U.S. patent application number 15/033361 was filed with the patent office on 2018-07-12 for heat exchange array.
This patent application is currently assigned to Heat Recovery Solutions Limited. The applicant listed for this patent is Heat Recovery Solutions Limited. Invention is credited to Neil Burton, Mark Wickham.
Application Number | 20180195807 15/033361 |
Document ID | / |
Family ID | 49767496 |
Filed Date | 2018-07-12 |
United States Patent
Application |
20180195807 |
Kind Code |
A1 |
Wickham; Mark ; et
al. |
July 12, 2018 |
HEAT EXCHANGE ARRAY
Abstract
A heat exchange array arranged to be used in a heat exchange
unit and further arranged to recover energy from an exhaust gas,
comprising: a first heat exchange tube and a second heat exchange
tube, each arranged to carry a heat exchange medium and further
each comprising a series of external fins; and wherein the first
heat exchange tube comprises a left-handed helically coiled tube
having an first elastic stress, and the second heat exchange coil
comprises a right-handed helically coiled tube having a second
elastic stress, and wherein the first and second heat exchange
tubes are interconnected such that the first elastic stress opposes
the second elastic stress.
Inventors: |
Wickham; Mark; (London,
GB) ; Burton; Neil; (London, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Heat Recovery Solutions Limited |
London |
|
GB |
|
|
Assignee: |
Heat Recovery Solutions
Limited
London
GB
|
Family ID: |
49767496 |
Appl. No.: |
15/033361 |
Filed: |
October 31, 2014 |
PCT Filed: |
October 31, 2014 |
PCT NO: |
PCT/GB2014/053247 |
371 Date: |
April 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21D 53/027 20130101;
B21D 11/06 20130101; F28D 7/022 20130101; F28F 2265/26 20130101;
F28F 9/0243 20130101; F28D 7/024 20130101; F28D 21/0003
20130101 |
International
Class: |
F28D 7/02 20060101
F28D007/02; F28F 9/02 20060101 F28F009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2013 |
GB |
1319284.4 |
Claims
1. A heat exchange array arranged to be used in a heat exchange
unit and further arranged to recover energy from an exhaust gas,
comprising: a first heat exchange tube and a second heat exchange
tube, each arranged to carry a heat exchange medium and further
each comprising a series of external fins; and wherein the first
heat exchange tube comprises a left-handed helically coiled tube
having an first elastic stress, and the second heat exchange coil
comprises a right-handed helically coiled tube having a second
elastic stress, and wherein the first and second heat exchange
tubes are interconnected such that the first elastic stress opposes
the second elastic stress.
2. A heat exchange array according to claim 1 wherein the first and
second heat exchange tubes are interconnected via a support member
arranged to hold the helically coiled tubes in a fixed shape.
3. A heat exchange array according to claim 2 wherein the support
member comprises at least one support bracket defining apertures
arranged to receive each turn of the helically coiled tubes.
4. A heat exchange array according to claim 3 wherein the or each
support member has a length along the circumferential direction of
the coils of the array such that the or each support member
supports a plurality of fins.
5. A heat exchange array according to claim 1, further comprising a
header connected to an end region of the first and an end region of
the second heat exchange tubes, the header arranged to provide an
input or output for a heat exchange medium into the tubes.
6. A heat exchange array according to claim 5 wherein the first and
second heat exchange tubes are connected to the header from
opposing directions.
7. A heat exchange array according to claim 1 wherein the first
heat exchange tube has substantially the same length as the second
heat exchange tube.
8. A heat exchange array according to claim 1 wherein the first
heat exchange tube comprises a left-handed helically coiled tube
having a first pitch and second heat exchange tube comprises a
right-handed helically coiled tube having a second pitch, wherein
the first pitch is not equal to the second pitch.
9. A heat exchange array according to claim 1 wherein the first
heat exchange tube and the second heat exchange tube are arranged
co-axially.
10. A heat exchange array according to claim 1 wherein the first
heat exchange tube surrounds the second heat exchange tube, or vice
versa.
11. A heat exchange array according to claim 10, further comprising
a plurality of first and/or second heat exchange tubes arranged
into a plurality of concentric layers.
12. A heat exchange array according to claim 11 wherein each of the
concentric layers comprises a plurality of left-handed helically
coiled tubes each having the same radius of curvature, or a
plurality of right-handed helically coiled tube tubes each having
the same radius of curvature.
13. A heat exchange array according to claim 11 wherein the
concentric layers alternate between comprising first heat exchange
tubes and comprising second heat exchange tubes.
14. A heat exchange array according to claim 1 comprising an equal
number of first and second heat exchange tubes.
