U.S. patent application number 15/956476 was filed with the patent office on 2018-08-23 for heat exchangers made from additively manufactured sacrificial templates.
The applicant listed for this patent is The Boeing Company, HRL LABORATORIES, LLC. Invention is credited to Charles Kusuda, Arun Muley, David Page, Christopher J. Ro, Christopher S. Roper, Randall C. Schubert.
Application Number | 20180238638 15/956476 |
Document ID | / |
Family ID | 62125441 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180238638 |
Kind Code |
A1 |
Roper; Christopher S. ; et
al. |
August 23, 2018 |
HEAT EXCHANGERS MADE FROM ADDITIVELY MANUFACTURED SACRIFICIAL
TEMPLATES
Abstract
A method of manufacturing a heat exchanger including a heat
exchanger core of a first material, the method including additive
manufacturing a sacrificial scaffold of a second material, the
sacrificial scaffold corresponding in shape to that of the heat
exchanger core, coating the sacrificial scaffold with a layer of
the first material, and removing the sacrificial scaffold to leave
behind the heat exchanger core with an integrated self-aligned
passage.
Inventors: |
Roper; Christopher S.;
(Santa Monica, CA) ; Page; David; (Malibu, CA)
; Schubert; Randall C.; (Malibu, CA) ; Ro;
Christopher J.; (Malibu, CA) ; Muley; Arun;
(San Pedro, CA) ; Kusuda; Charles; (Mukilteo,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HRL LABORATORIES, LLC
The Boeing Company |
Malibu
Irvine |
CA
CA |
US
US |
|
|
Family ID: |
62125441 |
Appl. No.: |
15/956476 |
Filed: |
April 18, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14185665 |
Feb 20, 2014 |
9976815 |
|
|
15956476 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29D 28/00 20130101;
B22F 2999/00 20130101; B22F 3/1121 20130101; B22F 3/1055 20130101;
B22F 7/004 20130101; F28D 7/08 20130101; B33Y 80/00 20141201; B33Y
10/00 20141201; B29C 64/40 20170801; B23P 15/26 20130101; B22F
2005/004 20130101; B22F 2003/1058 20130101; F28F 2210/02 20130101;
B22F 2998/10 20130101; Y02P 10/25 20151101; B22F 2999/00 20130101;
B22F 3/1055 20130101; B22F 3/1121 20130101; B22F 2999/00 20130101;
B22F 2005/004 20130101; B22F 7/002 20130101; B22F 2998/10 20130101;
B22F 7/002 20130101; B22F 3/1055 20130101; B22F 3/10 20130101 |
International
Class: |
F28F 1/10 20060101
F28F001/10; B23P 15/26 20060101 B23P015/26 |
Claims
1. A heat exchanger core comprising: a first passage, a second
passage, and a third passage, each of the first, second, and third
passages being configured to couple an inlet manifold and an outlet
manifold, wherein each of the first, second, and third passages has
a wavy pattern along a lengthwise direction of the first, second,
and third passages and has a shape in cross-section, the shape
having a first line of symmetry corresponding to a major axis of
the shape, and a second line of symmetry perpendicular to the first
line of symmetry and corresponding to a minor axis of the
shape.
2. The heat exchanger core of claim 1, wherein all shapes on planes
normal to the lengthwise direction have areas and shapes varying by
less than about 10%.
3. The heat exchanger core of claim 1, wherein the shape and area
of the cross-section vary by less than 10%.
4. The heat exchanger core of claim 1, wherein the shape has four
quadrant splines defined by the first and second lines of symmetry,
each quadrant spline having rotation symmetry about a midpoint of
the quadrant spline.
5. The heat exchanger core of claim 1, wherein the shape is a
tapered ellipse.
6. The heat exchanger core of claim 1, wherein the minor axes of
the first, second, and third passages are parallel, wherein the
second passage is arranged between the first and third passages
along a direction of the minor axis, and wherein for every point
along a direction corresponding to a major axis of the shape, a
summation of separations between the first and second passages and
the second and third passages along a direction of the minor axis
is within 10% of a median value.
7. A heat exchanger core comprising: a first set of helices and a
second set of helices, each of the first and second set of helices
being configured to couple an inlet manifold and an outlet
manifold, wherein each of the first and second set of helices
comprise two or more individual helices having cross sections in
shapes of ellipses.
8. The heat exchanger core of claim 7, wherein axes of the two or
more individual helices are collinear to within about 5.degree. and
to within about 5% of a spacing between the first and second set of
helices.
9. A heat exchanger core comprising: a first wavy passage; a second
wavy passage; a third wavy passage; and a fourth wavy passage,
wherein the first, second, third, and fourth wavy passages connect
at a plurality of nodes, and wherein a cross-sectional area of each
node is within 20% of a sum of cross-sectional areas of the first,
second, third, and fourth wavy passages.
10. The heat exchanger core of claim 9, wherein the plurality of
nodes are collinear and periodically positioned along a length of
the first, second, third, and fourth wavy passages.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/185,665, filed on Feb. 20, 2014, which relates to U.S.
Pat. No. 8,573,289, issued on Nov. 5, 2013; U.S. Pat. No.
9,527,261, issued on Dec. 27, 2016; and to U.S. Pat. No. 9,453,604,
issued on Sep. 27, 2016; the entire contents of all of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to methods of manufacturing
heat exchanging structures, and, more particularly, to methods for
additively manufacturing heat exchangers, and heat exchanger
structures manufactured thereby.
