U.S. patent application number 16/534887 was filed with the patent office on 2021-02-11 for heat exchangers and methods of making the same.
The applicant listed for this patent is MEGGITT AEROSPACE LIMITED. Invention is credited to JENNA NICOLE BECKER, STEVEN WILLIAM JAMES HENDERSON, RICCARDO MARIA LOMONACO.
Application Number | 20210041178 16/534887 |
Document ID | / |
Family ID | 1000004485817 |
Filed Date | 2021-02-11 |
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United States Patent
Application |
20210041178 |
Kind Code |
A1 |
HENDERSON; STEVEN WILLIAM JAMES ;
et al. |
February 11, 2021 |
HEAT EXCHANGERS AND METHODS OF MAKING THE SAME
Abstract
Heat exchanger designs incorporating helixes and methods for
making heat exchangers incorporating helixes are provided herein.
In preferred embodiments, the heat exchanger comprises a plurality
of fluid A channels each formed from a tube spiraled into a helix
to form a plurality of helixes wherein the plurality of helixes are
arranged in a hexagonal packing arrangement in a packing plane
perpendicular to the axes of rotation of the plurality of helixes
and wherein the pitch of each helix in the plurality of helixes is
matched to an exterior diameter of the tube such that each helix in
the plurality of helixes has a sealed interior that forms a
plurality of fluid B channels.
Inventors: |
HENDERSON; STEVEN WILLIAM
JAMES; (RUGBY, GB) ; BECKER; JENNA NICOLE;
(LEAMINGTON SPA, GB) ; LOMONACO; RICCARDO MARIA;
(CHRISTCHURCH, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEGGITT AEROSPACE LIMITED |
CHRISTCHURCH |
|
GB |
|
|
Family ID: |
1000004485817 |
Appl. No.: |
16/534887 |
Filed: |
August 7, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 7/0066
20130101 |
International
Class: |
F28D 7/00 20060101
F28D007/00 |
Claims
1. A heat exchanger comprising: a plurality of fluid B channels in
a heat exchanger matrix; a plurality of fluid A channels in the
heat exchanger matrix where each fluid A channel in the plurality
of fluid A channels is comprised of a hollow tube that spirals
around the outside of a fluid B channel from the plurality of fluid
B channels and forms a helix, and wherein each spiral in the helix
is close enough together to adjacent spirals so that an exterior of
the tube in each spiral is continuously touching an exterior of the
tube in each adjacent spiral such that the exterior of the tube the
forms the helix forms an interior of the fluid B channel.
2. The heat exchanger of claim 1, wherein the fluid B channels have
a longitudinal axis that is straight.
3. The heat exchanger of claim 1, wherein the fluid B channels are
all the same size diameter.
4. The heat exchanger of claim 1, wherein a plurality of helixes
are arranged with their longitudinal axis in a plurality of
parallel rows and wherein each row in the plurality of rows is
offset from an adjacent row by an exterior diameter of one
helix.
5. The heat exchanger of claim 4, wherein the offset of each row
alternates back and forth such that the longitudinal axes in every
other row align.
6. The heat exchanger of claim 5, wherein the rows are separated by
less than an exterior diameter of one helix.
7. The heat exchanger of claim 1, wherein the tubes have a round
exterior.
8. The heat exchanger of claim 1, further comprising a header that
is coupled to the plurality of fluid A channels and has openings
where the plurality of fluid B channels pass through the
header.
9. The heat exchanger of claim 2, wherein the plurality of fluid B
channels have a packing plane that is perpendicular to their
longitudinal axis and the plurality of fluid B channels are
arranged in a hexagonal packing arrangement.
10. A heat exchanger comprising: a plurality of helixes wherein a
longitudinal axis of rotation of each helix in the plurality of
helixes is parallel and wherein each helix in the plurality of
helixes is formed by a hollow tube that spirals around the
longitudinal axis of rotation and wherein each tube forms a fluid A
channel and wherein the pitch of each helix in the plurality of
helixes is matched to an exterior diameter of the tube that
comprises the helix such that each helix in the plurality of
helixes has a sealed interior and each sealed interior forms a
fluid B channel.
11. The heat exchanger of claim 10, wherein the longitudinal axis
of rotation of each helix is straight.
12. The heat exchanger of claim 10, wherein the fluid B channels
all have a same size exterior diameter.
13. The heat exchanger of claim 10, wherein the plurality of
helixes are arranged with their longitudinal axis of rotation in a
plurality of parallel rows and wherein each row in the plurality of
rows is offset from an adjacent row by an exterior diameter of one
helix.
14. The heat exchanger of claim 13, wherein the offset of each row
alternates back and forth such that all the longitudinal axes of
rotation in every other row align.
15. The heat exchanger of claim 14, wherein the rows are separated
by less than an exterior diameter of one helix.
16. The heat exchanger of claim 10, wherein the tubes have a round
exterior.
17. The heat exchanger of claim 10, further comprising a header
that is coupled to the plurality of fluid A channels and has
openings where the plurality of fluid B channels pass through the
header.
18. A heat exchanger comprising: a plurality of fluid A channels
each formed from a hollow tube spiralled into a helix to form a
plurality of helixes wherein the plurality of helixes are arranged
in a hexagonal packing arrangement in a packing plane perpendicular
to axes of rotation of the plurality of helixes and wherein the
pitch of each helix in the plurality of helixes is matched to an
exterior diameter of the tube such that each helix in the plurality
of helixes has a sealed interior that forms a plurality of fluid B
channels.
