient heat flow and mass flow from a first end to
a second end of the heat transfer device. In one embodiment, the
heat transfer device has a first section having a first
cross-sectional design proximately disposed to the first end where
heat is introduced into the heat transfer device, a second section
having a second cross-sectional design proximately disposed down
stream of the first section and a third section having a third
cross-sectional design proximately disposed downstream of the
second section.
[0026] The third section is proximately disposed to the second end
of the heat transfer device where the heat is removed from the heat
transfer device. The first end and the second end of the heat
transfer device are opposedly disposed to each other. Multiple
sequences of these sections or two dimensional variations are
feasible. If desired, the heat transfer device can have fourth,
fifth and sixth sections that have fourth, fifth and sixth
cross-sectional designs respectively.
[0027] The heat transfer device is an enclosed elongated device
that comprises a shell having a porous layer disposed thereon. The
pores of the porous layer are completely or partially filled with
saturated liquid. Disposed between opposing faces of the porous
layer is a region that permits the transport of a vapor. The shell
contacts a heat source and a heat sink and is closed, i.e., there
is no exchange of matter from outside the shell with that inside
the shell. When the heat transfer device contacts a heat source,
liquid inside the porous media evaporates and locally vapor is
generated, which is transported from the heat source end and
transported to the heat sink end, where it condenses on the porous
media which releases the heat to the heat sink.
[0028] In one embodiment, upon being heated the vapor that is
generated travels from the first section to the second section and
then to third section. Thus with reference to the vapor, the second
section is located downstream of the first section, while the third
section is downstream of the second section. The vapor condenses
into water in the third section. The water travels back to the
first section from the third section. Thus with respect to the
water, the second section is located downstream of the third
section, while the first section is located downstream of the
second section.
[0029] In one embodiment, the heat transfer device is a planar,
thermal expansion matched heat spreader that is capable of moving
heat from multiple sources (e.g., chips) to a remote thermal sink.
In one embodiment, the heat transfer device has an effective
thermal conductivity that is more than 100 times greater than other
comparative commercially available heat transfer device. The heat
transfer device is based on a heat pipe architecture where
particles of different sizes are selectively arranged in different
configurations in the various sections listed above to produce an
enhanced heat transport and mass transport.
[0030] In an exemplary embodiment, the first section is an
evaporator section that contacts the heat source. The first section
comprises a porous layer where the particles are arranged to form a
first cross-sectional design. In another exemplary embodiment, the
second section is a wicking or transport section that comprises a
plurality of layers of nanoparticles that are arranged to form a
second cross-sectional design, the second cross-sectional design
being different from the first cross-sectional design. In yet
another exemplary embodiment, the third section is a condenser
section that comprises a plurality of layers of nanoparticles that
are arranged to form a third cross-sectional design.
[0031] With reference to the FIG. 1, the heat transfer device 100
comprises a first section 10 (see portion to the left of section
AA' when facing the viewer) disposed proximate to the first end 12.
Heat from an external source may be input into the first end 12. A
second section 14 (see portion between the section AA' and BB') is
disposed downstream (proximate) of the first section 10, while a
third section 16 (see portion to the right of section BB' when
facing the viewer) is disposed proximate of the second section 12.
The third section 16 is disposed proximate to the second end 18 of
the heat transfer device 100. Heat is extracted from the second end
18 of the heat transfer device.
[0032] As can be seen in the FIG. 1, the heat transfer device 100
comprises a shell 20 and one or more porous layers 22 disposed upon
the shell. Porous media can exist on either side of the surface.
The shell 20 has an inner surface and an outer surface. The porous
layer 22 is a porous layer that is disposed on the inner surface of
the shell. The porous layer 22 contacts a fluid (e.g., water) that
is heated by the heat source to form a saturated vapor. The
opposing surfaces 21 and 23 of the porous layer 22 have disposed
therebetween a region 24 that permits convection of the saturated
vapor from the first end to the second end of the heat transfer
device. Porous layer 22 could extend between opposing surfaces 21
and 23 containing passages for vapor transport 24. The second end
of the heat transfer device contacts a heat sink. The condensation
of the saturated vapor at the second end of the heat transfer
device thus facilitates heat transfer from the heat source to the
heat sink.
[0033] The shell is a three-dimensional device that is closed at
all ends. Matter from within the shell is not exchanged with matter
that lies outside the shell. In other words, the shell serves as a
boundary to prevent matter from the within the shell from diffusing
outside the shell and vice-versa. Additionally the shell is
evacuated an resides at a pressure less than atmospheric pressure.
The shell has disposed on it a porous layer (sometimes called a
wick). It is desirable for the material of the shell to have a
coefficient of thermal expansion that is similar to those
components that it contacts in order to prevent dissimilar
expansion. Dissimilar expansion can lead to damage of either the
shell or the component that it contacts. The shell can comprise a
metal, a ceramic or a polymer depending upon the application.
[0034] In an exemplary embodiment, the shell comprises a metal.