BACKGROUND
[0003] Traditional heat exchangers include plate-fin heat
exchangers and shell-and-tube heat exchangers. Previous efforts to
improve upon traditional heat exchangers involve altering the heat
exchanger architecture so as to increase the heat transfer while
having minimal effect on pumping power. Straight fins gave rise to
a number of variations including staggered fins, wavy fins, offset
fins, and louvered fins. Twisted tape inserts have been placed
inside tubes in shell and tube heat exchangers. Elliptical tubes
have also been used. However, these architectures are constrained
by the shapes that can be easily fabricated. For example, it is
difficult and sometimes impossible to combine the advantages of
multiple individual heat transfer enhancement design features
utilizing existing methods.
[0004] Additive manufacturing (e.g. 3D printing) enables
significantly more complex designs than traditional heat exchanger
fabrication techniques and allows for individual heat transfer
enhancement features that can be combined into a complex
design.
[0005] Additive manufacturing has been used to print heat
exchangers by directly printing the heat exchanger walls. This
method has several limitations stemming from the minimum feature
size that may be printed. Thin walls are preferable in heat
exchangers to reduce the conductive thermal resistance across the
walls and thus increase heat transfer. In addition, thin walls
permit more of the heat exchanger volume to be occupied by the heat
transfer fluids, which keeps the ratio of actual to superficial
velocity low, and reduces (e.g., minimizes) the input pumping power
required to operate the heat exchanger. Typically, walls of
traditional heat exchangers may be as thin as 90 microns and more
compact heat exchangers could be made if thinner walls could be
reliably produced at large scales. Typical 3D-printed minimum
feature sizes are 50-100 microns. Making a 3D-printed heat
exchanger with one or only a few voxels through the thickness of
the wall leads to a high surface roughness (e.g., due to aliasing)
and leaky walls, both of which make for poor heat exchangers. Some
3D printers exist with feature sizes in one dimension as small as
16 microns, but as feature size is reduced, production time
increases superlinearly.
SUMMARY
[0006] Aspects of embodiments of the present invention are directed
to transporting a maximum amount heat from one fluid stream to
another fluid stream with reduced (e.g., minimal) pumping power
expended to drive the fluid flow.
[0007] Aspects of embodiments of the present invention are directed
to utilizing additive manufacturing (e.g. 3D printing) to fabricate
a sacrificial scaffold, to utilizing conformal coating to create
the heat exchanger walls around the sacrificial scaffold, and to
then removing the scaffold, thus forming a heat exchanger.
[0008] According to embodiments of the present preset invention,
there is provide a method of manufacturing a heat exchanger
including a heat exchanger core of a first material, the method
including: additive manufacturing a sacrificial scaffold of a
second material, the sacrificial scaffold corresponding in shape to
that of the heat exchanger core; coating the sacrificial scaffold
with a layer of the first material; and removing the sacrificial
scaffold to leave behind the heat exchanger core with an integrated
self-aligned passage.
[0009] In one embodiment, the additive manufacturing includes one
or more of fused deposition modeling (FDM), electron beam freeform
fabricating (EBF.sup.3), direct metal laser sintering (DMLS),
electron beam melting (EBM), selective laser melting (SLM),
selective heat sintering (SHS), selective laser sintering (SLS),
plaster-based 3D printing (PP), laminated object manufacturing
(LOM), stereolithography (SLA) manufacturing, and digital light
processing (DLP).
[0010] In one embodiment, the additive manufacturing of the
sacrificial scaffold includes forming a first block, a second
block, and a connection therebetween, the connection defining the
passage.
[0011] In one embodiment, the first material includes one or more
of metals, metal alloys, polymers, ceramics, and composites.
[0012] In one embodiment, the coating of the sacrificial scaffold
includes one or more of electroless deposition, electroplating,
chemical vapor deposition, vapor deposition, slurry coating and
sintering, electrophoretic coating and sintering, plasma spraying,
and dip coating.
[0013] In one embodiment, the removing of the sacrificial scaffold
includes forming an opening through the layer of the first material
for allowing access to the second material of the sacrificial
scaffold.
[0014] In one embodiment, the removing of the sacrificial scaffold
includes one or more of chemical etching, thermal depolymerizing,
sublimating, vaporizing, and melting.
[0015] In one embodiment, the method of manufacturing the heat
exchanger further includes strengthening the heat exchanger core by
applying heat treatment.
[0016] In one embodiment, the method of manufacturing the heat
exchanger further includes coupling headers to the heat exchanger
core to form the heat exchanger.
[0017] In one embodiment, the diameter of a cross section of the
passage is less than 1.5 mm.
[0018] According to embodiments of the present preset invention,
there is provide a heat exchanger structure including: an inlet
manifold; an outlet manifold; and a first passage, a second
passage, and a third passage, each of the first, second, and third
passages being configured to couple the inlet manifold and the
outlet manifold, wherein each of the first, second, and third
passages has a wavy pattern along a lengthwise direction of the
first, second, and third passages and has a cross-sectional shape,
the cross-sectional shape having a first line of symmetry
corresponding to a major axis of the cross-sectional shape, and a
second line of symmetry perpendicular to the first line of symmetry
and corresponding to a minor axis of the cross-sectional shape.
[0019] In one embodiment, all of the cross-sectional shapes on a
plane normal to the lengthwise direction have areas and shapes that
are constant to within about 10%.
[0020] In one embodiment, the cross-sectional shapes on a plane
normal to the wavy pattern at all point along the wavy pattern have
areas and shapes that are constant to within about 10%.
[0021] In one embodiment, the cross-sectional shape has four
quadrant splines defined by the first and second lines of symmetry,
each quadrant spline having rotation symmetry about a midpoint of
the quadrant spline.