15. A heat exchange array according to claim 1 wherein the first
and second heat exchange tubes are circular in cross section, and
have a diameter of approximately between 21 mm and 168 mm.
16. A heat exchange array according to claim 1 wherein the radius
of curvature of the left-handed helically coiled tube and
right-handed helically coiled tube is between 1 m and 4 m.
17. A heat exchange unit comprising the heat exchange array of
claim 1.
18. A method of manufacturing a heat exchange array comprising a
plurality of heat exchange tubes, which each heat exchange tube
comprising a plurality or external fins, using a rotatable mandrel,
the method comprising the steps of: (a) providing at least one
first support member on a roller portion of the mandrel to receive
a first heat exchange tube; (b) holding one end of a first heat
exchange tube to the first support member; (c) rotating the roller,
whilst feeding the first heat exchange tube along a length of the
roller in a first direction to form the first heat exchange tube
into a first helical coil; (d) attaching a second support member,
arranged to receive a second heat exchange tube, to the first
support member; (e) holding one end of the second heat exchange
tube to the second support member; and (f) rotating the roller in
the same direction, whilst feeding the second heat exchange tube
along a length of the roller in a second direction to form the
second heat exchange tube into a second helical coil, wherein the
first direction is opposite to the second direction such that first
helical coil is of opposite chirality to the second helical
coil.
19. A method of manufacturing a heat exchange array according to
claim 18 wherein the method further comprises repeating steps (a)
to (f) to provide a heat exchange array comprising a plurality of
the first and/or the second heat exchange coils in a plurality of
concentric layers.
20. A method of manufacturing a heat exchange array according to
claim 18 wherein step (b) comprises holding a plurality of first
heat exchange tubes to the first support member so that each
concentric layer comprises a plurality of first heat exchange
coils.
21. A method of manufacturing a heat exchange array according to
claim 18 wherein step (e) comprises holding a plurality of second
heat exchange tubes to the second support member so that each
concentric layer comprises a plurality of second heat exchange
coils.
22. A method of manufacturing a heat exchange array according to
claim 18 in which shims are placed at intermediate positions
between support members as the tubes are wound.
Description
[0001] The present invention relates to a heat exchange array for
use in a heat exchange unit for recovering energy from an exhaust
gas, and a method of manufacture of such a heat exchange array. In
particular, but not exclusively, the present invention relates to
heat arrays suitable for large-scale applications such for heat
exchange units associated with power plants.
[0002] A heat exchange unit is typically implemented to recover
energy from the exhaust gas of a gas turbine used in a power plant,
or the like. The use of such a heat exchange unit can significantly
increase the overall efficiency of the plant as less energy is lost
in the exhaust gas. In order to recover the heat energy, the
exhaust gas is passed through a heat exchange unit comprising a
heat exchange array. Such a heat exchange array comprises a series
of tubes arranged to carry a heat exchange medium (such as water).
The heat exchange medium is heated by the exhaust gas, and can be
used for further processes.
[0003] Typically, a heat exchange array is made up from a series of
concentric coils of tubing, manufactured by winding a straight
length of tube around a rotating body. As the tube is wound into a
coil, stresses are produced within the coil as the metal used to
manufacture the tubing undergoes plastic and elastic deformation.
Once wound into a coil, it can be difficult to keep the tubing
wound in a stable shape as the elastic stress forces act to unwind
the coil. This becomes less of a problem once the coil is installed
into the heat exchange unit, as it is typically fitted to an
external housing that adds strength and stability to the coil and
prevents it from unwinding.
[0004] Completely relieving the stress with in coils is known to be
difficult to achieve. A typical method of reducing stress within a
deformed metal would be to heat the finished structure. Some
embodiments of the heat exchange array in question are of such a
large size that it is not feasible to heat the entire array in an
oven to reduce the elastic stress.
[0005] U.S. Pat. No. 3,083,447 shows a method of bundling plain
coils without external fins.
[0006] In a first aspect, the present invention provides a heat
exchange array for use in a heat exchange unit for recovering
energy from an exhaust gas. Typically the heat exchange array
comprises at least a first heat exchange tube and a second heat
exchange tube, each arranged to carry a heat exchange medium. The
first heat exchange tube may comprise a left-handed helically
coiled tube having a first elastic stress. The second heat exchange
coil may comprise a right-handed helically coiled tube having a
second elastic stress. Typically the first and second heat exchange
tubes are interconnected such that the first elastic stress opposes
the second elastic stress.
[0007] Conveniently, either one, or both, of the first and second
heat exchange tubes comprises external fins. Typically both tubes
would comprise external fins. This increases the surface area of
the heat exchange coils to improve the efficiency of energy
transfer from an exhaust gas to the heat transfer medium within the
tubes.
