WO2008071983A2

WO2008071983A2 - Electric water heater

Info

Publication number: WO2008071983A2
Application number: PCT/GB2007/004797
Authority: WO
Inventors: Peter Hallam Wright; Andrew Mottram; Antonio Martin Gaeta; Andrew Karl Ashmore
Original assignee: Otter Controls Ltd
Priority date: 2006-12-14
Filing date: 2007-12-13
Publication date: 2008-06-19
Also published as: WO2008071983A3

Abstract

An electric water heater (1) comprises an element plate (5) with an electric heating element (6) on the underside and a heat diffusion layer (7) between the heating element and the element plate, wherein the heat diffusion layer is substantially thicker than the element plate so as to reduce noise generated while heating water. The element plate may have a noise reduction surface coating- (9) and/or treatment (10), the treatment preferably comprising surface roughening. The element plate may be incorporated in a vessel including an inhibitor (11) for inhibiting noise.

Description

Electric Water Heater

Field of the Invention

The present invention relates to electric water heaters for water heating vessels, and to water heating vessels incorporating such electric water heaters. In particular, the present invention relates to electric water heaters and vessels arranged to generate less noise when heating water than conventional electric water heaters and vessels.

Background to the Invention

It is desirable to heat water in water heating vessels such as kettles as quickly as possible, whether to boiling or to a lower temperature. For this reason, kettles with high power ratings of up to 3 kW have become popular, at least in countries where high mains voltages of 220-250 V AC are available. However, increasing the power levels of heaters in water heating vessels has also increased the noise generated during heating. One reason for the noise is the creation of bubbles by local boiling at the surface of the water heater; the bubbles then collapse as they rise through the water, generating noise. Increased noise levels are generally undesirable, particularly in a domestic environment. For example, the paper 'Simplified sound quality assessment for UK Manufacturers' by Churchill, Maluski and Cox, 33 ^rd International Congress and Exposition on Noise Control Engineering, 2004 states: '...the 3kW kettle has given rise to complaints by some consumers as having a sound which is like "a plane taking off."' GB 2386532 A proposes the application of a surface coating to the water-facing side of an electric heating element plate, so as to limit the size of bubbles grown as a result of nucleate boiling. A scale-shedding additive may be incorporated in the coating, but the amount of scale shedding additive is limited by the tendency to promote film boiling at the surface. GB 2411332 A proposes leaving a region of an element plate above a thermal sensor uncoated, to avoid film boiling above the thermal sensor. EP 1754435 Al proposes an element plate having a first region of discontinuous hydrophobic coating and second region free of coating. JP09023976A discloses a water heater with a set of protrusions formed at the bottom, which is said to reduce noise. Statement of the Invention

According to one aspect of the present invention, there is provided an electric water heating vessel comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, the upper side having a noise-reduction coating and/or treatment, the vessel further comprising a noise inhibitor arranged above and in proximity to the element plate and extending substantially over the electric heating element, the inhibitor comprising a surface that converges or diverges in an upward direction.

This arrangement is particularly advantageous in reducing heating noise with hard water. The noise reduction coating alone may reduce heating noise, but may cause a high-pitched whine or whistle when heating hard water. The noise inhibitor substantially reduces this noise, by encouraging steam bubbles to coalesce rather than to collapse. The converging or diverging surface carries the bubbles away from the heating element as they coalesce, to avoid 'film boiling' whereby a layer of steam gathers over the element, thereby insulating the element from the water and causing the element to overheat.

The noise inhibitor may be removable from or insertable in the vessel by the user. This allows the inhibitor to be removed where it is not needed, for example in soft water areas. The inhibitor may also be removed for cleaning or replacement. According to another aspect of the present invention, there is provided an electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element and at least one thermal sensor in thermal contact therewith, the upper side having a noise reduction coating and/or treatment above the element and the at least one thermal sensor, and an area substantially free of the noise reduction coating and/or treatment.

