GB1570033A

GB1570033A - Primary surface heat exchanger and method of making same

Info

Publication number: GB1570033A
Application number: GB4789477A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1977-03-28
Filing date: 1977-11-17
Publication date: 1980-06-25
Also published as: DE2812854A1; JPS53119457A; FR2386005A1

Description

(54) PRIMARY SURFACE HEAT EXCHANGER AND METHOD OF MAKING SAME (71) We, CATERPILLAR TRACTOR CO., a corporation organized and existing under the laws of the State of California, United States of America, of 100 N.E.

Adams Street, Peoria, Illinois 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to heat exchangers and, more particularly, to an improved primary surface heat exchanger tube and the method of making same.

Prior art heat exchangers are principally based on the thermal conductivity concept requiring a tube with radiating fins, both of which are made of a material having high thermal conductivity, such as the expensive metal copper. The fins are brazed on the tubes, with the tubes, in turn, being brazed to a top and bottom tank to form the heat exchanger. The brazed or soldered seams and joints are subject to corrosion and occasionally leak at the brazed or soldered joints.

Repairs to the seams and joints require removal of the heat exchanger from the heat source, such as a vehicle, repair of the leak and reinstalling the heat exchanger on the vehicle.

Another prior art heat exchanger, although it can be made of aluminum, a lessexpensive metal, operates, in part, as a primary surface heat exchanger but has the disadvantages of requiring a complex core and radiating fin arrangement and must be removed from the heat source to repair leaks.

According to the present invention, a method of manufacturing a heat exchanger tube comprises forming a piece of sheet material into a continuously corrugated sheet with a plurality of side-by-side corrugations having a generally undulating profile in the plane of the sheet; crushing and flattening portions of the sheet to produce two separate groups of corrugations each group surrounded by a flattened portion of the sheet; folding the sheet along the flattened portion between the groups so that one corrugated group aligns with the other corrugated group and a passageway is formed at the fold of the sheet; and joining together the edges of the sheet remote from the fold to form a second passageway.

The invention also includes a heat exchanger tube having two elongate body portions, each body portion comprising a plurality of side-by-side corrugations extending across the tube, each corrugation having a generally undulating profile along its length, the side of the corrugations lying transverse to the plane of the body portion and substantially parallel to one another, and the body portions being disposed side-byside with crests of the corrugations of one body portion abutting corresponding crests of the corrugations of the other body portion to form passages, adjacent side edges of each body portion being secured together to form passageways extending in the longitudinal direction of the tube and communicating with the passages between the corrugations.

All of the joints and seams are exposed for ready repair in place on the heat source in the event there is leaking at the joints or seams.

The areas of corrugated or ribbed stock serve as counterflow heat transfer surfaces extending from within the tube in intimate contact with one heated fluid or gas to the outside of the tube for exposure to another fluid or gas passing thereover.

Two examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is an elevational view of a sheet of narrowly grooved, convoluted or ribbed stock; Figure 2 is an elevational view of the sheet stock of Figure 1 with the peripheral edge portions and a centre section flattened; Figure 3 is a cross-sectional view taken along the line 3-3 of Figure 2; Figure 4 is a top plan view of the sheet stock of Figure 3 folded into a tube; Figure 5 is an exploded view of a heat exchanger incorporating a plurality of the improved heat exchanger tubes; Figure 6 is an enlarged exploded view of parts of Figure 5 showing one tube and its connection to the top and bottom tanks; Figure 7 is a cross-sectional view taken along the line 7-7 of Figure 6; Figure 8 is an exploded perpective view of a modified form of heat exchanger using the improved heat exchanger tube with different end connections thereon; Fig. 9 is an enlarged perspective view of the top end of one heat exchanger tube of Fig. 8; Fig. 10 is a cross-sectional view taken along the line 10-10 of Fig. 8; and Fig. 11 is a perspective view of one flattened edge portion and the end portions of several ribs of the ribbed stock area of Fig. 2.

Referring to the drawings, and in particular Figs. 1-3, 7 and 11, a continuously corrugated sheet of narrowly grooved or ribbed stock 10 is illustrated in three successive stages of preparation for final fabrication into a heat exchanger tube 12, such as shown in Fig. 4. The ribbed stock 10 is an article of manufacture having deeply drawn corrugations that can be formed on the apparatus and using the method shown in our U.S.

Patent Specification No. 3,892,119.

