U.S. patent application number 13/776459 was filed with the patent office on 2014-08-28 for sloped hierarchically-structured surface designs for enhanced condensation heat transfer.
This patent application is currently assigned to Alcatel-Lucent Ireland Ltd.. The applicant listed for this patent is ALCATEL-LUCENT IRELAND LTD.. Invention is credited to Ryan M. Enright.
Application Number | 20140238646 13/776459 |
Document ID | / |
Family ID | 50896334 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140238646 |
Kind Code |
A1 |
Enright; Ryan M. |
August 28, 2014 |
SLOPED HIERARCHICALLY-STRUCTURED SURFACE DESIGNS FOR ENHANCED
CONDENSATION HEAT TRANSFER
Abstract
An apparatus. The apparatus comprises a distribution of
microstructures on an area of a surface, each of the
microstructures having one or more sloping sides. The apparatus
comprises a distribution of nanostructures being located on the one
or more sloping sides. The distribution of microstructures on the
area of the surface is configured to nucleate and grow droplets of
liquid from a gas. The distribution of nanostructures forms a
superhydrophobic surface for the liquid.
Inventors: |
Enright; Ryan M.; (Dublin,
IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALCATEL-LUCENT IRELAND LTD. |
Dublin |
|
IE |
|
|
Assignee: |
Alcatel-Lucent Ireland Ltd.
Dublin
IE
|
Family ID: |
50896334 |
Appl. No.: |
13/776459 |
Filed: |
February 25, 2013 |
Current U.S.
Class: |
165/104.21 ;
29/890.03 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 23/427 20130101; H01L 2924/0002 20130101; Y10T 29/4935
20150115; H01L 2924/00 20130101; F28F 2245/04 20130101; F28F
2255/20 20130101; F28F 13/187 20130101; F28D 15/02 20130101; F28F
2260/00 20130101 |
Class at
Publication: |
165/104.21 ;
29/890.03 |
International
Class: |
F28D 15/02 20060101
F28D015/02 |
Claims
1. An apparatus, comprising: a distribution of microstructures on
an area of a surface, each of the microstructures having one or
more sloping sides; a distribution of nanostructures being located
on the one or more sloping sides; and wherein the distribution of
microstructures on the area of the surface is configured to
nucleate and grow droplets of liquid from a gas; and wherein the
distribution of nanostructures forms a superhydrophobic surface for
the liquid.
2. The apparatus of claim 1, wherein the microstructures are
configured to nucleate the droplets between the nanostructures.
3. The apparatus of claim 1, wherein the microstructures are
ridges.
4. The apparatus of claim 1, wherein the microstructures are
pointed structures.
5. The apparatus of claim 1, wherein each of the microstructures
are pyramidal-shaped structures.
6. The apparatus of claim 1, further including: a heat pipe or a
vapor chamber, the distribution of microstructures being located in
a condenser portion of the heat pipe or the vapor chamber.
7. The apparatus of claim 1, wherein the one or more sloping sides
intersects with at least one side of the microstructure to form an
apex shaped as a peak.
8. The apparatus of claim 1, wherein the separation distance
between apexes of adjacent ones of the microstructures is equal to
or less than about 10 microns.
9. The apparatus of claim 1, wherein at least one of the sloping
sides intersects with at another side of an adjacent one of the
microstructures at a base layer to form a valley.
10. The apparatus of claim 1, wherein at least one of the sloping
sides and another side of the one microstructure separately
intersect with a third side of the one microstructure to form an
apex shaped as a mesa.
11. The apparatus of claim 1, wherein at least one of the sloping
sides and another side of an adjacent one of the microstructures
separately intersect with a horizontally oriented layer that is
covered with the nanostructures and is adjacent to a base
layer.
12. The apparatus of claim 1, wherein at least one of the sloping
sides intersects with another side which forms a right angle with
respect to a base layer.
13. The apparatus of claim 15, wherein at least one of the sloping
sides intersects with another side of the one microstructure, and,
the other side forms a different acute angle with respect to the
line perpendicular to a base layer.
14. The apparatus of claim 1, wherein for at least one of the
sloping sides, there are sloped portions that have the acute angle
interspersed horizontal portions that are parallel with a base
layer.
15. The apparatus of claim 1, wherein a distance between adjacent
ones of the nanostructures is greater than a critical condensation
radius for a nucleating one of the liquid droplet.
16. A system, comprising: heat generating equipment; and a heat
transfer apparatus configured to remove heat generated by the
electronic equipment, wherein the apparatus includes: a
distribution of microstructures on an area of a surface, each of
the microstructures having one or more sloping sides; a
distribution of nanostructures being located on the one or more
sloping sides; and wherein the distribution of microstructures on
the area of the surface is configured to nucleate and grow droplets
of liquid from a gas; and wherein the distribution of
nanostructures forms a superhydrophobic surface for the liquid.
17. The system of claim 16, wherein the distribution of
microstructures is located on the surface of a condenser of the
apparatus
18. The system of claim 16, wherein the condenser is part of a heat
pipe.
19. The system of claim 16, wherein the condenser is part of a
vapor chamber.
20. A method, comprising: forming a distribution of microstructures
on an area of a surface, each of the microstructures having one or
more sloping sides, wherein the distribution of microstructures on
the area of the surface is configured to nucleate and grow droplets
of liquid from a gas; and forming a distribution of nanostructures
being located on the one or more sloping sides, wherein the
distribution of nanostructures forms a superhydrophobic surface for
the liquid.