An advantage of such an arrangement is that the insulation caused by the noise reduction coating above the element is similar to that above the thermal sensor, so that the temperature sensed by the sensor is representative of that of the element. Furthermore, the level of scale deposited over the sensor will be similar to that over the element. According to another aspect of the present invention, there is provided an electric water heating vessel including an electric heating element and a structure arranged to promote coalescence of steam bubbles rising from the electric heating element. The structure may comprise a funnel arranged to concentrate the flow of steam bubbles therethrough. The slope of the funnel may be sufficient to avoid film boiling above the heating element, while allowing bubbles to coalesce as they flow up within the funnel. The funnel may have an aperture bordered by a substantially horizontal portion, which allows greater control of flow and coalescence of bubbles. Alternatively, the structure may comprise a substantially horizontal surface arranged above the heating element. The structure may be rotatable within the vessel, either by the flow of water or bubbles, or driven by a motor, such as a magnetic stirrer. The rotation of the structure may cause vortex currents within the water, which may further reduce noise.

The structure may comprise a coil; the coil may be compressible to facilitate removal of the structure from the vessel. The coil may promote rotational flow of water as it is heated.

According to another aspect of the present invention, there is provided an electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, and a heat diffusion layer for diffusing heat from the heating element to the underside of the element plate, wherein the heat diffusion layer is substantially thicker than the element plate, and may be at least 3 mm thick. The thick heat diffusion layer helps to reduce hot spots on the element plate, and therefore reduces local boiling which is a cause of heating noise.

According to another aspect of the present invention, there is provided an electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, wherein the upper side is roughened by a surface treatment. The roughening may have a noise reduction effect without the need to provide a noise reduction coating, which may affect the taste of the water. Alternatively, the roughening may be applied to the surface of a noise reduction coating, to further enhance its noise reduction abilities. Brief Description of the Drawings

Embodiments of the invention will now be described with reference to the drawings identified below.

Figure Ia is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a first variant of a first embodiment.

Figure Ib is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a second variant of the first embodiment.

Figure Ic is a cross-sectional diagram of an electric heating element plate according to a third variant of the first embodiment, including a seal. Figure Id is a cross-sectional diagram of an electric heating element plate according to a fourth variant of the first embodiment, including a seal.

Figure 2a is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a first variant of a second embodiment.

Figure 2b is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a second variant of the second embodiment.

Figure 2c is a cross-sectional diagram of an electric heating element plate according to a third variant of the second embodiment, including a seal.

Figure 3 a is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a first variant of a third embodiment. Figure 3b is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a second variant of the third embodiment.

Figure 4a is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a first variant of a fourth embodiment.

Figure 4b is a cross-sectional diagram of a water heating vessel including an electric heating element plate according to a second variant of a fourth embodiment.

Figure 5 is a schematic plan view of an electric heating element plate in a first variant of a fifth embodiment. Figure 6 is a schematic plan view of an electric heating element plate in a second variant of the fifth embodiment.

Figure 7 is a schematic plan view of an electric heating element plate in a third variant of the fifth embodiment. Figure 8 is a schematic plan view of an electric heating element plate in a fourth variant of the fifth embodiment.

Figure 9a is a schematic plan view of the upper surface of an electric heating element plate in a fifth variant of the fifth embodiment.

Figure 9b is a schematic plan view of the underside of the electric heating element plate in the fifth variant of the fifth embodiment.

Figure 10a is a schematic plan view of the upper surface of an electric heating element plate in a sixth variant of the fifth embodiment.

Figure 10b is a schematic plan view of the underside of the electric heating element plate in the sixth variant of the fifth embodiment. Figure 1 Ia is a schematic plan view of the upper surface of an electric heating element plate in a seventh variant of the fifth embodiment.

Figure l ib is a schematic plan view of the underside of the electric heating element plate in the seventh variant of the fifth embodiment.

Figure 12a is a schematic plan view of the upper surface of an electric heating element plate in an eighth variant of the fifth embodiment.

Figure 12b is a schematic plan view of the underside of the electric heating element plate in the eighth variant of the fifth embodiment.

Figure 13a is a schematic plan view of the upper surface of an electric heating element plate in a ninth variant of the fifth embodiment. Figure 13b is a schematic plan view of the underside of the electric heating element plate in the ninth variant of the fifth embodiment.

Figure 14a is a schematic plan view of the upper surface of an electric heating element plate in a tenth variant of the fifth embodiment. Figure 14b is a schematic plan view of the underside of the electric heating element plate in the tenth variant of the fifth embodiment.