The ribbed stock 10 consists of a strip of thin, relatively deformable metallic or nonmetallic material. The metallic material, such as aluminium, mild steel, copper, or stainless steel, or the non-metallic material, such as plastic or plastic/metallic composites including A.B.S. (Acrylonitrile Butadiene Styrene). P.V.C. (Poly Vinyl Chloride), is formes into alternating opening, transversely extending external grooves 13 and internal grooves 15 defined by intermediate ribs 14. The ribs 14 define a sinuous wave profile 16 when viewed in cross section and as shown in Fig. 7. The ribs 14 have a transversely undulating serpentine profile 17 in the plane transverse thereto i.e. in the plane of the sheet, as shown in Fig. 1.

The ribbed stock 10 is cut into sheets, such as the square sheet shown in Fig. 1, whereupon the edge portions and a center section are flattened and crushed, as in a stamping die, to produce side edge portions 18,20, end edge portions 22, 24 and center section 26 in said ribbed stock sheet 10, as shown in Fig. 2.

As viewed in Fig. 3, the crushed ribbed stock sheet 10 has a configuration with two (or more) spaced apart, outwardly extending, in both directions from the plane of said sheet, groups or areas 28, 29 of radiating ribs 14 which have the undulating serpentine profile 17 in one plane i.e. in the plane of the sheet and the sinuous wave profile 16 in the plane transverse thereto. As shown in Fig. 11, the end 19 of each rib 14 above the plane containing the edge portions 18,20; 22,24 is sloped down and merges into the side edge portions 18,20 and center section 26 while the end 21 of each rib 14 below said plane is sloped up and merges into the side edge portions 18,20 and center section 26. The side edge portions 18,20 are shaped so as to be angled slightly upward with respect ot the plane of the sheet to provide a planar surface 30,32, respectively, which lie in a plane substantially coextensive with one plane containing the edges of the ribs 14.

The sheet of crushed ribbed stock 10, in the configuration of Fig. 3, is formed into a heat exchanger tube 12 by folding the ribbed stock 10 in half, along a centerline of the center section 26, with one half of the sheet of ribbed stock containing one group or area 29 of ribs 14 bent 1800 about said centerline until one face 34 of said group or area 29 of ribs 14 abuts one face 36 of the other group or area 28 of ribs 14. The one planar surface 32 at one side edge portion 20 abuts the planar surface 30 at the other side edge portion 18 with the exposed edges of said planar surfaces 30,32 being welded or soldered along a seam 38 into a fluid-tight seal. The folding over of the sheet 10, combined with the face 34 of group 29 of ribs 14 abutting the face 36 of the ribs 14 of group 28, produces two fluid passageways 40 and 42 which communicate with each other by means of the plurality of passages or grooves 15 extending between the adjacent ribs 14. The fluid passage-way 40 is bounded by the folded over, flattened center section 26 and by the ends 19 of the ribs 14 and by the ends of the passages or grooves 15 between the ribs 14. The second fluid passageway 42 is bounded by the outer edge portions 30,32 by the spaced flattened side edge portions 18,20, by the ends 19 of the ribs 14 and by the end of the passages or grooves 15 between the ribs 14. It is to be understood that the sheet of ribbed stock 10 may be made up of any even multiples of groups of ribs 14, such as four groups, six groups, or the like, with the tube being created by folding the sheet in the middle so as to abut the faces of one set of groups of ribs 14 against the faces of the other set of groups of ribs 14.

A novel heat exchanger tube 12 is provided which has primary surface heat exchange capabilities whereby the fluids and gases are in counterflow relationship for direct transfer of heat directly through the material from which the ribs are made.

Essentially, one seam or joint is needed to make the tube. The tube can be assembled for use with the seam or joint exposed for ready access for repair if needed. The passageways 40,42 of the tube are selectively closed off at one end or the other so that with passageway 40 placed in communication with a source of heat, such as the heated cooling water of an internal combustion engine, fluid will follow the arrows of Fig. 5 and flow into the open top of the passageway 40 and will contact the closed bottom of said passageway 40. The fluid will flow across grooves and passages 15 and through passageway 42 which is closed at the top and open at the bottom. The fluid is cooled by the cooling gas flowing across the exterior surface of the tube and through the external passages or grooves 13 between the ribs 14 on the outside of the tube. The cooling air through passages 13 flows from right to left as viewed in Fig. 5 with the fluid in the tubes essentially flowing from left to right. In the usual type of heat exchanger, fins are attached to a core so that as heated fluid flows through the core, heat is conducted through the material of the core and through the material of the fins so that air, or the like coolant, flowing over the surface of the fins will remove the heat from the fins. The present improved primary surface heat exchanger does not use fins but accomplishes equivalent or better cooling by placing the counterflowing fluids directly in contact with the ribs on opposite sides of the material of said ribs.