[0008] The skilled person will understand that many different kinds
of fins could be used. In particular some embodiments may use
circular fins and/or spiral fins may be used.
[0009] In embodiments wherein circular fins are used, each fin is
annular in shape.
[0010] In embodiments wherein spiral fins are used, each fin
spirals around the tube. There may be a single spiral fin on a tube
or multiple spiral fins. In such embodiments, each turn of
substantially 360.degree. of the or each spiral fin may be thought
of as a fin.
[0011] The skilled person will understand that various fin
thicknesses and fin spacings may be used without departing from the
scope of the invention. The spacing of the fins may be such that on
each 5 cm section of tube there are between substantially 1 and 20
fins, or preferably between substantially 5 and 15 fins, or more
preferably substantially 10 fins. Each fin may have a thickness of
between 0.5 and 5 mm, or more preferably between 1 and 3 mm.
[0012] However, the coiling of such finned coils is problematic and
they are harder to bend when compared to plain coils. The increased
difficulty in bending finned coils is due to the nature of the
fins. The skilled person will understand that fins are relatively
thin and may be fragile such that there is a risk of damage to the
fins on bending finned tubes. Further, the fins may be sufficiently
flexible to bend when the finned tube is bent. The skilled person
will understand that any damage or bending of the fins is generally
disfavoured as it can lead to a reduction in the available surface
area for heat transfer and/or to more uneven heat transfer.
[0013] Embodiments that are wound such that the first and second
heat exchange tubes have opposing chirality are believed
advantageous as the elastic stress forces therein will act in
opposite directions. By producing a heat exchange array from
interconnected right-handed and left handed helically coiled heat
exchange tubes, the elastic stress forces are (at least in part)
counterbalanced. Such embodiments should therefore have a reduced
overall resultant stress in the heat exchange array and reduces the
chances of its shape becoming distorted or the coils tending to
un-wind. The use of heat exchange tubes of opposite chirality may
also be advantageous because it may allow the tubes to be more
efficiently packed into a given volume and may allow the turns of
the coils to be distributed more evenly throughout the heat
exchange array.
[0014] Optionally, the first and second heat exchange tubes are
interconnected via a support member, which is typically rigid,
arranged to hold the helically coiled tubes in a fixed shape.
Embodiments having this feature are believed advantageous as the
heat exchange array is helped to stay in a stable shape. The
support member may act to transmit the elastic stress forces
between each coil such that they can be counterbalanced.
[0015] Optionally the support member comprises at least one support
bracket defining apertures each of which is arranged to receive a
turn of the helically coiled tubes. Each turn of the helical tubes
passes through an aperture in the support member to secure it in
position. The support member is typically arranged to hold the
turns of the helical coils in a fixed position relative to each
other such that they maintain their shape.
[0016] In at least some embodiments, the or each support member has
a length (ie a width) along the circumference of the coil supported
thereby such that the or each support bracket supports a plurality
of fins. Such an arrangement facilitates the use of finned tubes as
the load is distributed over a plurality of fins, so reducing the
likelihood and/or extent of bending or damage of fins. A typical
length for a support may be roughly between 20 and 100 mm, roughly
between 40 and 80 mm, or more preferably around 60 mm. The number
of fins supported by each support may be roughly between 3 and 20,
roughly between 5 and 15, or more preferably around 12.
[0017] In addition to providing support for the coils in use, the
support members may also be used in assembling the coils, as is
explained in more detail below.
[0018] Conveniently, the heat exchange array further comprises a
header connected to an end region of the first and an end region of
the second heat exchange tubes, the header arranged to provide an
input and/or output for a heat exchange medium into the tubes. A
single connection to the header may therefore be used to input
and/or output the heat exchange medium from all of the coils at the
same time.
[0019] In some embodiments, the first and second heat exchange
tubes are connected to the header from different directions, which
may typically be from different sides of an axis of the header and
in some embodiments may be opposing directions. Such embodiments
allow easier access to joints between the heat exchange tubes and
the header so that they can be more easily bonded together such as
by welding, brazing, or the like. By connecting to the header from
opposite directions the elastic stress forces acting on the header
are in opposing directions may, at least partly, be cancelled
out.
[0020] In additional or alternative embodiments, the first heat
exchange tube has substantially the same length as the second heat
exchange tube. Such an arrangement means that the heat exchange
medium, travelling at a given speed, spends the same amount of time
in each of the heat exchange tubes and so is imparted with an equal
amount of heat energy.