Figure 15a is a schematic plan view of the upper surface of an electric heating element plate in an eleventh variant of the fifth embodiment. Figure 15b is a schematic plan view of the underside of the electric heating element plate in the eleventh variant of the fifth embodiment.

Figure 16a is a schematic plan view of the upper surface of an electric heating element plate in a twelfth variant of the fifth embodiment.

Figure 16b is a schematic plan view of the underside of the electric heating element plate in the twelfth variant of the fifth embodiment.

Figure 17 is a cut-away view of a water heating vessel including an inhibitor, according to a first variant of a sixth embodiment.

Figure 18 is a cut-away view of a water heating vessel including an inhibitor, according to a second variant of the sixth embodiment. Figure 19 is a cut-away view of a water heating vessel including an inhibitor, according to a third variant of the sixth embodiment.

Figure 20 is a cut-away view of a water heating vessel including an inhibitor, according to a fourth variant of the sixth embodiment.

Figures 21a, 21b and 21c are perspective, vertical cross-section and plan views respectively of an inhibitor, according to a fifth variant of the sixth embodiment.

Figures 22a, 22b and 22c are perspective, vertical cross-section and plan views respectively of an inhibitor, according to a sixth variant of the sixth embodiment.

Figures 23a, 23b and 23c are perspective, vertical cross-section and plan views respectively of an inhibitor, according to a seventh variant of the sixth embodiment. Figures 24a and 24b are vertical cross-section and plan views respectively of an inhibitor, according to an eighth variant of the sixth embodiment.

Figure 25 is a cut-away view of a water heating vessel including an inhibitor, according to a first variant of a seventh embodiment. Figure 26 is a cut-away view of a water heating vessel including an inhibitor, according to a second variant of the seventh embodiment.

Figure 27 is a cut-away view of a water heating vessel including an inhibitor, according to a third variant of the seventh embodiment. Figure 28 is a cut-away view of a water heating vessel including an inhibitor, according to a fourth variant of the seventh embodiment.

Figure 29 is a cut-away view of a water heating vessel including an inhibitor, according to a fifth variant of the seventh embodiment.

Figure 30 is a cut-away view of a water heating vessel including an inhibitor, according to a sixth variant of the seventh embodiment.

Figure 31a is a cut-away view of a water heating vessel including an inhibitor, according to a seventh variant of the seventh embodiment.

Figure 31b is a detailed view of a portion of the embodiment of Figure 31a, showing a flap in a raised position. Figure 32a is a cut-away view of a water heating vessel including an inhibitor, according to an eighth variant of the seventh embodiment.

Figure 32b is a perspective view of the water heating vessel including an inhibitor, according to the eighth variant of the seventh embodiment.

Figure 33 is a cut-away view of a water heating vessel including an inhibitor, according to a first variant of an eighth embodiment.

Figure 34 is a perspective view of a water heating vessel including an inhibitor, according to a second variant of the eighth embodiment.

Figure 35 is a cut-away view of a water heating vessel including an inhibitor, according to a third variant of the eighth embodiment. Figure 36 is a cut-away view of a water heating vessel including an inhibitor, according to a fourth variant of the eighth embodiment.

Figures 37a and 37b are cut-away and perspective views of a water heating vessel including an inhibitor, according to a fifth variant of the eighth embodiment. Figure 38a is graph comparing the noise level as a function of time for the first cycle of hard water, between the sixth variant of the sixth embodiment, a conventional kettle, and a competitor's reduced noise kettle.

Figure 38b is graph comparing the noise level as a function of time after fifteen cycles using hard water, between the sixth variant of the sixth embodiment, a conventional kettle, and a competitor's reduced noise kettle.

Figure 39 is a perspective view of an inhibitor according to a ninth embodiment of the present invention.

Figure 40a, 40b are perspective and cut-away views respectively of an inhibitor according to a tenth embodiment of the present invention.

Figure 40c is a cut-away view of the inhibitor according to the tenth embodiment, in a compressed state.