[0022] In one embodiment, wherein the cross-sectional shape is a
tapered ellipse.
[0023] In one embodiment, the minor axes of the first, second, and
third passages are parallel, wherein the second passage is arranged
between the first and third passages along a direction of the minor
axis, and wherein for every point along a direction corresponding
to a major axis of the cross-sectional shape, a summation of
separations between the first and second passages and the second
and third passages along a direction of the minor axis is within
10% of a median value.
[0024] In one embodiment, a length to height ratio of the
cross-sectional shape is in a range of about 1.2:1 to about
10:1.
[0025] In one embodiment, a length to a height ratio of the
cross-sectional shape is about 3:1 to about 4:1.
[0026] In one embodiment, a waviness amplitude to a waviness period
ratio for each of the first and second passages is in a range of
about 1:1 to about 1:10.
[0027] According to embodiments of the present preset invention,
there is provide a heat exchanger structure including: an inlet
manifold; an outlet manifold; and a first set of helices and a
second set of helices, each of the first and second set of helices
being configured to couple the inlet manifold and the outlet
manifold, wherein each of the first and second set of helices
include two or more individual helices having cross sections in
shapes of ellipses.
[0028] In one embodiment, axes of the two or more individual
helices are collinear to within about 5.degree. and to within about
5% of a spacing between the first and second set of helices.
[0029] According to embodiments of the present preset invention,
there is provide a heat exchanger structure including: an inlet
manifold; an outlet manifold; a first wavy passage; a second wavy
passage; a third wavy passage; and a fourth wavy passage, wherein
the first, second, third, and fourth wavy passages connect at a
plurality of nodes, and wherein a cross-sectional area of each node
is within 20% of a sum of cross-sectional areas of the first,
second, third, and fourth wavy passages.
[0030] In one embodiment, the plurality of nodes are collinear and
periodically positioned along a length of the first, second, third,
and fourth wavy passages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] These and other features and advantages of the present
invention will be better understood by reference to the following
detailed description when considered in conjunction with the
following drawings, in which like elements are referenced with like
numerals. These drawings should not be construed as limiting the
present invention, but are intended to be illustrative only.
[0032] FIG. 1 is a schematic drawing illustrating a heat exchanger,
according to an illustrative embodiment of the present
invention.
[0033] FIGS. 2A-2E are schematic drawings illustrating the process
of manufacturing a heat exchanger utilizing additive manufacturing
and conformal coating, according to illustrative embodiments of the
present invention.
[0034] FIG. 3 is a flow diagram of a process for manufacturing a
heat exchanger utilizing additive manufacturing and conformal
coating, according to an illustrative embodiment of the present
invention.
[0035] FIGS. 4A-4D are schematic drawings illustrating a
double-tapered elliptical-cross-section heat exchanger core
fabricated utilizing the process of FIGS. 2A-2DF, according to an
illustrative embodiment of the present invention.
[0036] FIGS. 5A-5B are three-dimensional renderings illustrating a
helical elliptical heat exchanger core fabricated utilizing the
process of FIGS. 2A-2D, according to an illustrative embodiment of
the present invention.
[0037] FIG. 6A is a perspective view illustrating a heat exchanger
core having an interconnected network of wavy passages fabricated
utilizing the process of FIGS. 2A-2D, according to an illustrative
embodiment of the present invention. FIGS. 6B and 6C are schematic
drawings illustrating the pointed and round entrances and exits,
respectively, at connection nodes of wavy passages of the heat
exchanger core of FIG. 6A, according to illustrative embodiments of
the present invention.
DETAILED DESCRIPTION
[0038] The detailed description set forth below in connection with
the appended drawings is intended as a description of illustrative
embodiments of a system and method for manufacture of a heat
exchanger in accordance with the present invention, and is not
intended to represent the only forms in which the present invention
may be implemented or utilized. The description sets forth the
features of the present invention in connection with the
illustrated embodiments. It is to be understood, however, that the
same or equivalent functions and structures may be accomplished by
different embodiments that are also intended to be encompassed
within the spirit and scope of the present invention. As denoted
elsewhere herein, like element numbers are intended to indicate
like elements or features.
[0039] The present invention relates to methods of manufacturing
heat exchangers from additively formed sacrificial templates, and
example heat exchangers produced thereby.
[0040] The present invention overcomes the limitations of
traditional heat exchanger enhancement techniques through the use
of additive manufacturing. Additionally, the present invention
overcomes many of the limitations of previous applications of
additive manufacturing to heat exchangers. Embodiments of the
present invention use additive manufacturing (e.g. 3D printing) to
fabricate a sacrificial scaffold, use conformal coating to create
the heat exchanger walls around the sacrificial scaffold, and then
remove the scaffold, thus forming a heat exchanger.
[0041] By utilizing the additive manufacturing to make a
sacrificial scaffold instead of directly making the heat exchanger
walls, embodiment of the present invention enable additively
manufactured heat exchangers that have passage sizes, rather than
wall thicknesses, that are governed by the 3D printed voxel size.
Thus, embodiments of the present invention may enable about 10
times smaller passages, about 10 times more compact structures, and
more than 10 times higher heat transfer per unit volume as compared
to previous efforts in 3D printed heat exchangers. Furthermore, the
use of larger voxel sizes enhances (e.g., increases) the rate of
production.
[0042] Embodiments of the present invention include polymer heat
exchangers with thin walls, which facilitate heat transfer due to
the reduced conductive thermal resistance of the thin polymer
walls. Polymer heat exchangers may be well-suited in applications
requiring reduced weight and reduced cost, and/or in applications
requiring the handling of corrosive, reactive, and/or high purity
fluids.
