GB2466639A

GB2466639A - Heatable hose

Info

Publication number: GB2466639A
Application number: GB0823635A
Authority: GB
Inventors: Jason Daniel Harold O'connor; Neil Malone
Original assignee: Heat Trace Ltd
Current assignee: Heat Trace Ltd
Priority date: 2008-12-30
Filing date: 2008-12-30
Publication date: 2010-07-07
Anticipated expiration: 2028-12-30
Also published as: GB201307511D0; GB2501824A; GB2466639B; GB0823635D0; GB2501824B

Abstract

A heatable conduit comprising; a tube (10) through which a fluid may flow; a quantity of electrically conductive material (12) extending along and/or around the tube (10); a first conductor (14) disposed around and extending along the tube (10) to form a first conductor helix; and a second conductor (16) disposed along and/or around the tube (10), the first and second conductors (14, 16) being in electrical connection with the quantity of electrically conductive material (12).

Description

HEATABLE CONDUIT

The present invention relates to a heatable conduit (i.e. a conduit that may be heated). In particular, the present invention relates to a heatable conduit through which a fluid may pass (e.g. flow).

It is known to provide heatable conduits suitable for carrying a fluid. A known example of such a conduit comprises a tube through which a fluid may flow. Surrounding an outer surface of the tube, and extending along the outer surface of the tube, is provided a layer of material which has a positive temperature coefficient of resistance. Two electrical conductors are disposed in electrical contact with the layer of material that has a positive temperature coefficient of resistance (i.e. referred to as a layer of PTC material, PTC being an abbreviation of positive temperature coefficient of resistance). The conductors may be located on an outer surface of the layer of PTC material, such that the layer of PTC material separates the conductors from the tube which carries the fluid. In another alternative, the conductors may be embedded within the layer of material, or be provided in-between the layer of material and the tube. In such known examples, the two conductors are located on opposite sides of the tube (i.e. the conductors are diametrically opposed). The two conductors extend parallel to one another and along the length of the conduit.

Known examples of heatable conduits have found a wide variety of applications. For instance, heatable conduits may be used in the automotive industry to, for example, fluidly connect one or more windscreen washer nozzles to a reservoir containing water or the like. The heatable conduits may be heated by passing a current along the conductors, and the amount of heat may be chosen such that water within the conduit cannot become frozen, andlor so that any water is maintained or converted to a fluid state (for example, from a frozen state). In a different but related example, such a heatable conduit may be used to prevent water provided to a cold water tap from freezing, for example in a house, caravan, external supply, and the like.

Although known heatable conduits are found in a wide variety of applications, such known heatable conduits have disadvantages associated with them. As discussed above, in a known heatable conduit the two conductors are diametrically opposed from one another and extend along the heatable conduit parallel to one another. If the heatable conduit is bent, for example during installation or use, the conductor may be moved in an undesirable maimer. For example, bending such a heatable conduit around a corner may result in one or both of the two conductors becoming detached from the layer of PTC material, and this may result in a degradation in the performance of the heatable conduit in or around the region of the bend. In bending the heatable conduit, the conductors may alternatively or additionally move towards or away from one another around the circumference of the conduit. Such movement can result in a variation in the heat output of the heatable conduit in the regiOn of such movement, and this can be undesirable.

When a heatable conduit is designed, one of the design criteria is often the desired heat output of the heatable conduit, for example the heat output per unit length (e.g. per centimetre or metre). In order to meet such criteria the composition of the layer of PTC material has to be carefully designed and manufactured to ensure that the PTC material provides a desirable heat output. In order to ensure consistent heat output for heatable conduits of different diameters, a first heatable conduit having a first diameter may require a layer of PCT material having a first specific composition, and a second heatable conduit having a second diameter may require a layer of PCT material having a second specific composition. Having to design and manufacture different compositions of PCT material leads to an increase in design and manufacturing costs and complexity.

It is an object of the present invention to provide a heatable conduit which obviates or mitigates one or more problems of the prior art, whether identified herein or elsewhere.

According to a first aspect of the present invention, there is provided a heatable conduit comprising: a tube through which a fluid may flow; a quantity of electrically conductive material extending along andlor around the tube; a first conductor disposed around and extending along the tube to form a first conductor helix; and a second conductor disposed along and/or around the tube, the first and second conductors being in electrical connection with the quantity of electrically conductive material.

