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Title:
METHOD AND APPARATUS FOR PREFORMING A TUBE AND FOR THE MANUFACTURING OF COIL-ON-TUBE HEAT-EXCHANGERS THEREFROM
Document Type and Number:
WIPO Patent Application WO/2016/197226
Kind Code:
A1
Abstract:
A method for manufacturing a coil-on-tube heat exchanger is provided. The method comprises the steps of preforming a coil tube into a preformed coil tube, having an ovoid cross-section. The method further comprises exerting tension forces on the preformed coil tube and guiding the preformed coil tube to a central tube that is to be rotated and translated relative to the preformed coil tube and on which the preformed coil tube is to be wound. The winding of the preformed coil tube further deforms the preformed coil tube into a wound coil tube having an oval cross-section. An apparatus for manufacturing said coil-on-tube heat exchanger is further provided. A radially expandable shaft assembly for rotating the central tube that can be included in the apparatus is also described.

Inventors:
BARRIÈRE-MORIN BENOIT (CA)
FENG ZHENGKUN (CA)
CHAMPLIAUD HENRI (CA)
MICHEL FRANÇOIS (CA)
Application Number:
PCT/CA2015/050529
Publication Date:
December 15, 2016
Filing Date:
June 09, 2015
Export Citation:
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Assignee:
GROUPE FIMIRO INC (CA)
International Classes:
B21D53/08; B21D9/10; F28D7/02; F28F1/02
Foreign References:
US5099574A1992-03-31
US7322404B22008-01-29
US5238058A1993-08-24
US4154412A1979-05-15
JP2014005973A2014-01-16
JP2015045472A2015-03-12
EP2372284A12011-10-05
US5033544A1991-07-23
Attorney, Agent or Firm:
ROBIC LLP (1001 Square-Victoria Bloc E - 8th Floo, Montréal Québec H2Z 2B7, CA)
Download PDF:
Claims:
CLAIMS

1. A method of manufacturing a coil-on-tube heat exchanger, comprising the steps of:

a) providing a central tube having a longitudinal axis, first and second extremities, and inner and outer surfaces, and a coil tube having a longitudinal axis;

b) feeding the coil tube toward the central tube while shaping the coil tube into a preformed coil tube having an ovoid cross-section, the preformed coil tube comprising a major axis extending along a largest diameter of the ovoid cross-section;

c) applying a predetermined tension force to the preformed coil tube; d) orienting the preformed coil tube relative to the central tube, such that the preformed coil tube is fed tangentially to the outer surface of the central tube, such that respective longitudinal axes of the central tube and of the preformed coil tube are substantially perpendicular, and such that a first plane comprising said major axis and extending longitudinally through the preformed coil tube is substantially perpendicular to a second plane tangent to the outer surface of the central tube;

e) securing the preformed coil tube near the first extremity of the central tube;

f) rotating and translating one of the central tube and the preformed coil tube relative to the other of the central tube and the preformed coil tube in the direction of the longitudinal axis of the central tube, thereby helically winding the preformed coil tube around the central tube and causing a bottom portion of the preformed coil tube to flatten against the outer surface of the central tube;

g) stopping the rotation and translation of the central tube after a predetermined number of rotations; and h) securing the preformed coil tube to the central tube near the second extremity thereof.

2. The method as defined in claim 1 , wherein in step a), the coil tube is a circular tube having a diameter of about 0.25 inches (6.4 mm) to about 1.5 inches (38 mm).

3. The method as defined in claim 1 or 2, wherein in step a), the central tube is a circular tube having a diameter of about 2 inches (50.8 mm) to about 6 inches (152.4 mm).

4. The method as defined in any one of claims 1 to 3, wherein in step b), shaping the coil tube comprises an initial step of preforming the coil tube using rolling mills.

5. The method as defined in any one of claims 1 to 4, wherein in step b), shaping the coil tube is performed using a forming die, the forming die having a body provided with a preforming channel defined by an inner sidewall, said inner sidewall transitioning smoothly from a first cross- section to a second cross-section having an ovoid shape.

6. The method as defined in any one of claims 1 to 5, wherein in step b), the ovoid cross-section of the preformed coil tube has a shape defined by four adjacent arc segments comprising a first arc segment and a second arc segment defining left and right sides of the shape, respectively; a third arc segment defining a lower side of the shape, and a fourth arc segment defining an upper side of the shape, and wherein the first and second arc segments both have a radius R1 , the third arc segment has a radius R2 and the fourth arc segment has a radius R3; and wherein a ratio R3/R2 is greater than 1 and inferior or equal to 3, and R1 is greater than both R2 and R3.

7. The method as defined in any one of claims 1 to 6, wherein R1 is between about 0.7 inches (17.8 mm) to about 4 inches (101.6 mm); and R2 is between about 0.05 inches (1.27 mm) to about 0.45 inches (11.4 mm).

8. The method as defined in any one of claims 1 to 7, wherein in step c), the predetermined tension force is maintained between 1575 N and 7875 N.

9. The method as defined in any one of claims 1 to 8, wherein step c) is performed using a clamping die, the clamping die having a body provided with a clamping channel shaped and sized for receiving the preformed coil tube, the body having a slot extending therealong for adjusting the predetermined tension force applied on the preformed coil tube.

10. The method as defined in any one of claims 1 to 9, wherein in step d), the first plane of the preformed coil tube and the second plane tangent to the outer surface of the central tube form an angle between 80 and 100 degrees.

11. The method as defined in any one of claims 1 to 10, wherein in step d), the longitudinal axis of the central tube and the longitudinal axis of the preformed coil tube form an angle between 80 and 100 degrees.

12. The method as defined in any one of claims 1 to 11 , wherein in step f), winding the preformed coil tube around the central tube causes the top portion of the preformed coil tube to collapse toward the central tube in a direction substantially parallel to the major axis of the preformed coil tube.

13. The method as defined in any one of claims 1 to 12, wherein in step f), the bottom portion of the preformed coil tube flattens against the outer surface of the central tube, deforming the ovoid cross-section into a substantially oval cross-section.

14. The method as defined in any one of claims 1 to 13, wherein step f) comprises a step of inserting a radially expandable shaft assembly in the central tube and radially expanding the expandable shaft assembly to grip the inner surface of the central tube, and wherein rotating the central tube is performed by rotating the radially expandable shaft assembly.

15. The method as defined in any one of claims 1 to 14, wherein steps e) and h) comprise at least one of brazing and welding the preformed coil tube to the central tube.

16. The method as defined in any one of claims 1 to 15, comprising a step of cutting the preformed coil tube near the first and second extremities of the central tube.

17. An apparatus for manufacturing a coil-on-tube heat exchanger formed by a coil tube helically wound around a central tube, the apparatus comprising:

- a first assembly for shaping the coil tube having a first cross-section into a preformed coil tube having a second ovoid cross-section, for applying a predetermined tension force to the preformed coil tube and for orienting the preformed coil tube relative to the central tube;

- a rotating assembly to rotate the central tube; and

- a translating assembly to translate the central tube in the direction of the longitudinal axis of the central tube after exiting the assembly, the translating assembly serving to helically wind the preformed coil tube around the central tube.