[0043] Embodiments of the present invention may further be used in
a variety of applications including thermal management and
environmental control systems, such as, precoolers, intercoolers
(e.g., turbocharger intercoolers), engine coolant radiators, oil
coolers (e.g., air-cooled and liquid-coolant-cooled oil coolers),
condensers (e.g., air conditioning condensers), air conditioning
evaporators, environmental control system (ECS) air conditioning
packs, and/or the like.
[0044] FIG. 1 is a schematic drawing illustrating a heat exchanger
100, according to an illustrative embodiment of the present
invention. In an embodiment, the heat exchanger 100 includes
passages (e.g., internal passages) 112 for facilitating the flow of
a fluid (e.g., a cooling fluid), tubesheets 114 for directing fluid
(e.g., from/to an internal fluid inlet/outlet) to the passages 112,
and headers 116 for encapsulating the passages 112 and tubesheets
114 and to facilitate the inflow and outflow of one or more fluids
(e.g., coolants) into and out of the heat exchanger 100.
[0045] According to embodiments of the present invention, additive
manufacturing is used to fabricate, utilizing a sacrificial
material, a sacrificial scaffold including one or more inlet
manifold features, one or more internal passage features, and one
or more outlet manifold features. Each internal passage feature
connects to one or more manifolds and/or one or more internal
passage features. The inlet manifold, internal passages, and outlet
manifold features may be solid volumes (e.g., not be open/hollow
volumes) and define the fluid volume for an internal fluid 10 in
the heat exchanger 100. The sacrificial scaffold is conformal
coated by a coating material, and the coating defines the walls of
the one or more passages 112 (e.g., tube walls) and the tubesheets
114. Because the walls of the one or more passages 112 and
tubesheets 114 are created simultaneously by conformal coating a
single mold, the tubesheets 114 are self-aligned to the one or more
passages 112. The volume not occupied by the sacrificial scaffold
and not occupied by the conformal coating may define the volume for
an exterior fluid 20. After conformal coating, the sacrificial
scaffold is selectively removed and headers 116 can be added to
create a fully-functional heat exchanger 100.
[0046] FIGS. 2A-2E are schematic drawings illustrating the process
of manufacturing a heat exchanger utilizing additive manufacturing
and conformal coating, according to illustrative embodiments of the
present invention. For clarity of illustration purposes, the
example heat exchangers illustrated in FIGS. 2A-2E show a pair of
passages, however, embodiments of the present invention may be
practiced with one or more passages. For illustration purposes, the
example heat exchangers illustrated in FIGS. 2A-2E show curved
passages with loops, however, embodiments of the present invention
are not limited thereto and may be implemented with passages having
any or no curvature and/or any number of loops (e.g., no loops at
all).
[0047] With reference to the embodiment illustrated in FIG. 2A, the
process includes an act of utilizing additive manufacturing (e.g.,
3D-printing) to make an initial sacrificial scaffold 100a. The
sacrificial scaffold 100a and even the entire heat exchanger 100
may be designed with a computer program, which can generate a file
that can be read by an additive manufacturing machine (e.g., 3D
printer). The design may add mechanical support features to support
the structure during the additive manufacturing process.
[0048] The additive manufacturing technique used may include one or
more of fused deposition modeling (FDM), electron beam freeform
fabricating (EBF.sup.3), direct metal laser sintering (DMLS),
electron beam melting (EBM), selective laser melting (SLM),
selective heat sintering (SHS), selective laser sintering (SLS),
plaster-based 3D printing (PP), laminated object manufacturing
(LOM), stereolithography (SLA) manufacturing, and digital light
processing (DLP), and photo-polymer waveguide fabrication methods
(e.g. U.S. patent application Ser. No. 11/580,335, filed on Oct.
13, 2006, the entire content of which is incorporated herein by
reference.
[0049] In an embodiment, the material used in additive
manufacturing includes metals, polymers, ceramics, paper, fiber,
and/or the like.
[0050] According to an embodiment, the sacrificial scaffold 100a
includes an inlet-manifold-defining-feature (also referred to as an
inlet manifold defining feature) 102, an
outlet-manifold-defining-feature (also referred to as an outlet
manifold defining feature) 104, and internal-passage-defining
features 106 which together define the fluid volume for the
internal fluid in the heat exchanger 100. The inlet and/or outlet
manifold features 102/104 may be used to define only the
tubesheets, or the entire header including the tubesheets. The
latter approach may include a thicker feature to be additively
manufactured than that of the former. The internal-passage-defining
features (also referred to as passage-defining features) 106 may be
solid, or may be hollow (e.g. if annular features are desired). The
internal-passage-defining features 106 may include, for example, a
bank of solid cylinders and/or a network of struts, which may have
any cross-sectional shape including, for example, elliptical,
airfoil, tapered, fluted, scalloped, finned, and/or like. In an
embodiment, the cross-sectional shapes also vary with position in
the heat exchanger core to form, for example, twisting elliptical
cross sections on individual internal-passage-defining features
106. The passage-defining features 106 may also intersect,
converge, diverge, and/or follow any path (e.g., straight,
twisting, helical, tortuous, etc.) through the heat exchanger core.
In an embodiment, no empty region within the heat exchanger core is
completely enclosed by solid material, thus, all empty regions are
accessible.
[0051] In an embodiment, the inlet manifold defining feature 102 is
coupled to the internal-passage-defining features 106, which are
coupled to the outlet manifold feature 104. A manifold defining
feature 102/104 may be coupled to a single passage-defining feature
106 or multiple passage-defining features 106.
