AU2010233051A1

AU2010233051A1 - Heat Exchanger Tube Assembly

Info

Publication number: AU2010233051A1
Application number: AU2010233051A
Authority: AU
Inventors: Peter David Hall
Original assignee: AIRDRILL Pty Ltd
Current assignee: AIRDRILL Pty Ltd
Priority date: 2003-10-02
Filing date: 2010-10-14
Publication date: 2010-11-04
Also published as: US20050072562A1; AU2004216619A1

Description

P/00/011 28/5/91 Regulation 32 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Airdrill Pty Ltd Actual Inventor Peter David Hall Address for service is: WRAYS Ground Floor, 56 Ord Street West Perth WA 6006 Attorney code: WR Invention Title: Heat Exchanger Tube Assembly The following statement is a full description of this invention, including the best method of performing it known to me: 1 -2 "Heat Exchanger Tube Assembly" Field of the Invention The present invention relates to a heat exchanger tube suitable to be incorporated into a heat exchanger, as well as a method of manufacturing such a 5 heat exchanger tube. Background Art Heat exchangers are utilised in a broad range of applications where it is necessary to transfer heat to or from a particular item of equipment, such as an air compressor, air conditioning unit, booster or engine. 10 A typical heat exchanger commonly used in air or gas heating and cooling applications such as those identified above is that of the "cross-flow" type. Such exchangers generally comprise an arrangement of tubes through which a first fluid is passed and across which a second fluid (often a gas) is passed. A particular type of cross-flow exchanger comprises an arrangement of tubes, 15 each of which is provided with a plurality of fins along, and extending generally transverse to, its length. Where the heat exchanger is being utilised to cool the equipment concerned, hot fluid from that equipment is passed through the tubes whilst a cooler fluid (often a gas) is passed over the fins and tubes to extract heat therefrom and thus to cool the hot fluid. The fins assist In cooling the hot fluid by 20 providing a large heat transfer area. It is desirable that the fins be thin to maximise the surface area available for transfer of heat within the particular space available. In this particular type of cross-flow exchanger, it is often necessary that the fluid be passed through the tubes under relatively high pressures, As a result, it is in 25 many instances also desirable that the tubes be robust.

-3 Cross-flow heat exchangers generally use fins made of aluminium or copper due to the excellent heat conduction characteristics of those metals. However, their use introduces other problems. Generally the tubes used are not made of the same metal as they are required to 5 be more robust. Galvanic corrosion tends to occur as a result of the dissimilarity in the metals. Such galvanic corrosion gives rise to oxides which are poor conductors of heat and which thus compromises the heat transfer between the tubes and fins. A further dIsadvantage, Is the relative softness of those metals and thus the 10 vulnerability of the fins to damage, particularly from impact such as during cleaning with a high pressure hose. Moreover, those metals oxidise and/or -perish over time in harsh operating conditions. Disclosure of the Invention Accordingly, the invention resides in a heat exchanger tube assembly comprising 15 a tube having a plurality of fins mounted thereto at spaced intervals along its length, each fin having at least one aperture through which the tube is received, each fin having an integral spacer to define the spaced interval from an adjacent fin, the spacer extending from the rim of the aperture generally transversely to the fin to provide an inner surface profiled to contact and cooperate with the 20 external surface of the tube across substantially the entire length thereof between the fin to the adjacent fin to enhance heat transfer from the tube to the fin, the spacer being bonded to the tube by a thermally-conductive medium. According to a preferred feature of the invention, the fins are formed of generally the same material as the tube, 25 According to a preferred embodiment, said material Is a steel. According to a preferred feature of the invention, the thermally conductive medium occupies a region between the extemal surface of the tube and the inner -4 surface of the spacer to thereby enhance said heat transfer from. the tube to the fin. According to a preferred feature of the invention, each spacer Is configured as an annular flange. 6 According to a preferred embodiment, said annular flange is discontinuous around the circumference of said tube. According to a preferred embodiment, said annular flange comprises a plurality of tabs disposed around the circumference of said tube. According to a preferred feature of the invention, said fins are resistant to 10 permanent deformation under conditions typically encountered by a heat exchanger. According to a further preferred feature of the invention, each spacer is closely adjacent the external surface of said tube. According to a preferred feature of the invention, said heat exchanger tube 15 assembly Is covered with a corrosion-resistant material. According to a preferred feature of the invention, said corrosion-resistant material is said thermally-conductive medium. A heat exchanger tube assembly as claimed in any one of the preceding claims wherein said thermally-conductive medium is zinc or zinc alloy. 20 According to a further aspect the invention resides in a heat exchanger comprising a plurality of heat exchanger tube assemblies as previously described, said tubes being held in parallel spaced relation, adjacent tubes being interconnected by at least some of said fins, each tube being received through an aperture provided in said fins, each fin having at least two apertures to 25 thereby interconnect adjacent tubes.