Figure 41 is a perspective view of an inhibitor according to the sixth embodiment, with fixing portions. Figures 42a, 42b and 42c are partial cross-sectional views of first, second and third fixing arrangements respectively, for fixing the inhibitor of Figure 41 in a water heating vessel.

Detailed Description of Embodiments

In the embodiments described below, a water heating vessel 1 has a vessel wall 2 defining a water reservoir 3, and an electric heater 4 fitted within the vessel wall 2 so as to form the bottom of the water reservoir 3. The electric heater 4 comprises an element plate 5 having an electric heating element 6 on the underside. A seal 8 may be provided between the element plate 5 and the internal or external surface of the vessel wall 2, for example as described in WO 99/17645 and/or in the applicant's Easifix (RTM) sealing system.

In the first to fourth embodiments, the heating element 6 is a sheathed heating element. A diffuser plate 7 is provided between the heating element 6 and the element plate 5, so as to diffuse heat conducted from the heating element 6 to the element plate 5. The element plate 5 is preferably made of stainless steel, with a thickness of 0.3 mm to 0.7 mm, preferably about 0.5 mm. The diffuser plate 7 may comprise an aluminium plate brazed onto the element plate. However, the remaining embodiments are equally applicable to other types of heating element, such as thick film heating elements comprising one or more thick film heating tracks formed on the underside of the element plate 5. In that case, the diffuser plate 7 may or may not be present. The diffuser plate, if present, may have a thickness greater than 2 mm, and preferably 2.5 mm. This general arrangement is known per se, for example from the applicant's patent publication WO 99/17645. However, in at least the first to fourth embodiments, and optionally in the further embodiments, the diffuser plate 7 is substantially thicker than in the conventional arrangements: the diffuser plate 7 is greater than 3 mm thick, and most preferably greater than 3.9 mm thick; in the specific embodiments, it is 4 mm thick but an even greater thickness may be used, subject to constraints of cost, space and/or weight. Hence, the thickness ratio between the diffuser plate 7 and the element plate 5 is at least approximately 4, is preferably approximately 8 and may be 20 or greater. Surprisingly, the inventors have found that this significant increase in thickness of the diffuser plate 7 substantially reduces the noise generated by the electric heater 4, without the need to apply any noise-reducing coating to the water-facing side of the element plate 5. However in some of the embodiments, a heat-resistant noise reduction layer 9 and/or treatment 10 is additionally provided on the water-facing side of the element plate 5; this may have a synergistic effect with the thicker diffuser plate 7 in reducing noise. In some embodiments, the noise reduction layer 9 and/or treatment 10 may be applied without increasing the thickness of the diffuser plate 7. The noise reduction layer 9 may comprise a coating.

Thick Diffuser Plate - First Embodiment

In the first embodiment, variants of which are shown in Figures Ia to Id, the heating element plate 5 has a deep dished profile comprising an inner, planar portion 5a, an inner wall 5b extending substantially transversely to the planar portion 5a but flared outwardly at a small angle, an annular portion 5c substantially parallel to the planar portion 5a but raised by the height of the inner wall 5b, and a substantially transverse peripheral portion 5d that extends downwardly from the annular portion 5c. The diffuser plate 7 is planar and extends substantially over the whole undersurface of the inner planar portion 5a, both inwardly and outwardly of the heating element 6. In the variant shown in Figure Ia, the peripheral portion 5d terminates a short distance above the plane of the inner planar portion 5a. The transverse peripheral portion 5d is welded to the inner surface of the vessel wall 2. The diffuser plate 7 has a diameter of 130mm and a thickness of 4 mm.

The variant shown in Figure Ib differs from that of Figure Ia only in that the noise reduction layer 9 is provided on the water-facing side of the planar portion 5a.

The variant shown in Figure Ic differs from those of Figures Ia and Ib in that: the seal 8 is provided on the peripheral portion 5d, which includes an outwardly extending rim that engages a groove in the seal 8; the peripheral portion 5d extends below the plane of the inner planar portion 5a; and the diffuser plate 7 does not extend completely to the outer edge of the inner planar portion 5a.