The second conductor may be disposed around andlor along the tube and be configured to form a second conductor helix.

One or more dimensions of the first conductor helix and/or the second conductor helix may be configured to ensure that, in use, the heatable conduit has a pre-selected heat output.

A spacing between loops of the first conductor helix and the second conductor helix may be configured to ensure that, in use, the heatable conduit has a pre-selected heat output.

A pitch of the first conductor helix andlor the second conductor helix may be configured to ensure that, in use, the heatable conduit has a pre-selected heat output.

One or more loops of the first conductor helix may be equally spaced from or between one or more loops of the second conductor helix.

The quantity of electrically conductive material may at least partially surrounds the tube.

The heatable conduit of any preceding claim, wherein the first conductor and/or second conductor may be at least partially located: between the tube and the quantity of electrically conductive material; and/or within the quantity of electrically conductive material; and/or between the electrically conductive material and outer insulation; and/or such that at least a part of the quantity of electrically conductive material separates the first and/or second conductor from the tube.

The first conductor and the second conductor may sandwich the quantity of electrically conductive material. For example, the first conductor and second conductor may be located either side (i.e. be separated by) the quantity of electrically conductive material.

The first conductor, second conductor and the quantity of electrically conductive material may form a stack, the quantity of electrically conductive material being located between the first conductor and the second conductor in the stack.

The first conductor, second conductor and the quantity of electrically conductive material may lie in substantially a same plane. The first conductor, second conductor and the quantity of electrically conductive material may lie in substantially a different plane.

The first conductor, second conductor and the quantity of electrically conductive material may together form a flexible band suitable for winding around the tube.

The quantity of electrically conductive material may be a layer, extrusion or coating.

One or more of the first conductor, second conductor and the quantity of electrically conductive material may be provided in the form of a sheet or foil.

The quantity of electrically conductive material may have a positive temperature coefficient of resistance.

The quantity of electrically conductive material may have a positive temperature coefficient of resistance sufficient for the material to be self-regulating.

The first andlor second conductor may be provided with a quantity of material having a negative coefficient of resistance.

According to a second aspect of the present invention there is provided a method of forming a heatable conduit using a tube, a quantity of electrically conductive material, a first conductor and a second conductor, the method comprising, in no particular order: disposing the first conductor along and around the tube to form a first conductor helix; disposing the second conductor along and/or around the tube; and disposing the quantity of electrically conductive material along and/or around the tube, the first and second conductors being in electrical connection with the quantity of electrically conductive material..

Disposing the second conductor along and/or around the tube may comprise disposing the second conductor along and around the tube to form a second conductor helix.

It will be appreciated that the first conductor, second conductor andlor quantity of electrically conductive material may be disposed along and/or around the tube in any particular order.

The second aspect of the invention may include, where appropriate, one or more features of the first aspect of the present invention.

According to a third aspect of the present invention there is provided a heatable receptacle comprising: a quantity of electrically conductive material extending along and/or the receptacle; a first conductor disposed around and extending along the receptacle to form a first conductor helix; and a second conductor disposed around and/or along the receptacle, the first and second conductors being in electrical connection with the quantity of electrically conductive material.

The second conductor may be disposed around and extend along the receptacle and be configured to form a second conductor helix.

The quantity of electrically conductive material may at least partially surround the receptacle.

The heatable conduit of any preceding claim, wherein the first conductor andlor second conductor may be at least partially located: between the receptacle and the quantity of electrically conductive material; andlor within the quantity of electrically conductive material; andlor between the electrically conductive material and outer insulation; andlor such that at least a part of the quantity of electrically conductive material separates the first andlor second conductor from the receptacle.

The first conductor, second conductor and the quantity of electrically conductive material may together form a flexible band suitable for winding around the receptacle.

The first and/or second conductor may be provided with a quantity of material having a negative coefficient of resistance.

According to a fourth aspect of the present invention there is provided a method of forming a heatable receptacle using a receptacle, a quantity of electrically conductive material, a first conductor and a second conductor, the method comprising, in no particular order: disposing the first conductor along and around the receptacle to form a first conductor helix; disposing the second conductor along and/or around the receptacle; and disposing the quantity of electrically conductive material along and/or around the receptacle, the first and second conductors being in electrical connection with the quantity of electrically conductive material.