-5 According to a further aspect the invention resides in a heat exchanger comprising a plurality of heat exchanger tube assemblies as previously described, said tubes being held in parallel spaced relation, each tube being interconnected with at least one adjacent tube by a group of fins, each fin having 5 two apertures to receive said adjacent tubes to thereby interconnect adjacent tubes. According to a further aspect the invention resides in method of manufacturing a heat exchanger tube assembly, said method comprising the steps of mounting a plurality of fins to a tube and bonding the fins to the tube with a thermally 10 conductive medium, each fin having at least one aperture through which the tube is received, each fin having an integral spacer to define the spaced interval from an adjacent fin, the spacer extending from the rim of the aperture generally transversely to the fin to provide an Inner surface profiled to contact and cooperate with the external surface of the tube across substantially the entire 15 length thereof between the fin to the adjacent fin to enhance heat transfer from the tube to the fin. According to a preferred feature of the invention, the method further comprises the step of covering the fins and tube with a corrosion-resistant material. According to a preferred embodiment, the methods of bonding the fins to the 20 tube and covering of the fins and tube comprises a hot-dip, zinc or zinc-alloy galvanising procedure. The invention will be more fully understood In the light of the following description of specific embodiments. Brief Description of the Drawings 25 The description is made with reference to the accompanying drawings of which: Figure 1 is a perspective view of a heat exchanger tube according to the first embodiment with part of its coating shown cut-away (for clarity); -6 Figure 2 is a front elevation view of the heat exchanger of Figure 1; Figure 3 is a perspective view of a fin of the type incorporated in the heat exchanger tube of Figure 1; Figure 4 is a perspective view of a heat exchanger tube according to the second 5 embodiment; Figure 5 is a perspective. view of a fin of the type incorporated in the heat exchanger tube of Figure 4; Figure 6 is a perspective view of a heat exchanger tube assembly according to the third embodiment of the invention and comprising fins of the type depicted in 10 Figure 5; Figure 7 is a front elevation view of a repeating unit of the type incorporated In the heat exchanger tube assembly shown In Figure 6; and Figure 8 is a perspective view of a heat exchanger tube assembly according to a fourth embodiment of the invention and comprising fins of the type depicted in 15 Figure 5. Detailed Description of the Specific Embodiments Figures 1, 3 and 5 Illustrate the first, second and third embodiments respectively. Each of those embodiments comprises at least one tube and a plurality of fins mounted thereto. Each fin has at least one aperture through which the tube Is 20 received. The heat exchanger tube assembly 10 according to the first embodiment is shown at Figures 1 and 2 and comprises a tube 12 and a plurality of fins 14 mounted to the tube 12. The tube Is typically made from steel due to the robust properties provided by that material which enable it to withstand harsh 25 environments. In particular, it has the ability to resist fatigue when subject to -7 vibration, provided the system is designed appropriately. As well, it is able to withstand substantial knocks, impacts and the like. Each fin 14 has an aperture 16 through which the tube 12 is received and is also provided with a spacer 20 on an axial face thereof. In other embodiments, such 5 spacers may be provided on both axial faces of each fin. The spacers 20, which are located between adjacent fins 14, maintain a regular spacing between those fins 14 along the tube 12. The fins 14 are formed of generally the same material which, in the case of this embodiment, is steel. A detailed view of a fin 14 of the type used in the first embodiment is shown at 10 Figure 3. The spacer 20 is integrally formed with the fins 14 and extends from the rim of the aperture 16 generally transversely to the fin 14. It is thereby positioned so as to be closely adjacent to the external surface of the tube 12. The spacer 20 Is configured as an annular flange so as to conform with the external surface of the 15 tube 12. The annular flange is discontinuous around Its circumference to provide a plurality of tabs around the rim of the aperture 16. In this embodiment, the tabs are disposed at regular angular intervals around the rim of the aperture 16. The fin 14 is produced from steel sheeting, the aperture 16 being stamped therein to be of a diameter which is such that the aperture 16 which will snugly 20 receive the tube 12 therethrough. The stamping device is suitably formed to produce tabs 20, initially in the plane of the fin 14. The tabs 20 are then bent out of that plane to extend from the rim of the aperture. In the forming process, the tabs are suitably profiled to provide an inner surface to contact and cooperate with the external surface of the tube to enhance heat transfer from the tube to the 25 fin. In the case of the embodiments described herein, each of the fins 14 is discrete though, in alternative embodiments, the fins may be provided as a one-piece assembly such as in the form a helix.