18. The apparatus according to claim 17, wherein said first assembly comprises:

- a preforming section comprising a preforming channel defined by an inner sidewall transitioning smoothly from a first cross-section to a second ovoid cross-section, a major axis of said ovoid cross-section extending along a largest diameter of the ovoid cross-section;

- a clamping section comprising a mean to exert the predetermined tension force on the preformed coil tube; and

- a guiding section comprising a mean to orient the preformed coil tube relative to the central tube such that the preformed coil tube is directed tangentially to an outer surface of the central tube, such that respective longitudinal axes of the central tube and of the preformed coil tube are substantially perpendicular, and such that a first plane comprising the major axis of the ovoid cross-section of the guiding section is substantially perpendicular to a second plane tangent to the outer surface of the central tube.

19. The apparatus according to claim 18, wherein the preforming section comprises a preforming die having an elongated body provided with an entrance and an exit, the preforming channel extending from the entrance to the exit of the preforming die.

20. The apparatus according to claim 19, wherein the exit of the preforming die has a shape defined by four adjacent arc segments, comprising a first arc segment and a second arc segment, defining left and right sides of the shape, respectively; a third arc segment defining a lower side of the shape; and a fourth arc segment defining an upper side of the shape; and wherein the first and second arc segments have a radius R1 , the third arc segment has a radius R2 and the fourth arc segment has a radius R3; and wherein a ratio R3/R2 is greater than 1 and inferior or equal to 3 and R1 is greater than both R2 and R3.

21. The apparatus according to any one of claims 18 to 20, wherein the preforming section comprises rolling mills located upstream from the preforming die, the rolling mills being sized and configured to transform a shape of the coil tube from a circular cross-section to an elongated or oblong cross-section.

22. The apparatus according to any one of claims 18 to 21 , wherein the clamping section comprises a clamping die having a body provided with an entrance, an exit, and a clamping channel extending from the entrance to the exit, said clamping channel having a cross-section substantially corresponding to the second ovoid cross-section of the preforming section.

23. The apparatus according to claim 22, wherein the body of the clamping die comprises a slot extending therealong, the slot having a width, a length and a depth sized and configured to set the predetermined tension force exerted on the preformed coil tube.

24. The apparatus according to any one of claims 18 to 23, wherein the guiding section comprises a guiding ring having a body provided with an entrance, an exit and a guiding channel extending from the entrance to the exit of the guiding ring, said guiding channel having a longitudinal axis and a cross-section substantially corresponding to the second ovoid cross- section of preforming section, the guiding ring being rotatable at least about its longitudinal axis to orient the preformed coil tube relative to the central tube.

25. The apparatus according to any one of claims 18 to 24, wherein the rotating assembly comprises a radially expandable shaft assembly including:

- a shaft insertable into the central tube;

- at least one resilient ring engaged on the shaft and being radially expandable between a first configuration in which the at least one resilient ring has a diameter smaller than an inner diameter of the central tube, and a second configuration in which the at least one resilient ring has a diameter matching the inner diameter of central tube, thereby gripping an inner surface of the central tube; and

- a compressing and decompressing mechanism cooperating with the at least one resilient ring to expand or contract the at least one resilient ring between the first and second configurations.

26. The apparatus according to claim 25, wherein the at least one resilient ring comprises a plurality of resilient rings axially spaced apart from one another along the shaft.

27. The apparatus according to claim 25 or 26, wherein the compressing and decompressing mechanism comprises at least one nut threadably connected to one end of the shaft, whereby turning the nut on the shaft increases or decreases compressive forces applied axially on the at least one resilient ring.

28. The apparatus according to any one of claims 25 to 27, wherein the compressing and decompressing mechanism comprises at least one pair of rigid washers located on each side of said at least one the resilient ring.

29. The apparatus according to any one of claims 25 to 28, wherein the compressing and decompressing mechanism comprises at least one spacing collar slidably engaged on the shaft.

30. The apparatus accordingly to any one of claims 17 to 29, wherein the translating assembly comprises a motor translating the central tube or the preformed coil tube.

Description:
METHOD AND APPARATUS FOR PREFORMING A TUBE AND FOR THE MANUFACTURING OF COIL-ON-TUBE HEAT-EXCHANGERS THEREFROM

FIELD OF THE INVENTION

[001] The technical field relates to the manufacturing of coil-on-tube heat exchangers or similar devices, and to an apparatus for preforming a tube for the manufacturing of coil-on-tube heat exchangers or similar devices.

BACKGROUND

[002] Heat exchangers can be made of a central tube, allowing passage of a first medium, and of a coil tube wound around the central tube, allowing passage of a second medium. Heat can therefore be exchanged from the first medium to the second medium as they are respectively in contact with the walls of the central tube and of the coil of tube, thereby conducting heat from the first medium to the second medium.

[003] As this configuration is better suited for gaseous or liquid media, early variants of such coil-on-tube heat exchangers found use in recovering heat to provide hot water for domestic use. These units tended to be relatively primitive arrangements of metal tubing wrapped around a chimney. A modern example of a coil-on-tube heat exchanger is described in US 2003/0056944.

[004] With rising energy costs and an increased awareness of the need for efficient energy use, coil-on-tube heat exchangers have increasingly seen use in recovering heat from waste water streams in industrial, commercial and domestic applications. This type of heat exchanger provides inherent advantages in such applications. As they are generally formed of a coil (or coils) of tube wound around a larger tube or pipe, they provide a double walled design that reduces the risk of contamination between fluid streams, which is an important consideration when transferring heat from waste water to fresh potable water. [005] A further advantage presents itself when the heat exchanger is positioned in a vertical orientation, with the central pipe forming part of a vertical section of the drain pipe or stack. As a result of surface tension of water, waste water will tend to form a thin film and cling to the inner surface of the drain pipe as it flows downward under the force of gravity. This allows for a highly effective recovery of heat from the waste water without the need to slow or restrict its flow, thus avoiding clogging problems that other types of heat exchangers can suffer from in similar applications.

[006] As with any heat exchanger, increasing the heat transfer area leads to more efficient performance. This is generally achieved by ensuring proper contact between the tubes containing the first and second media, by means of a sufficiently tight fit, and seeking to provide the largest possible contact surface between the coil of tube and the central tube, in the case of a coil-on-tube heat exchanger.

[007] One of the first products to see widespread use in waste water heat recovery applications, generally sold under the trade name GFX™, consists of copper tubing wrapped in a helical coil fashion around a copper pipe selected to match standard drainpipe and fresh water plumbing sizes. The copper tubing is joined to the copper pipe, or central tube, usually by brazing, after which the central tube is rotated to wind the copper tubing around it, while said copper tubing is kept under tension to provide a firm contact between said copper tubing and the central pipe. The force with which the copper tubing is wound around the central pipe causes its surface to deform and form a somewhat flattened contact surface with the central pipe.