Disposing the second conductor along and around the tube may comprise disposing the second conductor along and around the tube to form a second conductor helix.

One or more dimensions of the first conductor helix and/or the second conductor helix may be configured to ensure that, in use, the heatable receptacle has a pre-selected heat output.

It will be appreciated that the first conductor, second conductor and/or quantity of electrically conductive material may be disposed along and/or around the receptacle in any particular order.

The fourth aspect of the invention may include, where appropriate, one or more features of the third aspect of the present invention.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which: Figures 1 a and lb schematically depict end-on views of prior art heatable conduits; Figure 1 c schematically depicts a perspective view of the prior art heatable conduit shown in and described with reference to Figure 1 a; Figure 2 schematically depicts a side-on view of a heatable conduit in accordance with an embodiment of the present invention; Figures 3a-3c schematically depict different embodiments of a heatable conduit in accordance with an embodiment of the present invention; Figures 4a and 4b schematically depict different arrangements for heating the heatable conduit in accordance with an embodiment of the present invention; and Figure 5 schematically depicts a side-on and perspective view of a heatable conduit in accordance with another embodiment of the present invention.

Figure 1 a schematically depicts an end-on view of a prior art heatable conduit. The heatable conduit comprises a tube 2. Surrounding the tube 2, and extending along a length of the tube 2, is a layer of material 4 having a positive temperature coefficient of resistance (i.e. hereinafter referred to as the layer of PTC material). Embedded within the layer of PTC material are two diametrically opposed conductors: a first conductor 6 and a second conductor 8. The conductors 6, 8 extend parallel to one another along a length of the heatable conduit in a linear manner. A fluid (not shown) may flow through a bore 9 which the tube 2 provides.

By establishing an appropriate potential difference between the first conductor 6 and the second conductor 8, the layer of PTC material 4 in which the conductors 6, 8 are embedded may become heated. Heating of the layer of PTC material 4 causes, in turn, heating of the tube 2 and any fluid flowing through the bore 9 of the tube 2.

Figure lb schematically depicts an alternative prior art heatable conduit. The heatable conduit is provided with a tube 2. Surrounding the tube is a layer of PTC material 4.

Located on an outside surface of the layer of PlC material 4 (i.e. away from the tube 2) are two diametrically opposed conductors: a first conductor 6 and a second conductor 8.

The conductors 6, 8 extend parallel to one another along a length of the heatable conduit in a linear manner.

The heatable conduit of Figure lb works in the same way as shown in and described with reference to the heatable conduit of Figure 1 a. The difference between the heatable conduits shown in Figure Ia and Figure lb respectively is that in Figure lb the conductors 6, 8 are not embedded within the PTC layer 4, but are instead located on an outside surface of the layer of PTC material 4.

Figure 1 c shows a perspective view of the heatable conduit shown in and described with reference to Figure 1 a, It can be seen that the conductors 6, 8 extend parallel to one another along the length of the heatable conduit. If the conductors 6, 8 were located on an outside surface of the PTC layer 4 (as shown in and described with reference to Figure ib) the conductors 6, 8 would also extend along the heatable conduit parallel to one another.

As discussed above, there are various disadvantages associated with the prior art heatable conduits shown in and described with reference to Figures 1 a to I c. One disadvantage arises when bending the prior art heatable conduits, since the conductors of the heatable conduits can become separated from layer of PTC material, or can move towards or away from another. Either may result in a degradation in the heating performance of the heatable conduit in or around at least the region in which the conduit is bent. Another disadvantage is the need to provide a layer of PTC material with specific electrical characteristics for a given diameter of conduit (i.e. provide a layer of PTC material with a specific composition).

According to an embodiment of the present invention, at least one of the disadvantages associated with the prior art can be overcome by providing a heatable conduit for which first and second conductors extend around and along the conduit in a helical manner. The helical maimer in which the conductors extend along the heatable conduit allows the beatable conduit to be bent with less degradation in the heating performance of the beatable conduit when compared to prior art beatable conduits (in which the conductors extend along the conduit parallel to one another in a linear manner). This is because the helical form in which the conductors are wound around the beatable conduit is a more flexible arrangement than the prior art linear arrangement. For instance, a helix formed by a helically wound conductor may compress or expand slightly in the region in which the conduit is bent, rather than becoming detached from layer of PTC material.

