GB2580948A

GB2580948A - Flow through heaters and methods of assembly

Info

Publication number: GB2580948A
Application number: GB1901362.2A
Authority: GB
Inventors: Johan Arnout Nieuwenuhuis Hendrick; Gerardus Maria Gelinck Johannes; Reinier Nijhoff Alex; Johannes Kloppers Gradus
Original assignee: FERRO TECH BV; Ferro Techniek BV
Current assignee: FERRO TECH BV; Ferro Techniek BV
Priority date: 2019-01-31
Filing date: 2019-01-31
Publication date: 2020-08-05
Anticipated expiration: 2039-01-31
Also published as: GB201901362D0; GB2580948B; CN211926148U

Abstract

A flow through heater comprises a thick film heating element 4, a channel plate 1 fixed to the heating element so as to form a channel for heating fluid, an aperture 2, 3 for fluid access to the channel and a tube 5 attached to a periphery of the aperture so as to provide a fluid inlet or outlet. The tube may be attached by brazing, soldering or welding. The aperture may be formed through the channel plate or through the heating element (figure 6). An area of attachment 7 of the tube to the corresponding aperture may be within the channel as a result of brazing, soldering or welding the tube to the channel plate or heating element on a side that is exposed to fluid during use.

Description

Flow through Heaters and Methods of Assembly

Field of the Invention

[0001] The present invention relates to flow through heaters, particularly but not exclusively thick film flow through heaters, and their methods of assembly.

Background of the Invention

[0002] Flow through heaters heat a fluid as it flows through the heater. These may be used for example for continuous or near-instantaneous dispensing of hot or boiling water.

[0003] A flow through heater described in patent publication GB-A-2481265 comprises a channel plate brazed to a planar thick film heating element. The thick film heating element comprises a substrate of material with good thermal conductive properties such as a metal, an electrically insulating layer, such as vitreous enamel, and at least one resistor track applied by a thick film technique. A channel, formed between the channel plate and the planar heating element, guides the fluid to be heated in a path corresponding to the layout of the heating track on the thick film heater. The low thermal mass of this type of flow through heater provides a fast response and a very controllable heater.

[0004] The flow through heater described in GB-A-2481265 uses a manifold to connect a fluid inlet and outlet to the channel. This manifold is sealed to the channel plate by clamping a seal member between the manifold and the channel plate. Whilst this arrangement works well, there are applications for the flow through heater which require that there are no non-metallic components in contact with the fluid to be heated.

Statements of the Invention

[0005] Aspects of the invention are defined by the accompanying claims.

[0006] In at least some embodiments of the invention, separate inlet and outlet tubes are sealingly fixed to apertures in either the channel plate or the substrate of the thick film heater.

[0007] The tubes can be fixed to the channel plate using a suitable welding technique or by brazing or soldering. If a brazing or soldering process is used, this can be performed at the same time that the channel plate is brazed or soldered to the heater substrate.

[0008] Corrosion can be a problem with flow through heaters using stainless steel. Stainless steel can suffer from a number of different corrosion mechanisms, such as pitting corrosion, crevice corrosion and to a lesser extent stress corrosion cracking. In particular crevice corrosion can be a problem. This type of corrosion is more likely to occur when chloride ions are present and there are areas of stagnation.

[0009] In a flow through heater the risk of stagnation occurs in sites such as cracks or fissures at the joints between the constituent parts. In at least some embodiments of the present invention, the interface between the channel plate and the tubes may be designed so that the parts can be joined together without creating cracks or fissures where corrosion can potentially occur. This can be achieved by performing the brazing or soldering or welding operation on a wet side of the assembly i.e. a side that is exposed to fluid during use.

Brief Description of the Drawings

[0010] Embodiments of the present invention are described with reference to the accompanying drawings as identified below.

Figure 1 shows a flow through heater, before attachment of the tubes.

Figure 2 is a sectional view of part of the flow through heater of Figure 1.

Figure 3 shows a tube suitable for attachment to the heater, in a first embodiment. Figures 4a and 4b show the tube of Figure 3 attached to the heater of Figure 1 and 2. Figures 5a and 5b are sectional views of the inlet or outlet of a flow through heater in a second embodiment, showing an alternative aperture design.