[0052] According to an embodiment, the interface between the
passage-defining features 106 and the manifold defining features
102/104 are ideally tapered or radiused in order to reduce pressure
loss due to sudden expansion or contraction.
[0053] In an embodiment of the present invention, the sacrificial
scaffold 100a further includes one or more mechanical support
features 108, which may be added to provide structural support to
the sacrificial scaffold 100a during the additive manufacturing
process.
[0054] With reference to the embodiment illustrated in FIG. 2B, the
process of manufacturing a heat exchanger 100 may further include
post-processing the additively manufactured sacrificial scaffold
100a to produce the sacrificial scaffold 100b. The post-processing
may include removing any existing mechanical support features 108
and/or altering the roughness of the walls of the passage-defining
features 106. Removing the one or more mechanical support features
108 may be performed mechanically, for example, through machining
(such as drilling, milling, and/or the like), cutting, filing,
and/or the like, or may be performed chemically, for example,
through the use of appropriate solvents and/or chemical etching.
Altering (e.g., smoothing) the roughness of walls of the
passage-defining features 106 may include vapor polishing with an
appropriate solvent and/or immersing the sacrificial scaffold 100a
in an appropriate solvent.
[0055] According to an embodiment of the present invention, the
process of manufacturing a heat exchanger 100 includes attaching
one or more additional pieces of sacrificial material (e.g.,
sacrificial facesheets) to the initial sacrificial scaffold
100a/100b. For example, sacrificial facesheets could be added to
extend the inlet and/or outlet defining manifolds 102/104, only a
part of which may be manufactured via 3D-printing. This additional
operation may allow for more efficient (e.g., less) use of the
3D-printing process by reserving the 3D-printing process for the
complex features of the heat exchanger 100, such as, the
passage-defining features 106, the interfaces between the
passage-defining features 106 and the inlet/outlet defining
manifolds 102/104, and only a part of the inlet/outlet defining
manifolds 102/104. The sacrificial sheets may also couple multiple
inlet manifold defining features 102 together and/or multiple
outlet manifold defining features 104 together. According to an
embodiment, the sacrificial sheets include the same sacrificial
material as that used to additively manufacture the features 102,
104, and 106. However, the material used in the sacrificial sheets
may also be different from that used in the features 102, 104, and
106.
[0056] With reference to the embodiment illustrated in FIG. 2C, the
process of manufacturing a heat exchanger 100 further includes
conformally coating the sacrificial scaffold 100a/100b with another
material to form a coated sacrificial scaffold 100c having a
coating 110. The material of the coating 110 may include, for
example, metals, metal alloys, polymers, ceramics, composites,
and/or the like. Coating with metal or metal alloys may include one
or more of electroless deposition, electroplating, chemical vapor
deposition, physical vapor deposition (e.g., through sputtering or
evaporation), slurry coating and sintering, electrophoretic coating
and sintering, and plasma spraying. Coating with one or more
polymers (e.g. parylene, such as, parylene-N, parylene-C, parylene
AF-4, and/or the like) may include vapor deposition and/or dip
coating. According to an embodiment, multiple coating materials are
used, which may be deposited in a number of ways, for example,
simultaneously, in a layered fashion, and/or the like. The coating
110 may be substantially uniform on all surfaces of the 3-D printed
scaffold and may be substantially pin-hole free. The material of
the sacrificial scaffold 100a/100b and the coating 110 are selected
such that the sacrificial scaffold 100a/100b may be selectively
removed from the coating. For example, in an embodiment in which
chemical etching is used to remove the sacrificial material from
the coating 110, the etchant may attack the sacrificial material
faster (e.g., more than 8 times faster) than the coating material.
In an embodiment, the coating 110 is self-supporting (e.g., can
support its own weight without buckling) once the sacrificial
material is removed, and forms a self-aligned tubesheet where each
scaffold sheet meets the connections.
[0057] With reference to the embodiment illustrated in FIG. 2D, the
process of manufacturing a heat exchanger 100 may further include
removing the sacrificial scaffold 100a/100b and any existing
sacrificial facesheet(s) to form a heat exchanger core 100d with
passages 112 and integrated, self-aligned tubesheets 114. In an
embodiment, one of more holes and/or slits are formed (e.g. cut) in
the coating 110 to provide access to the sacrificial scaffold
100a/100b before the sacrificial scaffold 100a/100b can be removed.
Removal of the sacrificial scaffold 100a/100b may be performed
though one or more processes including chemical etching, thermal
depolymerization, sublimation, vaporization (e.g., boiling), and/or
burning.
[0058] With reference to the embodiment illustrated in FIG. 2E, in
an embodiment of the present invention, the process of
manufacturing a heat exchanger 100 further includes coupling (e.g.,
attaching) the heat exchanger core 100d (including passages 112 and
self-aligned tubesheets 114) to headers 116 thus forming a heat
exchanger 100. In an embodiment, the headers 116 are formed through
traditional forming and machining operations, which includes sheet
metal fabrication, casting, computer numerical control (CNC)
milling, and/or the like. However, in another embodiment, headers
116 are formed utilizing additive manufacturing in substantially
the same manner as the heat exchanger core 100d. The coupling
(e.g., attaching) of the headers 116 to the heat exchange core 100d
may be performed through welding, soldering, brazing, adhesive
bonding, and/or the like.
[0059] According to an embodiment of the present invention, the
headers 116 are formed as part of the heat exchanger core 100d
utilizing the processes outlined above with reference to FIGS.
