WO1998027395A1

WO1998027395A1 - Formed tubing with longitudinally directed corrugations

Info

Publication number: WO1998027395A1
Application number: PCT/NZ1997/000163
Authority: WO
Inventors: Murray James Kite
Original assignee: K & M Kite Ltd
Current assignee: K & M Kite Ltd
Priority date: 1996-12-16
Filing date: 1997-12-11
Publication date: 1998-06-25
Anticipated expiration: 1999-06-16
Also published as: AU5418998A

Abstract

A formed tube (2) has a plurality of corrugations (3) extending along the wall of the tube (2) in a direction of its longitudinal axis. In its use in a heat exchanger (1) external housing (6) may be provided having inlet (9) and outlet (10) for the fluid required to be heated or cooled. In the embodiment shown a heat source (4) with flame (5) may be positioned at one end of the heat exchanger (1). In other embodiments an electric element includes at eleast on filament extending through the corrugated tube. A method of forming a tube is also claimed.

Description

FORMED TUBING WITH LONGITUDINALLY DIRECTED CORRUGATIONS BACKGROUND OF INVENTION

This invention relates to formed tubing and apparatus utilising such tubing.

A variety of tubing, particularly metal tubing, has been utilised in various heat exchangers and similar apparatus where it is desired to increase the surface area of a tube with respect to the outside diameter or internal area of the tube. Such tubing includes helically spiralled tubing, or tubing having fins, arranged about the circumference of the tube whether integrally formed or subsequently attached to the tube.

However, although helically spiralled or finned tubes may be suitable in some circumstances they have been found to be unsuitable in many cases especially in not providing an effective heat transfer when the tube is used in a heat exchanger.

The terms "formed tubing" and "formed tube" are used in this specification to describe a tube which is wholly or substantially hollow and which has been formed to provide a required design. The term "heat exchanger" is used throughout to refer to the heating or cooling of a fluid flowing through it.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a formed tubing and/or a method of forming such tubing which overcomes some of the disadvantages of the prior art or at least provides the public with a useful choice.

Further objects of this invention will become apparent from the following description.

STATEMENTS OF INVENTION

In a first aspect, the invention may broadly be said to consist in a formed tube including: a substantially elongate tube; and

a plurality of substantially longitudinally directed corrugations provided for a wall of said tubing and over at least a substantial portion of the length of said tube.

Preferably said corrugations are substantially uniformly distributed about the circumference of said tube.

Preferably each of said corrugations is of a height substantially greater than the thickness of said wall of said tube.

In a second aspect, the invention may broadly be said to consist in a conduit for a heat exchanger including a substantially elongate tube having a plurality of corrugations along a wall of said tube over at least a substantial portion of the length of said tube in a substantially longitudinal direction.

In a third aspect, the invention may broadly be said to consist in an electrical element including a conduit having a plurality of corrugations provided in a wall of said conduit extending in a substantially longitudinal direction along at least a substantial portion of said conduit and having at least one filament within said conduit.

In a fourth aspect, the invention may broadly be said to consist in a method of forming a tube including the steps of:

providing a substantially elongate tube; and

forming a plurality of corrugations in a wall of said tube over at least a substantial portion of the length of said tube and wherein said corrugations extend substantially longitudinally along said tube.

Further aspects of this invention which should be considered in all its novel aspects will become apparent to those skilled in the art upon reading the following description. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings in which:

Figure 1 : shows an elevation of a heat exchange conduit utilising one embodiment of the invention;

Figure 2: shows an elevational view of a further embodiment of the invention;

Figure 3: shows an electrical element for use in conjunction with an apparatus according to an embodiment of the invention;

Figure 4: shows an elevational view of an electrical element incorporated in an apparatus according to one embodiment of the invention;

Figure 5: shows a further electrical element utilising a further embodiment of the apparatus according to the present invention;

Figure 6: shows a cross-sectional view through an electrical element utilising an embodiment of the apparatus of the present invention;

Figure 7A: shows an elevational view of a heat exchanger with an electrical element in accordance with a further embodiment of the apparatus of the present invention;

Figure 7B: shows a cross-sectional view through the apparatus of Figure 7;

Figure 8: shows a further cross-sectional view through an alternative embodiment of the apparatus; Figure 9: shows a cross-sectional view through a further embodiment of the apparatus of the present invention; and

Figure 10: shows a yet further cross-sectional view through an embodiment of the apparatus of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, one embodiment of the invention is shown utilised in the heat exchanger in Figure 1 . The heat exchanger 1 can be seen to include a tube or conduit 2 having a plurality of corrugations 3 arranged about the circumference of the tube 2. The corrugations 3 run substantially longitudinally along the tube 2 to be substantially coaxial with the axis of the tube 2.