[008] US 7,322,404 discloses a coil-on-tube heat exchanger wherein the contact area between the wound coil tube and the central pipe has been increased by providing a flatter contact surface to the coil tube since multiple coils are wound around the central tube for a reduced pressure loss through the coils. Headers must then be used to join the coils together at each end of the heat exchanger. [009] In view of the above, there is a need for an improved method and apparatus for manufacturing coil-on-tube heat exchangers that would be more cost effective and that would provide a more efficient unit.

SUMMARY OF THE INVENTION

[0010] In accordance with a first aspect, there is provided a method of manufacturing a coil-on-tube heat exchanger. The method includes the following steps. a) Providing a central tube having a longitudinal axis, first and second extremities, and inner and outer surfaces, and a coil tube having a longitudinal axis. b) Feeding the coil tube toward the central tube while shaping the coil tube into a preformed coil tube having an ovoid cross-section. The preformed coil tube includes a major axis extending along a largest diameter of the ovoid cross- section. c) Applying a predetermined tension force to the preformed coil tube. d) Orienting the preformed coil tube relative to the central tube, such that the preformed coil tube is fed tangentially to the outer surface of the central tube, such that respective longitudinal axes of the central tube and of the preformed coil tube are substantially perpendicular, and such that a first plane including the major axis and extending longitudinally through the preformed coil tube is substantially perpendicular to a second plane tangent to the outer surface of the central tube. e) Securing the preformed coil tube near the first extremity of the central tube. f) Rotating and translating the central tube relative to the preformed coil tube in the direction of the longitudinal axis of the central tube, thereby helically winding the preformed coil tube around the central tube and causing a bottom portion of the preformed coil tube to flatten against the outer surface of the central tube. g) Stopping the rotation and translation of the central tube after a predetermined number of rotations. h) The final step involves securing the preformed coil tube to the central tube near the second extremity thereof.

[0011]Of course, other processing steps may be performed prior, during or after the above described steps. The order of the steps may also differ, and some of the steps may be combined.

[0012] In an embodiment, in step a), the coil tube is a circular tube having a diameter of about 0.25 inches (6.4 mm) to about 1.5 inches (38 mm).

[0013] In an embodiment, in step a), the central tube is a circular tube having a diameter of about 2 inches (50.8 mm) to about 6 inches (152.4 mm).

[0014]ln an embodiment, in step b), shaping the coil tube comprises an initial step of preforming the coil tube using rolling mills.

[0015] In an embodiment, in step b), shaping the coil tube is performed using a forming die. The forming die has a body provided with a preforming channel defined by an inner sidewall, said inner sidewall transitioning smoothly from a first cross-section to a second cross-section having an ovoid shape.

[0016] In an embodiment, in step b), the ovoid cross-section of the preformed coil tube has a shape defined by four adjacent arc segments comprising a first arc segment and a second arc segment defining left and right sides of the shape, respectively; a third arc segment defining a lower side of the shape, and a fourth arc segment defining an upper side of the shape. The first and second arc segments both have a radius R1 , the third arc segment has a radius R2 and the fourth arc segment has a radius R3. A ratio R3/R2 is greater than 1 and inferior or equal to 3, and R1 is greater than both R2 and R3. [0017] In an embodiment, R1 is between about 0.7 inches (17.8 mm) to about 4 inches (101.6 mm); and R2 is between about 0.05 inches (1.27 mm) to about 0.45 inches (11.4 mm).

[0018] In an embodiment, in step c), the predetermined tension force is maintained between 1575 N and 7875 N.

[0019] In some implementations, step c) is performed using a clamping die. The clamping die has a body provided with a clamping channel shaped and sized for receiving the preformed coil tube. The body has a slot extending therealong for adjusting the predetermined tension force applied on the preformed coil tube.

[0020] In some implementations, in step d), the first plane of the preformed coil tube and the second plane tangent to the outer surface of the central tube form an angle between 80 and 100 degrees.

[0021] In some implementations, in step d), the longitudinal axis of the central tube and the longitudinal axis of the preformed coil tube form an angle between 80 and 100 degrees.

[0022] In some implementations, in step f), winding the preformed coil tube around the central tube causes the top portion of the preformed coil tube to collapse toward the central tube in a direction substantially parallel to the major axis of the preformed coil tube.

[0023] In some implementations, in step f), the bottom portion of the preformed coil tube flattens against the outer surface of the central tube, deforming the ovoid cross-section into a substantially oval cross-section.

[0024] In some implementations, step f) includes a step of inserting a radially expandable shaft assembly in the central tube and radially expanding the expandable shaft assembly to grip the inner surface of the central tube. The rotation of the central tube is performed by rotating the radially expandable shaft assembly. [0025] In some implementations, steps e) and h) include at least one of brazing and welding the preformed coil tube to the central tube.

[0026] In some implementations, the method further includes a step of cutting the preformed coil tube near the first and second extremities of the central tube.

[0027] In accordance with another aspect, there is provided an apparatus for manufacturing a coil-on-tube heat exchanger formed by a coil tube helically wound around a central tube. The apparatus includes a first assembly for shaping the coil tube having a first cross-section into a preformed coil tube having a second ovoid cross-section, for applying a predetermined tension force to the preformed coil tube and for orienting the preformed coil tube relative to the central tube. The apparatus further includes a rotating assembly to rotate the central tube and a translating assembly to translate the central tube in the direction of the longitudinal axis of the central tube after exiting the assembly, the translating assembly serving to helically wind the preformed coil tube around the central tube.

[0028] In an embodiment, the first assembly includes a preforming section comprising a preforming channel defined by an inner sidewall transitioning smoothly from a first cross-section to a second ovoid cross-section, a major axis of said ovoid cross-section extending along a largest diameter of the ovoid cross- section. The first assembly further includes a clamping section comprising a mean to exert the predetermined tension force on the preformed coil tube, and a guiding section comprising a mean to orient the preformed coil tube relative to the central tube such that the preformed coil tube is directed tangentially to an outer surface of the central tube, such that respective longitudinal axes of the central tube and of the preformed coil tube are substantially perpendicular, and such that a first plane comprising the major axis of the ovoid cross-section of the guiding section is substantially perpendicular to a second plane tangent to the outer surface of the central tube. [0029]ln some implementations, the preforming section includes a preforming die having an elongated body provided with an entrance and an exit. The preforming channel extends from the entrance to the exit of the preforming die.

[0030] In some implementations, the exit of the preforming die has a shape defined by four adjacent arc segments, comprising a first arc segment and a second arc segment, defining left and right sides of the shape, respectively; a third arc segment defining a lower side of the shape; and a fourth arc segment defining an upper side of the shape. The first and second arc segments have a radius R1 , the third arc segment has a radius R2 and the fourth arc segment has a radius R3; and a ratio R3/R2 is greater than 1 and inferior or equal to 3 and R1 is greater than both R2 and R3.

[0031] In some implementations, the preforming section includes rolling mills located upstream from the preforming die. The rolling mills are sized and configured to transform a shape of the coil tube from a circular cross-section to an elongated or oblong cross-section.