19. The heat exchanger of claim 18, wherein the fluid B channels
are all the same size diameter.
20. The heat exchanger of claim 18, wherein the fluid B channels
have different size diameters.
21. The heat exchanger of claim 18, wherein a bend radius of the
hollow tube of the helix is varied along a length of the helix.
22. The heat exchanger of claim 18, wherein a plurality of fluid A
channels are intertwined to create a single fluid B channel.
Description
FIELD
[0001] This patent document relates to heat exchangers and methods
of making the same. In particular, this patent document relates to
new geometric designs for heat exchangers that result in heat
exchangers with improved efficiencies.
BACKGROUND
[0002] Heat exchangers are used in multiple applications within a
vast range of industries. Because of the importance of heat
exchangers, there is a constant push to develop heat exchangers
that are more efficient, lighter, more compact, more durable and
more cost effective. Generally, the industry is always looking for
improved heat exchanger designs that optimize one or more
parameters of the heat exchanger, depending on the application.
[0003] The demands on heat exchangers are becoming particularly
more challenging in the area of aircraft engines. Engines have
evolved dramatically in the last fifty years. Traditionally, engine
nacelles housed a multitude of components including the heat
exchangers. With increasing fan diameters, the drag generated by
the nacelle becomes too large, necessitating thinner, slim-line
nacelles. These thinner nacelles cannot house the components
traditionally housed within the nacelle. Instead, these components
have to be housed within the core zone. As the core zone already
houses ducting, pipework, bleed systems and other components,
relocating hardware previously housed within the nacelle can prove
to be a challenge due to envelope constraints.
[0004] As the fan diameter increases, it has become necessary to
reduce the fan speed, relative to the turbine speed, via a
reduction gearbox. Heat load from the accessories' gearbox,
bearings and generators is typically used to pre-heat the fuel with
excess heat being fed into the secondary flow air or air flow
external to the nacelle. It is estimated that the additional
gearbox will double the heat load introduced into the oil. This
additional heat load can only be dissipated into the secondary flow
air as the fuel cannot accept any further temperature
increases.
[0005] As engine manufacturers strive towards more fuel-efficient
architectures, systems which are usually driven by compressor
discharge pressure, such as ECS, are being powered by electric
systems. These systems put extra demand on the electrical
generators, again this additional energy results in extra heat load
being dissipated into the oil.
[0006] As the space around the core of the engine begins to fill
with equipment, emphasis is put on reducing the space taken up by
individual pieces of equipment. This begins a significant challenge
for the heat exchangers where they are required to manage
approximately double the heat load but in a smaller volume.
[0007] Applicant currently designs and manufactures plate and fin
construction heat exchangers for air oil and low-pressure fuel oil
applications. An illustration of a plate and fin heat exchanger can
be seen in FIG. 1.
[0008] Plate and fin heat exchangers are constructed from layers of
corrugated fins sandwiched between parting plates. The fins are
supported by bars which are located at either end of the fin layer.
The heat exchangers transfer heat from the hot fluid of the heat
exchanger (depending on the application of the heat exchanger) to
the metal surrounding the fluids. The fins act as secondary heat
transfer surface area and transfer the heat to the other fluid via
conduction. Side plates cap the top and bottom of the plate/fin
stack.
[0009] The fins and the parting plates are typically 3000 series
aluminum. The corrugated surfaces (fins) are produced on a fin
forming machine in a variety of patterns e.g. plain, lanced, wavy,
perforated or louvered. In most cases the height of the fin and fin
density can be tailored to the operating conditions and mechanical
constraints of the particular application. Parting plates, or
separator sheets as they are also known, are usually from thin
gauge material and are clad with a braze alloy on both sides to
allow bonding to the fin surfaces. Side plates may be cut from
sheet. This would be clad on one side only or, if thicker plates
are required for strength, a brazing shim may be added to allow
bonding. The bars that close each layer of the core are made from a
specific extruded section or may be machined from solid if a
particular feature in the core is a requirement.
[0010] The heat exchanger core is then assembled in purpose
designed fixtures and brazing jigs. The upper platform of the jig
is under spring pressure pushing the surfaces together as the core
contracts as the clad surfaces disperse to form the joints and fuse
together during the brazing process.
[0011] The resulting heat exchanger is restricted to rectangular
shapes by their construction. The construction also constrains the
heat exchanger to being formed in discrete layers. This results in
the necessity to use fins to add additional surface area. The fins
are classed as secondary heat transfer surface area which has an
inherent inefficiency associated with the convective and conductive
heat transfer. The layered construction also limits the variation
in the flow configurations that can be employed; where typically
for plate and fin heat exchangers cross-flow configurations are
used. Parallel flow or counter flow can be used but require complex
and expensive header constructions.
[0012] In recent years, advancements in additive manufacturing have
made it a viable option for the production of heat exchangers and
heat exchanger components. The use of additive manufacturing for
heat exchangers has opened up new possibilities for heat exchanger
geometries. In particular, heat exchangers can now be made with
geometries that do not have to conform to standard manufacturing
principals.