Description
TECHNICAL FIELD
[0001] The invention relates to in general, heat transfer
apparatuses, and methods for manufacturing the same.
BACKGROUND
[0002] This section introduces aspects that may help facilitate a
better understanding of the inventions. Accordingly, the statements
of this section are to be read in this light and are not to be
understood as admissions about what is prior art or what is not
prior art.
[0003] Condensation is an important process in a number of
two-phase heat transfer apparatuses implemented for thermal
management. Improving the efficiency of such condensation heat
transfer processes has the potential to enable size reductions of
heat transfer apparatuses while still achieving the same overall
heat transfer performance.
SUMMARY
[0004] One embodiment is an apparatus. The apparatus comprises a
distribution of microstructures on an area of a surface, each of
the microstructures having one or more sloping sides. The apparatus
comprises a distribution of nanostructures being located on the one
or more sloping sides. The distribution of microstructures on the
area of the surface is configured to nucleate and grow droplets of
liquid from a gas. The distribution of nanostructures forms a
superhydrophobic surface for the liquid.
[0005] In any of the above embodiments of the apparatus, the
microstructures are configured to nucleate the droplets between the
nanostructures. In some embodiments, the microstructures are
ridges. In some embodiments, the microstructures are pointed
structures. Any of the above embodiments of the apparatus can
further include a heat pipe or a vapor chamber, the distribution of
microstructures being located in a condenser portion of the heat
pipe or the vapor chamber. In some embodiments, the one or more
sloping sides intersects with at least one side of the
microstructure to form an apex shaped as a peak. In some
embodiments, the separation distance between apexes of adjacent
ones of the microstructures is equal to or less than about 10
microns. In some embodiments, at least one of the sloping sides
intersects with at another side of an adjacent one of the
microstructures at a base layer to form a valley. In some
embodiments, at least one of the sloping sides and another side of
the one microstructure separately intersect with a third side of
the one microstructure to form an apex shaped as a mesa. In some
embodiments, at least one of the sloping sides and another side of
an adjacent one of the microstructures separately intersect with a
horizontally oriented layer that is covered with the nanostructures
and is adjacent to a base layer. In some embodiments, at least one
of the sloping sides intersects with another side which forms a
right angle with respect to a base layer. In some embodiments, at
least one of the sloping sides intersects with another side of the
one microstructure, and, the other side forms a different acute
angle with respect to the line perpendicular to a base layer. In
some embodiments, for at least one of the sloping sides, there are
sloped portions that have the acute angle interspersed horizontal
portions that are parallel with a base layer. In some embodiments,
a distance between adjacent ones of the nanostructures is greater
than a critical condensation radius for a nucleating one of the
liquid droplet.
[0006] One embodiment is a system. The system comprises heat
generating equipment and a heat transfer apparatus configured to
remove heat generated by the electronic equipment. The apparatus
includes a distribution of microstructures on an area of a surface,
each of the microstructures having one or more sloping sides. The
apparatus comprises a distribution of nanostructures being located
on the one or more sloping sides. The distribution of
microstructures on the area of the surface is configured to
nucleate and grow droplets of liquid from a gas. The distribution
of nanostructures forms a superhydrophobic surface for the
liquid.
[0007] In some embodiments of the system, the distribution of
microstructures is located on the surface of a condenser of the
apparatus. In some embodiments, the condenser is part of a heat
pipe. In some embodiments, the condenser is part of a vapor
chamber.
[0008] One embodiment is a method. The method comprises forming a
distribution of microstructures on an area of a surface, each of
the microstructures having one or more sloping sides, wherein the
distribution of microstructures on the area of the surface is
configured to nucleate and grow droplets of liquid from a gas. The
method comprises forming a distribution of nanostructures being
located on the one or more sloping sides, wherein the distribution
of nanostructures forms a superhydrophobic surface for the
liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The embodiments of the disclosure are best understood from
the following detailed description, when read with the accompanying
FIGUREs. Some features in the figures may be described as, for
example, "top," "bottom," "vertical" or "lateral" for convenience
in referring to those features. Such descriptions do not limit the
orientation of such features with respect to the natural horizon or
gravity. Various features may not be drawn to scale and may be
arbitrarily increased or reduced in size for clarity of discussion.
Reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0010] FIG. 1A presents a perspective view of an embodiment heat
transfer apparatus;
[0011] FIG. 1B presents a perspective view of an alternative
embodiment of a heat transfer apparatus;
[0012] FIG. 1C presents a perspective view of another alternative
embodiment of a heat transfer apparatus;
[0013] FIG. 2A presents a cross-sectional view of the apparatus
shown in FIG. 1B along view line 2-2;
[0014] FIG. 2B presents a cross-sectional view of an alternative
embodiment of a heat transfer apparatus, analogous to the view
along line 2-2 in FIG. 1B;
[0015] FIG. 2C presents a cross-sectional view of an alternative
embodiment of the heat transfer apparatus, analogous to the view
along line 2-2 in FIG. 1B;
[0016] FIG. 2D presents a cross-sectional view of an alternative
embodiment of a heat transfer apparatus, analogous to the view
along line 2-2 in FIG. 1B;
[0017] FIG. 2E presents a cross-sectional view of an alternative
embodiment of a heat transfer apparatus, analogous to the view
along line 2-2 in FIG. 1B;
[0018] FIG. 3 presents a detailed cross-sectional view of a portion
of the apparatus shown in FIG. 2A;
[0019] FIG. 4 presents a perspective view of the portion of
apparatus presented in FIG. 3;
[0020] FIG. 5 presents a flow diagram of an example method of
manufacturing a heat transfer apparatus, such as any of the example
apparatuses described in the context of FIGS. 1A-4;
[0021] FIG. 6 presents a flow diagram of a method; and
[0022] FIG. 7 presents a block diagram of a system.