Examples of suitable metals are copper, aluminum, iron, titanium,
tin, tungsten, chromium, or the like, or a combination comprising
at least one of the foregoing metals. Examples of combinations of
metals include carbon steel, stainless steel, chromalloy, brass,
bronze, alnico, duralumin, nambe, silumin, AA-8000, magnalium,
.beta.-Al--Mg, .xi.'-Al--Pd--Mn, T-Al3Mn, wood's metal (alloy of
lead, tin and cadmium), rose metal (alloy of lead and tin),
megallium, stellite (alloy of chromium, tungsten and carbon),
talonite, vitallium, or the like. Exemplary metals for use in the
shell are copper laminates, copper tungsten alloys and
copper-molybdenum laminates.
[0035] Examples of suitable ceramics are metal oxides, metal
borides, metal nitrides, metal carbides, or the like, or a
combination comprising at least one of the foregoing ceramics.
Examples of suitable metal oxides are silica, titania, zirconia,
ceria, alumina, or the like, or a combination comprising at least
one of the foregoing oxides. Examples of metal borides, metal
nitrides and metal carbides are provided below. An exemplary
ceramic is aluminum nitride.
[0036] Organic polymers having glass transition temperatures
greater than or equal to about 150.degree. C. may be used for the
shell. Organic polymers that have glass transition temperatures
that are lower than room temperature, but which undergo thermal
degradation at temperatures greater than or equal to about
100.degree. C. may also be used. The organic polymers can be
thermoplastics, thermosets, blends of thermoplastics, blends of
thermosets, or blends of thermoplastics with thermosets. In one
embodiment, the shell can comprise an elastomer having an elastic
modulus at room temperature of about 10.sup.5 to about 10.sup.9
pascals.
[0037] Examples of suitable polymers are polyacetals, polyolefins,
polyacrylics, polycarbonates, polystyrenes, polyesters, polyamides,
polyamideimides, polyarylates, polyarylsulfones, polyethersulfones,
polyphenylene sulfides, polyvinyl chlorides, polysulfones,
polyimides, polyetherimides, polytetrafluoroethylenes,
polyetherketones, polyether etherketones, polyether ketone ketones,
polybenzoxazoles, polyphthalides, polyacetals, polyanhydrides,
polyvinyl ethers, polyvinyl thioethers, polyvinyl alcohols,
polyvinyl ketones, polyvinyl halides, polyvinyl nitriles, polyvinyl
esters, polysulfonates, polysulfides, polythioesters, polysulfones,
polysulfonamides, polyureas, polyphosphazenes, polysilazanes,
polysiloxanes, polybutadienes, polyisoprenes, polynitriles, or the
like, or a combination comprising at least one of the foregoing
polymers.
[0038] The shell can be a cylinder, a pyramid, a cube, an
ellipsoid, a sphere, a rectangular cuboid, a geodesic dome, an
n-sided antiprism, a cupola, a rhombohedron, a prism, or the like.
A cross-section of the shell can have a variety of different
geometries. Examples of suitable geometries are squares,
rectangles, circles, ellipses, polygons, or the like, or a
combination comprising at least one of the foregoing geometries. An
exemplary cross-section is a square or a rectangle.
[0039] As shown in the FIG. 1, the shell can have a length "l" and
a height "h" and a width "w" (not shown). The shell can have a
length "l" of about 10 millimeters to about 1 meter. In one
embodiment, the shell can have a length "l" of about 30 millimeters
(mm) to about 0.75 meter. In another embodiment, the shell can have
a length "l" of about 50 millimeters (mm) to about 0.50 meter. In
yet another embodiment, the shell can have a length "l" of about 75
millimeters (mm) to about 0.25 meter.
[0040] When the shell has a number of sides (e.g., when the
cross-section of the shell is a square or a rectangular (4 sides)
or a pentagon (5 sides)) the length of the smallest side (measured
in a direction perpendicular to the direction in which the length
"l" is measured) is greater than or equal to about 100 nanometers.
In one embodiment, the distance of the smallest side can be about
200 nanometers to about 20 centimeters. In another embodiment, the
distance of the smallest side can be about 500 nanometers to about
10 centimeters. In yet another embodiment, the distance of the
smallest side can be about 1,000 nanometers to about 1
centimeter.
[0041] When the shell has a circular or an elliptical cross
section, the diameter or the minor axis the shell (measured in a
direction perpendicular to the direction in which the length "l" is
measured) is greater than or equal to about 100 nanometers. In one
embodiment, the diameter or the minor axis the shell can be about
200 nanometers to about 20 centimeters. In another embodiment, the
diameter or the minor axis the shell can be about 500 nanometers to
about 10 centimeters. In yet another embodiment, the diameter or
the minor axis the shell can be about 1,000 nanometers to about 1
millimeter.
[0042] Thus, for example, with respect to the FIG. 1, when the
cross-sectional area of the heat transfer device is a square, the
sides of the square (e.g., the width (not shown) and the height "h"
of the square) can be greater than or equal to about 100
nanometers. In one embodiment, the sides of the square can be about
200 nanometers to about 20 centimeters. In another embodiment, the
sides of the square can be about 500 nanometers to about 10
centimeters. In yet another embodiment, the height of the square
can be about 1,000 nanometers to about 1 millimeter.