Alternatively or additionally, by arranging the conductors in this helical manner, the problems associated with having to specifically design a layer of PTC material with specific characteristics for a given diameter of conduit is obviated or mitigated. This is because with a helical conductor arrangement the heat output of the heatable conduit may be controlled by appropriate variation of the pitch of each helix, andlor the pitch between (or space in-between) each respective helix formed by respective conductors. Thus, if greater heat output is required for a given cable, the pitch and separation of helices formed by the conductors can be reduced, whereas if the heat output needs to be lower, the pitch or spacing can be increased.

Figure 2 is a side-on view schematically depicting a heatable conduit in accordance with an embodiment of the present invention. The construction of the heatable conduit shown in Figure 2 is, in many ways, similar to the prior art constructions shown in and described with reference to Figures 1 a to 1 c. For instance, the heatable conduit of Figure 2 comprises of a tube 10 (shown in dashed outline in the Figure, because it is not visible in a side-on view) surround by a layer of PlC material 12. Furthermore, extending along the beatable conduit are two electrical conductors: a first electrical conductor 14 and a second electrical conductor 16. The conductors 14, 16 are in physical contact with the layer of PTC material 12 and are also in electrical connection with the layer of PlC material 12. The first conductor 14 and second conductor 16 are helically wound around and along (i.e. disposed around and along) the beatable conduit. Such an arrangement is in contrast to the constructions of the prior art beatable conduits shown in and described with reference to Figures 1 a to 1 c, where the conductors of the prior art beatable conduits are disposed in a diametrically-opposed arrangement, and extend parallel to one another along the heatable conduit in a linear manner.

Referring back to Figure 2, preferably the helix formed by the first conductor 14 is not in physical contact with the helix formed by the second conductor 16. This avoids any short circuits, and ensures that a potential difference is established between the conductors 14, 16 and across a region of PTC material.

The heat output of the heatable conduit shown in Figure 2 can be controlled by appropriate selection (i.e. control) of dimensions of the helices formed by the first conductor 14 and second conductor 16 that are helically wound around the layer of PCI material 12. For instance, the heat output of the heatable conduit will depend upon the distance between the first conductor 14 and second conductor 16 at any one region along the heatable conduit. This distance can be controlled in one of a number of ways. For instance, a pitch P1 of the helix formed by the first conductor 14 may be varied to affect the distance between the first and second conductors 14, 16. Alternatively or additionally, a pitch P2 of the helix formed by the second conductor 16 can be varied to control the distance between the first and second conductor 14, 16, Alternatively or additionally, the spacing between the first and second conductors 14, 16 can be controlled by controlling the distance D12 between the helices (or loops or windings of the helices) formed by the first and second conductors 14, 16. This may be achieved, for example, by the appropriate location of each of the helices relative to one another along the length of the conduit.

In one example, the pitch P1 of the helix formed by the first conductor 14 may be substantially equal to the pitch P2 of the helix formed by the second conductor 16. So long at the helices formed by each conductor are suitably displaced, the first and second conductors 14, 16 will never come into physical contact with one another along the length of the cable.

In another example, the pitch P1, P2 of each helix, andlor the space in-between each helix, can be controlled such that a spacing D12 between loops (or in other words windings) of adjacent helices is constant, thus providing a constant heat output along the length of the cable.

By varying the pitch of one or more of the helices, the spacing between the helices, and/or the space in-between the ioops of the helices, the heat output can be appropriately increased or decreased and controlled to have (substantially) a pre-selected magnitude. In stark contrast with the prior art, it is not necessary to design, formulate and manufacture different compositions of PTC material to provide different heat outputs.

Figure 2 shows an example of a heatable conduit for which the first and second conductors are wound around an outside surface of a layer of PTC material forming the heatable conduit. Other arrangements are also possible.