[0023] In the Figures and text, similar or like reference symbols
indicate elements with similar or the same functions and/or
structures.
[0024] In the Figures, the relative dimensions of some features may
be exaggerated to more clearly illustrate one or more of the
structures or features therein.
[0025] Herein, various embodiments are described more fully by the
Figures and the Detailed Description. Nevertheless, the inventions
may be embodied in various forms and are not limited to the
embodiments described in the Figures and Detailed Description of
Illustrative Embodiments.
DETAILED DESCRIPTION
[0026] The description and drawings merely illustrate the
principles of the inventions. It will thus be appreciated that a
person of ordinary skill in the relevant arts will be able to
devise various arrangements that, although not explicitly described
or shown herein, embody the principles of the inventions and are
included within its scope. Furthermore, all examples recited herein
are principally intended expressly to be for pedagogical purposes
to aid the reader in understanding the principles of the inventions
and concepts contributed by the inventor(s) to furthering the art,
and are to be construed as being without limitation to such
specifically recited examples and conditions. Moreover, all
statements herein reciting principles, aspects, and embodiments of
the inventions, as well as specific examples thereof, are intended
to encompass equivalents thereof. Additionally, the term, "or," as
used herein, refers to a non-exclusive or, unless otherwise
indicated. Also, the various embodiments described herein are not
necessarily mutually exclusive, as some embodiments can be combined
with one or more other embodiments to form new embodiments.
[0027] Various heat transfer apparatuses of the disclosure have
hierarchically structured condensation surfaces which enhance
condensation heat transfer. The hierarchically structured surfaces
may, e.g., have both micron-scaled structural features
("microstructures") and nanometer-scaled structural features
("nanostructures").
[0028] The use of non-wetting surfaces (synonymous with the term
superhydrophobic surface as used herein) can enhance heat transfer
coefficients, in comparison to the heat transfer via smooth
surfaces. Surprisingly, when the non-wetting surface is a surface
covered with nanostructures, similar enhancements to heat transfer
coefficients have typically not been realized. As droplets form and
grow on a surface covered with nanostructures, the droplet gets to
a certain critical size, and heat conduction through the bulk of
the droplet begins to limit the heat transfer rate. It is therefore
desirable for the droplet to leave the surface (often referred to
droplet jumping) before the droplet reaches its critical size.
However, there is a characteristic droplet diameter, below which
dissipation effects, e.g., viscous effects, form drag, surface
adhesion, etc., can dominate or suppress droplet jumping.
Furthermore, droplet jumping typically requires the coalescence of
two or more droplets, which, in turn, is dictated by the number
density of droplets nucleated on the surface. Thus, the minimum
jumping droplet diameter may be also restricted by a small number
of nucleated droplets (large droplet spacing).
[0029] Providing a hierarchically structured condensation surface,
with separated microstructures having nanostructures thereon, may
provide an efficient heat transfer surface. Providing
microstructures having at least one sloped side may help to move
larger droplets to the apexes of the microstructures, thereby
freeing up surfaces for new droplet nucleation on condensation
surfaces and promoting droplet jumping before a droplet reaches a
critical size, which is heat-conduction limiting. Providing
nanostructures on the microstructures can create a non-wetting
surface that increases the apparent contact angle and reduces the
contact angle hysteresis of droplets forming on the
microstructures. Thus, such nanostructures may facilitate the
movement of the droplets away from droplet nucleation sites and
towards apexes of the nanostructures. A further benefit of using a
hierarchically structured condensation surface with both
microstructures and nanostructures thereon is that the effective
heat transfer surface area is increased. Thus, there can be an
increased number of nucleation sites on the condensing surface,
leading to greater heat transfer rates compared to a condensing
surface having only nanostructures.
[0030] FIGS. 1A-1C presents perspective views of different
embodiments of heat transfer apparatuses 100. FIG. 2A presents a
cross-sectional view of the apparatus shown in FIG. 1B along view
line 2A-2A. FIG. 2A could also depict analogous cross-sectional
views of the apparatuses shown in FIGS. 1A or 1C. FIG. 3 presents a
detailed view of a portion of the apparatus shown in FIG. 2A,
although this figure could also depict analogous detailed views of
the apparatuses shown in FIG. 1A or 1C.
[0031] In some embodiments, the apparatus 100 comprises a condenser
105. The condenser 105 can be part of a variety of different
two-phase heat transfer apparatuses such as, but not limited to,
heat pipes, vapor chambers, looped heat pipes, two-phase forced
convection flow loops or shell-and-tube surface condensers. For
example, in some cases, the condenser 105 can be a portion of the
heat transfer apparatus 100 configured as a heat pipe which further
includes an evaporator portion 107. In still other embodiments the
condenser 105 can be used in heat transfer apparatuses such as
compact condensers for electronics thermal management, e.g., in
telecommunications and data centers, industrial condensation heat
exchangers, evaporator coils, dehumidifying coils, and/or water
harvesting apparatuses.
[0032] The condenser 105 includes a base layer 110 and
microstructures 115 (e.g., a distribution of microstructures)
located on the base layer 110. Each microstructure 115 includes at
least one sloped side 120 that forms an acute angle 125 with
respect to a line 130 perpendicular to the base layer 110.