[0043] When, for example, the cross-sectional area of the heat
transfer device is a rectangle, the smallest side of the rectangle
can be greater than or equal to about 100 nanometers. In one
embodiment, the smallest side of the rectangle can be about 200
nanometers to about 20 centimeters. In another embodiment, the
smallest side of the rectangle can be about 500 nanometers to about
10 centimeters. In yet another embodiment, the smallest side of the
rectangle can be about 1,000 nanometers to about 1 millimeter.
[0044] The shell can have an aspect ratio of greater than or equal
to about 2. The aspect ratio is equal to the length "l" of heat
transfer device divided by the largest linear cross-sectional
dimension of the heat transfer device measured perpendicular to the
length. In one embodiment, the shell can have an aspect ratio of to
about 5 to about 10,000. In another embodiment, the shell can have
an aspect ratio of to about 10 to about 5,000. In yet another
embodiment, the shell can have an aspect ratio of to about 20 to
about 1,000.
[0045] The porous layer can comprise particles of various sizes and
having various surface chemistries. The surface chemistry (e.g.,
the hydrophobicity or hydrophilicity) of the particles in the
porous layer can be also be used to effect heat and mass
transfer.
[0046] The capillary forces in the pores can be varied with
particle size. In general, capillary forces increase with
decreasing pore size. Pore sizes decrease with decreasing particle
size. The increase in the capillary forces as a result of decrease
in particle size restricts mass flow. As the pore size is decreased
however, the surface area per unit volume of the particles is
increased. With the increase in the surface area of the particles,
the available area for the formation of a fluid thin film on the
particle surface is increased. A larger surface area permits better
heat transfer by evaporation and condensation. It is therefore
desirable to balance these competing effects, additionally taking
into account any gravitational forces the device may encounter in
order to bring about the desired amount of heat transfer and mass
transfer to the second section.
[0047] In one embodiment, the particle size can be tailored to
effect the pore sizes and consequently the mass transfer. The
particles can be nanometer-sized particles or micrometer-sized
particles. The particles can have average particle sizes of about
10 nanometers to about 100,000 nanometers. In one embodiment, the
particles can have average particle sizes of about 100 to about
5,000 nanometers. In another embodiment, the particles can have
average particle sizes of about 200 to about 3,000 nanometers. In
yet another embodiment, the particles can have average particle
sizes of about 300 to about 1,000 nanometers.
[0048] The particles can have a unimodal or multimodal particle
size distribution. In one embodiment, the particles can have a
bimodal size distribution. In another embodiment, the particles can
have a trimodal size distribution. Within a particular particle
size distribution, it is desirable for the particles to have a
polydispersity index of about 1 to about 1.25. In one embodiment,
the particles have a polydispersity index of about 1.02 to about
1.15. In another embodiment, the particles have a polydispersity
index of about 1.03 to about 1.10.
[0049] The contact angle of the particles can be changed by varying
the surface chemistry. The surface chemistry of the particles can
be varied by coating the particles with materials that are
hydrophobic or hydrophilic. In order to render the particles
hydrophobic, materials such as polyfluorocarbons, polysiloxanes,
trichloromethylsilane, hexamethylenedisilazane, and the like, can
be used to coat the particles. The particles can be rendered
hydrophilic by coating them with polyamides, polyvinylalcohols,
urea, urethanes, and the like. The contact angles of the particles
with water can be varied in an amount of about zero degrees to
about 120 degrees. In one embodiment, the contact of the particles
with water can be varied in an amount of about 5 degrees to about
80 degrees. In another embodiment, the contact angle of the
particles with water can be varied in an amount of about 10 degrees
to about 50 degrees. Since a lower contact angle represents a
larger degree of wetting than a larger contact angle, particles
that have lower contact angles assist thin film production on their
surfaces and are therefore better for heat transfer purposes.
[0050] The porous layer contacts the shell intimately along the
inner surface of the shell. The porous layer is of a thickness
effective to facilitate the formation of a region between opposing
surfaces of the porous layer, where the saturated vapor can be
transported from the first end to the second end (or vice versa) of
the heat transfer device. In one embodiment, the porous layer has a
thickness of about 10 nanometers to about 10 millimeters. In
another embodiment, the porous layer has a thickness of about 100
nanometers to about 1 millimeter. In yet another embodiment, the
porous layer has a thickness of about 1 micrometer to about 300
micrometers.
[0051] The porous layer has a thermal conductivity of about 0.1 to
about 2000 watts per meter-kelvin (W/m-K). In one embodiment, the
porous layer has a thermal conductivity of about 10 to about 1000
W/m-K. In another embodiment, the porous layer has a thermal
conductivity of about 50 to about 500 W/m-K. In yet another
embodiment, the porous layer has a thermal conductivity of about
100 to 400 W/m-K.
[0052] The porous layer provides for a mass flow rate of about
10.sup.-9 to about 10.sup.-4 kilograms per second (kg/s). In one
embodiment, the porous layer provides for a mass flow rate of about
10.sup.-9 to about 10.sup.-5 kg/s. In one embodiment, the porous
layer provides for a mass flow rate of about 10.sup.-8 to about
10.sup.-6 kg/s. In another embodiment, the porous layer provides
for a mass flow rate of about 10.sup.-10 to about 10.sup.-4 kg/s.