-8 The fins 14 are bonded to the tube 12 by zInc 11 which is a thermally-conductive and corrosion resistant medium. The zinc 11 occupies the regions between the external surface of the tube 12 and the inner radial faces both of the fins 14 and the tabs 20, giving rise to a substantially continuous bond between the fins 14 5 and the tube 12. The manner in which this is achieved is discussed further below. The substantially continuous bond provides for efficient heat transfer from the tube to the fins and also creates a relatively robust mounting of the fins 14 to the tube 12. The entire exterior of the heat exchanger tube 10 is also coated in zinc to render it corrosion-resistant. 10 The method of manufacturing the heat exchanger tube 10 will now be described with reference to the drawings. Firstly, the fins 14, which may have been formed in the manner described above, are received over the tube 12 such that the spacer 20 of each fin 14 abuts an adjacent fin 14 (best shown at FIgure 2). If It Is felt necessary, the fins 14 may then be tack welded to the tube 12 to assist in 15 locating the fins 14 in their desired position on the tube 12 prior to coating with the zinc 11. Alternatively, they may be of a sufficiently snug fit that no such welding is needed. The fins 14 and tube 12 forming the heat exchanger tube 10 are then hot-dipped In molten zinc to galvanise the heat exchanger tube 10. Hot-dipping of the heat 20 exchanger tube 10 in zinc is advantageous in that it not only renders the heat exchanger tube 10 corrosion-resistant but simultaneously bonds the fins 14 to the tube 12. Moreover, the zinc, as applied by hot-dipping is pervasive and occupies the regions between the external surface of the tube 12 and the inner radial faces both of the fins 14 and the tabs 20, giving rise to the substantially 25 continuous bond between the fins 14 and the tube 12 and thus providing for efficient heat transfer, as described above. It will thus be appreciated that the spacer 20 provides two functions: namely it acts to provide a definite, predefined spacing between adjoining fins to simply assembly of the fins as one fin may be pressed along the tube 12 until it contacts 30 the spacer of the previous fin, and more importantly, the inner surface of the spacer 20 provides a broad area of contact with tube 12 to enable better transfer -9 of heat fmm the tube 12 to the fin 14. In this regard a spacer comprising a continuous annular flange might well provide the best solution from this point of view. However, by segmenting the spacer 20 into tabs the fins 14 are more easily mounted to the tube 12 and it is even less likely that zinc will fail to 5 penetrate between the tube 12 and the inner surface of the spacer 20 during the hot-dip process. The heat exchanger tube 10 is relatively robust, owing to the fins 14 being formed of steel, which is resistant to permanent deformation, and also due to the continuity and area, and thus the strength, of the zinc bond between the external 10 surface of the tube 12 and the Inner radial faces both of the fins 14 and the tabs 20. It has been found that the use of steel fins with the inherently lower heat conductivity as compared with metals such as copper and aluminium results in little deterioration in overall performance of the heat exchanger. It is believed 15 that this is partly due to the high thermal conductivity of the zinc and because the reduction, in conductivity is compensated for by the improvement in the bond, and thus in the heat conductivity of the junction, between the fins 14 and the tube 12. Furthermore, galvanic corrosion between the fins 14 and the tube 12 Is eliminated because the fins 14 and the tube 12 are made of substantially the 20 same material, while the zinc coating provides the well known galvanic protection to the assembly, In particular, corrosion at the junction between the fins and the tubes is eliminated. At the same time, the zinc coating provides stiffness to the fins and the tubes. In particular, in use, the steel fins are able to withstand the force of high pressure sprays used for cleaning without permanent deflection 25 thereby better maintaining their cooling effectiveness during the life of the heat exchanger. The heat exchanger tube assembly 10, in addition to offering the abovementioned advantages, Is relatively economic to manufacture.