2A-2D, thus, obviating the need for separately coupling the headers
116 to the heat exchanger core 100d as described above with respect
to FIG. 2E.
[0060] Further, with reference to the embodiments illustrated in
FIGS. 2D and 2E, according to an embodiment of the present
invention, the process of manufacturing a heat exchanger 100
further includes applying heat treatment to the heat exchanger core
100d or the heat exchanger 100 to increase the strength of
heat-treatable metal alloys.
[0061] In an embodiment of the present invention, the heat
exchanger 100 created as described above is itself used as a
sacrificial scaffold to form a replica heat exchanger in a
different material (e.g., final material). For instance, a polymer
heat exchanger may be used in an investment casting process to
create a metal alloy heat exchanger. This process could be applied
to the entire heat exchanger 100 (e.g., including headers 116) or
only to the heat exchanger core 100d (with the headers 116 in the
final material being later added).
[0062] FIG. 3 is a flow diagram of a process 300 for manufacturing
a heat exchanger 100 utilizing additive manufacturing and conformal
coating with a first material (e.g., coating material), according
to an illustrative embodiment of the present invention.
[0063] At act 302, an additive manufacturing machine (e.g., a 3D
printer) is used to additive manufacture a sacrificial scaffold
100a of a second material (e.g., sacrificial material). The
sacrificial scaffold 100a may correspond in shape to that of the
heat exchanger core 100d.
[0064] In an embodiment, the sacrificial scaffold includes one or
more mechanical support features 108 added to provide structural
support to the sacrificial scaffold 100b during the additive
manufacturing process. Upon completion of the additive
manufacturing process, the one or more mechanical support features
108 may be removed mechanically or chemically.
[0065] The material (e.g., second material) of the sacrificial
scaffold 100a/100b may include metals, polymers, ceramics, paper,
fiber, and/or the like.
[0066] At act 304, the sacrificial scaffold 100a/100b is coated
with a layer of the first material to form a coating 110. The first
material may include, for example, metals, metal alloys, polymers,
ceramics, composites, and/or the like. The first and second
materials are chosen such that the second material may be
selectively removed from the first material.
[0067] At act 306, the sacrificial scaffold 100a/100b is removed to
leave behind the heat exchanger core 100d with one or more passages
112 and integrated self-aligned tubesheets 114. In an embodiment,
one of more holes and/or slits are cut into the coating 110 to
provide access to the sacrificial scaffold 100a/100b to facilitate
the removal of the sacrificial scaffold 100a/100b utilizing a
solvent.
[0068] In an embodiment of the present invention, at act 308, the
heat exchanger core 100d is strengthened (e.g., made more rigid) by
applying heat treatment. Whether or not act 308 is performed may
depend on the intended application of the heat exchanger (e.g. if
the heat exchanger 100 must withstand a heavy mechanical load or
significant mechanical vibration) and on the coating material used
(e.g., whether or not a heat-treatable polymer or metal alloy is
used).
[0069] At act 310, headers 116 may be coupled (e.g., attached) to
the heat exchanger core 100d to form the heat exchanger 100. The
headers 116 encapsulate the heat exchanger core 100d and facilitate
the inflow and outflow of one or more fluids (e.g., coolants) into
and out of the heat exchanger 100 inside and/or around the passages
112. The headers 116 may be formed through traditional techniques
(e.g., metal casting/milling techniques) or through additive
manufacturing. In an embodiment, the headers 116 is formed, in acts
302-308, along with the heat exchanger core 100d as an integrated
whole, thus eliminating the need for separate attachment of the
header 116 in act 310.
[0070] FIGS. 4A-4D are schematic drawings illustrating a
double-tapered elliptical-cross-section heat exchanger core 400
fabricated utilizing the process of FIGS. 2A-2D, according to an
illustrative embodiment of the present invention. FIG. 4A is a side
view illustrating a single internal flow path through the
double-tapered elliptical-cross-section heat exchanger core 400,
according to an embodiment of the present invention. FIG. 4B is a
top view illustrating the external flow paths through the
double-tapered elliptical-cross-section heat exchanger core 400,
according to an illustrative embodiment of the present invention.
FIG. 4C is a cross-sectional view illustrating a cross-sectional
shape of the passages 401, according to an embodiment of the
present invention. FIG. 4D is an isometric view illustrating the
double-tapered elliptical-cross-section heat exchanger core 400,
according to an embodiment of the present invention. In FIG. 4C,
the inlet and outlet manifolds are represented by sheets having a
brick pattern, which do not demonstrate the inlet and outlet
holes.
[0071] The heat exchanger core 400 includes two separate flow
paths, each having features that promote heat transfer and promote
reduced pressure drop. According to an embodiment, the passages
401, through which the internal fluid flows and around which the
external flows, have a wavy pattern (e.g., a periodic wavy
pattern), as, for example, illustrated in FIG. 4A. In one
embodiment, the cross-sectional shape 402 of the passages 401 has a
first line of symmetry 420 (e.g., corresponding to the major axis
of the cross-sectional shape 402) and a second line of symmetry 421
crossing (e.g., perpendicular to) the first line of symmetry 420
(e.g., corresponding to the minor axis of the cross-sectional shape
402), as illustrated in FIG. 4C. As such, the cross-sectional shape
402 includes four splines (e.g., quadrant splines) 430-433, each
spline existing in one of four quadrants defined by the two lines
of symmetry 420 and 421. Each of the four splines 430-433 have
rotational symmetry about a midpoint of the spline. For example the
cross-sectional shape 402 of the passages 401 may be a tapered
ellipse, as illustrated in FIGS. 4B and 4C.