An example of the tube 2 in cross-section can be seen in subsequent figures such as Figure 7B and Figure 9.

It can be seen that rather than being helically spiralled along the length of the tube 2, the corrugations 3 are substantially coaxial with the tube 2 to provide advantages in specific conditions where it is desirable to increase the surface area of the tube without increasing the turbulence associated with a helically spiralled tube. As can be seen in Figure 1 , the tube 2 may be incorporated within the heat exchanger 1 having heating source 4 providing, for example, a flame 5 to heat the fluid within the conduit 2. An outer housing 6 may enclose the conduit 2 over the corrugated portion and be sealed against the conduit 2 adjacent ends 7 and 8 about the corrugations 3. An inlet 9 and outlet 1 0 may be provided in the outer housing 6 for the introduction of a fluid to be heated on the outside of the conduit 2. Normally, such an inlet 9 and outlet 10 may be disposed at opposed ends of the portion of the conduit 2 carrying the corrugations 3.

The conduit 2 may be made from a variety of materials. Depending upon the use to which the conduit is to be put and the method of formation, the conduit may be made from metals or, alternatively, plastics or ceramic materials. It may be preferred that metallic conduits are used in the majority of applications. Further, although the figures generally show conduits formed from a cylinder of substantially constant cross-section, tapered conduits may be used and formed to provide a tapered conduit having the same general cross- r sectional shapes.

Turning to Figure 2, a similar conduit 2 having corrugations 3 is shown for use, again with some form of heat source 4. In this case, the heat exchanger is provided as an open form to exchange heat with a surrounding , _n fluid including air or similar.

Another use for the conduit 2 having longitudinal corrugations 3 may be as an electrical element. Such an example is shown in Figure 3 where an element 1 1 is provided. This element may have at least one filament 1 2 running through the conduit 2. Typically, the internal space 50 inside the

15 conduit 2 and surrounding the filament 1 2 would be filled with an electrically insulating material such as magnesium oxide or similar material. To make such an element, the conduit 2 may be provided with suitable corrugations 3 and the filament 1 2 placed internally. Magnesium oxide may then be poured into the conduit 2. Compression of the magnesium oxide may be desirable.

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In Figure 4 a further electrical element 1 3 is shown having a filament 1 2 surrounded by a suitable material such as magnesium oxide 1 4 and encompassed within a conduit 2 having corrugations 3 to increase the surface area of the overall element 1 3 through which the heat is dispersed.

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Figure 5 shows a further electrical element 1 5 with a filament 1 2 and the entire internal core of the conduit 2 and about the filament 1 2 may be filed with magnesium oxide. The depth of the corrugations 3 may be varied for different circumstances as shown in a comparison of Figure 4 and Figure 5.

30 When embodied within a further conduit 6, cross-sections through Figures 4 and 5 are shown in Figures 9 and 1 0 to demonstrate the variation in the form of the corrugations 3. It is preferred that the depth of the corrugation is significantly greater than the wall thickness of the conduit and, as shown in the examples, the depth is many times the wall thickness.

As shown in Figure 6, an electrical element formed from the conduit 2 may be provided with a plurality of filaments 1 2 with each filament 1 2 running within the corrugations 3. This is an alternative configuration to the single filament centrally through the conduit 2. Again magnesium oxide or other suitable material 1 4 can be provided about the filaments 1 2.

5

Figure 7A and the cross-section of the apparatus 51 of Figure 7A shown in Figure 7B again show a heat exchanger, however, this time, an electrical element 1 2 is incorporated.

, _n In these figures, the filament 1 2 may be inside a core of magnesium oxide 1 4 which itself resides within the conduit 2. A surrounding housing 6 allows water or fluid to pass around the outer circumference of the conduit 2 between an inlet 1 7 and an outlet 1 8. Again, corrugations 3 seek to increase the surface area of the element to improve contact with the fluid between the conduit 2 and the outer housing 1 6. It can be seen that the inlet 1 7 and 1 8

15 may be separated by a barrier 1 9 running the length of the overall heat exchanger element so that the fluid must traverse both circumferentially and longitudinally about the tube 2 between the inlet and the outlet.

Figure 8 shows a cross-section through a yet further embodiment of an

20 electrical element having a filament 1 2 within the conduit 2 again suitably within a material such as magnesium oxide 1 4. This conduit 2 is shown with a relatively small diameter central portion to maximise the depth of the corrugations 3 with respect to the overall diameter of the conduit 2. The corrugations 3 here are shown internally being wholly or substantially closed up

25 or crimped internally.

To form the tubing, a standard cylindrical tube may be extruded or, alternatively, a multi-sided die may be used to press the corrugations into the sides of the conduit.