-10 The second embodiment of the Invention. is illustrated at Figure 4. The second embodiment is a variation of the first embodiment though the heat exchanger tube 10 comprises a pair of parallel tubes 12 respectively received through a pair of apertures 16. 5 A fin 14 of the type used in the second embodiment is shown at Figure 5. The fin 14 is manufactured in an identical fashion to that which is incorporated in the first embodiment though it is formed with a pair of apertures 16 each of which is provided with a spacer 20 identical to that described in connection with the first embodiment. 10 The advantage offered by the second embodiment, over the first, is that a given number of fins 14 in this embodiment Is sufficient for two tubes 12 rather than just one tube. This results in a saving in manufacturing costs because the labour required in cutting andlor stamping a single fin is not significantly greater than that required to produce a fin in accordance with the first embodiment. 15 A further advantage is a stiffening effect which is created along the axis between the pair of adjacent tubes 12 as a result of their being tied together by the fins 14. This can reduce vibration, both of the heat exchanger tube 10 and in the heat exchanger generally, and thus increase the life of the heat exchanger. The third embodiment of the invention, which is illustrated at Figure 6, is a heat 20 exchanger tube assembly 100 based on a variation of the heat exchanger tube 10 according to the second embodiment. The heat exchanger tube assembly 100 comprises a plurality of tubes 12 interconnected by fins 14 of the type illustrated in Figure 5. The heat exchanger tube assembly 100 Is comprised of a series of repeating 25 units, one such unit 40 being illustrated at Figure 7. The unit 40 is similar to the heat exchanger tube 10 depicted at Figure 4 though alternate fins 14', along the length of one of the tubes 12', do not extend to the other tube 12" in that unit 40, the unoccupied apertures 16' of those alternate fins 14' instead being intended to receive another tube 12" of an identical unit 40 shown in broken lines.

-11 The assembly 100 is formed from the desired number of units 40 prior to hot-dipping. As can be seen at Figure 6, the tubes 12 in that assembly 100 need not be coplanar, thus enabling the configuration of the assembly 100 to be adjusted so as to conform with space restrictions and/or the layout of adjacent 5 equipment. Indeed, the ability. to interlink tubes with the fins in this manner enables novel heat exchanger configurations to be devised. Figure 8 illustrates a fourth embodiment which shows an arrangement 110 providing a group of 8 tubes 12 which are disposed in a octagonal configuration and interlinked with fins 14. As there are no end tubes, such a configuration has a high degree of 10 inherent rigidity requiring little additional support. As well, such a configuration allows the cooling fluid to be either supplied or withdrawn from a direction parallel to the tubes 12, rather than transverse to them, which may be beneficial in certain applications. Once that configuration has been suitably adjusted, the fins 14 may be tack 15 welded to the respective tubes 12, prior to hot-dipping, so as to assist in locating the fins 14 in their desired position on the tubes 12 and to maintain the configuration of the assembly 100. An advantage offered by this embodiment, and shared by the second embodiment, is the stiffening effect which is created along the axis between the 20 pairs of adjacent tubes 12' and 12" as a result of their being tied together by the fins 14'. Such a stiffening effect is also realised along the axis between the pairs of adjacent tubes 12' and 12" as a result of their being tied together by the fins 14' and also the fins 14". The fins 14' and 14" thus offer lateral restraint to tubes 12' and 12" throughout the assembly 100, thus possibly reducing vibration, both 25 of the assembly 100 and in the heat exchanger generally and Increasing the life of the heat exchanger. Moreover, it can be seen that the tube which is second-from-right in Figure 5 is, advantageously, laterally restrained in two different axes, those axes extending between that tube and the tubes to its left and right (which are not coplanar) respectively. 30 As an alternative to the unit 40 shown in Figure 7, units comprising fins of other profiles and having any number of apertures (i.e. possibly more than two -12 apertures) are possible. It Is clear that such units may be tied to other units, whether like or unlike, using suitably-profiled fins having appropriately-spaced apertures, those fins, depending on the arrangement of the apertures, being able to provide stiffening and lateral restraint along several different lateral axes. 5 It should also be appreciated that the arrangement of the fins 14' with respect to the fins 14" need not be staggered as depicted in Figure 6, provided those fins still provide adequate lateral restraint, stiffening and heat transfer characteristics throughout the heat exchanger assembly. It should be appreciated that the scope of the present invention need not be 10 limited to the particular scope of the embodiments described above. Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 15