In an exemplary embodiment, the porous layer has a mass flow rate
of about 10.sup.-7 kg/s.
[0053] The particles in the porous layer can be arranged in a
number of different configurations to achieve a suitable
combination of heat transfer and mass transfer. FIG. 2 depicts
various combinations of particles in the porous layer of the first
section. The exemplary views depicted in the FIGS. 2(a), (b), (c),
(d) and (e) are expanded views of the section C-C' taken from the
FIG. 1. These views are cross-sectional views taken in a direction
perpendicular to the length "l" of the heat transfer device at
A-A'.
[0054] FIGS. 2(a) and 2(b) are exemplary schematics each of which
depict a plurality of particles in the porous layer. The porous
layer is disposed on the shell 20 of the heat transfer device 100.
The particles of the FIGS. 2(a) and 2(b) are of a unimodal size
distribution, with the particles 40 of the FIG. 2(a) having a
larger particle size than the particles 42 of the FIG. 2(b). The
larger particle sizes generally produce larger pore sizes than the
pore sizes produced by the smaller particles. In general, for
capillary driven mass transport in porous media, the smaller the
pores the larger the potential capillary forces and the larger the
viscous flow resistance. Conversely, the larger the pores the
smaller the capillary forces and the viscous flow resistance. To
maximize capillary-driven mass transport in uniform porous media
these competing effects must be balanced to maximize
performance.
[0055] In general, for mass transport in porous media, permeability
is determined by the pore sizes and porosity of the porous
structure. Larger pores facilitate mass transport as larger mass
flow rates can be achieved given a fixed pressure difference. As
critical heat flux requires the surface to be wetted, sufficient
permeability and therefore pore size is required to sustain
sufficient mass flow.
[0056] In general, for heat transport in uniform porous media, the
smaller the particles (and pores) making up the porous media the
larger the thin film heat transfer coefficients because of the
higher surface area to volume ratios. The larger the particles (and
pores) making up the porous media the larger the nucleate boiling
heat transfer coefficients because of the lower resistance to
venting bubbles that would otherwise conglomerate to form a
insulating vapor layers at the critical heat flux.
[0057] FIGS. 2(c) and 2(d) are exemplary depictions of porous
layers where the particles have a bimodal distribution. As can be
seen in the FIGS. 2(c) and 2(d), the particles are arranged in a
plurality of layers 50, 52. A first layer 52 has particles of a
first particle size distribution while a second layer 50 has
particles of a second particle size distribution. In the FIG. 2(c),
the first layer 52 has particles of a smaller particle size
disposed upon the second layer 50 of particles that have a larger
particle size. The combination of the smaller particle sizes with
larger particle sizes can be used to enhance the heat and mass
transfer. In particular, the configuration displayed in the FIG.
2(c) can be tailored for thin film heat transfer.
[0058] The FIG. 2(d) depicts an exemplary variation of the porous
layers, wherein the first layer 60 has particles of a larger
particle size disposed upon a second layer 62 of particles that
have a smaller particle size. In one embodiment, the configuration
displayed in the FIG. 2(d) can be tailored for good nucleate
boiling. Thus the configurations displayed in the FIGS. 2(c) and
2(d) can be selected to produce good heat transfer and good mass
transfer in various evaporation regimes.
[0059] The FIG. 2(e) depicts a plurality of layers of different
particle sizes. As can be seen in the FIG. 2(e), the porous layer
comprises three layers of particles--a first layer 70, a second
layer 72 and a third layer 74. The first layer 70 has the smallest
particle sizes. Disposed upon the first layer 70 is the second
layer 72 of particles whose particles have a larger particle size
than those of the first layer 70. Disposed upon the second layer is
the third layer 74 of particles whose particles have a larger
particle size than those of the second layer 72. The larger
particles of the second and the third layers are bounded on both
sides by the smaller particles of the first layer. By gradually
increasing the particle sizes from the first layer to the third
layer, the venting (mass transfer) can be increased toward the
surface of the porous layer furthest from the shell, while
providing for heat transfer in the immediate vicinity of the
shell.
[0060] When particles having a unimodal particle size distribution
are used, average particle sizes are about 10 nanometers to about
10,000,000 nanometers. When a bimodal or higher distribution of
particles are used in the porous layer, the smallest particles have
an average particle size of about 10 to about 10,000 nanometers,
with larger particles having an average particle size of about
10,001 nanometers to about 100,000 nanometers. If a trimodal
particle distribution is used, larger particles having an average
particle size of about 100,001 to about 10,000,000 nanometers can
be used. Other combinations of particles sizes and particle size
ranges may be used if desired.
[0061] The porous layer can comprise a metal, a polymer, a ceramic,
or a combination comprising at least one of the foregoing metals,
polymers or ceramics. In one embodiment, the porous layer generally
comprises particles that can exist in the form of agglomerates and
aggregates, thus providing a porous layer having a high surface
area. An aggregate comprises more than one particle in physical
contact with one another, while an agglomerate comprises more than
one aggregate in physical contact with one another. In one
embodiment, the particles may agglomerate to form a structure with
a fractal dimension of about 1 to about 3, i.e., it can be a mass
fractal. In another embodiment, the particles may agglomerate to
form a structure with a fractal dimension of about 3 to about 4,
i.e., it can be a surface fractal. The fractal dimensions can be
measured using scattering techniques.