[0032] In an embodiment, the clamping section includes a clamping die having a body provided with an entrance, an exit, and a clamping channel extending from the entrance to the exit. The clamping channel has a cross-section substantially corresponding to the second ovoid cross-section of the preforming section.

[0033] In some implementations, the body of the clamping die includes a slot extending therealong. The slot has a width, a length and a depth sized and configured to set the predetermined tension force exerted on the preformed coil tube.

[0034] In some implementations, the guiding section includes a guiding ring having a body provided with an entrance, an exit and a guiding channel extending from the entrance to the exit of the guiding ring. The guiding channel has a longitudinal axis and a cross-section substantially corresponding to the second ovoid cross-section of preforming section. The guiding ring is rotatable at least about its longitudinal axis to orient the preformed coil tube relative to the central tube.

[0035] In accordance with yet another aspect, the rotating assembly described above includes a radially expandable shaft assembly. The radially expandable shaft assembly includes a shaft insertable into the central tube, at least one resilient ring engaged on the shaft and being radially expandable between a first configuration in which the at least one resilient ring has a diameter smaller than an inner diameter of the central tube, and a second configuration in which the at least one resilient ring has a diameter matching the inner diameter of central tube, thereby gripping an inner surface of the central tube; and a compressing and decompressing mechanism cooperating with the at least one resilient ring to expand or contract the at least one resilient ring between the first and second configurations.

[0036] In some implementations, the at least one resilient ring includes a plurality of resilient rings axially spaced apart from one another along the shaft.

[0037] In an embodiment, the compressing and decompressing mechanism includes at least one nut threadably connected to one end of the shaft. Turning the nut on the shaft increases or decreases compressive forces applied axially on the at least one resilient ring.

[0038] In an embodiment, the compressing and decompressing mechanism includes at least one pair of rigid washers located on each side of said at least one the resilient ring.

[0039] In some implementations, the compressing and decompressing mechanism includes at least one spacing collar slidably engaged on the shaft.

[0040] In an embodiment, the translating assembly includes a motor translating the central tube or the preformed coil tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a top perspective view of an apparatus for manufacturing a coil- on-tube heat exchanger, in accordance with an embodiment.

[0042] Figure 2A is a cross-section view of a typical coil tube obtained with prior art methods.

[0043] Figure 2B is a cross-section view of a coil tube formed by a method and apparatus for manufacturing a coil-on-tube heat exchanger, in accordance with an embodiment.

[0044] Figure 3A is front elevation view of a forming die, viewed from an entrance end, in accordance with an embodiment.

[0045] Figure 3B is a rear elevation view of the forming die of Figure 3A, viewed from an exit end.

[0046]Figure 3C is a top perspective view of the forming die of Figure 3A.

[0047] Figure 4A is a cross-section view of a preformed coil tube, in accordance with an embodiment.

[0048] Figure 4B is a side perspective view, fragmented, of the preformed coil tube of Figure 4A.

[0049] Figure 5A is a top perspective view of a clamping ring, in accordance with an embodiment.

[0050]Figure 5B is a top perspective view of the clamping ring of Figure 4A with hidden lines depicting interior features.

[0051] Figure 6 is a top perspective view of a guiding ring in accordance with an embodiment, with hidden lines depicting interior features. [0052] Figures 7A and 7B are cross-section views of a preformed coil tube shown during winding around a central tube, in accordance with an embodiment.

[0053] Figure 8 is a cross-section view of a radially expandable shaft in a central tube, in accordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0054] In the following description, the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several references numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom.

[0055]Although the embodiments of a method and of an apparatus for manufacturing a coil-on-tube heat exchanger formed by a coil tube helically wound around a central tube, and corresponding parts thereof, consist of certain geometrical configurations as explained and illustrated herein, not all of these components and geometries are essential and thus should not be taken in their restrictive sense. It is to be understood, and also apparent to a person skilled in the art, that other suitable components and cooperation thereinbetween, as well as other suitable geometrical configurations, may be used for the method and apparatus for manufacturing a coil-on-tube heat exchanger formed by a coil tube helically wound around a central tube, as will be briefly explained herein and as can be easily inferred herefrom, by a person skilled in the art.

[0056] Moreover, it will be appreciated that positional descriptions such as "above", "below", "left", "right", "top", "bottom", "around" and the like should, unless otherwise indicated, be taken in the context of the figures and should not be considered limiting. [0057]More particularly, in the present specification, it is to be understood that the expression "substantially perpendicular" refers to an angle of 90 degrees ± 30 degrees between two axes, components or planes. Thus, the angle can be comprised between 60 and 120 degrees. Preferably, the angle is comprised between 80 and 100 degrees. Most preferably, the angle is comprised between 85 and 95 degrees.

[0058]Similarly, in the present specification, it is to be understood that the expression "substantially parallel" refers to an angle of 0 ± 30 degrees between two axes, components or planes. Thus, the angle between can be comprised between -30 and 30 degrees. Preferably, the angle is comprised between -10 and 10 degrees. Most preferably, the angle is comprised between -5 and 5 degrees.

[0059] In the following description, the expression "ovoid" is to be understood as a shape resembling the cross-section of an egg. Typically, this cross-section is taken along a plane comprising the major or longest axis of the ovoid shape. The ovoid shape can also to be understood as a broadly oval shape, wherein the arcs intersecting the major axis of the shape have different radii, one being larger than the other. Typically, an "ovoid" shape has a single axis of symmetry, this axis of symmetry coinciding with the major axis. The major axis extends along the largest diameter of the ovoid shape.

[0060] Moreover, in the following description, the expression "oval" that is used to characterize the shape of a cross-section of a component is to be understood as a shape that is broadly elliptical. Contrary to the above-mentioned ovoid shape, the oval shape can include more than one axis of symmetry and can even include one rather straight segment.

[0061] Referring now to the drawings and, more particularly, referring to Figure 1 , a coil-on-tube heat exchanger 100 is shown during its manufacturing. It is formed by a coil tube 200 helically wound around a central tube 102. An apparatus 800 for manufacturing a coil-on-tube heat exchanger 100 is also shown, according to a possible embodiment. The apparatus 800 includes three main systems or assemblies: a first assembly 750 for shaping the coil tube 200, applying a tension to the coil tube 200, and for orienting the coil tube 200 prior to its winding around the central tube 102; a second assembly 760 for rotating the central tube 102, and a third assembly 770 for moving the central tube 102 relative to the coil tube 200 during the winding step. It is to be understood that the assembly 770 for moving the central tube 102 relative to the coil tube 200 can either move the central tube 102 relative to the coil tube 200 or move the coil tube 200 relative to the central tube 102, i.e. one of the coil tube 200 and the central tube 102 is moved relative to the other.

[0062]The method for manufacturing a coil-on-tube heat exchanger will be described with reference to Figure 1. First, a central tube 102 and a coil tube 200 are provided. It will be noted that reference numbers 200, 200', 200" and 200'" refer to the same coil tube at different stages of the manufacturing process. The central tube 102 has a longitudinal axis 114 and inner and outer surfaces 104, 106. The coil tube 200 also has a longitudinal axis 220.