[0033] The at least one sloped side 120 connects to an apex 135 of
the microstructure 115 located above the base layer 110. An outer
surface 140 of the sloped side 120 has nanostructures 305 (e.g., a
distribution of nanostructures) thereon, wherein the nanostructures
305 are spaced apart from each other and project out from the outer
surfaces 140, e.g., as shown in FIG. 3.
[0034] As used herein, the term microstructure 115, as used herein,
refers to a structure that has at least linear one-dimension 145
adjacent to the base layer 110 (e.g., a base width or depth) that
extends a distance across the microstructure 115 in a range of 1 to
1000 microns.
[0035] As used herein, the term nanostructure 305, as used herein,
refers to a structure that has at least one linear dimension (e.g.
height, width, or depth) that extends a distance from one side to
an opposing side (e.g., opposing lateral sides 310, 312, or, top
and bottom sides 315, 317) of the nanostructure 305 in a range from
1 to 1000 nanometers. Additionally, the one linear dimension of the
nanostructure 305 is at least 10 times smaller than the one
dimension 145 of the microstructure 115. As a non-limiting example,
when the one dimension 145 of the microstructure 115 equals 1
micron, then the one dimension of the nanostructure 305 can be up
to 100 nanometers. Consequently, in this example, the at least one
linear dimension of the nanostructure 305 (e.g., height, width, or
depth), can be in a range of 1 to 100 nanometers. As another
non-limiting example, when the one dimension 145 of the
microstructure 115 equals 100 microns, then the one dimension of
the nanostructure 305 (e.g., height, width, or depth), can be up to
1000 nanometers. Consequently, in this example, the one dimension
of the nanostructure 305, can be in a range of 1 to 1000
nanometers.
[0036] As used herein, the term acute angle refers to an angle that
is greater than zero degrees and less than 90 degrees. In some
embodiments, to increase the surface area of the condenser 105, the
acute angle 125 is more preferably in a range from about 25 degrees
to 65 degrees, and even more preferably, in a range from about 40
to 55 degrees.
[0037] In some embodiments of the apparatus 100, such as
illustrated in FIG. 1A, there is a single sloped side 120 that
curves continuously around the entire microstructure 115, and each
one of the microstructures 115 is a cone-shaped structure.
[0038] In other embodiments, such as illustrated in FIG. 1B or 1C,
the at least one sloped side 120 joins with at least one other side
150 of the microstructure 115 at the apex 135, wherein an outer
surface 155 of the at least other side 150 have the nanostructures
305 thereon.
[0039] For instance, as illustrated in FIG. 1B, the at least one
sloped side 120 can have a planar surface 140 and join with at
least one other side 150 which also has a planar surface 155 to
form ridge-shaped microstructures 115. Similar ridge-shaped
microstructures could be formed where one or both of the surfaces
140, 155 of the sides 120, 150 are curved (e.g., curving inwards or
curving outwards).
[0040] For instance, as illustrated in FIG. 1C, the at least one
sloped side 120 can join with two or more other sides 150, 160, 165
at the apex 135 to form pyramidal-shaped microstructures structures
(e.g., structures with three or more planar or curved sides joining
at the apex 135).
[0041] As further illustrated in FIG. 2A, in some cases, the at
least one other side 150 that joins the sloped side 120 at the apex
135 is another sloped side that forms another acute angle 210 with
respect to the line 130 perpendicular to the base layer 110. For
instance, the other sloped side 150 can form an acute angle 210
that is about equal in magnitude but opposite in sign to the acute
angle 125 of the sloped side 120. Similarly, in some embodiments,
with more than two sides, such as illustrated in FIG. 1C, each of
the other sides 150, 160, 165 can be sloped sides and form about
the same acute angles with respect to the line 130.
[0042] Referring to FIG. 2A, it is believed that the sloped side
120 (or other sloped sides 150, 160, 165 in some cases) helps to
force a growing droplet 220 in a direction 222 away from droplet
nucleation sites, e.g., sites in-between the nanostructures 305,
towards the apexes 135 of the microstructures 115. E.g., the sloped
side 120 may help such droplets 220 to move towards the apexes 135
of the microstructures 115. Although, in FIG. 2A, droplet
nucleation is depicted as originating at a valley 225 between
adjacent microstructures 115, a person of ordinary skill in the
relevant arts would understand that droplet nucleation could
originate at sites anywhere on the surfaces 140, 155, of the sides
120, 150.
[0043] Referring again to FIG. 2A, the apexes 135 of the
microstructures 115 are separated from each other by a separation
distance 230. The selection of the separation distance 230 between
adjacent microstructures 115 is important to aiding the droplet 220
moving away the droplet nucleation sites, and to promote droplet
jumping, before the droplet growth rate becomes heat conduction
limited. As an example, water droplet growth become heat conduction
limited at a droplet radius of about 5 microns or greater.
Therefore, for certain embodiments of the apparatus 100, where heat
transfer involves water condensation (e.g., occurs through a water
condensation heat transfer processes), the separation distance 230
is preferably equal or less than about 10 microns. A person of
ordinary skill in the relevant arts would understand how to
determine a preferred maximal allowable droplet radius for
different types of fluids, before the fluid's droplet growth rate
becomes heat conduction limited. Accordingly, the separation
distances 230 of a distribution of microstructures 115 could be set
equal to or less than two times the preferred maximal allowable
droplet radius. For instance, in some embodiments the separation
distance 230 between the apexes 115 of adjacent ones of the
microstructures 115 is in a range of 100 microns to 1 micron, and
in some cases a range of 10 microns to 1 micron.