[0062] The porous layer can comprise a metal. Examples of metals
are transition metals and platinum group metals from the periodic
table. Examples of suitable metals are gold, platinum, silver,
palladium, copper, aluminum, nickel, cobalt, titanium, tin, or the
like, or a combination comprising at least one of the foregoing
metals.
[0063] The porous layer can comprise a ceramic, such as inorganic
oxides, metal oxides, silicates, borides, carbides, nitrides,
perovskites and perovskites derivatives, or the like, or a
combination comprising at least one of the foregoing. Examples of
inorganic oxides include calcium oxide, silicon dioxide, or the
like, or a combination comprising at least one of the foregoing
inorganic oxides. In one embodiment, the ceramic comprises metal
oxides of alkali metals, alkaline earth metals, transition metals,
metalloids, poor metals, or the like, or a combination comprising
at least one of the foregoing. In one embodiment, the ceramic can
be in the form of an aerogel.
[0064] Examples of inorganic oxide and/or metal oxides are silicon
dioxide, cerium oxide, magnesium oxide, titanium oxide, zinc oxide,
copper oxide, cerium oxide, niobium oxide, tantalum oxide, yttrium
oxide, zirconium oxide, aluminum oxide (e.g., alumina and/or fumed
alumina), CaTiO.sub.3, MgZrSrTiO.sub.6, MgTiO.sub.3,
MgAl.sub.2O.sub.4, BaZrO.sub.3, BaSnO.sub.3, BaNb.sub.2O.sub.6,
BaTa.sub.2O.sub.6, WO.sub.3, MnO.sub.2, SrZrO.sub.3, SnTiO.sub.4,
ZrTiO.sub.4, CaZrO.sub.3, CaSnO.sub.3, CaWO.sub.4,
MgTa.sub.2O.sub.6, MgZrO.sub.3, La.sub.2O.sub.3, CaZrO.sub.3,
MgSnO.sub.3, MgNb.sub.2O.sub.6, SrNb.sub.2O.sub.6,
MgTa.sub.2O.sub.6, Ta.sub.2O.sub.3, or the like, or a combination
comprising at least one of the foregoing metal oxides.
[0065] Examples of silicates are Na.sub.2SiO.sub.3, LiAlSiO.sub.4,
Li.sub.4SiO.sub.4, BaTiSi.sub.3O.sub.9, Al.sub.2Si.sub.2O.sub.7,
ZrSiO.sub.4, KAlSi.sub.3O.sub.8, NaAlSi.sub.3O.sub.8,
CaAl.sub.2Si.sub.2O.sub.8, CaMgSi.sub.2O.sub.6, Zn.sub.2SiO.sub.4,
or the like, or a combination comprising at least one of the
foregoing silicates.
[0066] Examples of borides are lanthanum boride (LaB.sub.6), cerium
boride (CeB.sub.6), strontium boride (SrB.sub.6), aluminum boride,
calcium boride (CaB.sub.6), titanium boride (TiB.sub.2), zirconium
boride (ZrB.sub.2), vanadium boride (VB.sub.2), tantalum boride
(TaB.sub.2), chromium borides (CrB and CrB.sub.2), molybdenum
borides (MoB.sub.2, Mo.sub.2B.sub.5 and MoB), tungsten boride
(W.sub.2B.sub.5), or the like, or a combination comprising at least
one of the foregoing borides.
[0067] Examples of carbides are silicon carbide, tungsten carbide,
tantalum carbide, iron carbide, titanium carbide, or the like, or a
combination comprising at least one of the foregoing carbides.
[0068] Examples of nitrides include silicon nitride, boron nitride,
titanium nitride, aluminum nitride, molybdenum nitride, or the
like, or a combination comprising at least one of the foregoing
nitrides.
[0069] Examples of perovskites and perovskite derivatives include
barium titanate (BaTiO.sub.3), strontium titanate (SrTiO.sub.3),
barium strontium titanate, strontium-doped lanthanum manganate,
lanthanum aluminum oxides (LaAlO.sub.3), calcium copper titanate
(CaCu.sub.3Ti.sub.4O.sub.12), cadmium copper titanate
(CdCu.sub.3Ti.sub.4O.sub.12), Ca.sub.1-xLa.sub.xMnO.sub.3, (Li, Ti)
doped NiO, lanthanum strontium copper oxides (LSCO), yttrium barium
copper oxides (YBa.sub.2Cu.sub.3O.sub.7), lead zirconate titanate,
lanthanum-modified lead zirconate titanate, or the like, or a
combination comprising at least one of the foregoing perovskites
and perovskite derivatives.