[0063]At the beginning of the process, the coil tube 200 has a first or initial cross- section which is typically round or circular, but it is possible for the coil tube 200 to have a slightly oval or oblong cross-section, for example if it has been already slightly deformed previously. Typically, the coil tube 200 is a circular tube having a diameter of about 0.25 inches (6.4 mm) to about 1.5 inches (38 mm). The coil tube 200 can be made of any heat conducting material suited to form a heat exchanger, such as copper.

[0064]The coil tube 200 is fed toward the central tube while being shaped into a preformed coil tube 200", in this case through a preforming section 755 of the apparatus. In this particular embodiment, the preforming section 755 includes both rolling mills or rollers 350, and a preforming die 300; however, it is possible that the preforming section 755 includes solely a preforming die 300, or solely rolling mills or rollers 350. The coil tube 200 can be straighten or shaped by the rolling mills 350 so as to provide a coil tube 200' with an intermediate shape that is best suited for the subsequent steps. The rolling mills 350 is preferably located upstream of any other forming means of the apparatus 800. The rolling mills 350 can be sized and configured to transform the shape of the coil tube 200 from an initial circular cross-section to an elongated or oblong cross-section, facilitating the following forming step.

[0065]After exiting the preforming section 755, the preformed coil tube 200" preferably has an ovoid or egg-shaped cross-section. This ovoid cross-section typically includes a major or main axis extending along the largest diameter of the preformed coil tube 200". An example of a preformed coil tube 200" obtained after being shaped or preformed is shown in Figure 4A. As can be noted, the major axis 208 extends from the narrower bottom portion 222 to the wider top portion 224 of the preformed coil tube 200".

[0066]Back to Figure 1 , a tension force is applied to the preformed coil tube 200", either while deforming the coil tube 200', or after it has been deformed. Accordingly, it is to be understood that, in an alternative embodiment to the one shown in Figure 1 , the section generating the tension force can be positioned upstream or downstream of the preforming section 755. Typically, this "tensioning" step is achieved by applying friction or resistive forces on the outer surface of preformed coil tube 200". In this particular embodiment, applying the tension force on the preformed coil tube 200" is performed by a clamping section 757 of the apparatus, which in this case consists of a clamping or tensioning die 400. The clamping die 400 generates the predetermined tension efforts on the preformed coil tube 200". Of course, it is possible to use other means to apply friction to the preformed tube 200", so as to controllably tension the tube.

[0067]The preformed coil tube 200" is then oriented or guided relative to the central tube 102 such that the preformed coil tube 200" is fed tangentially to the outer surface 106 of the central tube 102, such that the respective longitudinal axes 114, 220 are substantially perpendicular (i.e. ± 20 degrees); and such that a first plane extending longitudinally through the preformed coil tube, and comprising the major axis, is substantially perpendicular {i.e. ± 20 degrees) to a second plane tangent to the outer surface 106 of the central tube 102. In other words, the guiding section 759 orients and guides the preformed coil tube 200", such that the base or narrower portion of the preformed tube contacts the outer surface 106 prior to being wound. The guiding section 759 orients the preformed coil tube relative to the central tube and directs the preformed coil tube tangentially to the outer surface 106 of the central tube 102, with the respective longitudinal axes 114, 220 of the central tube and of the preformed coil tube being substantially perpendicular. The guiding section 759 also orients the preformed coil tube 200" such that a first plane comprising the major axis of the ovoid cross-section of the preformed tube 200" is substantially perpendicular to a second plane, tangent to the outer surface 106 of the central tube 102, as best shown in Figure 7A. In the example provided, the guiding section 759 consists of a guiding die or ring 500, but other guiding means are possible.

[0068]While in Figure 1 the assembly 750 comprises distinct preforming, clamping and guiding sections, it is possible to merge all or some of these sections into a single component, such as within a die similar to the forming die 300. However, it is preferred to have different components for each of these steps, since it allows to better control each step.

[0069] Next, the preformed, tensioned and oriented preformed coil tube 200" is secured or affixed to the outer surface 106 of the central tube 102, toward a first extremity 108, for example by brazing or welding the preformed coil tube 200" to the central tube 102.

[0070]The central tube 102 is then rotated while the properly oriented preformed coil tube 200" is translated in a direction substantially parallel to the longitudinal axis 114 of the central tube 102. As mentioned above, it can be considered to translate the central tube 102 relative to the preformed coil tube 200" or vice- versa to achieve the same result. In the embodiment shown in Figure 1 , the central tube 102 is translated in the direction of the longitudinal axis 114 of the central tube 102 and is rotated about said longitudinal axis 114. As a result, the preformed coil tube 200" is helically wound around the central tube 102. The rotation and the translation of the central tube 102 relative to the preformed coil tube 200" causes a top portion 224 of the preformed coil tube 200" to collapse toward the central tube 102 and a bottom portion 222 of the preformed coil tube 200" to flatten against the outer surface 106 of the central tube 102. It is to be understood that the collapsing of the preformed coil tube 200" means that the preformed coil tube 200" shrinks together or is crushed or folds down into a more compact shape. In other words, the preformed coil tube 200" is deformed into a coil tube having an oval cross-section as the bottom portion 222 flattens against the outer surface 106 of the central tube. Thus, the preformed coil tube 200" is deformed upon winding on the outer surface 106 of the central tube 102 from the second, ovoid cross-section to a third, oblong or oval cross-section, forming a wound coil tube 200"'. The preformed coil tube 200" provides a contact area between the wound coil tube 200"' and the central tube 102 that advantageously lead to a coil-on-tube heat exchanger 100 having better general performances than those found in the prior art.

[0071]The final steps consists in stopping the rotation and the translation of the central tube 102 after a predetermined number of rotations, and securing the wound coil tube 200"' near the second extremity 110 of the central tube 102. Typically, the performed coil tube 200" is cut near the first and second extremities 108, 110 of the central tube 102, in order to form a complete coil-on- tube heat exchanger 100.

[0072] Referring to Figure 2A and 2B, when a tube of a material, such as copper, is deformed plastically to form a helical coil around a central shaft or tube, its cross-section is inevitably deformed, as the material on the outer regions of the coil must stretch to a longer length than the material on the inner regions of the coil. Figure 2A illustrates a prior art tube 10 having a typical cross-section shape resulting from winding a tube 10 having an initial round cross-section around a central tube 12. As can be seen in Figure 2A, the prior art tube 10 will tend to deform in such a manner that a large portion of the side facing the outer surface 16 of the central tube 12 is actually no longer in contact with said central tube 12, thus limiting heat transfer from a medium in contact with the inner surface 14 of the central tube 12 to a medium inside the coil tube 10. Figure 2B illustrates the cross-section of a wound coil tube 200"' obtained by the apparatus and method described in the present specification. It can be seen that the wound coil tube 200"' has more contact surface with an outer surface 106 of a central tube 102, thereby increasing the heat transfer from a medium in contact with an inner surface 104 of the central tube 102 to a medium inside the wound coil tube 200"'.