[0021] Optionally, the first heat exchange tube comprises a
left-handed helically coiled tube having a first pitch and second
heat exchange tube comprises a right-handed helically coiled tube
having a second pitch, wherein the first pitch is not equal to the
second pitch. By altering the pitch of the coils they can have the
substantially the same length whilst also ending at the same
position. By increasing the pitch a helical coil with larger radius
of curvature can be made the same length as a helical coil of
smaller radius of curvature. By all ending at the same position,
the first and second heat exchange tubes are more easily attached
to the header.
[0022] In some embodiments the first heat exchange tube and the
second heat exchange tube are arranged co-axially and such
embodiments provide a compact arrangement of coils.
[0023] Optionally, the first heat exchange tube surrounds the
second heat exchange tube, or vice versa (i.e. the radius of
curvature of the left-handed helically coiled tube is greater than
the radius of curvature of the left-handed helically coiled tube,
or vice versa). This allows first and second heat exchange tubes to
be formed into concentric layers of helical coils.
[0024] Conveniently, the heat exchange array comprises a plurality
of first and/or second heat exchange tubes arranged into a
plurality of concentric layers. This compact formation gives a
large number of coils in a small space and so improves the energy
transfer to the heat exchange medium.
[0025] Optionally, each of the concentric layers comprises a
plurality of left-handed helically coiled tubes each having the
same radius of curvature, or a plurality of right-handed helically
coiled tube tubes each having the same radius of curvature. This
increases the number of each type of coil in each layer thus
producing a compact formation of coils.
[0026] In some embodiments, the concentric layers alternate between
comprising first heat exchange tubes and comprising second heat
exchange tubes. By alternating between left and right handed
helical coils, the elastic stresses are more evenly balanced
throughout the heat exchange array and its shape is less likely to
be distorted.
[0027] Optionally, the heat exchange array comprises an equal
number of first and second heat exchange tubes. By having an equal
number of left and right handed helical coils, there may be more of
a balance of stress forces acting in each of the opposing
directions which may effectively balancing out the overall
forces.
[0028] Optionally, the first and second heat exchange tubes are
circular in cross section, and have a diameter of approximately 21
mm and 168 mm. Such diameters are suited to use for heat
reclamation from an exhaust gas of a power station turbine. For
such large scale applications the elastic stress created in winding
such large diameter tubes is particularly large and so it is
advantages to balance out the stress forces using coils of opposite
chirality.
[0029] Optionally, the radius of the left-handed helically coiled
tube and right-handed helically coiled tube is between
substantially 1 m and 4 m. Such sized coils are suitable for use in
a heat exchange unit for a power station or similar large scale
application.
[0030] In a second aspect, the present invention provides a heat
exchange unit comprising the heat exchange array described above.
Such a heat exchange unit is suitable for use in heat recovery from
gas exhaust from a power plant from example.
[0031] In a third aspect, the present invention provides a method
of manufacturing a heat exchange array comprising a plurality of
heat exchange tubes using a rotatable mandrel, the method
comprising one or more of the following steps: [0032] (a) providing
at least one first support member on a roller portion of the
mandrel to receive a first heat exchange tube; [0033] (b) holding
one end of a first heat exchange tube to the first support member;
[0034] (c) rotating the roller, whilst feeding the first heat
exchange tube along a length of the roller in a first direction to
form the first heat exchange tube into a first helical coil; [0035]
(d) attaching a second support member, arranged to receive a second
heat exchange tube, to the first support member; [0036] (e) holding
one end of the second heat exchange tube to the second support
member; and [0037] (f) rotating the roller in the same direction,
whilst feeding the second heat exchange tube along a length of the
roller in a second direction to form the second heat exchange tube
into a second helical coil, wherein the first direction is opposite
to the second direction such that first helical coil is of opposite
chirality to the second helical coil.
[0038] Such a method produces an array of heat exchange coils
comprising a heat exchange coil that has a right-handed helix and a
heat exchange coil that has a left-handed helix.
[0039] As described above, the elastic stress forces in such an
arrangement of coils will be cancelled out to help stabilise the
shape of the coils.
[0040] Optionally, the method further comprises repeating steps (a)
to (f) to provide a heat exchange array comprising a plurality of
the first and/or the second heat exchange coils in a plurality of
concentric layers. This builds the heat exchange array into a
series of concentric layers.
[0041] Optionally, step (b) comprises holding a plurality of first
heat exchange tubes to the first support member so that each
concentric layer comprises a plurality of first heat exchange
coils. This adds additional tubes of the same helically chirality
to each layer.
[0042] Conveniently, steps (c) and (f) comprise applying a pulling
force to the heat exchange tubes in a direction away from the
roller as the roller is rotated. Advantageously, the pulling force
helps to ensure that the heat exchange tubes are coiled under
tension. The skilled person will understand that, if the heat
exchange tubes were wound on loosely, the heat exchange tubes could
spring off the support members.