[0070] As noted above, the ceramic particles may comprise
nanoparticles. Commercially available examples of nanoparticles
that can be used in the composition are calcium oxide commercially
available as NANOACTIVE CALCIUM OXIDE.TM. or NANOACTIVE CALCIUM
OXIDE PLUS.TM., cerium oxide commercially available as NANOACTIVE
CERIUM OXIDE.TM. magnesium oxide commercially available as
NANOACTIVE MAGNESIUM OXIDE.TM. or NANOACTIVE MAGNESIUM OXIDE
PLUS.TM., titanium oxide commercially available as NANOACTIVE
TITANIUM OXIDE.TM., zinc oxide commercially available as NANOACTIVE
ZINC OXIDE.TM., silicon oxide commercially available as NANOACTIVE
SILICON OXIDE.TM. copper oxide commercially available as NANOACTIVE
COPPER OXIDE.TM., aluminum oxide commercially available as
NANOACTIVE ALUMINUM OXIDE.TM. or NANOACTIVE ALUMINUM OXIDE
PLUS.TM., all of which are commercially available from NanoScale
Materials Incorporated. Another commercially available set of
nanoparticles are aluminum oxide nanoparticles sold as NANODUR.TM.
from Nanophase Technologies Corporation.
[0071] Polymers that can be used in the porous layers are generally
aerogels or xerogels. Examples of polymeric aerogels or xerogels
are resorcinol-formaldehyde aerogels or xerogels,
phenol-formaldehyde aerogels or xerogels, or the like, or a
combination comprising at least one of the foregoing polymeric
aerogels.
[0072] The porous layer can also comprise carbonaceous materials.
Examples of porous layers that are carbonaceous are carbon black
coatings, carbon nanotube coatings, carbon aerogel coatings, or the
like, or a combination comprising at least one of the foregoing
carbonaceous coatings. Carbon aerogels can be obtained by
pyrolyzing the aforementioned polymeric aerogels.
[0073] In an exemplary embodiment, the porous layer can comprise
nanoparticles having any geometry. There is no particular
limitation to the shape of the nanoparticles, which may be, for
example, spherical, irregular, plate-like or whisker like.
[0074] The porous layer can have a surface area of about 50 to
about 1,200 square meters per gram (m.sup.2/gm). In one embodiment,
porous layer can have a surface area of about 100 to about 1,000
square meters per gram (m.sup.2/gm). In another embodiment, the
porous layer can have a surface area of about 150 to about 800
square meters per gram (m.sup.2/gm). In yet another embodiment, the
porous layer can have a surface area of about 200 to about 700
square meters per gram (m.sup.2/gm).
[0075] The porous layer has pore sizes of about 10 to about
10,000,000 nanometers. In one embodiment, the porous layer has pore
sizes of about 1,000 to about 1,000,000 nanometers. In another
embodiment, the porous layer has pore sizes of about 10,000 to
about 100,000 nanometers.
[0076] The porous layer has a porosity of about 10 to about 99.9
volume percent, based on the total volume of the coating. In one
embodiment, the porous layer has a porosity of about 20 to about 90
volume percent, based on the total volume of the coating. In yet
another embodiment, the porous layer has a porosity of about 30 to
about 70 volume percent, based on the total volume of the
coating.
[0077] The porous layer has a thickness of about 5 nanometers to
about 10 millimeters. In one embodiment, the porous layer has a
thickness of about 5 nanometers to about 5 micrometers. In another
embodiment, the porous layer has a thickness of about 75 nanometers
to about 20 micrometers. In an exemplary embodiment, the porous
layer has a thickness of about 100 nanometers to about 100
micrometer.
[0078] With reference now again to the FIG. 1, the region 24 is
filled with a fluid. A suitable fluid is a saturated vapor. The
vapor can comprise water, alcohol, ketones, ether, halogenated
solvents, and the like. A list of solvents are provided below. An
exemplary saturated vapor comprises water.
[0079] In one embodiment, the region 24 can be filled with larger
sized particles (not shown) than those used in porous layer. The
particles used in the region 24 can have the same composition as
the particles used in the porous layer. In one embodiment, the
larger sized particles can have average particle size of about
10,000 nanometers to about 10,000,000 nanometers. In another
embodiment, the larger sized particles can have average particle
size of about 100,000 nanometers to about 1,000,000 nanometers.
[0080] There are several different methods by which the porous
layer can be manufactured. In one embodiment, in one method of
manufacturing the porous layer, a slurry comprising the
nanoparticles described above and a suitable liquid is disposed
upon the shell. The slurry can optionally contain a binder and an
acid. The slurry may be disposed upon the shell by spin coating,
dip coating, brush painting, spray painting, electrostatic spray
painting, or the like, or a combination comprising at least one of
the foregoing methods.
[0081] The shell with the slurry disposed thereon is then subjected
to drying. The liquid from the slurry is evaporated during the
drying, leaving behind the porous layer. In one embodiment, this
layer may be the first layer of the porous layer. In one
embodiment, the drying can be conducted by subjecting the liquid in
the slurry to heating causing it to evaporate. The heating can be
brought about by conduction, convection and/or radiation. Radiation
involving radio-waves, microwaves, or infrared waves can be
used.
[0082] In one embodiment, a second slurry having particles of
different sizes from those of the first slurry can then be disposed
upon the first layer to form a second layer. In another embodiment,
a third slurry having particles of different sizes from those of
the first slurry and/or the second slurry can then be disposed upon
the second layer to form the third layer. In this manner, a
plurality of layers can be disposed on the shell to form the porous
layer.