[0073] Referring now to Figures 3A to 3C, a preferred embodiment of a forming die is shown. The illustrated forming die 300 consists of an elongated cylindrical body 302 having an entrance 306 and an exit 308 and including a preforming channel 310. The entrance 306 of the forming die 300 has a substantially circular cross-section 316 to accept the round coil tube 200'. The exit 308 of the forming die 300 has an ovoid cross-section 318 that is substantially equal to the desired ovoid cross-sectional shape of the preformed coil tube 200". The preforming channel 310 is defined by an inner sidewall 314. The inner sidewall 314 transitions smoothly from the first cross-section at the entrance 306 to the second cross-section having an ovoid shape at the exit 308. The length of the forming die 300 is selected to provide a suitably gradual transition in cross-sectional shape for deforming the coil tube 200'. The preferred length of the forming die 300, when forming commonly used copper coil tube, is approximately between 2 and 20 inches.

[0074]Still referring to Figures 3A to 3C, the forming die 300 is preferably made from a single piece of material, such as a polymer or metal, to provide a smooth and uninterrupted inner sidewall 314 in the forming channel 310. The illustrated forming die 300 also includes a collar 304 to hold in place the forming die 300, as the coil tube 200' is shaped in the forming die 300. The illustrated forming die 300 is also provided with a groove 312 formed along a central plane of the forming die 300 for aiding in positioning the forming die 300 when in use. For instance, the groove 312 can coincide with the major axis 208 of the ovoid cross-section 202. Although it is preferred to use a single-piece die to obtain a smooth inner sidewall 314, it is to be understood that in alternative embodiments, it is possible to use a forming die 300 formed of two or more parts.

[0075] Although such features have been omitted from figures 3A to 3C for simplicity and clarity, the forming die 300 may be equipped with suitable means to secure it in place, or with clamping parts of a multi-part die, together during use and for opening and closing such forming die when desired. The forming die may be constructed from any suitable material, including metals, polymers or ceramics. In some implementations, the forming die 300 can be used in combination with a lubricant to control the friction between the forming channel 310 and the preformed coil tube 200".

[0076] It is to be understood by the skilled person that, although the illustrated forming die 300 has been found to be a preferred means of forming the preformed coil tube to the desired shape, other known means, such as rolling mills, may be employed to achieve the ovoid shape for carrying out the described method. In such variation, rolling mills could be used to provide all or part of the preforming to achieve the pre-formed ovoid shape described above. Should rolling mills be used to partially preform the coil tube 200', a forming die similar to the one illustrated in Figures 3A to 3C could also be used to provide final shaping to the preformed coil tube 200". In that case, the entrance of the forming die 300 would be of a shape corresponding to the cross-section of the coil tube 200' after it has passed through the rolling mills.

[0077] Referring to Figures 3A to 4B and also to Figure 1 , the forming die 300 shapes the coil tube 200' into the preformed coil tube 200", i.e. the preformed coil tube 200" having an ovoid cross-section 202. The ovoid cross-section 202 of the preformed coil tube 200" will now be described in further detail. [0078] Referring to Figures 4A and 4B, the shape of the ovoid cross-section 202 of the preformed coil tube 200" is constructed of four arc segments: a first arc segment 212 and a second arc segment 214 defining left and right portions 226, 228 of the shape, respectively; a third arc segment 218 defining a bottom portion 222 of the shape, and a fourth arc segment 216 defining an top portion 224 of the shape. The first and second arc segments 212, 214 both have a radius R1 , the third arc segment 218 has a radius R2 and the fourth arc segment 216 has a radius R3. As described above and in order to provide the shape of the ovoid cross-section 202, the ratio R3/R2 is preferably greater than 1 and inferior or equal to 3, and R1 is greater than both R2 and R3. The shape of the ovoid cross- section 202 is also defined by an angle a. The angle a is selected to provide a perimeter equal to the circumference of the original round cross-sectional shape of the coil tube 200". In an embodiment, the angle alpha is comprised between 50 and 90 degrees.

[0079]The values of R1 , R2, and R3 can be varied to provide for different diameters of coil tube 200 and central tube 102, as well as to adjust for any desired variations in the final cross-section of the wound coil tube 200"'. Each of the three radius variables can have a different effect on the final cross-section of the wound coil tube 200"'. R1 can affect the ratio of height to width, with larger values generally yielding a higher ratio. R2 can affect the quality of the contact between the wound coil tube 200"' and the outer surface 106 of the central tube 102, with smaller values generally yielding a better contact. R3 tends to affect the shape of the top of the cross-section, which forms the outer surface of the wound coil tube 200"' of the heat exchanger 100. A high value of R3 can cause this outer surface to curve inwardly, while a low value of R3 can cause it to curve outwardly.

[0080]The skilled person will understand that there is some room to select different values for the variables, as long as their relationships fall within the boundaries described above. Whereas selecting values to provide a final cross- section that is roughly as desired will generally yield useable results, the present specification further contemplates using simulations or tests to obtain more precise optimal values of these variables for particular diameters of coil tube 200 and central tube 102. It has generally been found that values of R1 in the range of about 0.7 inches (17.8 mm) to about 4 inches (101.6 mm); and R2 in the range of about 0.05 inches (1.27 mm) to about 0.45 inches (11.4 mm) provide the best results when manufacturing coil-on-tube heat exchangers in dimensions suitable for conventional plumbing systems.

[0081] In addition, the person skilled in the art understands that the ovoid cross- section here described can be obtained with an infinity of arcs of differing radii. Therefore, the implementation described is non limitative, in the sense that many other geometrical configurations can lead to an ovoid cross-section suitable for the use in an apparatus and method for forming a coil-on-tube heat exchanger.

[0082] Referring to Figure 4B, the preformed coil tube 200" having the above- described ovoid cross-section 202 is illustrated. This ovoid cross-section 202 has a major axis 208 extending along a largest diameter of the ovoid cross-section 202. The major axis 208 coincides with an axis of symmetry of the ovoid cross- section 202. The major axis 208 also coincides with a first plane 210, extending longitudinally through the preformed coil tube 200" and along the longitudinal axis 220 of the preformed coil tube 200". The first plane 210 will be referred to further below, when the positioning of the preformed coil tube 200" with respect with the central tube 102, will be described.

[0083] Referring now to Figures 5A and 5B, a possible embodiment of a clamping die is shown. The clamping die 400 includes a cylindrical body 402 and a collar 404. The collar 404 can be used to hold the clamping die 400 in place when in use. The clamping die 400 also includes a clamping channel 410 having an entrance 406 and an exit 408. The clamping channel 410 is shaped to be in close relation with the preformed coil tube 200", and thus presents a constant ovoid cross-section matching the ovoid cross-section 202 of the preformed coil tube 200". The clamping die 400 further includes a slot 412 defined along the longitudinal axis of the clamping die 400. The slot 412 can be used to adjust the clamping force exerted on the preformed coil tube 200" passing through the clamping die 400. In an embodiment, the clamping force can be applied externally to the clamping die 400 through a clamping ring (not illustrated).