[0044] As further illustrated in FIG. 2A, in some embodiments of
the apparatus 100, the sloped side 120 intersects with at least one
other side 150 of the microstructure 115 to form the apex 135
shaped as a peak. It is believed that a peaked-shaped apex 135 can
reduce a growing droplet's 220 surface contact with the
microstructures 115, and, thereby facilitate droplet jumping.
[0045] As further illustrated in FIG. 2A, in some embodiments of
the apparatus 100, the sloped side 120 of the microstructure 115
intersects with at least one side (one of sides 120, 150) of an
adjacent microstructure 115 at the base layer 110 to form a valley
225. Configuring the condenser 105 such that the sides of the
adjacent microstructures 115 intersect at the base layer 110 helps
to increase the total surface area of the condensation surface,
and, can enhance condensation heat transfer by also providing a
number of potential droplet nucleation sites.
[0046] In still other embodiments of the apparatus 100, however,
the at least one sloped side 120 does not intersect with other
sloping sides of the same microstructure 115 or of adjacent
microstructures 115. For example, as illustrated in FIG. 2B, the
sloped side 120 and another side 150 of the same microstructure 115
can separately intersect with a third side 235 (e.g., a planar
horizontally oriented side) of the microstructure 115 to form the
apex 135 shaped as a mesa. For example, as further illustrated in
FIG. 2B, the sloped side 120 of one of the microstructures 115,
and, another side 150 of an adjacent one of the microstructures 115
can separately intersect with a nanostructure 305 covered
horizontally oriented layer 240 that is adjacent to the base layer
110.
[0047] The microstructures 115 can have various other shapes to
increase the surface area upon which condensation can occur.
[0048] For instance, in other embodiments of the apparatus 100, as
illustrated in FIG. 2C, the at least one sloped side 120 can
intersect with another side 150 of the microstructure 115 which
forms a right angle 250 with respect to the base layer 110, to form
the apex 135, e.g., shaped as a peak. That is, the other side 150
has a surface 155 that is parallel with respect to a line 130
perpendicular to the base layer 110.
[0049] In other embodiments of the apparatus 100, as illustrated in
FIG. 2D, the at least one sloped side 120 of one microstructure 115
can intersect with another side 150 of the same microstructure 115.
The other sloped side forms a different magnitude acute angle 210
(e.g., at least about 10 percent different than the acute angle
125) with respect to the line 130 perpendicular to the base layer
110, to form the apex 135, e.g., shaped as a peak.
[0050] A person of ordinary skill in the relevant arts would
appreciate how the sloped side 120 and the other sloped side 150,
such as depicted in FIGS. 2C and 2D, could separately intersect
with a third layer 235 or fourth layer 240 to form structures
analogous to that shown in FIG. 2B.
[0051] In still other embodiments of the apparatus 100, as
illustrated in FIG. 2E, the at least one sloped side 120, and in
some cases, the other side 140, (or sides 140, 160, 165, FIG. 1C)
which are sloped, includes sloped portions 250 that have the acute
angle 125 interspersed with horizontal portions 255 which are
parallel with the base layer 110.
[0052] In some embodiments of the apparatus, such as depicted in
FIGS. 1A-2E, the microstructures 115 of the condenser 105 can have
the same shape and be about uniformly separated from each other.
However, in other embodiments, microstructures 115 of the condenser
105 can have a variety of different shapes, such as, but not
limited to, combinations of any of the shapes discussed in the
context of FIGS. 1A-2E, and/or, the microstructures 115 can have
different separation distances 230, such as progressively
increasing or decreasing distances 230 along one or more directions
parallel to the base layer 110. For example, the separation
distance 230 may monotonically increase or decrease with along one
direction parallel to the base layer 110.
[0053] FIG. 4 presents a perspective view of the portion of example
apparatus 100 presented in FIG. 3, depicting example nanostructures
305 of the apparatus 100. As illustrated, the nanostructures 305
can be ridged-shaped, and, the ridges are spaced apart from each
other. In other embodiments, the nanostructures 305 can be
pillar-shaped and the pillars are spaced apart from each other. The
nanostructures 305 can cover the sloped side 120, and any of the
other sides 150, 160, 165, peaked or mesa shaped apex 135, or
horizontal layer 240 discussed in the context of FIGS. 1A-2E.
[0054] The use of nanostructures 305 to provide a non-wetting
surface can be advantageous over conventional non-wetting
condensing surfaces. Droplet adhesion to the condensation surface
can be reduced with the appropriate nanostructure configuration.
For instance, to reduce droplet adhesion, it is desirable for
nanostructures to be configured to facilitate the droplet taking on
a Cassie wetting state through contact line pinning at the base of
the droplet. A person of ordinary skill in the relevant arts would
understand that Cassie state refers to wetting state of the droplet
where the droplet rests on the tops 315 of the nanostructures 305
in the vicinity of the droplet. For instance, in some cases, less
than 10 percent of the nanostructure 305 nearest the top 315 is in
contact with the droplet when the droplet is in a Cassie state.
When in a Cassie state, most of the droplet is not in contact with
the nanostructures 305, so that the droplet's adhesion to the
nanostructures 305 is reduced. Additionally, because most of the
droplet in a Cassie state rests on the tops 315 of the
nanostructures 305, the sides 310, 312, and the surfaces 140, 155
that support the nanostructures 305, are available as sites for new
droplet nucleation.
[0055] There are several structural attributes that the
nanostructures 305 can have to facilitate a droplet in attaining a
Cassie state.