As shown in Figs. 5 and 6, several tubes 12 may be assembled in a heat exchanger 43 having spaced apart tanks or headers 44 and 58. The header or tank 44, which may have two parts 46,48 welded together along the seam 50 or which may have a one-piece construction, has a plurality of parallel shaped slots 52 formed in one surface 54 thereof, each slot 52 having a narrow straight portion 51 and an enlarged shaped portion 53.

After the tube 12 has been formed by folding the ribbed stock sheet to produce the two passageways 40,42, the end edge portions 22 and 24 project outwardly from said passageways and from the body of said tube in the shape of an elongate ellipse or oval. A part of the long sides of the oval of the end edge portions 22 are crimped together and welded or soldered into a seam 41 along the edge to form an internal end passage 15', as shown in Fig. 7. The passage 15' is closed off at one end 55 to block off flow from passageway 40 through passage 15' directly into the passageway 42, as shown in Fig. 6. The remainder of the edge portion 22 is shaped into a sleeve 45 which is in communication with and is aligned with the passageway 40. The tubes 12 are assembled with the slots 52 in the tank 44 by inserting the seam 41 in the narrow, straight portion 51 of the slot 52 with the shaped sleeve 45 being inserted in the enlarged portion 53 of said slot 52. Preferably, the edge portion 22 and the sleeve 45 are then soldered respectively to the straight portion 51 and the enlarged portion 53.

The second header or tank 58, which may be of a two-piece construction 60,62, as shown, or which may be a one-piece construction, has a plurality of slots 64, each slot 64 having a narrow, straight portion 63 and an enlarged shaped portion 65 formed in one surface 66 of the tank half 60. At the end of the tube 12, having the edge portion 24 projecting therefrom, part of the edge portion 24 is crimped and welded or soldered together into a seam 47 to form an internal passage 15', which passage is closed off at one end 57 to block flow of fluid from the passageway 40 directly into passage 15'. The remainder of the edge portion 24 is shaped into a sleeve 49 which is a communication with and is aligned with the passageway 42.

The closed edge portion 63 of the slot 64 with the shaped sleeve 49 being inserted in the enlarged portion 65 of the slot 64.

To assemble the complete heat exchanger 43, one tube 12 will have the crimped part 41 and the sleeve 45 of the edge portion 22 inserted, respectively, in the appropriate straight portion 51 and the enlarged portion 53 of the slot 52 in the tank 44 whereupon the parts are welded or soldered in place in a fluid-tight manner. Each additional tube 12 is positioned adjacent the previously secured tube, the sleeve 45 and crimped part 41 of edge portion 22 being inserted in a slot 52 and being, likewise, welded or soldered in place. The slots 64 in the surface 66 of the tank half 60 are aligned with and receive the crimped part 47 and sleeve 49 of edge portion 24 which part 47 and sleeve 49 are then welded or soldered in place on the tank 58.

The sleeve 45 aligns with the passageway 40 to convey heated fluid from the tank 44 into passageway 40, across passages 15 and into passageway 42 where it flows through sleeve 49 into the bottom tank 58.

A complete heat exchanger 43 is thus provided wherein the fluid flows from tank 44 through passageway 40, passages 15 and passageway 42 into the tank 58 with the ribs 14 extending from within the tube 12, where they are in intimate contact with the heated fluid in passages 15, to without the tube, where they are exposed to the flow of a cooling gas or fluid, such as air, through the outer passages or grooves 13 between the ribs 14.

The number of tubes 12 that go to make up a core 70 of the heat exchanger is a matter of design based on the heat exchange requirements of the system. The heat exchanger 43 is filled with fluid through opening 72 in tank 44 and is connected to a heat source (not shown) to be cooled by means of piping extending from the tanks 58,44 to the heat source in a conventional manner.

A modified form of invention is shown in Figs. 8, 9 and 10, wherein a plurality of heat exchange tubes 12 are assembled with spaced tanks 44' and 58' by means of hollow, fluid conveying trunnions 80 so that the tubes 12 may be pivoted about the axes of the trunnions 80 to expose the opposite faces 81,82 of said tubes 12 to the oncoming air.