Figures 6a and 6b show the tube fixed to the thick film heating element in a third embodiment.

Figure 7 shows a first method of assembly of one or more of the embodiments. Figure 8 shows a second method of assembly of one or more of the embodiments. Figure 9 shows a third method of assembly of one or more of the embodiments.

Detailed Description of Embodiments

[0011] In the following description, similar parts carry the same reference numeral between the different embodiments.

[0012] Figure 1 shows a flow through heater, before any tubes for the inlet and outlet are added, comprising a channel plate 1 attached to the thick film heating element 4, for example by brazing or welding. The thick film heating element 4 comprises a substrate, which may be substantially planar, and one or more electrical heating (e.g. resistor) tracks deposited on the substrate using a thick film printing or deposition process. The substrate may be of thermally conducting material, such as a metal. Where the substrate is electrically conductive, an electrically insulating layer may be applied to a surface of the substrate before the electrical heating track(s) is deposited, to electrically insulate the tracks from the substrate. This electrically insulating layer should have reasonable or good thermal conducting properties, and may for example comprise vitreous enamel. Alternatively, the substrate may be of an electrically insulating material, such as ceramic. Preferably, a further electrically insulating layer is applied over the heating track, to electrically insulate the track.

[0013] The channel plate 1 is preferably attached to the opposite face of the substrate to the one on which the heating track(s) is deposited. Hence, the heating track(s) and the electrically insulating layers may be deposited either before or after the channel plate 1 is attached to the substrate.

[0014] The channel plate 1 has first and second apertures 2, 3 which act as the inlet and outlet for the fluid channel 10. Either aperture 2, 3 can be used as the inlet with the other acting as the outlet. The apertures 2, 3 may be formed in the channel plate 1 after the channel plate 1 is fixed to the thick film heating element 4, as shown in steps 7.1 and 7.2 of Figure 7, or before the channel plate 1 is fixed to the thick film heating element 4, as shown in steps 8.1 and 8.3 of Figure 8. In the latter case, the apertures 2, 3 may have been formed as part of the manufacturing process of the channel plate 1. In either case, the tubes 5 are attached to the apertures 2, 3 after the apertures 2, 3 are formed (steps 7.3, 8.2).

[0015] The tubes 5 can be made from the same material as the channel plate 1 or the substrate of the thick film heating element 4, such as stainless steel, or a material compatible with these components and the chosen fixing method.

[0016] Figure 2 is a sectional view of part of the flow through heater showing the channel plate 1 and first and second apertures 2, 3 in greater detail. A fluid channel 10 is formed between a raised channel portion 9 of the channel plate 1 and the surface of the thick film heating element 4. Preferably, the fluid channel 10 is aligned with the heating track, for efficient heating of the fluid. Other, flat portions 11 of the channel plate 1 contact the surface of the thick film heating element 4 and form a brazed or welded seal.

[0017] The following description of embodiments relates to the attachment of one or more tubes to the flow through heater described above, although aspects of the embodiments may be applied to other arrangements of flow-through heater.

[0018] Figure 3 shows a tube 5 for attachment to the periphery of either of the first and second apertures 2, 3. The tube 5 has a spigot 6 on one end, arranged to fit within the aperture 2, 3 and position the end of the tube 5 in the aperture 2, 3. The spigot 6 has a geometry that conforms to the periphery of the aperture 2, 3, to facilitate welding the tube 5 to the channel plate 1 in fluid communication with the aperture 2, 3. For example, as shown in the figures, the outer surface of the spigot 6 is of narrower diameter than the remainder of the tube 5 so that a shoulder is formed for abutment against the channel plate 1.

[0019] Figures 4a and 4b show the tube 5 assembled to the flow through heater by attachment to the periphery of the aperture 2, preferably by brazing or welding. Figure 4a shows the tube 5 in position in the aperture 2 before welding. Figure 4b shows the arrangement after welding, in which a weld fillet 7 is formed at the junction between the spigot 6 and the periphery of the aperture 2, thereby fixing and sealing the tube 5 to the channel plate 1. The weld can be of any suitable type, but laser welding or TIG welding (in particular micro TIG welding) are particularly advantageous in order to limit the size of the weld so as to reduce the risk of corrosion.