[0043] Conveniently, step (e) comprises holding a plurality of
second heat exchange tubes to the second support member so that
each concentric layer comprises a plurality of second heat exchange
coils. This adds additional tubes of the same helical chirality to
each layer.
[0044] In some embodiments, the or each heat exchange tube is a
finned tube. Preferably, some or all of the support members used
have a width sufficient to encompass a plurality of fins on the
finned tube. Advantageously, this distributes the load over the
plurality of fins, so reducing the force on each fin and reducing
the likelihood and/or extent of bending or damage of fins.
[0045] Conveniently, one or more shims are inserted between the
support members during steps (a) to (f). In some embodiments, the
shims may be positioned parallel to the support members.
[0046] The height of each shim is preferably selected such that the
heat exchange tube is supported at the same radius from the coil
axis by the shim as by the support members. The height of each shim
typically extends between the outer edge of the fins of one heat
exchange tube to the inner edge of the fins of the next heat
exchange tube. The shims are typically located between the
concentric layers of coils.
[0047] Advantageously, use of the shims helps to ensure that the
heat exchange tubes do not kink at the support members and that the
coils are substantially circular in cross-section/that the diameter
of the coil is constant.
[0048] Typically, between 1 and 10 and more preferably from 3 to 4
shims are used per support member. The width of the shims may be
between 20 and 100 mm, between 40 and 80 mm, or more preferably
around 60 mm.
[0049] Preferably, the shims are removed once the coil is
completed.
[0050] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
[0051] FIG. 1 shows a perspective view of a heat exchange array
according to an embodiment of the present invention;
[0052] FIG. 1A shows expanded views of region A in FIG. 1;
[0053] FIG. 1B shows an expanded view of region B in Figure;
[0054] FIG. 2 shows a cross-section view through the heat exchange
array shown in FIG. 1;
[0055] FIG. 3 shows cross-section view through a rotatable mandrel
used to manufacture the heat exchange array shown in FIG. 2, the
heat exchange array being at a first stage of production;
[0056] FIG. 4 shows cross-section view through a rotatable mandrel
used to manufacture the heat exchange array shown in FIG. 2, the
heat exchange array being at a second stage of production;
[0057] FIG. 5 shows a perspective view of a rotatable mandrel used
to manufacture the heat exchange array shown in FIG. 2, the heat
exchange array being at a third stage of production;
[0058] FIG. 6 shows a perspective view of a prior art heat exchange
array;
[0059] FIG. 7 shows a cross section view of the prior art heat
exchange array shown in FIG. 6;
[0060] FIG. 8a shows a segment of a tube with external fins;
and
[0061] FIG. 8b shows a cross-sectional view of a segment of a tube
with external fins.
[0062] A typical prior art heat exchange array 600 is shown in FIG.
6. The heat exchange array comprises a plurality of helically
coiled tubes, the first of which is labelled 602. Each of the coils
runs from an input header 604 to an output header 606. All of the
coils of the heat exchange array 600 have the same chirality, and
so are attached to each of the input header and output header from
the same direction. The stress forces within the coils will
therefore combine such that they may cause a distortion in the
shape of the heat exchange array 600.
[0063] A cross sectional view of the prior art heat exchange array
600 is shown in FIG. 7. This view shows how helical coils of the
same chirality are also difficult to pack efficiently, and cannot
be easily distributed uniformly throughout the heat exchange
array.
[0064] FIG. 1 shows a heat exchange array 100 according to an
embodiment of the present invention. The heat exchange array 100
comprises first heat exchange tubes 102 and second heat exchange
tubes 104. In the embodiment shown in FIGS. 1, 1A, 1B and 2, there
are eight first heat exchange tubes 102a, 102b, 102c, 102d, 102e,
102d, 102e, 102f and six second heat exchange tubes 104a, 104b,
104c, 104d, 104e, 104f. Each of the heat exchange tubes is arranged
to carry a heat exchange medium. The heat exchange medium may be
water, or any other suitable fluid such as steam, oil, gas. The
first heat exchange tubes 102 each comprise a left-handed helically
coiled tube. The second heat exchange tubes 104 each comprise a
right-handed helically coiled tube. A left-handed helix is defined
as a helix where when viewed along the helix's axis, a clockwise
screwing motion moves the helix towards the observer. A
right-handed helix is defined as a helix where when viewed along
the helix's axis, a clockwise screwing motion moves the helix away
the observer.