The noise reduction layer 9 may be absent (as shown in Figure Ic), or may extend across the surface of the inner peripheral portion 5a, as in the variant of Figure Ib. The variant of Figure Id differs from that of Figure Ic in that the diffuser plate 7 has a diameter substantially less than that of the inner planar portion 5a, and the annular portion 5c is broader; in this variant, the diffuser plate 7 has a diameter of 110 mm.

Thick Diffuser Plate - Second Embodiment In the second embodiment, variants of which are as shown in Figures 2a, 2b and 2c, the diffuser plate 7 extends substantially over the whole undersurface of the inner planar portion 5a, and has a peripheral rim 7a that turns away from the inner planar portion 5a and hence from the element plate 5. In other words, the peripheral rim 7a has a thickness tl (6 mm in this example) greater than the thickness t2 (4 mm in this example) of the inner portion 7b of the diffuser plate 7, and the heating element 6 is attached to the inner portion 7b. Preferably, the peripheral rim 7a extends substantially continuously around the periphery of the diffuser plate 7. In each of the variants of the second embodiment, the diffuser plate has a diameter of 120mm.

In the variants of Figures 2a and 2b, the heating element plate 5 has a dished profile similar to that of the first embodiment, but shallower in that the inner wall 5b is very short so that the inner planar portion 5a is only slightly lower than the annular portion

5c and the transverse peripheral portion 5d terminates at a significant distance below the inner planar portion 5a. These variants differ only in that the noise reduction layer 9 is provided on the water-facing side of the planar portion 5a in the variant of Figure 2b, but not in the variant of Figure 2a.

In the variant of Figure 2c, the element plate 5 has a profile similar to the variant of the first embodiment shown in Figure Id.

Thick Diffuser Plate - Third Embodiment

In the third embodiment, variants of which are as shown in Figures 3a and 3b, the element plate has a ridged profile comprising an inner planar portion 5a, at the periphery of which is a hollow circumferential ridge 5b projecting upwardly into the reservoir 3. Radially outwardly from the circumferential ridge 5b is provided an annular portion 5c, from the periphery of which a substantially transverse peripheral portion 5d extends downwardly. The annular portion 5c is substantially coplanar with the inner planar portion 5a. The peripheral portion 5d is welded to the inner surface of the vessel wall 2. The diffuser plate 7 is planar and extends substantially over the whole undersurface of the inner planar portion 5a, both inwardly and outwardly of the heating element 6, but does not extend under the hollow circumferential ridge 5b.

The variants differ only in that the noise reduction layer 9 is provided on the water- facing side of the planar portion 5a in the variant of Figure 3b, but not in the variant of Figure 3a.

Thick Diffuser Plate - Fourth Embodiment

In the fourth embodiment, variants of which are as shown in Figures 4a and 4b, the element plate 5 has a deep dished profile similar to that of the variant of the first embodiment shown in Figure Ia, except that the inner wall 5b is not flared, but extends substantially transversely to planar portion 5a, and the annular portion 5c is broader, with a width similar to the variant of Figure Id.

The diffuser plate 7 extends beyond the inner planar portion 5a, and has a peripheral rim 7a that turns upwardly, around the bottom of and preferably in contact with the inner wall 5b. The peripheral rim 7a has a thickness tl (6mm in this example) greater than the thickness t2 (4 mm in this example) of the inner portion 7b of the diffuser plate 7, and the heating element 6 is attached to the inner portion 7b. Preferably, the peripheral rim 7a extends substantially continuously around the periphery of the diffuser plate 7. In each of the variants of the fourth embodiment, the diffuser plate 7 has a diameter of 120 mm. The variants differ only in that the noise reduction layer 9 is provided on the water- facing side of the planar portion 5a and the inner wall 5b in the variant of Figure 4b, but not in the variant of Figure 4a.

Noise Reduction Layer

The noise reduction layer 9 described above may comprise a resin-based coating that is applied to the water-facing side of the element plate 5 and fired during manufacture. The resin component may comprise one or more of polyethersulphone (PES), polyphenylenesulphide (PPS), polyethylene terephthalate (PET), and polyamide/imide (PAI).

The coating additionally comprises a non-stick or hydrophobic component, such as a fluoropolymer. The fluoropolymer may comprise one or more of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and perfluoroalkoxy (PFA).