[0013] Applicant has previously recognized the advantages of using
additive manufacturing in the manufacture of heat exchangers. U.S.
patent application Ser. No. 16/242,432 (hereinafter "'432
application") was filed on Jan. 8, 2019, and covers a series of
designs for heat exchangers manufactured using additive
manufacturing. Although the heat exchanger designs in the '432
application are created using additive manufacturing, they are very
different from heat exchanger designs disclosed herein.
[0014] For at least the reasons above, there is a need for new heat
exchanger designs that improve on previous designs in any of the
heat exchangers criteria but in particular in the areas of
efficiency, size and weight.
SUMMARY OF THE EMBODIMENTS
[0015] Objects of the present patent document are to provide an
improved heat exchanger and improved methods for making heat
exchangers. To this end, various embodiments of heat exchangers and
methods of making heat exchangers are provided. In preferred
embodiments, the heat exchanger comprises: a plurality of fluid B
channels in a heat exchanger matrix; a plurality of fluid A
channels in the heat exchanger matrix where each fluid A channel in
the plurality of fluid A channels is comprised of a tube that
spirals around the outside of a fluid B channel from the plurality
of fluid B channels and forms a helix, and wherein each spiral in
the helix is close enough together to adjacent spirals such that an
exterior of the tube in each spiral is continuously touching an
exterior of the tube in each adjacent spiral such that the exterior
of the tube forms an interior of the fluid B channel.
[0016] In preferred embodiments, the heat exchanger has fluid B
channels with a longitudinal axis that is straight. In addition,
the fluid B channels are preferably all the same size diameter. Of
course, in other embodiments, the fluid B channels can have
different sized diameters. This may be beneficial for the packing
density of the fluid B channels.
[0017] In preferred embodiments, the heat exchanger comprises a
plurality of helixes that are arranged with their longitudinal axis
in a plurality of parallel rows, wherein each row in the plurality
of rows is offset from an adjacent row by an exterior diameter of
one helix.
[0018] In some embodiments, the offset of each row of helixes in
the heat exchanger matrix alternates back and forth such that all
the longitudinal axis of the helixes in every other row align. In
some embodiments, the rows are separated by less than an exterior
diameter of one helix.
[0019] Generally speaking, the tubes that comprise the fluid A
channels, and whose touching exteriors form the fluid B channels
have a round exterior. However, the tube exterior may be any shape
including square, hexagon or triangular, to name a few.
[0020] In preferred embodiments, the heat exchanger further
comprises a header that is coupled to the plurality of fluid A
channels and has openings where the plurality of fluid B channels
pass through the header.
[0021] In preferred embodiments, the fluid B channels are packed as
tightly as possible to maximize efficiency of the heat exchanger.
Accordingly, the plurality of fluid B channels may have a packing
plane that is perpendicular to their longitudinal axis and the
plurality of fluid B channels are arranged in a hexagonal packing
arrangement.
[0022] In yet other embodiments of heat exchangers taught herein,
the heat exchangers comprise a plurality of helixes wherein a
longitudinal axis of rotation of each helix in the plurality of
helixes is parallel and wherein each helix in the plurality of
helixes is formed by a tube that spirals around the longitudinal
axis of rotation and wherein each tube is hollow and forms a fluid
A channel and wherein the pitch of each helix in the plurality of
helixes is matched to an exterior diameter of the tube such that
each helix in the plurality of helixes has a sealed interior and
each sealed interior forms a fluid B channel for the heat
exchanger.
[0023] In some embodiments, the heat exchangers are designed to
have the plurality of helixes arranged with their longitudinal axis
of rotation in a plurality of parallel rows and each row in the
plurality of rows is offset from an adjacent row by an exterior
diameter of one helix.
[0024] In yet other embodiments heat exchangers are provided that
comprise a plurality of fluid A channels each formed from a tube
spiraled into a helix and collectively forming a plurality of
helixes wherein each helix has an axis of rotation that is parallel
to each other helix in the plurality of helixes and wherein the
plurality of helixes are arranged in a hexagonal packing
arrangement in a packing plane perpendicular to the axis of
rotation of the plurality of helixes and wherein the pitch of each
helix in the plurality of helixes is less than or equal to an
exterior diameter of the tube such that each helix in the plurality
of helixes has a sealed interior that forms a plurality of fluid B
channels.
[0025] As may be appreciated, the embodiments described herein are
especially efficient because the larger fluid B channels have no
additional structure of their own and are comprised entirely from
the tubes of the helix shaped fluid A channels.
[0026] The heat exchangers discussed herein may use a header to
feed the smaller fluid A channels. Accordingly, the heat exchangers
may further comprise a header that is coupled to the plurality of
fluid A channels but has openings where the gas or liquid feeding
the plurality of fluid B channels washes over the outer wall of the
header prior to entering the fluid B channels. To this end,
embodiments herein may have thermally active headers.
[0027] The headers that feed and drain the fluid A channels are
separated by the heat exchanger matrix and may be found on opposite
sides of the heat exchanger matrix. These headers may be thought of
as secondary headers and may each be fed by a primary header. To
this end, in some embodiments, the heat exchanger further comprises
an input primary header coupled to a secondary header on a first
side of the heat exchanger matrix and an output primary header
coupled to a secondary header on a second side opposite to the
first side of the heat exchanger matrix.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 illustrates an exterior isometric view of a plate and
fin heat exchanger according to the prior art.
[0029] FIG. 2 illustrates a cut-away schematic view of the plate
and fin heat exchanger of FIG. 1.