[0065] The first 102 and second 104 heat exchange tubes are
manufactured by winding a straight length of tubing into a helical
coil. As the tubing is wound an elastic stress is generated within
each tube that acts to return the tube to its original shape. The
elastic stress generated within the first heat exchange tubes 102
will act in an opposite direction to that found in the second heat
exchange coils 104 due to the tubes being wound into left-handed
and right-handed helixes. The first 102 and second 104 heat
exchange tubes are interconnected such that the elastic stress in
the first heat exchange tubes 102 opposes the elastic stress in the
second heat exchange tubes 104. The elastic stresses are therefore
balanced and at least partly cancel out, thus reducing the overall
stress within the heat exchange array 100.
[0066] The first heat exchange coils 102 and the second heat
exchange coils 104 are arranged coaxially such that the heat
exchange array 100 is made up of layers of concentric helical
coils. Each layer of the heat exchange array 100 is made up of
first heat exchange tubes 102 (having a left-handed helix) or
second heat exchange tubes 104 (each having a right-handed helix).
Each layer of heat exchange tubes surrounds the layer before--i.e.
the radius of curvature of the helical coils of each layer
increases further from the central axis). The composition of each
layer alternates between being made up only of first heat exchange
tubes 102 and only of second heat exchange tubes 104. In the
embodiment of FIGS. 1, 1A, 1B and 2, the inner most layer comprises
a pair of left-handed helical coils 102a, 102b. The next layer
comprises a pair of right-handed helical coils 104a, 104b. The
third layer comprises a pair of left-handed coils 102c, 102d and so
on until the seventh layer, which comprises a pair of left-handed
coils 102g, 102h. Hence there are four layers of first heat
exchange tubes 102 and three layers of second heat exchange tubes
104. In other embodiments, there may be an equal number of layers
of first heat exchange tubes 102 and second heat exchange tubes
104.
[0067] In other embodiments, each layer may comprise only one first
102 or second 104 heat exchange tube. In other embodiments, each
layer may comprise any other suitable number of first 102 or second
104 heat exchange tubes depending on the size requirement of the
heat exchange array. For example, each layer may comprise 3, 4, 5,
6 or more first or second heat exchange tubes.
[0068] The first 102 and second heat 104 exchange tubes are
interconnected via support members 106, which in this embodiment
are rigid, arranged to hold the helically coiled tubes 102, 104 in
a fixed shape. In the embodiment shown in FIGS. 1, 1A, 1B and 2
there are six support members 106a, 106b, 106c, 106d, 106e, 106f.
In other embodiments there may be any other suitable number of
support members.
[0069] The support members 106 each comprise a support bracket
defining apertures arranged to receive each turn of the helically
coiled tubes 102,104. The support members 106 are arranged to keep
the heat exchange tubes 102, 104 in their coiled up shape.
[0070] In embodiments wherein the heat exchange tubes have fins,
the support members 106 have a width sufficient to support a
plurality of fins.
[0071] The heat exchange tubes are mechanically locked to the
support members to secure them in position perhaps via a tang
dependent from the support members 106. In some embodiments, the
heat exchange tubes may have a tight friction fit with the
apertures of the support member to secure them in place. As the
tubes are fixed to the support members they may be more effectively
interconnected such that the elastic stress forces can be
counterbalanced. The support members may comprise two parts, each
having a series of indentations arranged to receive the turns of
the coils as they are wound. When the two parts are attached
together the indentations are closed off to form apertures to fix
the coils in place. Thus, each indentation may comprise a
complementarily shaped recess arranged to receive a portion of a
heat exchange tube.
[0072] The heat exchange array 100 further comprises an input
header 108 and an output header 110. The headers 108, 110 are
arranged to provide an input or output for a heat exchange medium
into the tubes. The input header 108 is connected to a first end of
each of the first 102 and second 104 heat exchange tubes. The
output header 110 is connected to a second end of each of the first
102 and second 104 heat exchange tubes. The heat exchange medium
can therefore flow into one end of the tubes via the input header,
through the tubes such that heat exchange can occur, and then exit
the tubes via the output header.
[0073] As can be seen more clearly in FIG. 1b, each of the first
heat exchange tubes 102 are connected to the output header 110 from
an opposite direction (ie from either side of a vertical, as viewed
in the figure, axis through the header) to each of the second heat
exchange tubes 104. Similarly, each of the second heat exchange
tubes 104 are connected to the input header 108 from an opposite
direction (ie from either side of a vertical, as viewed in the
figure, axis through the header) to each of the first heat exchange
tubes 102. This improves access to the heat exchange tubes and
allows them to be more easily welded, or otherwise attached, onto
the input 108 and output 110 headers. Attaching the heat exchange
tubes from opposite directions may also allow the elastic stresses
within the first heat exchange tubes 102 acting on the headers 108,
110 to oppose the elastic stresses within the second heat exchange
tubes 104.