The coating may further comprise one or more fillers or pigments, such as aluminium, barium sulphate, barytes, carbon black, chlorite, copper chrome spinel black, glass, iron oxide, mica, quartz, silica, talc and titanium dioxide.

The coating may further comprise a flow additive such as acrylate resin.

In one preferred embodiment, the composition of the dry coating (e.g. after firing) includes 50-65% resin component and 10-20% non-stick component. Preferably, the resin component comprises PAI. Preferably, the non-stick component comprises PTFE. One particularly preferred coating is a Greblon™ coating available from Weilburger Coatings GmbH, particularly a Greblon 1215 coating comprising PAI and PTFE with fillers and a flow additive, or a variant known as 'Ultra Serene' (TM).

When applied, the coating may include one or more solvents, which evaporate during firing. The coating may be applied by spray painting, printing or other coating techniques. The coating may be applied as one or more layers, and may comprise a plurality of layers having a different composition, or a similar composition. A scale- resistant coating may be applied as an additional layer on some or all areas of the noise reduction layer.

In an alternative, the noise reduction layer 9 may comprise glass or ceramic material, preferably formed using a sol-gel process. In one preferred embodiment, the sol-gel material comprises the Equadur™ heat resistant coating supplied by Eques Coatings BV (Holland).

A surface treatment 10 may be applied to the water-facing side of the element plate 5 before application of the noise reduction layer 9. For example, the surface may be roughened to improve adhesion of the noise reduction layer 9. Alternatively, the noise reduction layer 9 may be applied to the surface of the element plate 5 without first applying the surface treatment 10.

Surface Treatment

In a variant of the above embodiments, a surface treatment 10 is applied to at least a portion of the surface on the water-facing side of the element plate 5, instead of the noise reduction layer 9. Preferably, the surface treatment 10 roughens a least a portion of the water-facing side of the element plate; in other words, at least a portion of the surface of the element plate 5 itself, which may be of stainless steel, is roughened by the surface treatment 10, without applying a noise reduction layer 9 onto the roughened surface.

In one example, the surface is roughened with a finish of 0.5 - 4 Ra (average surface roughness), but most preferably approximately 2 Ra. The surface may be abraded, roughened (e.g. by grit blasting), scoured (e.g. with Scotchbrite™), surface etched and/or blast finished. In this way, nucleation sites may be provided on the water-facing side of the element plate 5, without the need for a separate noise reduction layer 9. This feature may be used independently of the thick diffuser plate 7 in the first to fourth embodiments.

Surface Treatment of Noise Reduction Layer

In another variant of the above embodiments, a surface treatment 10 is applied to the noise reduction layer 9, preferably after firing. The surface treatment 10 may roughen the surface of the noise reduction layer 9, using one or more of the techniques described above for treatment of the element plate 5. Additionally, the surface of the element plate 5 may be roughened before application of the noise reduction layer 9, as described above. Surprisingly, the inventors have found that roughening the surface of the noise reduction layer 9 improves the noise reduction qualities thereof, without including large particles in the noise reduction layer as proposed in GB2386532A. Hence, in embodiments of the present invention, the average additive particle size may be less than 100 microns, less than 50 microns, or less than 20 microns. In particular, the applicant has found that the use of large additive particles as described in GB2386532A may cause a high-pitched squealing or whistling noise during heating. The roughening surface treatment described above, either directly on the element plate 5 or on the surface coating 9, appears substantially to reduce this type of high-pitched noise. This feature may be used independently of the thick diffuser plate 7 in the first to fourth embodiments. The use of surface roughening instead of a surface coating may be advantageous, since some users have reporting tainting of water by certain noise-reduction coatings.

Fifth Embodiment - Noise Reduction Layer/Surface Treatment distribution

In a first variant of a fifth embodiment, as shown in Figure 5, the noise reduction layer 9 and/or surface treatment 10 may be applied to substantially the whole water-facing surface of the element plate 5, or at least the inner planar portion 5a. Alternatively, the noise reduction layer 9 and/or the surface treatment 10 may be applied only to one or more areas of the water-facing surface of the element plate 5. The area(s) may include an area above the heating element 6. The area(s) may be intermittently or continuously coated and/or treated. The area(s) may be substantially congruent with the width of the element 6, or may extend a small distance beyond, or a small distance short of the width of the element 6. The width of the area(s) may be selected according to the type of element used.