[0083] The particles are generally present in an amount of about
0.0001 volume percent (vol %) to about 60 vol %, based upon the
total volume of the slurry. In another embodiment, the particles
are present in an amount of about 0.001 vol % to about 0.1 vol %,
based upon the total volume of the slurry.
[0084] The liquid can be present in the slurry in an amount of
about 30 to about 99.9 vol %. In one embodiment, the liquid can be
present in the slurry in an amount of about 60 to about 99 vol %.
In another embodiment, the liquid can be present in the slurry in
an amount of about 70 to about 98 vol %.
[0085] In another embodiment, pertaining to the manufacturing of
the porous layer, a reactive solution comprising a particle
precursor such as an inorganic alkoxide is mixed in a vessel with a
suitable solvent, a modifier, and an optional suitable surfactant.
The reactive solution, which is initially in the form of a sol is
converted to a gel by the sol gel process. The reactive solution in
the form of a sol is then disposed on the shell. In one embodiment,
the gel disposed on the shell is optionally washed, dried and
calcined to yield a nanoporous composition that is disposed upon
the shell. In another embodiment, the solvent present in the gel is
exchanged with a supercritical fluid (e.g., supercritical carbon
dioxide) to yield an aerogel. In yet another embodiment, the gel is
treated with an agent such as trimethylchlorosilane,
hexamethylenedisilazane, or the like, or combinations comprising at
least one of trimethylchlorosilane or hexamethylenedisilazane to
yield an aerogel.
[0086] Examples of suitable inorganic alkoxides are
tetraethylorthosilicate, tetramethylorthosilicate, aluminum
isopropoxide, aluminum tributoxide, aluminum ethoxide,
aluminum-tri-sec-butoxide, aluminum tert-butoxide, antimony(III)
ethoxide, antimony(III) isopropoxide, antimony(III) methoxide,
antimony(III) propoxide, barium isopropoxide, calcium isopropoxide,
calcium methoxide, chlorotriisopropoxytitanium, magnesium
di-tert-butoxide, magnesium ethoxide, magnesium methoxide,
strontium isopropoxide, tantalum(V) butoxide, tantalum(V) ethoxide,
tantalum(V) ethoxide, tantalum(V) methoxide, tin(IV) tert-butoxide,
diisopropoxytitanium bis(acetylacetonate) solution, titanium(IV)
(triethanolaminato)isopropoxide solution, titanium(IV)
2-ethylhexyloxide, titanium(IV) bis(ethyl
acetoacetato)diisopropoxide, titanium(IV) butoxide, titanium(IV)
butoxide, titanium(IV)
diisopropoxidebis(2,2,6,6-tetramethyl-3,5-heptanedionate),
titanium(IV) ethoxide, titanium(IV) isopropoxide, titanium(IV)
methoxide, titanium(IV) tert-butoxide, vanadium(V) oxytriethoxide,
vanadium(V) oxytriisopropoxide, yttrium(III) butoxide, yttrium(III)
isopropoxide, zirconium(IV) bis(diethyl citrato)dipropoxide,
zirconium(IV) butoxide, zirconium(IV)
diisopropoxidebis(2,2,6,6-tetramethyl-3,5-heptanedionate),
zirconium(IV) ethoxide, zirconium(IV) isopropoxide zirconium(IV)
tert-butoxide, zirconium(IV) tert-butoxide, or the like, or a
combination comprising at least one of the foregoing inorganic
alkoxides. Exemplary inorganic alkoxides are
tetraethylorthosilicate or aluminum sec-butoxide.
[0087] The reactive solution generally contains an inorganic
alkoxide in an amount of about 1 to about 50 wt %, based upon the
weight of the reactive solution. In one embodiment, the reactive
solution generally contains an inorganic alkoxide in an amount of
about 5 to about 20 wt %, based upon the weight of the reactive
solution.
[0088] Solvents that are used may be aprotic polar solvents, polar
protic solvents, non-polar solvents Examples of aprotic polar
solvents are propylene carbonate, ethylene carbonate,
butyrolactone, acetonitrile, benzonitrile, nitromethane,
nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, or
the like, or combinations comprising at least one of the foregoing
aprotic polar solvents. Examples of polar protic solvents are
water, methanol, acetonitrile, nitromethane, ethanol, propanol,
isopropanol, butanol, or the like, or combinations comprising at
least one of the foregoing polar protic solvents. Examples of non
polar solvents include benzene, toluene, methylene chloride, carbon
tetrachloride, hexane, diethyl ether, tetrahydrofuran, or the like,
or combinations comprising at least one of the foregoing non polar
solvents. Co-solvents may also be used. Ionic liquids may also be
utilized as solvents during the gelation. An exemplary solvent is
ethanol.
[0089] Solvents are generally added in an amount of about 0.5 wt %
to about 300 wt %, specifically about 1 to about 200 wt %, more
specifically about 70 to about 100 wt %, based on the total weight
of the reactive solution.
[0090] The modifiers may control the hydrolysis kinetics of the
inorganic alkoxides. Examples of suitable modifiers are ethyl
acetoacetate, ethylene glycol, or the like, or a combination
comprising at least one of the foregoing modifiers. The reactive
solution generally contains the modifier in an amount of about 0.1
to about 5 wt %, based upon the weight of the reactive
solution.