[0030] FIG. 3 illustrates an exterior isometric view of a heat
exchanger according to the teachings herein.
[0031] FIG. 4 illustrates a cross-sectional view of the heat
exchanger matrix of the heat exchanger in FIG. 3.
[0032] FIG. 5A is an isometric view of the heat exchanger of FIGS.
3A and 3B with a plurality of the flow paths of the hot fluid, or
first fluid ("A Channels"), schematically illustrated.
[0033] FIG. 5B is an isometric view of the heat exchanger of FIGS.
4A, 3A and 3B with the flow path of the cold fluid, or second fluid
("B Channel"), schematically illustrated.
[0034] FIG. 6A illustrates a cross-sectional view of a helix where
the pitch of the helix is equal or about equal to the diameter of
the tube.
[0035] FIG. 6B illustrates a cross-sectional view of a helix where
the pitch of the helix is less than the diameter of the tube.
[0036] FIG. 7 illustrates an embodiment where helical fluid A
channels are intertwined in parallel within a single column.
[0037] FIG. 8 illustrates an example of a helix where the bend
radius of the helical tubes is varied along the coil's length.
DETAILED DESCRIPTION OF THE DRAWINGS
[0038] The present patent document describes embodiments of heat
exchangers that eliminate or at least ameliorate some of the
problems with previous heat exchanger designs. FIG. 3 illustrates
an exterior isometric view of a heat exchanger 10 according to the
teachings herein. The heat exchanger in FIG. 3 is comprised of
three main components: the heat exchanger matrix 12, also known as
the heat exchanger core 12, secondary headers 14 and feeder
(primary) headers 16. As may be seen in FIG. 3, the heat exchanger
matrix 12 is comprised of a plurality of helixes 11 that extend up
and down along an axis of rotation, in this embodiment, the Z-axis.
In other words, the helixes 11 have axes of rotations that are all
parallel to the Z-axis. It may also be appreciated that the helixes
11 are arranged or packed along both the X and Y axis. Accordingly,
the helixes 11 have a packing plane perpendicular to the
Z-axis.
[0039] Each helix 11 in the matrix core 12 is comprised by a tube
that spirals around an axis of rotation to create a helix. The
tubes are hollow and allow the flow of air or fluid through their
interiors.
[0040] FIG. 4 illustrates a cross-sectional view of the heat
exchanger matrix of the heat exchanger in FIG. 3. The spiraling
tubes create the individual helixes 11 and the interior of each
tube is a fluid A channel 22 of the heat exchanger 10. Accordingly,
the heat exchangers of the present patent document are comprised of
a plurality of fluid A channels 22 each consisting of a tube that
spirals around an axis of rotation 15 to form a helix 11.
[0041] The interior of each helix 11 forms a fluid B channel 24. In
order to maintain unmixed flow, the interior of each helix 11 is
designed to be continuous such that fluid cannot leak between the
interiors of different helixes 11, fluid B channels 24. To this
end, in preferred embodiments, each spiral in the helix 11 is close
enough together to adjacent spirals above and below such that an
exterior of the tube in each spiral is continuously touching an
exterior of the tube in each adjacent spiral. Said another way, the
pitch of each helix 11 is matched to the exterior diameter of the
tube that comprises the helix 11 such that each helix 11 has a
sealed interior and each sealed interior forms a fluid B channel
24. By "matched" it is meant that the pitch is small enough with
respect to the tube diameter to seal the interior once
manufactured. To this end, embodiments herein require the pitch of
each helix 11 to be less than or equal to the outside diameter of
the tube creating the helix 11. Consequently, the exterior of the
tube that spirals around and is the fluid A channel 22 forms an
interior of the fluid B channel 24.
[0042] To this end, each fluid A channel 22 in the plurality of
fluid A channels 22 spirals around the outside of a fluid B channel
24. The fluid B channels 24 are formed from the interior of each
helix 11. As may be appreciated, the axis of rotation 15 of each
helix 11 forms the longitudinal axis or central axis of each fluid
B channel 24. As a fluid or gas spirals around the helix 11 inside
the tube that comprises the helix 11, the fluid or gas traverses in
a negative Z-axis direction. A second fluid or gas may then be
passed in the opposite direction, the positive Z-axis direction, up
through the interior of the helixes 11, which define the fluid B
channels 24.
[0043] Accordingly, the exterior walls of the smaller fluid A
channels 22 all come in contact to form the larger fluid B channels
24. Each fluid B channel 24 in the plurality of fluid B channels 24
is formed by a spiraling a fluid A channel 22 around an axis of
rotation 15 to form a helix 11.
[0044] The fluid A channels 22 are helical tubes grouped tightly to
form the matrix 12, and the fluid B channels 24 are formed from the
interior of each helix 11. By using helical tubes, the fluid A
channels 22 have an increased heat transfer length and heat
transfer surface area per volume. Helical channels also offer
increased heat transfer performance over a straight channel of the
same length, due to centrifugal forces inducing a secondary flow in
the form of Dean vortices.
[0045] Because the fluid B channels 24 are formed from the interior
of the fluid A channels 22, the fluid B channels 24 are ribbed
which leads to increased heat transfer area. The novel channel
packaging, with the fluid A channels 22 tightly packed around the
fluid B channels 24, means that the heat transfer surface area of
the fluid B channels 24 is entirely primary surface area; this
results in increased heat transfer performance as there is no
compound restriction on secondary surface area efficiency. Although
the figures in this document present the fluid A and fluid B
channels as circular, these channels can be any shape that fulfils
the performance and packaging requirements.