[0056] For instance, in some preferred embodiments, it is desirable
for the nanostructures 305 to provide the condensation surface with
a certain amount of surface roughness to deter a droplet from
taking on an undesirable Wenzel state. A Wenzel state refers to a
wetting state where the droplet substantially contacts the entire
surfaces of the nanostructures in the vicinity of the droplet. For
example, in a Wenzel state, substantially the entire height of the
droplet may contact the sides 310, 312 and tops 315 of the
nanostructures 305 support surfaces 140, 155. In various
embodiments, it is often undesirable that a droplet take Wenzel
states, because the large contact area of the droplet in such a
state can provide a large adhesion that pins the droplet in-between
the nanostructures 305.
[0057] Wenzel state formation therefore impedes the droplet from
moving away from its nucleation site to the apexes 135 of the
microstructures 115, which in turn may reduce the efficiency of
condensation heat transfer.
[0058] To help avoid growing droplets taking such a Wenzel state,
it is desirable for the surface 140, or surfaces 140, 155 that have
the nanostructures 305 thereon, to satisfy the following condition
when a liquid droplet rests on the surface: -1/r*cos.theta.a<1.
Here, the parameter r is the surface roughness factor of the
surfaces of the nanostructure, and .theta.a is an intrinsic
advancing contact angle of the liquid droplet. Herein, the surface
roughness factor, r, is defined as the total surface area,
including the areas of the sides 310, 312, and tops 315 and support
surfaces 140, 150 in between the nanostructures divided by
projected surface area of the surfaces 140, 150, e.g., the area
support surfaces 140, 150 with no nanostructures 305 thereon. The
intrinsic advancing contact angle, .theta.a, refers to the contact
angle that the fluid droplet would have on a smooth surface, e.g.,
the support surfaces 140, 150 with no nanostructures 305
thereon.
[0059] For instance, in some preferred embodiments, it is desirable
for the adjacent nanostructures 305 to be spaced apart by a minimum
separation distance 320 (e.g., the distance from the side 310 of
one nanostructure 305 to the side 312 of an adjacent nanostructure
305). The suitable minimum separation distance 320 is that which
allows the droplets to form and grow in-between the nanostructures
305 while avoiding undesirable capillary evaporation effects.
[0060] Preferably, the distance 320 is greater than a critical
condensation radius 410, r.sub.c, for a nucleating fluid droplet.
The critical condensation radius can be estimated by the
formula:
r.sub.c=2.UPSILON..orgate./(kTlnS),
Here, .UPSILON. is the ratio of liquid to vapor surface tension,
.orgate. is a molecular volume of the liquid phase, k is the
Boltzmann constant, S is defined as the ratio of the vapor pressure
pv to the saturation pressure at the condensing surface temperature
T. For example, in some embodiments of the apparatus 100, for a
water droplet, the distance 320 separating adjacent nanostructures
is equal to of greater than about 10 nanometers. For example, in
some embodiments of the device 100, the distance 320 is in a range
of about 1 to 100 nanometers, and in some cases in a range of about
10 to 20 nanometers.
[0061] Preferably, the distance 320 between adjacent ones of the
nanostructures 305 has a value that promotes a droplet to attain
the Cassie state before the droplet radius 410, R, grows to size
that is heat conduction limiting. For example, for water droplet
this value of the radius 410 is about 5 microns or larger. The
Cassie state, in turn, is promoted by spacing the nanostructures
apart by a preferred distance 320 and by having a height 420 that
facilitates the growing droplet to have a receding contact angle
430, .theta.r, of at least about 90 degrees.
[0062] For instance, in some preferred embodiments, the
nanostructures satisfies the relationship:
cos.theta..sub.r<-(1+h/R)/(1+2h/w),
Here, .theta.r is a receding contact angle 430 of at least 90
degrees for a maximally desired size of droplet located on tops of
the nanostructures, h is the uniform height 420 of the
nanostructures 305, R is a radius 410 of the fluid droplet and w is
a uniform separation distance 320 between adjacent ones of the
nanostructures 305.
[0063] The term receding contact angle 430 as used herein is
defined as the minimum stable angle that the droplet achieves while
on the nanostructures 305. A person of ordinary skill in the
relevant arts would be familiar with methods to measure the
receding contact angle 430 of a droplet 220 (see e.g.,
"Condensation on Superhydrophobic Surfaces: The Role of Local
Energy Barriers and Structure Length Scale" and Supporting
Information, by Enright et al., Langmuir pub. Aug 29, 2012
("Enright-1"), incorporated by reference herein in its
entirety).
[0064] Herein, the term receding contact angle 430 is defined as
the minimum stable angle that the droplet achieves while on the
nanostructures 305. A person of ordinary skill in the relevant arts
would be familiar with methods to measure the receding contact
angle 430 of a droplet 220 (see e.g., "Condensation on
Superhydrophobic Surfaces: The Role of Local Energy Barriers and
Structure Length Scale" and Supporting Information, by Enright et
al., Langmuir pub. Aug 29, 2012 ("Enright-1"), incorporated by
reference herein in its entirety).
[0065] The receding contact angle 140 for a droplet to
spontaneously achieve a Cassie state can be reduced by reducing the
ratio h/R, and/or, increasing the ratio h/w.