30

An alternative form of manufacture to produce an indefinite length of the article is to utilise forming wheels acting on the outer circumference to form the corrugations through the wall of the tube. Such a method of manufacture is disclosed in International Patent Application No. PCT/NZ93/00087. This international application relates to the formation of helically corrugated tube and the apparatus may be adapted to form the longitudinally progressing corrugations of the present invention. The preference between pressing, extruding or casting such conduits may vary according to the material chosen. Furthermore, it may be determined by the final shape desired and, in particular, whether standard length items such as those shown in Figure 2 are made or whether a long run extruded or continuously formed process is preferred.

In Figures 9 and 10 the tubes or conduits 2 with varying depths of corrugations 3 and with their filaments 1 2 are shown positioned within their outer housings 6 a relatively large space 52 being shown in these embodiments being provided between the outer surface of the tubes 2 and the inner wall surface of the housings 6.

In further uses of the conduits, plastics may be preferred if it is to be used as tubing in solar heat exchangers. Again, the increased surface area available through the use of this conduit may be of value in a solar heat exchanger.

By forming such a conduit, the conduit or tube provides a greater surface area for a set outer diameter on both the inside and outside of the tube. Furthermore, with the corrugations being formed in a wave like manner about the outer circumference, some expansion of the conduit can be easily provided through the opening of those corrugations. This may benefit uses in circumstances where a conduit is subject to potential freezing of the fluid within it, or other significant heat changes that require some expansion and contraction of the conduit to avoid breakage or fracture.

Thus, it can be seen that the invention provides a tube, a method of forming a tube and apparatus utilising the formed tube with advantages over previously available proposals.

Where in the foregoing description reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although external corrugations 3 are shown provided in the above embodiments along the external wall it is envisaged that in some instances the corrugations 3 could be provided along the internal wall of the tube 2 as well as or instead of the external wall.

Although this invention has been described by way of example and with reference to possible embodiments thereof it is to be understood that modifications or improvements may be made thereto without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

1 . A formed tube including:

a substantially elongate tube; and a plurality of substantially longitudinally directed corrugations provided for a wall of said tube and over at least a substantial portion of the length of said tube.

2. A formed tube as claimed in claim 1 wherein said corrugations are substantially uniformly distributed about the circumference of said tube.

3. A formed tube as claimed in claim 1 or claim 2 wherein each of said corrugations is of a height substantially greater than the thickness of said wall of said tube.

4. A formed tube as claimed in any one claims 1 to 3 wherein said corrugations extend substantially coaxially with the longitudinal axis of the tube.

5. A tube as claimed in any one of claims 1 to 4 wherein the tube is tapered between its respective ends.

6. A tube as claimed in any one of claims 1 to 5 wherein the height of each corrugation is substantially greater than the diameter of a central portion of said tube.

7. A tube as claimed in any one of claims 1 to 6 wherein the corrugations do not extend to the respective ends of the tube.

8. A tube as claimed in any one of claims 1 to 7 of a metallic, plastics or ceramic material.

9. A tube substantially as herein described with reference to any one of the embodiments of the accompanying drawings.

10. A conduit for a heat exchanger including a tube as claimed in any one of the preceding claims.

c 1 1 . A conduit as claimed in claim 10 wherein said tube is positioned within an external housing so that a fluid to be heated or cooled can pass between said corrugations and an internal wall of said housing.

1 2. A conduit as claimed in claim 1 1 wherein said housing is secured at , . opposite ends of said tube beyond the extent of said corrugations.

1 3. A conduit as claimed in claim 1 1 or claim 1 2 wherein said housing is provided with at least one fluid inlet and at least one fluid outlet.

1 4. A conduit as claimed in claim 1 3 wherein a barrier means is provided

15 between said at least one inlet and said at least one outlet whereby said fluid must traverse both circumferentially and longitudinally about said tube between said inlet(s) and said outlet(s).

„ _n 1 5. A conduit as claimed in any one of claims 1 0 to 14 wherein each of said corrugations is of a height such that a space exists between the corrugations and the internal wall of said housing.

1 6. A conduit substantially as herein described with reference to any one of the embodiments of the invention shown in the accompanying drawings.

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1 7. An electric element including a conduit as claimed in any one of claims 1 0 to 1 6 and including at least one filament extending through said tube.

1 8. An electrical element as claimed in claim 1 7 wherein a plurality of said

30 filaments are provided with at least one of said filaments extending through each of said corrugations.

1 9. An electrical element as claimed in claim 1 7 or claim 1 8 wherein an electrically insulating material is provided about the or each filament.

20. An electrical element substantially as herein described with reference to any one of the embodiments of the accompanying drawings. ethod of forming a tube including the steps of:

providing a substantially elongate tube; and forming a plurality of corrugations in a wall of said tube over at least a substantial portion of the length of said tube and wherein said corrugations extend substantially longitudinally along said tube.