[0046] FIG. 5A is an isometric view of the heat exchanger of FIGS.
3 and 4 with a plurality of the flow paths of the hot fluid, or
fluid A channels, schematically illustrated. As may be seen in FIG.
5A, in operation, hot fluid enters the feeder header, or primary
header, 16 through the input port 18. As the hot fluid begins to
fill the feeder header 16, the hot fluid moves in the positive X
direction along the length of the feeder header 16. The feeder
header 16 is in communication with the secondary headers 14 that
stretch in the positive Y direction across the tops of the inputs
to the fluid A channels 22. The primary headers 16 hold the full
mass flow rate of the fluid A channels 22 and feed the plurality of
secondary headers 14. The secondary headers 14 in turn feed each
layer of the fluid A channels 11.
[0047] In the embodiments shown herein, the secondary headers 14
are S-shaped and follow the contours of the tops of the plurality
of fluid A channels 22 as the secondary headers 14 stretch across
the heat exchanger matrix 12. This allows the secondary headers 14
to feed the fluid A channels 22, while not blocking the fluid B
channels 24. Accordingly, the fluid B channels 24 pass completely
through the secondary headers 14 on both sides of the heat
exchanger. In operation, the outer surfaces of the secondary
headers 14 are washed by the fluid B flow entering and exiting the
fluid B channels 24 of the heat exchanger 10 and therefore allow
for the transfer of heat from fluid A within the headers 11 to
fluid B.
[0048] As the hot fluid fills the secondary headers 14 that stretch
across the top of the heat exchanger 10, the hot fluid begins to
pass down the fluid A channels 22 in the negative Z direction
towards the bottom of the heat exchanger 10. Accordingly, the hot
fluid spirals around each helix 11 as it traverses in the negative
Z direction. Eventually the hot fluid reaches the bottom of the
fluid A channels 22 and then passes back into a secondary header 14
at the bottom of the heat exchanger 10.
[0049] The secondary headers 14 at the bottom of the heat exchanger
10 are similar to the secondary headers on the top of the heat
exchanger 10 but just on the bottom instead of on the top. Just
like on the top, the secondary headers 14 on the bottom run
primarily in the Y direction across the bottom of the fluid A
channels 22 and are fed by the fluid A channels 22 and the feeder
header 16 on the bottom of the heat exchange 10. The hot fluid then
flows through the secondary headers 14 on the bottom of the heat
exchanger 10 in the positive Y direction towards the bottom feeder
header (output header) 16. Eventually the hot fluid enters the
bottom feeder header 16 and exits through the exit port 19.
[0050] Although the entrance and exit 18 and 19 of the primary
headers 16 of the embodiment shown in FIG. 5A illustrate the fluid
entering and exiting from the same side, in other embodiments, the
primary headers 16 can be adapted to allow fluid to enter and exit
on opposite sides or from above or below or any other direction.
Likewise, the inlet and outlet headers 16 are pictured as being on
opposite sides, but could also be positioned on the same side.
[0051] FIG. 5B is an isometric view of the heat exchanger of FIG.
5A with the flow path of the cold fluid, or second fluid ("fluid B
channels") 24, schematically illustrated. While the "hot fluid" is
flowing through the fluid A channels 22, the cold gas or cold fluid
enters the fluid B channels on the bottom of the heat exchanger 10
and flows up in the positive Z direction towards the top of the
heat exchanger 10 and out the top of the fluid B channels 24 and
heat exchanger 10. As the cold air flows up in the positive Z
direction through the fluid B channels 24 and the hot fluid flows
down in the negative Z direction through the fluid A channels, the
heat is transferred from the hot fluid into the cold air. To this
end, the temperature of the hot fluid is reduced as it passes
through the heat exchanger 10.
[0052] In the example of operation above, the terms hot fluid and
cold gas were used but in either case the substances could be in
gas or fluid phase. In addition, while typically the hot fluid
would be passed through the fluid A channels 22, and the cold gas
or fluid through the fluid B channels 24, in some embodiments the
cold fluid could be used in the fluid A channels 22 and the hot gas
in the fluid B channels 24. Moreover, the heat exchanger 10 could
be run in reverse with the hot fluid flowing up and the cold fluid
flowing down. In the embodiments herein, the heat exchanger 10 is
designed and manufactured so that it can be used in a counter flow
or parallel flow configuration. While counter flow is the optimal
configuration for maximum heat transfer performance, there may be
scenarios where parallel flow configuration is preferred.
Accordingly, the embodiments herein can be run in a parallel flow
configuration or a counterflow configuration.
[0053] As may be appreciated, the designs suggested herein would be
incredibly difficult, if not completely impossible, to manufacture
using any type of conventional manufacturing method. To this end,
the designs herein are preferably manufactured using additive
manufacturing. The additive manufacturing techniques allow for the
compact packaging of the heat exchanger flow channels and enable
the novel designs and the flexibility in design embodied herein.
Moreover, the additive manufacturing process allows the heat
exchanger to be built as a single piece.