[0066] For instance, consider a fluid whose critical size, where
heat conduction through the bulk of the droplet begins to limit the
heat transfer rate, and, that critical size corresponds to a
droplet radius 410 of 5 microns or greater. Assuming a desired
receding contact angle 430, .theta..sub.r, equal to 120 degrees, to
make the ratio of h, the uniform height 420 of the nanostructures
305 to R, a radius 410 of the fluid droplet less than or equal to
0.1 (i.e., h/R.ltoreq.0.1) requires h.ltoreq.0.5 .mu.m. For a h/R
ratio equal to 0.1 and the height 420, h, equal to 0.5 .mu.m, the
separation distance 320 between microstructures, w, is then equal
to 833 nanometers and the h/w ratio equals 0.6. Continuing with the
same example, where the h/R ratio equals 0.1 and h equals 0.5
.mu.m, for a receding contact angle 430, .theta..sub.r, equal to
110 degrees, w, is then equal to 451 nanometers and the h/w ratio
equals 1.1, or, for a receding contact angle 430, .theta..sub.r,
equal to 100 degrees, w, is then equal to 187 nanometers, and the
h/w ratio equals 2.7, or, for a receding contact angle 430,
.theta..sub.r, equal to 90 degrees, w, is then equal to 16
nanometers, and the h/w ratio equals 31.3.
[0067] In some embodiments of the apparatus 100, reduce the
adhesion of a de-wetted droplet (e.g., a droplet in a Cassie state)
it is desirable to reduce the fraction of space occupied by the
nanostructures 305 relative to the open space in-between adjacent
ones of the nanostructures. For instance, in some embodiments, the
solid fraction occupied by the nanostructures 305 is equal to or
less than 0.1. As used herein the term solid fraction herein is
equal to d/(d+w), where d is the width 435 of the nanostructure and
w is the separation distance 320 between adjacent ones of the
nanostructures 305.
[0068] As a non-limiting example, in cases where the separation
distance 320 is equal to 833 nanometers, then the width 435 is
preferably equal or less than 93 nanometers. Or, when the
separation distance 320 is equal to 451 nanometers, then the width
435 is preferably equal or less than 50 nanometers. Or, when the
separation distance 320 is equal to 451 nanometers, then the width
435 is preferably equal or less than 50 nanometers. Or, when the
separation distance 320 is equal to 187 nanometers, then the width
435 is preferably equal or less than 21 nanometers. Or, when the
separation distance 320 is equal to 16 nanometers, then the width
435 is preferably equal or less than 1.8 nanometers.
[0069] Referring to any of FIGS. 1A-4, another apparatus 100
embodiment comprises a distribution of microstructures 115 on an
area of a surface 180 (e.g., a condensation surface), each of the
microstructures 115 having one or more sloping sides 120, 155, 160,
165. The apparatus 100 also comprises a distribution of
nanostructures 310 being located on the one or more sloping sides
120, 155, 160, 165. The distribution of microstructures 115 on the
area of the surface 180 is configured to nucleate and grow droplets
230 of liquid from a gas. The distribution of nanostructures 310
forms a superhydrophobic surface 325 for the liquid.
[0070] As used herein, a surface 325 is considered to be a
superhydrophobic surface 325 (synonymous with the term non-wetting
surface as used herein) when a fluid droplet 230 of the fluid
laying on the surface 325 has a contact angle 325 of equal to or
greater than about 90 degrees. This is in contrast to a
hydrophillic surface (synonymous with the term wetting surface as
used herein) where a fluid droplet 145 laying on the surface 325
has a contact angle 140 of less or equal to 90 degrees.
[0071] In some embodiments of the apparatus 100 the microstructures
115 are configured to nucleate the droplets between the
nanostructures 310. In some embodiments, the microstructures 115
are ridges. In some embodiments, the microstructures 115 are
pointed structures (e.g., the apexes 135 have a pointed shape). In
some embodiments, the apparatus 100 further includes a heat pipe
170 or a vapor chamber 170, the distribution of microstructures
being located in a condenser 105 portion of the heat pipe 170 or
vapor chamber 170.
[0072] The distribution of microstructures 115 and the distribution
of nanostructures 310 could include any combination of any or all
of the microstructures 115 or nanostructures 310 configurations
disclosed herein.
[0073] Still another embodiment is a method that comprises
manufacturing a heat transfer apparatus. With continuing reference
to FIGS. 1A-4 throughout, FIG. 5 presents a flow diagram of an
example method of manufacturing a heat transfer apparatus of the
disclosure, such as any of the example apparatuses 100 described in
the context of FIGS. 1A-4.
[0074] As illustrated in FIG. 5, the method includes a step 505 of
manufacturing a condenser. Manufacturing the condenser (step 505)
includes a step 510 providing a base layer 110 and step 515 of
forming microstructures 115 on the base layer 110. Each
microstructure 115 includes at least one sloped side 120 that forms
an acute angle 125 with respect to a line 130 perpendicular to the
base layer 110. The at least one sloped side 120 connects to an
apex 135 of the microstructure 115 located above the base layer
110. The method also includes a step 520 of forming nanostructures
305 on a surface 140 of the at least one sloped side 120, wherein
the nanostructures 305 are spaced apart from each other and project
out from the surface 140.
[0075] In some cases, providing the base layer 110 in step 510 can
simply include providing a material layer 170, e.g., of copper,
aluminum, semiconductor material upon which the microstructures 115
are directly formed from in step 515. In some cases the use of a
highly heat conductive material layer 170 such copper, aluminum is
preferred. In other cases, the providing the base layer 110 in step
510 can include a step 525 of depositing a second material layer
175 on the first material layer 170, where the microstructures 115
is formed from the second material layer 175. For instance, a
second material layer 175 of copper or aluminum could be deposited
on a first material layer 170 of steel, via electrolytic,
electroless or other deposition processes familiar to a person of
ordinary skill in the relevant arts.