[0084] In other embodiments (not illustrated), the clamping die can be replaced with friction pads, holders, friction rollers or any other suitable means sized and configured to apply friction efforts to the outer surface of the preformed coil tube 200" but ensuring that the shape of the preformed coil tube 200" is preserved. For instance, if the clamping die 400 is replaced by friction rollers, the passage of the preformed coil tube 200" is opposed to by the resistance generated by the friction rollers, wherein the surface of the friction rollers in contact with the preformed coil tube 200" has a friction coefficient selected so that the preformed coil tube 200" does not slip relative to said friction rollers.

[0085]The role of the clamping die 400 is to apply a clamping force to the preformed coil tube 200". It is to be understood that, in an alternative embodiment (not shown), the clamping die 400 can be positioned upstream of the forming die 300. In turn, the clamping force generates a predetermined tension force on the preformed coil tube 200" through friction between the outer wall 206 of the preformed coil tube 200" with the clamping channel 410, as the preformed coil tube 200" is wound around the central tube 102. In some implementations, the clamping die 400 can be used in combination with a lubricant to control the friction between the clamping channel 410 and the outer wall 206 of the preformed coil tube 200". The predetermined tension force, combined with the torque that is applied to the central tube 102 during winding, has an impact on the final shape of the cross-section of the wound coil tube 200"'. The amount of clamping force, and thus the resulting predetermined tension, can be predetermined by the shape of the clamping channel 410, the length of the slot 412, the material selected to form the clamping die 400 and the clamping force externally applied to the clamping die 400 by, for example, a clamping ring (not illustrated). The amount of clamping force can otherwise be adjusted by conventional means such as applying further clamping force to the clamping die 400. In a preferred embodiment, the predetermined tension force is maintained between 1575 N and 7875 N. In an alternative embodiment, a multipart clamping die can be used, and the person skilled in the art understands that a number of commercially available components could be adapted to supply the required clamping function, provided they are capable of sufficiently controlling the friction exerted on the preformed coil tube 200".

[0086] Referring now to Figure 6, and also to Figure 1 , an example of a guiding die or ring 500 is provided. The role of the guiding ring 500 can be described as follows. As the preformed coil tube 200" is wound around the central tube 102 in a helical coil fashion, the force applied to the preformed coil tube 200" in a direction parallel to the longitudinal axis 114 of the central tube 102, combined with the coiling of the preformed coil tube 200" about said central tube 102, causes the preformed coil tube 200" to twist. In other methods, this undesirable twisting effect is perceptible in a finished coil-on-tube heat exchanger, as the somewhat squared but twisted coils of tubing yielded a slight saw-tooth profile. This result is not merely of aesthetic consideration, as such twisting of the tubing as it is coiled can affect the quality of the contact between the coil tube and the central tube. In order to mitigate this effect, the present apparatus and method make use of a guiding means, which in an exemplary embodiment takes the form of the guiding ring 500.

[0087] In the exemplary embodiment illustrated in Figure 6, the guiding ring 500 includes a cylindrical body 502 having an inner guiding channel 510 along the longitudinal axis of the cylindrical body 502. The inner guiding channel 510 has an entrance 506 and an exit 508. The cross-section of the inner guiding channel 510 closely matches the shape of the ovoid cross-section 202 of the preformed coil tube 200", as the guiding channel 510 is intended to guide and orient the preformed coil tube 200". As with the forming die 300 and clamping die 400, the cylindrical body 502 of the guiding ring 500 may be split, such as in two pieces along its length, to allow it to be opened and closed around the preformed coil tube 200". The length of the guiding ring 500 is selected to effectively guide the preformed coil tube 200". In an embodiment, the length of the guiding ring ranges from about 1 to 5 inches. The guiding ring 500 also includes a groove 512, to orient the guiding ring 500. The groove 512 can coincide with the major axis 208 of the ovoid cross-section 202 of the preformed coil tube 200". The guiding ring 500 further includes a collar 504. The collar 504 can be used to hold the guiding ring 500 in place when in use.

[0088] Referring now to Figures 1 and 7, the positioning and orientation of the preformed coil tube 200" exiting the guiding ring 500 with respect to the central tube 102 will be described. The guiding ring 500 ensures the preformed coil tube 200" is kept in the proper position and orientation with respect to the central tube 102, as the preformed coil tube 200" is wound around said central tube 102. The orientation of the guiding ring 500 about its longitudinal axis can be adjusted to maintain a desired orientation of the preformed coil tube 200" for optimal contact between wound coil tube 200"' and central tube 102 in the finished coil-on-tube heat exchanger.

[0089]Still referring to Figures 1 and 7, the preformed coil tube 200" is oriented with respect to the central tube 102, such that the preformed coil tube 200" is fed tangentially to the outer surface 106 of the central tube 102. Moreover, the first plane 210, comprising the major axis 208 and extending longitudinally through the preformed coil tube 200", is substantially perpendicular to a second plane 112, tangent to the outer surface 106 of the central tube 102. An angle β is defined between said first plane 210 and second plane 112. The angle β can be selected by orienting the guiding ring 500 along its longitudinal axis. It has been found that an optimal range for the angle β of orientation of the preformed coil tube 200" lies approximately between 80 and 100 degrees. Furthermore, the preformed coil tube 200" is oriented with respect to the central tube 102, such that the longitudinal axis 114 of the central tube 102 and the longitudinal axis 220 of the preformed coil tube 200" are substantially perpendicular. This angle is selected to control the pitch of the wound coil tube 200"' around the central tube 102.

[0090]The arrangement of the forming die 300, clamping die 400, and guiding ring 500 discussed above, are provided as examples of a preferred configuration for the preforming and guiding of the coil tube 200'. In alternative embodiments (not illustrated), a single die can perform simultaneously at least one of the preforming, clamping and guiding of the preformed coil tube, thus limiting the number of components required to carry out the method here described.

[0091]The next step involves rotating the central tube 102 while translating the preformed coil tube 200" or the central tube 102 in a direction parallel to the longitudinal axis 114 of the central tube 102. In the embodiment shown in Figure 1 , the central tube 102 is translated along the displacement arrow D, using a translating assembly 770. In some implementations, the translating assembly 770 typically includes a guiding system (not illustrated), comprising guides and rails, and a power transmission system (not illustrated), comprising gears and a rack, or pulleys and a belt. In another embodiment (not shown), the central tube 102 is rotated about its longitudinal axis 114, while the preformed coil tube 200", exiting the shaping, clamping and guiding dies 300, 400, 500, is translated in a direction parallel to the longitudinal axis 114 of the central tube 102, in a plane including the second plane 112.

[0092]The combined rotation of the central tube 102 and the translation of the central tube 102 with respect to the preformed coil tube 200" have the effect of helically winding the preformed coil tube 200" around the central tube 102. Referring to Figure 7B, this winding causes a top portion 224 of the preformed coil tube 200" to collapse toward the central tube 102. Combined with the predetermined tension force exerted by the clamping die 400, the bottom portion 222 of the preformed coil tube 200" flattens against the outer surface 106 of the central tube 102 and thus forms the wound coil tube 200"', as illustrated in Figure 7B. In Figures 7A and 7B, it is shown that the top portion 224 of the preformed coil tube 200" collapses toward the central tube 102, forming the wound coil tube 200"' wherein the top portion 224 is located outwardly relative to the central tube 102, and wherein the bottom portion 222 is in contact with the outer surface 106 of central tube 102. It can also be seen that the respective left and right portions 226, 228 of the preformed coil tube 200" are deformed upon winding and define the left and right portions of the wound coil tube 200"'.