[0054] Many different types of materials may be used with the
additive manufacturing process. To this end, the designs herein may
be made from aluminum (and associated alloys), steel (and
associated alloys), titanium (and associated alloys), Inconel (and
associated alloys) or any other type of metal that may be used in
the additive manufacturing process. Some prototype heat exchangers
were manufactured in aluminum using additive manufacturing and
these prototypes are expected to achieve a circa five-fold increase
in the yield strength compared to conventional 3000 series aluminum
used in the plate and fin construction. Depending on the
application, it may also be possible to use a hardened resin or
even a ceramic. Basically, any material that may be used in the
additive manufacturing process may be used and that includes
materials that may be not yet available for the process but
available in the future. Of course, materials with good heat
transfer properties are desirable.
[0055] In various different embodiments, the general concepts of
the heat exchangers taught herein may be modified to optimise the
performance for a particular application. To this end, the
embodiments herein may be optimized for their performance and
pressure drop through the heat exchanger for bespoke applications.
For example, the cross-section of the fluid A channels 22 is shown
as round or tubular. However, other shapes may be used for the
cross-section of the fluid A channels 22 including squares,
triangles, hexagons or ellipses, to name a few. Moreover, the
interior of the tubes or fluid A channels 22 could be one shape and
the exterior could be a different shape. As just one example, the
exterior of the tubes may be round while the interior is a more
complex shape. The interior of the fluid A channels 22 may also
include flow features on their surface. The shape of the
cross-section of the fluid A channels 22 may be changed to any
shape in order to fulfil the performance, structural, and packaging
requirements of any particular application.
[0056] In addition, the layout and packing of the fluid B channels
may be changed. As may be seen in FIG. 4, in the embodiments shown
herein, a plurality of helixes 11 are arranged with their
longitudinal axis 15, a.k.a. axis of rotation 15, in a plurality of
parallel rows that run along the X axis. In the embodiment shown in
FIG. 4, each row of helixes 11 in the plurality of rows is offset
from an adjacent row by an exterior diameter of one helix. The
offset of each row alternates back and forth such that the
longitudinal axes 15 in every other row align in the Y-axis
direction. In the embodiment shown in FIG. 4, the rows are
separated by less than an exterior diameter of one helix to pack
the helixes closely.
[0057] While a particular packing of helixes 11 or packing of the
fluid B channels 24 is described and shown with respect to FIG. 4,
various other packing or packaging methods may be used. As may be
appreciated, a cross-section of the heat exchanger matrix 12 may be
considered a packing plane. The study of packing geometric shapes
into various different configurations within a packing plane is
well studied. The cross-section of a helix is typically a circle
and the study of packing circles in a plane is extensive. Circles
may be packed in triangular, diamond, or hexagonal packing
arrangements with the hexagonal packing arrangement being the
densest arrangement and therefore, most desirable. Moreover, it is
also known that packing densities of circles may be increased by
allowing the diameter of the circles to vary and accordingly, heat
exchangers may be constructed with varying diameter helixes 11 to
allow for a denser packing. As discussed in more detail below, the
diameter of the helixes 11 may also be varied for performance
reasons and both design criteria may be considered in finding the
optimal helix size, spacing and packing for any particular
application.
[0058] In preferred embodiments, the packing is designed for
maximum density and thus, the helixes are packed with their
external surfaces touching. Packing arrangements for the helixes
11, such as hexagonal packing, may be further selected to maximize
density.
[0059] In other embodiments, the helixes may be constructed such
that their cross-sections are oval or some other shape rather than
circles. In yet other embodiments, the cross-sections of different
helixes within the heat exchanger matrix may vary in shape. In all
these embodiments, different packing arrangements within the
packing plane may be used to optimize performance for any
particular application.
[0060] In the embodiments illustrated in the figures herein, the
heat exchanger matrix is shown generally as a square block where
the fluid B channels 24 have a straight axis of rotation 15 and the
number of helixes 11 are grouped to allow the heat exchanger to
have approximately the same dimension along the X and Y axes.
However, for applications where the flow path is not a straight
line, the geometries of the fluid B channels may be changed and may
include fluid B channels 24 with an axis of rotation that is a
"swept path" (e.g. curved, wavy, zigzag, helix etc.) to conform to
the desired flow path. In more complex embodiments, the diameter of
the tube of each helix 11 may vary along different parts of the
helix 11 to allow the interior of the fluid B channels 24 to stay
continuous and sealed as the axis of rotation 15 of the helix 11
curves. Changing the diameter of the tube along the length of the
helix can allow the thickness of the walls of the tube to stay
consistent even as the axis of rotation of the helix curves. In
general, it is preferable that the thickness of the tubes that
comprise the helixes 11/fluid A channels 22 remains constant.
However, in yet other embodiments, the thickness of the walls of
the tube that forms the helixes 11 may also vary to accommodate
various design constraints.
[0061] In some embodiments, the secondary headers 14 on the top
and/or bottom of the heat exchanger 10 may be profiled or shaped to
promote turning of the fluid B flow in inclined or other
applications. This allows the secondary headers 14 to perform their
function both as headers and also as air foils to direct the B
flow. This type of dual-purpose header is only possible in designs
where the A channel headers are actively in the path of the channel
B flow. The integrated thermally active headers 14 can be profiled
or shaped to reduce entrance pressure losses into the fluid B flow
channels 24 for flows which are both normal to and angled relative
to the channel flow stream. The angle range covers 0 degrees to 90
degrees and can be a compound angle relative to more than one
axis.