Figure 3a shows another example of a heatable conduit in accordance with an embodiment of the present invention. The heatable conduit comprises of a tube 10 provided with a bore 18 through which, for example, a fluid may flow. The first and second conductors 14, 16 are helically wound around the tube 10. A layer of PCT material 12 is then provided which surrounds the tube 10 and also the first and second conductors 14, 16. Finally, an (optional) insulation layer 20 is provided along the length of the heatable conduit to cover the layer of PTC material 12.

Figure 3a shows that a section of the PTC layer 12 has been cut away. In practice, this may not be undertaken. The cut away is shown in the Figure to aid the understanding of the present invention.

Figure 3b shows that instead of helically winding the first and second conductors 14, 16 around the tube 10 and then covering the tube and the conductors 14, 16 with a layer of PTC material, the conductors 14, 16 can instead be provided on an outer surface of the layer of PTC material 12 after the layer of the PCT material 12 has been provided along and around the tube 10. An (optional) insulating layer 20 can be provided to surround the first and second conductors 14, 16 and also the layer of PTC material 12.

Figure 3c shows that instead of the conductors being located on an outer surface of the tube 10 or the layer of PTC material 12, the first and second conductors 14, 16 can instead be located within (e.g. embedded within) the layer of PTC material 12. An (optional) insulation layer 20 may be provided along the length of the heatable conduit to cover the layer of PTC material 12.

Figure 3c shows that a section of the PTC layer 12 has been cut away. In practice, this may not be undertaken. The cut away is shown in the Figure to aid the understanding of the present invention.

In the embodiments described above, the first and second conductors have been described as being distinct and separated from one another as first and second helices wound around the heatable conduits. Other arrangements of the first and second helices are possible.

Figures 4a and 4b schematically depict two alternative arrangements.

Figure 4a shows that a sandwich structure may be formed by a first conductor 30, a second conductor 32 and a PTC layer 34. The sandwich structure is formed by stacking the first conductor 30 and the second conductor 32 either side of and in contact with the PTC layer 34. The sandwich structure may, for example, form a (preferably flexible) heating element tape or band. The tape or band may be helically wound around a tube 36 to form a beatable conduit in accordance with an embodiment of the present invention.

The heat output of the beatable conduit may be pre-selected by choosing a specific pitch at which to wind the tape or band around the tube 36.

In another example, Figure 4b shows that a sandwich structure may be formed by a first conductor 40, a second conductor 42 and a PTC layer 44. The sandwich structure is formed by locating the first conductor 40 and the second conductor 42 either side of and in contact with the PTC layer 44, the first conductor 40, second conductor 42, and PTC layer 44 all being arranged to lie in substantially the same plane. The sandwich structure may, for example, form a (preferably flexible) heating element tape or band. The tape or band may be helically wound around a tube 46 to form a heatable conduit in accordance with an embodiment of the present invention. The heat output of the heatable conduit may be pre-selected by choosing a specific pitch at which to wind the tape or band around the tube 46, andlor by varying a distance between the first and second conductors 40, 42 (e.g. by reducing the width of the PTC layer 44).

The arrangements shown and described with reference to Figures 4a and 4b may be advantageous, since they facilitate the straightforward and rapid helical deployment of conductors around a tube or the like. One or more elements of the arrangements shown in Figures 4a and 4b could be provided with an adhesive (preferably an adhesive with good heat conduction) for use in attaching the arrangement to a tube or the like.

In any of the embodiments described herein, one or more of the conductors, andlor the PTC material may be provided in the form of a foil or sheet. The foil or sheet may be flexible, and may have a larger surface area than, for example, a conductor in the form of a wire.

The tube described above through which, for example, a fluid may flow may be formed from plastic, for example a thermo plastic. The tube may alternatively be formed from an elastomer. Preferably, the tube is resistant to the fluid which flows through the tube. For example, the fluid might desirably be resistant to fuel, oil, or coolant if the beatable conduit is used, for example, in a fuel system of an aircraft or an automobile.

In the above embodiments, a heatable conduit has been described. The concept and advantages of the helically winding of power conductors may also be used to heat receptacles such as beverage containers or containers for foodstuffs (i.e. to form or provide a heatable receptacle). The conductors and PTC layer may be made small enough to easily fit below a label of the receptacle, or form a part of the label of the receptacle.

The receptacle could be heated by connecting the conductors to a power supply of the like.