More specifically, the edge portions 22 on one end of each tube 12 are folded toward each other and welded or soldered along a seam 84 to form a fluid passage 85 connecting the end of fluid passageway 40 with the trunnion 80.

Referring to Fig. 9, it can be seen that the edge portion 22 is welded together along the seam 84 from the trunnion 80 to a junction 83 so that fluid will flow through the trunnion 80 to the passageway 40. On the other side of the trunnion 80, the seam 84 extends part way and then dips down and over to a junction with the seam 38. The edge portion 22 and seam 84 close off at 87 the upper end of the passageway 42 so that fluid will flow directly from trunnion 80 to the passageway 42. The opposite end of the heat exchange tube 12 of Figs. 8 and 9 has a centrally disposed trunnion 80' with the edge portion 24 crimped and welded or soldered in the manner of seam 84, only with the lower end of passageway 40 closed off and with the lower end of passageway 42 Communicating with the lower trunnion 80'. Fluid will flow from tank 44' through trunnion 80, passage 85, passageway 40, passages 15, passageway 42, the other passage 85, and trunnion 80'. The axes of the trunnions 80,80' on each tube 12 lie on a common centerline. The trunnions 80,80' are assembled in openings 86,88 in the spaced tanks 44' and 58', respectively, with the openings 86,88 in the spaced tanks 44' and 58', respectively, with the openings 86 in tank 44' and openings 88 in tank 58' being spaced apart a predetermined distance for a reason that will be apparent hereinafter.

The trunnions 80,80' are able to be turned in the openings 86,88 so that one face 81 or the other face 82 of each tube 12 can be selectively exposed to oncoming air. That is, assuming cooling air is flowing from left to right, as viewed in Fig. 10, the one face 81 of every other tube 12 faces into the oncoming air while the alternating tubes have the opposite faces 82 facing into the oncoming air.

Rotating the tubes 12 about the axes of the trunnions 80,80' will reverse the orientation of the tubes 12 resulting in air striking the opposite faces 82,81 of the tubes. Being able to reverse the orientation of the tubes 12 provides a self-cleaning capability to the heat exchanger 43' in that the air flowing over surfaces 81,82 of the bottom two tubes of Fig. 10 will have a tendency to pack up debris in the apex of the two tubes which debris will be released when the tubes are rotated about the axis of the trunnions 80,80' from the solid line position to the dotted line position of Fig. 10.

Fluid, such as water, may circulate between the spaced tanks 44' and 58' through the trunnions 80, end passages 85 through passageway 40, across grooves 15 and through second fluid passage 42. Fluid such as air, will flow in the external grooves 13 and over the exterior surfaces of the tube and ribs 14 to extract heat from said fluid inside the tube 12.

The heat exchanger of either illustrated embodiment is of the primary surface type permitting cooling directly through the walls of the tubes 12, such as through center section 26, through edge portions 18,20 and through the walls of the ribs 14. Traditional heat exchangers will often spring leaks at the seams or weld lines. The present improved construction of Figs. 5 and 6 has the seams or welds 38,41,47 and the seam or weld joining each tube 12 to the tanks. It is possible to assemble the tubes 12 with the welds 38 all facing forward such that the welds are all accessable from the front making it possible to repair the heat exchanger without removing it from its setting. The heat exchanger being of the primary surface type, may have the tubes 12 fabricated from non-strategic metals, such as stainless or mild steel, or of non-metals, such as plastic or metal plastic composites. The material selected can also be noncorrosive with the cooling media used.

By changing the rib pitch and shape, the heat exchanger performance can be further tailored to the engine cooling requirements thereby reducing heat exchanger frontal areas, fan sizes, fan drive horsepower and noise.

WHAT WE CLAIM IS: 1. A method of manufacturing a heat exchanger tube, the method comprising forming a piece of sheet material into a continuously corrugated sheet with a plurality of side-by-side corrugations having a generally undulating profile in the plane of the sheet; crushing and flattening portions of the sheet to produce two separate groups of corrugations each group surrounded by a flattened portion of the sheet; folding the sheet along the flattened portion between the groups so that one corrugated group aligns with the other corrugated group and a passageway is formed at the fold of the sheet; and joining together the edges of the sheet remote from the fold to form a second passageway.