[0072] In one embodiment, the cross-sectional shapes 402 on a plane
normal to the wavy pattern (e.g., a plane defined by the X and Y
axes illustrated in FIG. 4B) at all points along the wavy pattern
is the same and have areas that are nearly the same (e.g., constant
to within about 10%). In one example, all of the cross-sectional
shapes 402 on a plane normal to the lengthwise direction of the
passages 401 are the same and have areas that are nearly the same
(e.g., constant to within about 10%).
[0073] According to an embodiment, the tapered elliptical
cross-sectional shape 402 has a high aspect ratio, for example, the
length-to-height ratio is about 1.2:1 to about 10:1. In one
example, the length-to-height ratio is about 3.5:1. The high aspect
ratio of the tapered elliptical cross-sectional shape 402 of the
passages 401 reduces the fluid pressure drop as compared to tubes
with circular cross sections, which, in turn, leads to improved
(e.g., higher) heat transfer through the passages 401 as compared
to tubes with circular cross sections. The tapered elliptical
cross-sectional shape 402 in the direction of fluid may reduce the
pressure drop through the passages 401 by streamlining the ellipse
in the fluid flow direction.
[0074] In an embodiment, the cross-sectional shape 402 is
single-tapered (e.g., tapered on only one side along the major axis
of the ellipse). In another embodiment, the cross-sectional shape
402 is double-tapered (e.g., tapered on both ends along the major
axis of the ellipse), as shown in FIG. 4B.
[0075] According to an embodiment, the passages 401 are arranged in
a manner such that, with the exception of the entrance and exit
regions 408, where an external fluid may flow into or out of the
heat exchanger core 400, all cross section planes normal to the
major axis of the tapered ellipses define areas outside of the
passages 401 (e.g., between adjacent passages 401) that are the
same (to within 10%) for any such cross section plane. In other
words, for every point along a direction corresponding to a major
axis of the cross-sectional shape 402, but not within the entrance
and exit regions 408, a summation of separations between adjacent
passages 401 along a direction of the minor axis (e.g., a direction
normal to the lengthwise direction of the passage 401 and normal to
the major axis) of the tapered ellipses is within 10% of a median
value. In some examples, the summation of separations is within 5%
or 2.5% of a median value.
[0076] In an embodiment, one or more of the internal flow path
(e.g., fluid path through the passages 401) 404 and the external
flow path (e.g., fluid path outside and around the passages 401)
406 are wavy. For example, the waviness of the external flow path
406 is produced by flow around the tapered ellipses 402. The
waviness amplitude-to-period ratio may be matched with the tapered
ellipse 402 aspect ratio for constriction-free flow paths. However,
for flow paths with constrictions, the waviness amplitude-to-period
ratio can vary from about 1:1 to about 1:10. Internal flow path 404
waviness may be produced by waviness introduced along the length of
individual passages 401. Waviness amplitude-to-period ratio of the
internal flow path 404 may be matched with the tapered ellipse 402
aspect ratio. The waviness in both fluid streams may promote fluid
mixing in both fluids separately, increasing overall heat transfer
performance of the heat exchanger core 400.
[0077] According to an embodiment of the present invention, the
passages 401 is arranged such that the cross section for the
external flow path 406 is approximately or about constant (e.g.,
constant). For example, if the periodicity of the arrangement of
the passages 401 along the X direction (which corresponds in
direction to the major axis of the cross-sectional shape 402) is
equal to the length of the cross-sectional shape 402 along the X
direction, and the periodicity of the arrangement of the passages
401 along the Y direction (which corresponds in direction to the
minor axis of the cross-sectional shape 402) is equal to the width
of the cross-sectional shape 402 along the Y direction, then the
external flow path 406 may have a constant cross section.
[0078] According to an embodiment, both the internal and external
flow paths 404/406 have constant cross-sectional areas, which
reduces (e.g., eliminates) fluid pressure drop due to flow
constriction or expansion. Lowering pressure loss associated with
expansion and contraction may lead to higher efficiency use of
kinetic energy to promote heat transfer.
[0079] FIGS. 5A-5B are three-dimensional renderings illustrating a
helical elliptical heat exchanger core (e.g., a double-helix
cross-flow heat exchanger core) 500 fabricated utilizing the
process of FIGS. 2A-2D, according to an illustrative embodiment of
the present invention. FIG. 5A is a side view illustrating the
helical elliptical heat exchanger core 500, according to an
embodiment of the present invention. FIG. 5B is an isometric view
illustrating the helical elliptical heat exchanger core 500,
according to an embodiment of the present invention. For clarity of
illustration, only one of the inlet and outlet manifolds (e.g.,
tubesheets) 504 has been shown in FIGS. 5A and 5B.
[0080] According to an embodiment of the present invention, one
fluid volume flows through the helical coils (or passages) 502 and
the second fluid volume passes around the helical coils 502
exchanging heat at the interface between them. According to an
embodiment, the heat exchanger core 500 includes a double helix
structure, as shown in FIGS. 5A and 5B. The helical coil structure
may offer a higher heat transfer rate as compared to straight
tubes, and the double helix structure may further improve (e.g.,
increases) heat transfer due to the compactness of its
structure.
[0081] The curvature of the helical coils 502 acts to impose a
centrifugal force on the fluid motion, generating secondary flow at
multiple length scales. This secondary swirling flow may increase
heat transfer as the strength and mixing intensity increases. The
helical vortices formed in the helical coils 502 may delay
transition from laminar to turbulent regimes, thus reducing the
pressure drop through the helical coils 502, as compared to
straight tubes. Further, the elliptical cross section of the
helical coils 502 may reduce the pressure drop in the cross-flow
(e.g., the flow around the helical coils 502) direction over a
circular cross section as elliptical shapes have roughly a factor
of two reduction in drag coefficient over a circular shape at
varying Reynolds number.