In the above embodiments, both conductors have been described as extending along and around the heatable conduit andlor beatable receptacle in a helical manner. One or more advantages of the present invention may be realised by disposing only one of the two conductors along and around the heatable conduit andlor heatable receptacle in a helical manner. The other conductor may extend along andlor around the heatable conduit and/or heatable receptacle in a non-helical manner. For example, the other conductor may extend along and/or around the heatable conduit and/or beatable receptacle in a linear manner. In another example, the other conductor may be a continuous coating, foil or sheath that extends along and around the beatable conduit and/or heatable receptacle. When one of the conductors is not helically wound around the heatable conduit and/or beatable receptacle, one conductor may be separated from the other by, for example, the PTC layer (or, in more general terms a quantity of electrically conductive material).

Figure 5 shows a heatable conduit where a first conductor 50 is a continuous coating, foil or sheath that extends along and around a tube 52 of the beatable conduit. A quantity of electrically conductive material 54 (e.g. a PTC layer or extrusion) extends along and around the tube 52, and also along and around the first conductor 50. A second conductor 56 extends along and around the tube 52 in a helical manner, and also along and around the quantity of electrically conductive material 54 (e.g. a PTC layer or extrusion) in a helical manner.

In another example of a heatable conduit (not shown), a first conductor extends along and around a tube of the beatable conduit in a helical manner. A quantity of electrically conductive material (e.g. a PTC layer or extrusion) extends along and around the tube, and also along and around the first conductor. A second conductor is a continuous coating, foil or sheath that extends along and around the tube of the heatable conduit and also along and around the quantity of electrically conductive material (e.g. a PTC layer or extrusion) in a helical manner.

The PTC material forming the layer of PTC material described above may be formed from any one of a number of materials or combination of materials known in the art, Preferably, the PCT material is a polymer and/or a semi-conductor. Such a choice is preferable, since these materials are cheap, easy to produce, resilient and flexible. The PTC material could be provided in any quantity along and around the tube, for example in the form of a sheath, a coating, a foil, a strip, and/or could be extruded along the length of the tube. Extrusion may be preferable, since it allows a close fit between the tube and the PTC material, and thus efficient heating of fluid within the tube.

Because the electrical conductors extend along the length of the heatable conduit, a parallel connection of the layer of PTC material along the length of the heatable conduit over which the conductors extend is provided. If, for example, there are air pockets in the fluid to be heated, the PlC material self-regulates the current at this location of the beatable conduit. Because heat is not being transferred to the fluid at the location of the air pocket, the temperature of the PTC material in the region of the air pockets will rise.

As the temperature of the region of the PTC material rises, so does the electrical resistance of the region of the PTC material, thereby causing a reduction in the current flow through the region of the PTC material. This means that the PTC material is self-regulating. Therefore, air pockets (or other areas of high resistance in or around the heatable conduit) may be accounted for without overheating of either the fluid or materials forming the beatable conduit.

In the embodiments described above, a layer of PTC material has been described. The electrical conductors are shown as being in electrical contact with the layer of PTC material, either by being located in contact with the surface of the layer of PTC material, or by being embedded within the layer of PTC material. One or more of the conductors may be provided with a layer, coating extrusion or the like of a material having a negative temperature coefficient of resistance. The negative temperature coefficient of resistance material may serve as a cold start limiter which acts to limit the power dissipated by the heatable conduit when it is at a low temperature. This arrangement may be reversed, such that one or more of the conductors are provided with a layer, coating, extrusion or the like of a PTC material, and the conductors are then located in contact with or embedded within a material having a negative temperature coefficient of resistance. In other embodiments, one or both conductors can be located in or in contact with a layer of negative temperature coefficient of resistance material which surrounds the tube through which a fluid may flow. No additional (for example, PTC) coating, layer, or the like may be required.

It will be appreciated that the above embodiments have been given by way of example only. Various modifications may be made to the described embodiments, and embodiments not described, without departing from the invention as defined by the claims that follow.