2. A method according to claim 1, wherein the flattened end edges of the tube are welded together throughout a portion of each to define a passage within the tube and to define a sleeve throughout the remainder of the end in communication with one of the passageways.

3. A method according to claim 2, wherein the welded end edges close off the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figs. 8, 9 and 10, wherein a plurality of heat exchange tubes 12 are assembled with spaced tanks 44' and 58' by means of hollow, fluid conveying trunnions 80 so that the tubes 12 may be pivoted about the axes of the trunnions 80 to expose the opposite faces 81,82 of said tubes 12 to the oncoming air. More specifically, the edge portions 22 on one end of each tube 12 are folded toward each other and welded or soldered along a seam 84 to form a fluid passage 85 connecting the end of fluid passageway 40 with the trunnion 80. Referring to Fig. 9, it can be seen that the edge portion 22 is welded together along the seam 84 from the trunnion 80 to a junction 83 so that fluid will flow through the trunnion 80 to the passageway 40. On the other side of the trunnion 80, the seam 84 extends part way and then dips down and over to a junction with the seam 38. The edge portion 22 and seam 84 close off at 87 the upper end of the passageway 42 so that fluid will flow directly from trunnion 80 to the passageway 42. The opposite end of the heat exchange tube 12 of Figs. 8 and 9 has a centrally disposed trunnion 80' with the edge portion 24 crimped and welded or soldered in the manner of seam 84, only with the lower end of passageway 40 closed off and with the lower end of passageway 42 Communicating with the lower trunnion 80'. Fluid will flow from tank 44' through trunnion 80, passage 85, passageway 40, passages 15, passageway 42, the other passage 85, and trunnion 80'. The axes of the trunnions 80,80' on each tube 12 lie on a common centerline. The trunnions 80,80' are assembled in openings 86,88 in the spaced tanks 44' and 58', respectively, with the openings 86,88 in the spaced tanks 44' and 58', respectively, with the openings 86 in tank 44' and openings 88 in tank 58' being spaced apart a predetermined distance for a reason that will be apparent hereinafter. The trunnions 80,80' are able to be turned in the openings 86,88 so that one face 81 or the other face 82 of each tube 12 can be selectively exposed to oncoming air. That is, assuming cooling air is flowing from left to right, as viewed in Fig. 10, the one face 81 of every other tube 12 faces into the oncoming air while the alternating tubes have the opposite faces 82 facing into the oncoming air. Rotating the tubes 12 about the axes of the trunnions 80,80' will reverse the orientation of the tubes 12 resulting in air striking the opposite faces 82,81 of the tubes. Being able to reverse the orientation of the tubes 12 provides a self-cleaning capability to the heat exchanger 43' in that the air flowing over surfaces 81,82 of the bottom two tubes of Fig. 10 will have a tendency to pack up debris in the apex of the two tubes which debris will be released when the tubes are rotated about the axis of the trunnions 80,80' from the solid line position to the dotted line position of Fig. 10. Fluid, such as water, may circulate between the spaced tanks 44' and 58' through the trunnions 80, end passages 85 through passageway 40, across grooves 15 and through second fluid passage 42. Fluid such as air, will flow in the external grooves 13 and over the exterior surfaces of the tube and ribs 14 to extract heat from said fluid inside the tube 12. The heat exchanger of either illustrated embodiment is of the primary surface type permitting cooling directly through the walls of the tubes 12, such as through center section 26, through edge portions 18,20 and through the walls of the ribs 14. Traditional heat exchangers will often spring leaks at the seams or weld lines. The present improved construction of Figs. 5 and 6 has the seams or welds 38,41,47 and the seam or weld joining each tube 12 to the tanks. It is possible to assemble the tubes 12 with the welds 38 all facing forward such that the welds are all accessable from the front making it possible to repair the heat exchanger without removing it from its setting. The heat exchanger being of the primary surface type, may have the tubes 12 fabricated from non-strategic metals, such as stainless or mild steel, or of non-metals, such as plastic or metal plastic composites. The material selected can also be noncorrosive with the cooling media used. By changing the rib pitch and shape, the heat exchanger performance can be further tailored to the engine cooling requirements thereby reducing heat exchanger frontal areas, fan sizes, fan drive horsepower and noise. WHAT WE CLAIM IS:

1. A method of manufacturing a heat exchanger tube, the method comprising forming a piece of sheet material into a continuously corrugated sheet with a plurality of side-by-side corrugations having a generally undulating profile in the plane of the sheet; crushing and flattening portions of the sheet to produce two separate groups of corrugations each group surrounded by a flattened portion of the sheet; folding the sheet along the flattened portion between the groups so that one corrugated group aligns with the other corrugated group and a passageway is formed at the fold of the sheet; and joining together the edges of the sheet remote from the fold to form a second passageway.