[0093] In the embodiment shown in Figures 2B and 7B, the wound coil tube 200"' has an oval cross-section 230. In the embodiment shown, winding the preformed coil tube 200" around the central tube 102 deforms the preformed coil tube 200" in the following ways: the top portion 224 of the preformed coil tube 200" collapses toward the central tube 102 in a direction substantially parallel to the major axis 208 of the preformed coil tube 200"; the bottom portion 222 of the preformed coil tube 200" flattens against the outer surface 106 of the central tube 102; and the respective left and right portions 226, 228 of the preformed coil tube 200" are deformed upon winding and define the left and right portions of the wound coil tube 200"'. The top, bottom, left and right portions 224, 222, 226, 228 thereby form the oval cross-section 230 of the wound coil tube 200"'. In an embodiment, the angle β described above can be adjusted prior to, or during winding of the preformed coil tube 200", to control how the preformed coil tube 200" deforms, and thereby controlling the shape of the oval cross-section 230 of the wound coil tube 200"'.

[0094] Referring to Figures 1 and 7B, the wound coil tube 200"' can have an oval cross-section 230 similar in shape to what is shown in Figure 2B since winding the preformed coil tube 200" around the central tube 102 deforms the ovoid cross-section 202 of the preformed coil tube 200" into an oval cross-section 230. This oval cross-section 230 shown in Figure 2B is an example cross-section obtained using 3/4 inch (19.1 mm) copper tubing coiled around a 4 inch (101.6 mm) central tube. It has been found that using copper coil tube preformed in the above described ovoid cross section 202 provides a consistent final cross- sectional shape once the coil tube is wound around the central tube. This result holds for a broad range of coil tube sizes and central tube sizes, such as 1/4 inch to 1.5 inches (6.4mm to 38.1 mm) and 2 to 6 inches (5.1mm to 15.2 mm), respectively.

[0095]According to a second aspect, an exemplary embodiment of the rotating means used for rotating the central tube will be described. Since the tension necessary to wind the coil tube around the central tube whilst ensuring a tight contact between them can be significant, and can vary with the strength of the materials used to form the heat exchanger, the rotating means needs to overcome various challenges. Previous attempts to provide the necessary torque to the central tube during winding have focused on holding the ends of the central tube securely via clamping means, sometimes aided by adhesive coatings to increase grip. However, depending on the properties of the material of the central tube (e.g. copper), such solutions can lead to difficulties, as the strength of the material may not be sufficient to withstand the attendant shear forces without unacceptable deformation or failure. To make matters worse, the tension force on the coil tube applies a bending moment to the central tube, which can distort the central tube.

[0096]To overcome these problems, in an exemplary embodiment, the present method makes use of a radially expandable shaft assembly. The radially expandable shaft assembly can be used as a rotating mean, for rotating the central shaft for winding the preformed coil tube. For instance, the radially expandable shaft can be placed inside the central tube, providing the necessary grip to transfer torque for winding, and rigidly supporting said central tube along its entire length to prevent bending thereof.

[0097]A preferred embodiment of a radially expandable shaft assembly 700 is shown in Figures 1 and 8. A shaft 702 is disposed coaxially within the central tube 102, and can be made from any suitable material, preferably a metallic material. The shaft 702 is provided with a thread on at least part of its length. The threaded length of the shaft 702 can be longer or shorter than the length of central tube 112, without affecting the function of the assembly in general, as long as access is provided to nuts 704 located on at least one end of the shaft 702. The radially expandable shaft assembly 700 further includes a plurality of resilient rings 710 that are slidably engaged on the threaded shaft 702. The rings 710 are made of a suitable resilient material, such as a rubber compound, that can deform when a force is applied to it, and also provide a sufficient coefficient of friction between an outer surface of the resilient ring 710 and the inner surface 104 of the central tube 102. Adjacent to the opposing end faces of each resilient ring 710, a rigid washer 706 is slidably engaged on the shaft 702. Between each group of resilient rings 710 and rigid washers 706, a spacer collar 708 is slidably engaged on the shaft 702 to ensure a constant predetermined distance between each of said groups. To maintain the desired distance between the resilient rings 710 and to help ensure an optimal transfer of compressive forces along the longitudinal axis of the shaft 702, the spacer collars 708 are preferably made of a rigid material, such as steel. Although it is generally preferred to use spacer collars 708 of equal length to provide a uniform distribution of forces, it is not necessary for all of the collars 708 to be of equal length. The collars 708 at each end, between a threaded nut 704 and the first or last rigid washer 706, may be of different lengths from each other and from the remaining collars 708, so that the nuts 704 can be accessible should their positions need to be adjusted. If desired, some or all of the collars 708 and washers 706 could be formed as unitary parts without affecting the function of the radially expanding shaft assembly 700.

[0098]Still referring to Figure 8, the operation of the radially expanding shaft assembly 700 will be described. The threaded nuts 704 can be rotated along the shaft 702 to move them closer or further away from each other along the length of the shaft 702. Moving the nuts 704 toward each other generates a compressive force to the resilient rings 710 along their respective longitudinal axis. As the rigid washers 706 transfer the compressive force over substantially the entire end faces of each resilient ring 710, each one of the resilient ring 710 expands radially, thus contacting the inner surface 104 of the central tube 102. With sufficient compressive forces applied to the resilient rings 710, the resulting contact between the rings 710 and the inner surface 104 of the central tube 102 grips and secures the central tube 102 to the radially expandable shaft assembly 700, so that the necessary torque required to wind the preformed coil tube can be applied to the central tube 102.

[0099] In some implementations, a pair of nuts 704 can be provided at one end of the shaft 702 and a single nut 704 can be provided at the other end, as seen in Figure 8. In this embodiment, the pair of nuts 704 remains in a fixed position on the shaft 702, while the position of the single nut 704 can be adjusted. Alternatively, the pair of nuts 704 can be replaced at one end of the shaft 702 by a stopper (not illustrated) secured onto the shaft 702, while the position of a single nut 704 at the other end of the shaft 702 can be adjusted.

[00100] It can be appreciated by the person skilled in the art that the number and length of the resilient rings 710 can be selected as appropriate for the length of the coil-on-tube heat exchanger to be formed, the materials being used and the compressive efforts being applied. The skilled person can also appreciate that other known means for expanding the resilient rings, such as pneumatic or hydraulic bladders, can be used in place of the preferred embodiment discussed above, while still functioning within the scope of the present invention. Furthermore, other rotating means such as a powered mandrel or an expanding shaft, can be used to rotate the central tube 102.

[00101] The present invention should not be limited to the preferred embodiment set forth in the examples but should be given the broadest interpretation consistent with the description as a whole.