Claims

1. A heat exchanger tube assembly comprising a tube having a plurality of fins mounted thereto at spaced intervals along its length, each fin having at least one aperture through which the tube is received, each fin having an integral spacer to 5 define the spaced interval from an adjacent fin, the spacer extending from the rim of the aperture generally transversely to the fin to provide an inner surface profiled to contact and cooperate with the external surface of the tube across substantially the entire length thereof between the fin to the adjacent fin to enhance heat transfer from the tube to the fin, the spacer being bonded to the tube by a 10 thermally-conductive medium.

2. A heat exchanger tube assembly as claimed in claim 1 wherein the fins are formed of generally the same material as the tube.

3. A heat exchanger tube assembly as claimed in claim 2 wherein said material is a steel. 15

4. A heat exchanger tube assembly as claimed in any one of the preceding claims wherein the thermally conductive medium occupies a region between the external surface of the tube and the inner surface of the spacer to thereby enhance said heat transfer from the tube to the fin.

5. A heat exchanger tube assembly as claimed in any one of the preceding 20 claims wherein each spacer is configured as an annular flange.

6. A heat exchanger tube assembly as claimed in claim 5 wherein said annular flange is discontinuous around the circumference of said tube.

7. A heat exchanger tube assembly as claimed in claim 5 or claim 6 wherein said annular flange comprises a plurality of tabs disposed around the 25 circumference of said tube. -14

8. A heat exchanger tube assembly as claimed in any one of the preceding claims wherein said heat exchanger tube assembly is covered with a corrosion-resistant material.

9. A heat exchanger tube assembly as claimed in claim 8 wherein said 5 corrosion-resistant material is said thermally-conductive medium.

10. A heat exchanger tube assembly as claimed in any one of the preceding claims wherein said thermally-conductive medium is zinc or zinc alloy.

11. A heat exchanger comprising a plurality of heat exchanger tube assemblies as claimed in any one of the preceding claims, said tubes being held in parallel 10 spaced relation, adjacent tubes being interconnected by at least some of said fins, each tube being received through an aperture provided in said fins, each fin having at least two apertures to thereby interconnect adjacent tubes.

12. A heat exchanger comprising a plurality of heat exchanger tube assemblies as claimed in any one claims 1 to 10, said tubes being held in parallel spaced 15 -relation, each tube being interconnected with at least one adjacent tube by a group of fins, each fin having two apertures to receive said adjacent tubes to thereby interconnect adjacent tubes.

13. A method of manufacturing a heat exchanger tube assembly, said method comprising the steps of mounting a plurality of fins to a tube and bonding the fins 20 to the tube with a thermally-conductive medium, each fin having at least one aperture through which the tube is received, each fin having an integral spacer to define the spaced interval from an adjacent fin, the spacer extending from the rim of the aperture generally transversely to the fin to provide an inner surface profiled to contact and cooperate with the external surface of the tube across substantially 25 the entire length thereof between the fin to the adjacent fin to enhance heat transfer from the tube to the fin,

14, A method of manufacturing a heat exchanger tube assembly as claimed in claim 13 further comprising the step of covering the fins and tube with a corrosion-resistant material.

- 15 15. A method of manufacturing a heat exchanger tube assembly as claimed in claim 14 wherein the methods of bonding the fins to the tube and covering of the fins and tube comprises a hot-dip, zinc or zinc-alloy galvanising procedure.

16, A heat exchanger tube assembly substantially as herein described. 5

17. A heat exchanger tube assembly substantially as herein described with reference to the accompanying drawings.