[0091] The surfactants are optional and can be anionic surfactants,
cationic surfactants, non-ionic surfactants, zwitterionic
surfactants, or a combination comprising at least one of the
foregoing surfactants. The surfactants serve as templates and
facilitate the production of shells containing directionally
aligned tubular mesochannels forms. The reactive solution generally
contains the surfactant in an amount of about 0.1 to about 5 wt %,
based upon the weight of the reactive solution. An exemplary
surfactant is octylphenol ethoxylate commercially available as
TRITON X 114.RTM..
[0092] An acid catalyst or a basic catalyst may be used to promote
gelation of the metal alkoxide. Acid catalysts (having a pH of
about 1 to about 6) generally promote ramified porous structures,
while basic catalysts (having a pH of about 8 to about 14) promote
compact porous structures. Acid catalysts generally promote the
formation of mass fractals having fractal dimensions from about 1
to about 3, while basic catalysts generally promote the formation
of surface fractals having fractal dimensions of about 3 to about
4.
[0093] In yet another embodiment, pertaining to the manufacturing
of the porous layer, a reactive solution comprising a particle
precursor such as an inorganic alkoxide is mixed in a vessel with a
suitable solvent, metal particles, a modifier, and an optional
suitable surfactant. The sol with the metal particles is disposed
on the shell. As noted above, the reactive solution, which is
initially in the form of a sol is converted to a gel by the sol gel
process. The gel holds the metal particles together to form a
composite. Following gelation, the composite is annealed at an
elevated temperature to evaporate the solvent. The gel may then be
fired to convert the gel to a glass. The porous layer thus
comprises metal particles bound together by a glass.
[0094] In an exemplary embodiment, the shell with the porous layer
disposed thereon is part of a heat transfer device. The heat
transfer device may be used in electronic devices, in nuclear
facilities, as insulation on pipes in chemical plants or in
supercomputers, or the like.
[0095] The following examples, which are meant to be exemplary, not
limiting, illustrate compositions and methods of manufacturing of
some of the porous layers described herein as well as their
properties when used in a heat transfer device.
EXAMPLES
Example 1
[0096] This example is conducted to demonstrate the properties of
contact angle and its effect on film thickness on particles that
are used to form the porous layer. The porous layer comprises
particles as shown in the FIG. 3. The FIG. 3 depicts a unit cell
formed by the particles. With respect to the FIG. 3, the unit cell
comprises two particles 202 and 204. The particles have a diameter
D.sub.p and a contact angle ".theta." that may be varied with
tailored coatings.
[0097] Upon contact the fluid spreads over the particles in the
porous layer to form a film. The thickness of the film depends upon
the pore sizes and the contact angle of the particle with the
fluid.
[0098] FIG. 4 is a graph that depicts a calculated geometric thin
film area per unit cell at a contact angle of 10 degrees and a fill
factor, defined to be the ratio of the liquid area to total area
per unit cell, of 50%. From the FIG. 4 it can be seen that the thin
film area increases rapidly as particle size decreases. As the
particle size increases into the micrometer range from the
nanometer range, it can be seen that the thin film area
plateau.
[0099] FIG. 5 is a graph that depicts a calculated geometric thin
film area per unit cell versus the contact angle for particles
having a radius of 8 micrometers. The fill factor is 80%. As can be
seen from the FIG. 5, as the contact angle is decreased the thin
film area increases.
[0100] The above results demonstrate that by using smaller
particles the thin film area can be increased. Similar results can
be obtained by decreasing the contact angle.
[0101] The results also show that by using particles having a
variety of different sizes, a desirable mass flow and a desirable
heat flow can be achieved in the heat transfer device.
Example 2
[0102] This example demonstrates the formation of a porous layer
comprising copper particles. Copper particles having an average
particle size of 50 micrometers and a unimodal particle size
distribution with a polydispersity index of about 1.15. The FIG. 6
depicts the manufacturing of a porous layer that comprises copper
particles. The copper particles were pre-pressurized in a die at
.about.22 kilo pounds per square inch (Kpsi), and then sintered
between 850 to 950.degree. C. for 6 hours. Then the copper porous
layer in an amount of .about.3 grams was then coated with
.about.0.03 grams of silica. The silica was added via chemical
vapor deposition, during which SiCl.sub.4 gas was passed across the
surfaces of the copper particles via a nitrogen carrying gas. The
SiCl.sub.4 condenses to form a SiO.sub.2 network on the particle
surfaces through hydrolization. The contact angle of the SiO.sub.2
coated copper particles is less than 5 degrees after the coating.
It is to be noted that the sintering to form copper layer conducted
prior to silica formation.
Example 3
[0103] This example demonstrates the manufacturing of a porous
layer that comprises silica nanoparticles. The silica nanoparticles
like the copper particles in Example 2, have a unimodal particle
size distribution with a polydispersity index of about 1. The
silica nanoparticles have a particle size diameter of about 300
nanometers. The silica particles were dispersed in a volatile
solvent, for example, isopropanol, with a concentration of up to 30
weight percent. The solution was spray coated on a silicon
substrate and sintered at 900.degree. C. for 6 hours in a vacuum
oven.
[0104] While the invention has 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 invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention.
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