3. A method according to claim 2, wherein the welded end edges close off the

ends of the passageways communicating with the welded end edge sleeve.

4. A method according to claim 1, wherein the flattened end edges of the tube are welded together except for a connecting opening for permitting fluid flow from and to the tube.

5. A method according to claim 1, substantially as described with reference to Figures 1 to 7 and 11 or Figures 1 to 4 and 7 to 11 of the accompanying drawings.

6. A heat exchanger tube manufactured by a method according to claim 1, the tube having two elongate body portions, each body portion comprising a plurality of sideby-side corrugations extending across the tube, each corrugation having a generally undulating profile along its length, the sides of the corrugations lying transverse to the plane of the body portion and substantially parallel to one another, and the body portions being disposed side-by-side with crests of the corrugations of one body portion abutting corresponding crests of the corrugations of the other body portion to form passages, adjacent side edges of each body portion being secured together to form passageways extending to the longitudinal direction of the tube and communicating with the passages between the corrugations.

7. A heat exchanger tube according to claim 6, wherein the end edges of each portion are flattened, the end edges being connected together to form end passages, and including means for connecting the end passages to a heat source.

8. A heat exchanger tube according to any of claims 6 or 7 which is made of aluminium.

9. A heat exchanger tube according to any of claims 6 or 7, which is made of a metal from the group consisting of stainless steel, and mild steel.

10. A heat exchanger according to any of claims 6 or 7, which is made of a non-metallic material from the group consisting of A.B.S.

(Acrylonitrile Butadiene Styrene) and P.V.C. (Poly Vinyl Chloride).

11. A heat exchanger tube according to claim 6, substantially as described with reference to Figures 1 to 7 and 11, or Figures 1 to 4 and 7 to 11, of the accompanying drawings.

12. A heat exchanger including one or more heat exchanger tubes according to any of claims 6 to 11.

13. A heat exchanger according to claim 12, having at least one heat exchanger tube interposed between a pair of tanks and permitting fluid to flow between the tanks.

14. A heat exchanger according to claim 13, wherein a plurality of heat exchanger tubes extend between the tanks.

15. A heat exchanger according to claim 14, wherein the tubes are juxtaposed in closely spaced, substantially parallel relationship.

16. A heat exchanger according to claim 14, wherein the tubes have passages at each end thereof, and carry hollow trunnions communicating with the passages; the heat exchanger including means for pivotally mounting the trunnions in a respective tank.

17. A heat exchanger according to claim 14 or claim 15, wherein each end of each tube is welded to form a passage within the tube and to form the opening, which opens into the passage from one of the tanks.

18. A heat exchanger according to claim 17, wherein the openings are aligned each with one of the passageways, the respective passage associated with the opening being blocked from access to the other passageway.

19. A heat exchanger according to claim 18, wherein the opening is a trunnion about which the tube can rotate and the passage formed by the welding of each end communicates with only one of the passageways in the tube.

20. A heat exchanger according to claim 13, substantially as described with reference to Figures 1 to 7 and 11 or Figures 1 to 4 and 7 to 11.

21. A method of manufacting a heat exchanger, the method comprising mounting a plurality of heat exchanger tubes manufactured according to any one of claims 1 to 5 between a pair of tanks, the passageways in each tube communicating with the tanks.

22. A method of manufacturing a heat exchanger, the method comprising mounting a plurality of heat exchanger tubes according to any of claims 6 to 11 between a pair of tanks, the passageways in each tube communicating with the tanks.

23. A method according to claim 22, wherein the tubes are positioned side by side, flattened end edges of each tube being welded together, throughout a portion of each end to define a passage within the tube and to define a sleeve throughout the remainder of the end in communication with one of the passageways, the welded end edges and the sleeve being inserted in openings in the tanks and a weld being applied to the junction between the tubes and the tanks.

24. A method according to claim 21, substantially as described with reference to Figures 1 to 7 and 11 or Figures 1 to 4 and 7 to 11 of the accompanying drawings.