[0074] Each of the first heat exchange tubes 102 has substantially
the same length as each of the second heat exchange tubes 104. This
means that the heat exchange medium travels the same distance in
each of the heat exchange tubes, and therefore spends an equal
amount of time in each of the heat exchange tubes if the heat
exchange medium travels at the same speed. As a result the energy
imparted to the heat exchange medium is substantially the same for
each of the heat exchange tubes.
[0075] In order to allow the heat exchange tubes 102, 104 to have
substantially the same length, the first heat exchange tube 102
comprise a left-handed helically coiled tube having a pitch that is
different to that of the second heat exchange tube 104. The pitch
of the helical coils increases in each consecutive layer moving
outward from the central axis. The increasing helical radius of
curvature in coils further from the central axis is therefore
counter balanced by a change in pitch reducing the number of turns
required in the coil.
[0076] In some embodiments (not shown in FIGS. 1 and 2) either one,
or both, of the first 102 and second 104 heat exchange tubes
comprise external fins or other similar protrusions. Typically both
heat exchange tubs comprise external fins. These increase the
surface area of heat exchange tubes in order to improve the heat
exchange efficiency. In some embodiments the fins or protrusions
may also engage with the support member (i.e. are disposed on
either side of the support member at the position where it is
connect to the heat exchange tube) to help keep the tube fixed
relative to the support member.
[0077] FIGS. 8a and 8b show schematics of segments 800a, 800b of
tubes 102 and/or 104 in an embodiment wherein one or both of the
tubes comprise external fins 802a, 802b. In the embodiment shown in
FIGS. 8a and 8b the external fins 802a, 802b are spiral fins. In
the embodiment shown, the turns of the external fins 802a, 802b are
equi-spaced along the length of the tube. The individual turns of
the spiral fin are referred to as external fins below for
simplicity. The skilled person will understand that equi-spacing of
the external fins is not a necessary feature, but may be preferable
for even heat distribution in some embodiments.
[0078] In the embodiment shown in FIGS. 8a and 8b, the external
fins 802a, 802b are substantially parallel to each other and
substantially perpendicular to the tube surface. The skilled person
will understand that, as the tubes 102, 104 are coiled, the tube
surfaces bend. The angle between the tube surface and the external
fins 802a, 802b may change as the tubes are coiled such that
adjacent external fins may no longer be parallel to each other and
may even touch within the inner circumference of the coiled tube
102, 104. The skilled person will understand that the extent of the
deviation of positioning and angle from that shown in FIGS. 8a and
8b is dependent on the radius of curvature of the tubes 102, 104
once coiled, the diameter of the tubes 102,104 and the depth of the
external fin 802a, 802b.
[0079] In some embodiments, the support members 106 are
sufficiently wide (ie have a sufficient width) to support more than
one external fin 802a, 802b on each turn of the helically coiled
tubes 102,104 received.
[0080] In the embodiment shown in FIGS. 1, 1A, 1B and 2 the first
102 and second 104 heat exchange tubes are circular in cross
section, and have a diameter of between approximately 21.3 mm and
168.3 mm. The radius of curvature of the left-handed helically
coiled tube and right-handed helically coiled tube is between
roughly 1 m and 4 m.
[0081] In the embodiment shown in FIGS. 1, 1A, 1B and 2 the
external fins 802a, 802b of the first 102 and second 104 heat
exchange tubes have heights of between approximately 10 mm and 240
mm, and more preferably between 20 mm and 50 mm.
[0082] The heat exchange array 100 may be assembled into a heat
exchange unit by enclosing the heat exchange tubes in a duct
through which exhaust gas is passed.
[0083] FIGS. 3 and 4 show a method of producing the heat exchange
array 100 using a rotating mandrel 200. The mandrel 200 comprises a
drive means 202 which is arranged to rotate a roller portion 204.
The rotating portion is substantially cylindrical in shape and is
rotated by an axle 205 about central axis XX shown in FIGS. 3 and
4. Thus, it will be appreciate that the line XX lies substantially
along an axial direction of the array that is formed by the method.
The axle 205 is driven at one end by the drive means 202 and
supported at the other by a supporting means 206. Coil support
frame 208 is provided at the ends of the rolling portion 204 to
keep the heat exchange tubes in place.
[0084] The method of producing the heat exchange coil comprises the
following steps:
(a) A first support member 212 is attached to the roller portion
204, aligned with its length parallel to the axis of rotation XX.