[0062] In yet other embodiments, the channel packing and channel
geometry or cross section may be variable and may be made to match
the fluid B flow profile. In order to enhance the ducted systems
performance, variable channel geometries can be used within the
heat exchanger to take advantage of non-uniform velocity profiles
at the heat exchanger inlet. For example, the size of or density of
the fluid A and/or B channels 22 and/or 24 may be varied across the
profile of the heat exchanger 10 to match the flow distribution.
Changing channel density or size to match the flow distribution can
help with pressure drop and efficiency. To this end, the size of
the fluid A and/or B channels 22 and/or 24 may increase from one
side of the heat exchanger 10 to another. In yet other embodiments,
the size of the fluid B channels 24 may be larger in any particular
row or column of the cross section. In yet other embodiments,
multiple strategically placed rows or columns of the cross-section
have larger fluid B channels 24 to accommodate the flow profile. As
discussed above, the diameter of the fluid B channels 24 may also
be varied to increase packing density and both design criteria can
drive the size and placement of the fluid A and/or B channels 22
and/or 24.
[0063] Further improvements to the heat exchanger performance can
also be made with a variable cold flow length to further maximise
performance with non-uniform velocity profiles, the manifestation
of this concept would include curved inlet and/or outlet faces.
[0064] In some embodiments, the primary headers 16 may fully
encompass the heat exchanger perimeter, which could act as flanges
for integration with ducting. In a conventional plate & fin
heat exchanger, flanges are typically added around the perimeter of
the airflow entrance and exit planes. These flanges are used as
attachment points to the inlet and outlet air ducts. In the designs
proposed herein, the primary headers 16, which are each along one
edge of the airflow entrance/exit perimeters, can be extended to
encompass the entire perimeter, and the primary headers 16 can
mount directly to the inlet/outlet ducting. This would make the
primary headers 16 dual-purpose and eliminate the need for mounting
flanges.
[0065] When manufacturing the embodiments herein, additive
manufacturing may be used to create the entire structure as one
piece. Manufacturing the entire heat exchanger as one piece reduces
the secondary machining process or joining methods, reduces part
count and simplifies the supply chain. In yet other embodiments,
the primary headers 16 may be made separately and coupled to the
heat exchanger matrix 12 and secondary headers 14 after they have
been manufactured. In yet other embodiments, the heat exchanger
matrix 12 is made with additive manufacturing and both the primary
headers 16 and secondary headers 14 are manufactured separately and
coupled to the heat exchanger matrix 12 after the three components
are manufactured.
[0066] The heat exchanger has been designed and manufactured with
fluid A channel wall thicknesses ranging from 0.2 mm to 0.5 mm. The
wall thickness can be used as a design variable, where the wall
thicknesses can be tailored to suit the operating pressures while
minimizing the weight and maximising the compactness of the heat
exchanger. Wall thicknesses between 0.1 mm and 10 mm may be used
depending on the application and structural and thermal
requirements. The thinner the wall thickness the better the thermal
performance at the expense of the structural performance. The
thicker the walls the better the structural performance at the
expense of the thermal performance.
[0067] In some embodiments, additional secondary heat transfer
`micro features` can be added to the surfaces of the fluid A 22
and/or B channels 24. As just a few non-limiting examples of
micro-features, dimples, protrusions, vortex generators etc., may
be added to the surfaces of the fluid A channels 22 and/or fluid B
channels 24. Such micro features are used to further increase heat
transfer surface area and convective heat transfer.
[0068] In the embodiments taught and disclosed herein, the fluid B
channels 24 are created entirely from the negative space not used
by the construction of the fluid A channels. Consequently, no
additional material is required to create the fluid B channels.
This leads to weight reduction (no extra materials required to
separate the fluids) and increased primary surface (approaching
100%).
[0069] In preferred embodiments, the pitch of the helixes of the
fluid A channels 22 is designed to be matched with the diameter of
the tubes creating the fluid A channels 22 such that the interior
of the helixes are sealed. However, in some embodiments, the pitch
of the helixes may be less than the diameter of the tubes such that
the walls of the coils in the helix overlap. FIG. 6A illustrates a
cross-sectional view of a helix where the pitch of the helix is
equal or approximately equal to the diameter of the tube. FIG. 6B
illustrates a cross-sectional view of a helix where the pitch of
the helix is less than the diameter of the tube. Accordingly, it
can be seen that the upper and lower walls of the fluid A channels
22 in each turn of the helix overlap with the walls of each
adjacent spiral. The amount of overlap can be any amount but
preferably the amount of overlap never exceeds the thickness of one
tube. Otherwise, the adjacent tubes would protrude into the
interiors of each adjacent tube, which is not ideal.
[0070] Where neighboring spirals within a given helix 11 share
walls, i.e. the pitch 33A/33B of the helix is less than the
exterior diameter of the tube 32, a weight reduction and volume
reduction may occur while maintaining the same surface area. As may
be appreciated by comparing FIG. 6A to FIG. 6B, a helix 11 with the
same number of spirals and the same interior and exterior diameter
tube 32, may be compressed into a smaller height by overlapping the
walls of the spirals within the helix 11. Accordingly, in comparing
FIG. 6A to 6B, it will be appreciated that while the exterior
diameter 32 of the tube is identical in the two examples, the pitch
33A of the helix 11 in FIG. 6A is slightly larger than the pitch
33B of the helix 11 in FIG. 6B.