[0082] According to an embodiment, the double-helix cross-flow heat
exchanger core 500 has a high aspect ratio elliptical cross
section. The ratio of major diameter to minor diameter of the
elliptical cross section may be about 1:1 to about 1:10. In one
example, the aspect ratio may be 3:1.
[0083] In an embodiment, the axes of individual helical coils
(e.g., the helical coils of a double-helix) 502 are collinear to
within about 5.degree. and to within about 5% of a spacing between
a first and a second set of helical coils 502 (e.g., a first and a
second pair of double-helical coils 502).
[0084] According to embodiments of the present invention, the heat
exchanger core 500 includes a single, double, triple, quadruple, or
higher order helix pattern. The multi-helices may be arranged in a
square, rectangular, triangular, or the like, array.
[0085] In an embodiment of the present invention, the helical coils
502 are compressed when the heat exchanger is not in use, thus
enabling a deployable heat exchanger.
[0086] FIG. 6A is a perspective view illustrating a heat exchanger
core 600 having an interconnected network of wavy passages
fabricated utilizing the process of FIGS. 2A-2D, according to an
illustrative embodiment of the present invention. FIGS. 6B and 6C
are schematic drawings illustrating the pointed entrances and exits
610 and round entrances and exits 612, respectively, at connection
nodes 608 of wavy passages 606 of the heat exchanger core of FIG.
6A, according to embodiments of the present invention.
[0087] The heat exchanger core 600 may include one or more strands
602 arranged in parallel between an inlet and outlet manifolds
(e.g., tubesheets) 604, each strand 602 including, two or more wavy
passages 606 that are interconnected at connection nodes (e.g.,
connection points) 608. In one example, each strand 602 includes
four wavy passages 606, as shown in FIG. 6. The connection nodes
608 may be collinear along the length of the strands 602.
[0088] According to an embodiment, one fluid flows through the
interconnected wavy-passage network while another fluid flows
around the connected network exchanging heat at the interface
between them. Wavy passages (e.g., channels) 606 may improve (e.g.,
increase) heat transfer by disrupting a boundary layer, which may
develop in a flowing fluid. By connecting a network of such
passages mixing is allowed to occur at connection nodes 608 where
the wavy passages 606 meet, further enhancing (e.g., increasing)
heat transfer and reducing the internal fluid's temperature
gradient.
[0089] In some examples, the cross section of the wavy passages 606
may be circular or elliptical. However, embodiments of the present
invention are not limited thereto and other cross-sectional shapes
may be possible.
[0090] According to an embodiment of the present invention, the
area of the connection nodes 608 is within 20% (and in an example,
within 10%) of the sum of cross-sectional areas of the wavy
passages 606 that meet at the node, which yields a nearly constant
internal flow area and reduces (e.g., eliminates) the pressure drop
associated with expanding and contracting flows. The connection
nodes 608 may also provide mechanical support for the wavy passages
606 inside the heat exchange core. In an embodiment, the connection
nodes 608 include pointed entrances and exits 610 (as shown in FIG.
6B) and/or rounded entrances and exits 612 (as shown in FIG. 6C) at
the passage connection locations. The pointed entrances and exits
610 may reduce (e.g., eliminate) internal stagnation points for
flow entering a passage connection nodes 608 and, thus, reduce
fluid flow pressure loss. The pointed entrances and exits 610 may
further delay the onset of flow separation and vortex shedding for
flow leaving a passage connection location and, thus, further
reduce fluid flow pressure loss.
[0091] According to an embodiment, the connection nodes 608 are
arranged in a pattern (e.g., a periodic pattern). In one example,
the pattern is a rectangular prism with the external flow oriented
normal to (or perpendicular to) the two long sides of the
rectangles.
[0092] In an embodiment, the manifolds 604 do not have a
constriction compared to flow inside the passages. Further, fillets
at the connections to the manifold 604 smoothly transition the
cross-sectional area from inside the passages to inside the header,
thus providing reduced pressure drop at entrance and exit of heat
exchanger compared to abrupt transitions.
[0093] As recognized by a person of ordinary skill in the art, the
design of any of the heat exchangers illustrated in FIGS. 4-6, can
be repeated in one, two, or three axes to form a larger heat
exchanger. Characteristic dimensions of the repeat units (e.g.
aspect ratios, diameters, slenderness, cross-sectional shape,
and/or the like) of these heat exchangers can be scaled to tune the
fluid and heat transfer response of the heat exchangers.
Additionally, the heat exchangers may be readily applied in the
cross-flow configuration. However, with more complex (e.g.,
slightly more complex) manifolding, the heat exchangers could be
applied in a co-current or counter-current configuration as well.
Furthermore, baffles may be added (either in the additive
manufacturing process or afterward) to create multiple passes on
the external flow side. Multiple passes on the internal flow side
are also possible and may be enabled by more complex manifolds
and/or during the design of the sacrificial scaffold.
[0094] The present invention is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present invention, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
invention. Further, although the present invention has been
described herein in the context of a particular implementation in a
particular environment for a particular purpose, those of ordinary
skill in the art will recognize that its usefulness is not limited
thereto and that the present invention may be beneficially
implemented in any number of environments for any number of
purposes. Accordingly, the claims set forth below should be
construed in view of the full breadth and spirit of the present
invention as described herein and equivalents thereof.
* * * * *