[0020] Figures 5a and 5b show a second embodiment in which the tubes 5 are designed for brazing or soldering to the periphery of the apertures 2, 3. In this embodiment, the spigot 6 is longer than the thickness of the channel plate 1, so that it projects through the aperture 2, 3. Figure 5a shows the tube 5 in position before the brazing or soldering process. Figure 5b shows the arrangement after brazing, in which a braze filler material 8 fixes and seals the spigot 6 to the periphery of the aperture 2, 3, and hence the tube 5 to the channel plate 1.

[0021] The joint between the tube 5 and the aperture 2, 3, may be optimised for the brazing process. The joint is preferably designed to provide the required gaps between the components and a significant overlap of the components. The components are preferably fixed in position during the brazing process, for example by using suitable jigs, by a push fit between the parts (e.g. of the tube 5 within the aperture 2, 3) and/or by a small tack weld. The tack weld can be made by a resistance, TIG or any other suitable welding process.

[0022] In the welded embodiment the tube 5 is preferably welded to the channel plate 1 before the channel plate 1 is brazed to the thick film heating element 4, as shown for example in Figure 8, to avoid problems during the manufacturing process of the thick film heating element 4.

[0023] In the embodiment where the tube 5 is fixed to the channel plate 1 by brazing, this can be done at the same time as the channel plate 1 is brazed to the thick film heating element 4, as shown in step 9.2 of Figure 9, after the apertures 2, 3 are formed in step 9.1. Alternatively, the tube 5 can be brazed to the channel plate 1 prior to brazing the channel plate 1 to the thick film heating element 4, as shown in Figure 8. In the latter case, the melting point of the braze material used for the joint between the tube 5 and the channel plate 1 is preferably higher than the melting point of the braze material used for the joint between the channel plate 1 and the thick film heating element 4.

[0024] Figures 6a and 6b show a third embodiment in which the tube 5 is fixed to an aperture 12 that passes through the thick film heating element 4 in order to provide an inlet or outlet to the fluid channel 10. Another aperture (not shown), either in the channel plate 1 or through the thick film heating element 4, provides a corresponding outlet or inlet. In this embodiment, the apertures may be formed either before the channel plate 1 is attached to the heating element, as shown in Figure 8 or Figure 9, or after the channel plate 1 is attached to the heating element, as shown in Figure 7.

[0025] The tube 5 is arranged on an opposite side of the thick film heating element 4 from the channel plate 1.

[0026] In this embodiment, one end of the tube 5 has a spigot 6 that is at least as long as, and preferably longer than the depth of the aperture 12, so that the spigot 6 projects into the fluid channel.

[0027] Figure 6a shows the assembly before the brazing or soldering process, with the spigot 6 located in the aperture 12. Figure 6b shows the assembly after brazing or soldering, with braze or solder material 8 formed around the portion of the spigot 6 that projects through the aperture 12 into the fluid channel 10. Hence, the braze or solder material 8 is provided on a wet side of the flow through heater.

[0028] In a variant of the third embodiment, the tube 5 may be welded instead of brazed or soldered to the periphery of the aperture 12.

[0029] The tube 5, or at least a part thereof that is in contact with the fluid, is preferably of metal so as to meet a requirement that no non-metal parts are in contact with the liquid. When the thick film heater is assembled into an appliance, the tube 5 provides a connection for attachment of a fluid conduit of the appliance.

[0030] The tube 5 is generally hollow cylindrical, but may be of any shape or dimension suitable for the required application. For example, the tube 5 may be straight, curved or bent and may have a circular, square, polygonal or other cross-section. The aperture(s) 2, 3, 12 may be circular, square, polygonal or other cross-section, and the spigot(s) 6 may have a corresponding cross-sectional shape. For example, in applications where the rotational orientation of the tube 5 is important, the aperture(s) 2, 3, 12 and corresponding spigot(s) 6 may have a non-circular cross-sectional shape.

Alternative Embodiments [0031] Different aspects of the above embodiments may be combined. For example, one aperture 2, 3 may be provided in the channel plate 1 and another aperture 12 may be provided in the thick film heating element 4, and corresponding tubes 5 may be attached to these apertures so as to provide an inlet and an outlet on different sides of the flow through heater.