Claims

CLAIMS1. A heatable conduit comprising: a tube through which a fluid may flow; a quantity of electrically conductive material extending along andlor around the tube; a first conductor disposed around and extending along the tube and configured to form a first conductor helix; and a second conductor disposed around andlor along the tube, the first and second conductors being in electrical connection with the quantity of electrically conductive material.
2. The heatable conduit of claim 1, wherein the second conductor is disposed around and extends along the tube and is configured to form a second conductor helix.
3. The heatable conduit of claim 1 or claim 2, wherein one or more dimensions of the first conductor helix and/or the second conductor helix are configured to ensure that, in use, the heatable conduit has a pre-selected heat output.
4. The heatable conduit of any preceding claim, wherein a spacing between loops of the first conductor helix and/or the second conductor helix are configured to ensure that, in use, the heatable conduit has a pre-selected heat output.
5. The heatable conduit of any preceding claim, wherein a pitch of the first conductor helix and/or the second conductor helix is configured to ensure that, in use, the heatable conduit has a pre-selected heat output.
6. The heatable conduit of any preceding claim, wherein the second conductor is disposed around and extends along the tube and is configured to form a second conductor helix, and wherein one or more loops of the first conductor helix are equally spaced from or between one or more loops of the second conductor helix.
7. The heatable conduit of any preceding claim, wherein the quantity of electrically conductive material at least partially surrounds the tube.
8. The heatable conduit of any preceding claim, wherein the first conductor and/or second conductor is at least partially located: between the tube and the quantity of electrically conductive material; and/or within the quantity of electrically conductive material; and/or between the electrically conductive material and insulation; and/or such that at least a part of the quantity of electrically conductive material separates the first and/or second conductor from the tube.
9. The heatable conduit of any preceding claim, wherein the first conductor and the second conductor sandwich the quantity of electrically conductive material.
10. The heatable conduit of claim 9, wherein the first conductor, second conductor and electrically conductive material form a stack, the electrically conductive material being located between the first conductor and the second conductor in the stack.
11. The heatable conduit of claim 9, wherein the first conductor, second conductor and electrically conductive material lie in substantially a same plane.
12. The heatable conduit of claim 9, wherein the first conductor, second conductor and electrically conductive material lie in substantially different planes.
13. The heatable conduit of any of claims 9 to 12, wherein the first conductor, second conductor and electrically conductive material together form a flexible band suitable for winding around the tube.
14. The heatable conduit of any preceding claim, wherein the quantity of electrically conductive material is a layer, extrusion or coating.
15. The heatable conduit of any preceding claim, wherein one or more of the first conductor, second conductor and electrically conductive material are provided in the form of a sheet or foil.
16. The heatable conduit of any preceding claim, wherein the quantity of electrically conductive material has a positive temperature coefficient of resistance
17. The heatable conduit of claim 16, wherein the quantity of electrically conductive material has a positive temperature coefficient of resistance sufficient for the material to be self-regulating.
18. The heatable conduit of any preceding claim, wherein the first andlor second conductor is provided with a quantity of material having a negative coefficient of resistance.
19. A method of forming a heatable conduit using a tube, a quantity of electrically conductive material, a first conductor and a second conductor, the method comprising, in no particular order: disposing the first conductor along and around the tube to form a first conductor helix; disposing the second conductor along andlor around the tube; and disposing the quantity of electrically conductive material along andlor around the tube, the first and second conductors being in electrical connection with the quantity of electrically conductive material.
20. The method of claim 19, wherein disposing the second conductor along and around the tube comprises disposing the second conductor along and around the tube to form a second conductor helix.
21. The method of claim 19 or claim 20, wherein one or more dimensions of the first conductor helix and/or the second conductor helix are configured to ensure that, in use, the heatable conduit has a pre-selected heat output.
22. A heatable receptacle comprising: a quantity of electrically conductive material extending along andlor around the receptacle; a first conductor disposed around and extending along the receptacle and configured to form a first conductor helix; and a second conductor disposed around and/or along the receptacle;, the first and second conductors being in electrical connection with the quantity of electrically conductive material.
23. A method of forming a heatable receptacle using a receptacle, a quantity of electrically conductive material, a first conductor and a second conductor, the method comprising, in no particular order: disposing the first conductor along and around the receptacle to form a first conductor helix; disposing the second conductor along and/or around the receptacle; and disposing the quantity of electrically conductive material along and/or around the receptacle, the first and second conductors being in electrical connection with the quantity of electrically conductive material.