In other embodiments there may be more than one first support
member, arranged around the circumference of the roller portion
204. In the embodiment being described, there are 6 support members
but in other embodiments there may be typically 3, 4, 5, 7, 8, 10,
12, support members.
[0085] The first support member 212 is arranged to receive the
first heat exchange tube 102 as it is wound onto the roller portion
204. The first support member 212 comprises a series of grooves or
indentations arranged to receive each turn of the first heat
exchange tube 102.
(b) One end of the first heat exchange tube 102 is held to the
first support member 212 towards a first end 210 of the roller
portion 204. (c) As the roller portion 204 is rotated, the first
heat exchange tube 102 is fed towards the roller portion 204 whilst
simultaneously moving the feed point (the point at which it is held
to the support member) along the length of the roller 204 in a
first direction (shown by the arrow marked Y in FIG. 3) parallel to
the central axis XX of rotation. This winds the first heat exchange
tube into a helical coil around the roller portion 204, with each
turn of the coil kept in place by being received by the
indentations of the first support member 212. (d) Once the first
heat exchange tube 102 has been wound into a helical coil, a second
support member 213 is attached the first support member 212,
arranged to receive a second heat exchange tube 104. The first 212
and second 213 support members are fixed together to close the
indentations of the first support member 212 and secure the first
heat exchange tube 102 in place. The second support member 213 is
arranged to receive the second heat exchange tube 104 as it is
wound onto the roller portion 204. The second support 213 member
comprises a series of grooves or indentations arranged to receive
each turn of the second heat exchange tube 104. (e) One end of the
second heat exchange tube 104 is held to the second support member
213 towards a second end 211 of the roller portion 204. The first
end 210 is opposite to the first end 211, i.e. at distal ends of
the roller portion 204. (f) Whilst rotating the roller in the same
direction, the second heat exchange tube 104 is fed towards the
roller portion 204 and the feed point simultaneously moved along
the length of the roller in a second direction parallel to the axis
of rotation (shown by the arrow marked Z in FIG. 4). This winds the
second heat exchange tube 104 into a helical coil around the roller
portion 204, with each turn of the coil kept in place by the
indentations of the second support member 213.
[0086] Conveniently, shims are periodically placed upon the inner
heat exchange tube is a outer heat exchange tube is wound
therearound. Typically, the shim is placed at intermediate
positions between the support members and helps to ensure that the
tubes bend between the support members, and take a curved shape, as
the mandrel 200 is rotated. The shims may or may not be removed
from the after the heat exchange array has been fabricated.
[0087] As the first direction (arrow Y) is opposite to the second
direction (arrow Z) first heat exchange tube 102 is wound into a
helical coil within an opposite chirality to that of the second
heat exchange tube 104 (i.e. one forms a left-handed helix and the
other a right-handed helix).
[0088] Steps (a) to (f) above may be repeated to build up a heat
exchange array comprising a plurality of the first 102 and/or the
second 104 heat exchange coils in a plurality of concentric layers
as shown in FIG. 5. It can be seen with reference to FIG. 5 that
each of the support member has a length along the circumferential
length of a coil such that the or each support member supports a
plurality of fins.
[0089] FIG. 5 also has labelled for ease of reference two axes: the
axial direction 500 of the coils and the array; and the radial
direction 502 of the coils and the array. When referring to the
support members and the shims, it is convenient to think of the
height thereof as being in the radial direction 502 and the width
being substantially in the circumferential direction of a coil
supported by the shim/support member.
[0090] In step (b) a plurality of first heat exchange tubes 102 may
be held to the first support member 212 so that each concentric
layer comprises a plurality of first heat exchange coils 102.
Similarly, in step (e), a plurality of second heat exchange tubes
104 may be held to the second support member 213 so that each
concentric layer comprises a plurality of first heat exchange coils
104.
[0091] During steps (c) and (f), a pulling force away from the
roller portion 204 is applied to the heat exchange tubes 102, 104.
The pulling force helps to ensure that the heat exchange tubes 102,
104 are coiled tightly. If the heat exchange tubes 102, 104 are
coiled too loosely, the coil may spring away from the support
members 212 and not retain the desired shape.
[0092] In order to control the pitch of each of the helical coils,
the spacing between the indentations of the support members may be
adjusted. By increasing the spacing of the indentations along the
length of the rotating portion 204, the pitch of the helical coil
wound onto it will be increased.
[0093] Various modifications will be apparent to the skilled
person. For example, the first direction Y and the second direction
Z could be the same i.e. the first and second heat exchange tubes
are wound onto the roller portion 204 from the same end. In this
case the direction of rotation of the roller portion 204 can be
reversed between each layer to produce helical coils with opposite
chirality.
* * * * *