[0032] There may be more than one, discrete or interconnected fluid channel 10 between the channel plate 1 and the thick film heater 4. Hence, there may be more than one inlet and/or outlet provided by corresponding apertures 2, 3, 12 and tubes S. [0033] The embodiments described above are illustrative of rather than limiting to the present invention. Alternative embodiments apparent on reading the above description may nevertheless fall within the scope of the invention.

Claims

Claims 1. A flow through heater comprising: a thick film heating element, a channel plate fixed to the heating element to form a channel for heating fluid, at least one aperture for fluid access to the channel; and at least one tube sealingly attached to a periphery of a corresponding said aperture to provide an inlet and/or outlet to the channel.
2. The flow through heater of claim 1, wherein at least one said aperture is provided through the channel plate.
3. The flow through heater of claim 1 or claim 2, wherein at least one said aperture is provided through the thick film heating element.
4. The flow through heater of any preceding claim, wherein at least one said tube is brazed or soldered to the periphery of the corresponding said aperture.
S. The flow through heater of any one of claims 1 to 3, wherein at least one said tube is welded to the periphery of the corresponding said aperture.
6. The flow through heater of claim 5, wherein at least one said tube is laser welded to the periphery of the corresponding said aperture.
7. The flow through heater of claim 5, wherein at least one said tube is TIG welded or micro TIG welded to the periphery of the corresponding said aperture.
8. The flow through heater of any preceding claim, wherein an area of attachment of at least one said tube to the periphery of the corresponding said aperture is within the channel.
9. The flow through heater of any preceding claim, wherein an end of at least one said tube is arranged to fit within the corresponding said aperture.
10. The flow through heater of claim 9, wherein the end of at least one said tube is arranged to extend through the corresponding said aperture.
11. The flow through heater of claim 9 or 10, wherein the end of at least one said tube is of reduced diameter.
12. A method of assembling a flow through heater, comprising: a) fixing a channel plate to a thick film heating element to form a channel for heating fluid, the channel having at least one aperture for fluid access to the channel; and b) sealingly attaching at least one tube to a periphery of a corresponding said aperture to provide a fluid inlet and/or outlet to the channel.
13. The method of claim 12, wherein at least one said aperture is provided through the channel plate.
14. The method of claim 12, wherein at least one said aperture is provided through the thick film heating element.
15. The method of claim 13 or claim 14, wherein at least one said aperture is provided before the channel plate is fixed to the thick film heating element.
16. The method of claim 13 or claim 14, wherein at least one said aperture is provided after the channel plate is fixed to the thick film heating element.
17. The method of any one of claims 12 to 16, wherein at least one said tube is brazed or soldered to the periphery of the corresponding said aperture.
18. The method of claim 17, wherein at least one said tube is brazed to the periphery of the corresponding said aperture while the channel plate is brazed to the thick film heating element.
19. The method of any one of claims 12 to 17, wherein the channel plate is fixed to the thick film heating element before at least one said tube is attached to the periphery of the corresponding said aperture.
20. The method of any one of claims 12 to 17, wherein the channel plate is fixed to the thick film heating element after at least one said tube is attached to the periphery of the corresponding said aperture.
21. The method of any one of claims 12 to 14, or claim 19 or 20 each when dependent any one of claims 12 to 14, wherein at least one said tube is welded to the periphery of the corresponding said aperture.
22. The method of claim 19, wherein at least one said tube is laser welded to the periphery of the corresponding said aperture.
23. The method of claim 19, wherein at least one said tube is TIG welded or micro TIG welded to the periphery of the corresponding said aperture.
24. The method of any one of claims 12 to 23, wherein an area of attachment of at least one said tube to the periphery of the corresponding said aperture is within the channel.
25. The method of any one of claims 12 to 24, wherein an end of at least one said tube is arranged to fit within the corresponding said aperture.
26. The method of claim 25, wherein the end of at least one said tube is arranged to extend through the corresponding said aperture.
27. The method of claim 25 or 26, wherein the end of at least one said tube is of reduced diameter.
28. The method of any one of claims 12 to 27, wherein at least one said tube is temporarily fixed in position during the attachment process.
29. The method of any one of claims 12 to 28, wherein one or more heating tracks are applied to a substrate of the heating element after the channel plate is attached to the substrate of the heating element.