[0076] In some embodiments of the method, forming the
microstructures 115 (step 515) includes a step 530 of mechanically
modifying portions of the base layer 110. For instance, a base
layer 110 of copper or aluminum, or, a second layer 175 of the base
layer 110, can be mechanically indented, machined, stamped,
embossed or otherwise mechanically modified to form any of the
microstructure 115 shapes discussed in the context of FIGS.
1A-4.
[0077] In some embodiments of the method, forming microstructures
115 (step 515) includes a step 535 of etching portions of the base
layer 110. For instance, a base layer 110 or a second layer 175,
composed of a semiconductor material, such as a silicon layer, can
be etched by wet or dry etching processes, or laser etching
processes, familiar to a person of ordinary skill in the relevant
arts to form the microstructures 115.
[0078] In some embodiments of the method, forming the
nanostructures 305 (step 520) includes a step 540 of wherein
forming the nanostructures includes exposing the surface 140 of the
sloped side 120, (or surfaces 140, 155 of the sides 120, 150) of
the microstructure 115 to an oxidation process. For instance a
copper base layer 110 of second layer 175 can be exposed to
chemical oxidation conditions such as in "Condensation on
Superhydrophobic Copper Oxide Nanostructures," by Enright et al.
Proceedings of the 3rd Micro/Nanoscale Heat and Mass Transfer
International Conference, Atlanta, Ga., Mar. 3-6, 2012,
MNHMT2012-75277 ("Enright-2"), incorporated by reference herein in
its entirety, to form the nanostructures 305 therefrom. For
instance, an aluminum base layer 110 or second layer 175 can be
exposed to well-known hydrothermal oxidation processes to form the
nanostructures 305 therefrom.
[0079] In some embodiments of the method, forming the
nanostructures 305 (step 520) includes exposing the surface 140 of
the sloped side 120, (or surfaces 140, 155 of the sides 120, 150)
of the microstructure 115 to an etch process in step 545. For
instance, microstructures 115 composed of a semiconductor material,
such as silicon, can be subjected to a reactive ion etching process
to form the nanostructures 305, such as black silicon
nanostructures. Other examples of etching process for forming
nanostructures are presented in Enright-1.
[0080] In some embodiments of the method, part of forming the
nanostructures 305 (step 520) includes functionalizing the
nanostructures 305 in step 550 with a low surface energy material.
The term low surface energy material, as used herein, refers to a
material having a surface energy of about 22 dynes/cm (about
22.times.10-5 N/cm) or less as disclosed in U.S. Pat. No. 7,695,550
to Krupenkin et al. ("Krupenkin"), incorporated by reference herein
in its entirety.
[0081] Non-limiting examples of functionalizing nanostructures in
accordance with step 550 includes coating nanostructures 305 with
chlorosilanes, fluorosilanes or fluorinated polymers, such as
disclosed in Krupenkin, Enright-1 or Enright-2.
[0082] With continuing reference to FIGS. 1A-4 throughout, FIG. 6
presents a flow diagram of another method embodiment of the
disclosure. The method comprises a step 610 of forming a
distribution of microstructures 115 on an area of a surface 180,
each of the microstructures 115 having one or more sloping sides
120, 155, 160, 165. The distribution of microstructures 115 on the
area of the surface 180 is configured to nucleate and grow droplets
230 of liquid from a gas. The method comprises a step 620 of
forming a distribution of nanostructures 310 being located on the
one or more sloping sides 120, 155, 160, 165. The distribution of
nanostructures forms a superhydrophobic surface 325 for the
liquid.
[0083] The steps 610, 620 of forming the distribution of
microstructures 115 and the distribution of nanostructures 310
could include any or all of the microstructures 115 or
nanostructures 310 configurations disclosed herein and any
combination of any or all of the method steps for of forming the
microstructures 115 or nanostructures 310 disclosed herein.
[0084] FIG. 7 illustrates another embodiment of the disclosure, a
system 700. In some embodiments the system 700 can be communication
system such as a telecommunication system or a system component
(e.g., electronic cabinet) of a communication system. The system
700 comprises heat generating equipment 710, such electrical
equipment, e.g., circuit boards having heat generating components
thereon. The system 700 also comprises a heat transfer apparatus
720. The heat transfer apparatus 720 can be configured to remove
heat generated by the equipment 710 of the system 700.
[0085] The heat transfer apparatus 720 can be or include any
apparatuses described herein. In some cases, for instance,
referring to FIGS. 1A-4, the apparatus 720 can include a
distribution of microstructures 115 on an area of a surface 180
(e.g., a condensation surface), each of the microstructures 115
having one or more sloping sides 120, 155, 160, 165. The apparatus
720 also comprises a distribution of nanostructures 310 being
located on the one or more sloping sides 120, 155, 160, 165. The
distribution of microstructures 115 on the area of the surface 180
is configured to nucleate and grow droplets 230 of liquid from a
gas. The distribution of nanostructures 310 forms a
superhydrophobic surface 325 for the liquid.
[0086] In some cases, for instance, with continuing reference to
FIGS. 1A-4, in some embodiments of the system 700, the distribution
of microstructures 115 is located on the surface 180 of a condenser
105 of the apparatus 710. In some embodiments, the condenser 105 is
part of a heat pipe 170, while in other embodiments, the condenser
105 is part of a vapor chamber 170.
[0087] Although the present disclosure has been described in
detail, a person of ordinary skill in the relevant arts should
understand that they can make various changes, substitutions and
alterations herein without departing from the scope of the
invention.
* * * * *