[0071] In preferred embodiments, the overlap of the walls of the
tube is 50% of the wall thickness. In yet other embodiments, the
overlap is greater and is between 50% and 90% of the wall
thickness. In yet other embodiments, the overlap of the walls is
less than 50% of the wall thickness. In yet other embodiments the
walls overlap almost completely and the overlap is between 90% and
100% of the wall thickness. As may be appreciated, the pitch of the
helix is equal to the diameter of the tube minus 2 times the
overlap distance.
[0072] In addition to a pitch reduction that results in an overlap
of the walls of the tube within each helix, the helixes may be
spaced in the packing plane such that their walls overlap. This may
be done independently or in combination with overlapping the walls
within a helix. Neighboring coils can share walls by simply
reducing the distance between their axes of rotation, for example,
in the packing plane. Sharing walls between neighboring helixes can
not only reduce the size of the heat exchanger but can also reduce
weight and add structural stiffness. To this end, it is recommended
that helixes actually do overlap. Similar to the overlap within the
helixes themselves, the amount of overlap between neighboring
helixes can vary but should not exceed the thickness of the tube
wall.
[0073] In preferred embodiments, the overlap of the walls of
neighboring helixes is 50% of the wall thickness. In yet other
embodiments, the overlap is greater and is between 50% and 90% of
the wall thickness. In yet other embodiments, the overlap of the
walls is less than 50% of the wall thickness. In yet other
embodiments the walls overlap almost completely and the overlap is
between 90% and 100% of the wall thickness.
[0074] FIG. 7 illustrates an embodiment where helical channels 41,
42 and 43 are intertwined parallel within a single column. To this
end, more than one fluid A channel 22 is combined to create a
single fluid B channel 24. As shown in FIG. 7, three fluid A
channel 22 helixes are combined to create a single fluid B channel
24; however, in other embodiments, 2, 4, 5 or more fluid A channels
can be combined to create a single B channel 24. In the embodiment
of FIG. 7, all three helixes are designed to have the identical
pitch which is equal to or less than the sum of the diameters of
the three tubes. As explained above, if the tube walls are designed
to overlap, the pitch may be less than the sum of the three
diameters by an amount proportional to the wall overlap. In
different embodiments, helical channels can be intertwined in a
single column, either in parallel or in series. Any number of
helical fluid A channels 22 can be combined to create a single
fluid B channel 24.
[0075] FIG. 8 illustrates an example of a helix where the bend
radius of the helical tubes is varied along the coil's length. This
results in a conical shaped coil. In embodiments of heat
exchangers, helixes with varied bend radius along their lengths can
be used. In some embodiments, every other helix has a bend radius
that varies in the opposite direction along its length such that
the resulting cones fit tight together with a helix with a large
base surrounded by helixes with small bases and vice versa.
[0076] As may be appreciated from the specification herein, there
are a number of design choices that may be changed to allow the
design of a heat exchanger to fit a particular set of requirements
without departing from the scope of what is taught herein. This
leads to the ability to modify the overall heat exchanger form to
be curved, conical, and/or include conformal regions to enable
design flexibility when integrating the heat exchanger design into
the engine environment or some other environment.
[0077] There is no limit whatsoever on the type of application the
heat exchangers described herein may be used for. The applications
for the heat exchanger include but are not limited to Air-Oil
cooling such as: main oil circuit, oil cooling; power gearbox (fan
reduction) oil circuit; integrated drive generator (IDG) oil
circuit, oil cooling; variable frequency generator (VFG) oil
circuit, oil cooling; permanent magnet generator (PMG) oil circuit,
oil cooling. The applications for the heat exchanger may also be
used for Air to Air cooling such as: Turbine blade/guide vane
cooling; and buffer seal air cooling.
[0078] While there is no limit on the type of applications the heat
exchangers described herein may be used for, the Applicant designed
the heat exchangers herein to be used in aerospace applications and
believes they are particularly suited for those types of
applications. As one example, the heat exchanger can be integrated
within a Ducted Air Oil Mini System. The ducting within the mini
system connects the heat exchanger to the bypass duct air flow. In
this configuration the air flow is directed through the heat
exchanger prior to being returned to the bypass duct. The air
entering the heat exchanger is used as a heat sink for the hotter
fluid being passed through the fluid channels within the heat
exchanger. In order for the ducting and heat exchanger to be
integrated, the primary header can be designed and manufactured so
that the header fully encompasses the core of the heat exchanger
and becomes the mounting interface between the ducting and the heat
exchanger.
[0079] Some of the advantages of the heat exchanger designs
discussed herein are: 1) A counter flow configuration with novel
thermally active header arrangement; A header that aids the heat
transfer performance by being in the fluid B pathway; 3) 100%
primary heat transfer surface area improving heat transfer
performance per unit volume; 4) Compact fluid A and fluid B
packaging arrangement, which increases the flow area and heat
transfer surface area per unit volume; 5) Helical construction is
structurally robust and offers improved heat transfer over a
straight tube; 6) Can be constructed in a one-piece build, reducing
part count and the secondary machining process or joining methods;
7) Secondary surface area can be added to the fluid A and B
channels to further enhance the heat transfer performance; 8)
Shaped fluid A headers can be used, which could act as turning
features in inclined heat exchanger applications; and 9) Variable
fluid B channel dimensions that match the inlet flow profile can be
used to further improve the efficiency of the system.
* * * * *