Where both a surface treatment 10 and a noise reduction layer 9 are applied to the element plate 5, the surface treatment 10 need not be congruent with the noise reduction layer 9. In other words, the element plate 5 may include at least one region to which the surface treatment 10 is applied without the noise reduction layer 9 and/or to which the noise reduction layer 9 is applied without the surface treatment 10. The region(s) to which the surface treatment 10 is applied may be entirely separate from those to which the noise reduction layer is applied, or there may be at least one region to which both the surface treatment 10 and the noise reduction layer 9 are applied, in either order. A region of the surface treatment 10 may partially overlap a region of the noise reduction layer 9.

In a second variant, as shown in Figure 6, only an annular area Al of the surface, located above the heating element 6, is treated and/or coated. In a third variant, shown in Figure 7, an angular section A2 of the surface, located above the heating element 6, is treated and/or coated. In a fourth variant shown in Figure 8, the coating and/or treatment is intermittently applied in a hexagonal matrix pattern A3.

As mentioned above, GB 2411332 A proposes leaving a region of an element plate above a thermal sensor uncoated, to avoid film boiling which would cause the sensor to overheat and lead to false detection of a dry boil condition. The region above the element is coated, to reduce noise. However, the present inventors have realised that the temperature sensed by the thermal sensor will then be disassociated from the true temperature of the element. For example, the coating may provide thermal insulation above the heater that is not present above the thermal sensor. Alternatively or additionally, scale may build up above the thermal sensor without a corresponding build up of scale above the element. Hence, the risk of the element overheating is increased. It would be safer to provide a similar coating and/or treatment above both the thermal sensor and the element.

Accordingly, in the following variants of the fifth embodiment, only part of the surface of the element plate 5 is treated and/or coated, and both an area above a thermal sensor and an area above the heating element 6 are treated and/or coated. These areas may be discrete or continuous with one another. Preferably, the areas are similarly treated.

In a fifth variant shown in Figures 9a and 9b, an annular area A4 is treated and/or coated above the element 6, and discrete areas A5 are treated and/or coated above a pair of thermal sensors 20 for use as dry boil protectors to detect an overheat condition of the element 6. The thermal sensors 20 are preferably bimetallic discs, in which case the areas A5 are approximately circular.

In a sixth variant shown in Figures 10a and 10b, the areas above the sensors 20 are continuous with the area above the element 6, giving a single area A6 that is annular, with additional portions extending towards the centre of the element plate 5 to cover the sensors 20.

A seventh variant shown in Figures 1 Ia and 1 Ib differs from the sixth variant in that the area A7 extends over only part of the element 6, in this case over an angle of approximately 180°, so that the area A7 comprises a semicircular annulus with portions extending towards the centre at each end.

An eighth variant shown in Figures 12a and 12b differs from the seventh variant in that the portions extend inwardly completely across the element plate 5 so that they join, giving an area A8 comprising a semicircular annular portion and a diametric portion.

A ninth variant shown in Figures 13a and 13b differs from the fourth variant in that an area A9 extends over substantially all of the element 6, apart from the cold tails at each end, but does not form a complete annulus, extending instead over approximately 300°. Discrete areas AlO extend over the thermal sensors 20.

In a tenth variant, as shown in Figures 14a and 14b, the area Al 1 is circular and covers the element 6 and the sensors 20. Only a radially outer portion of the element plate 5 is left untreated and/or uncoated.

In an eleventh variant, as shown in Figures 15a and 15b, area Al 2 comprises an annular portion extending over the element 6, and a continuous diametric portion extending across the centre of the element plate over the thermal sensors 20.

In a twelfth variant, as shown in Figures 16a and 16b, area Al 3 comprises an approximately semicircular portion A13 extending over the sensors 20 and the majority of the element 6 (in this case subtending an angle of approximately 180°).

Inhibitor

In combination with any of the above embodiments, or independently, the water heating vessel 1 may include a inhibitor 11 comprising one or more structures arranged within the water reservoir 3 to modify the flow of water, the formation of steam bubbles and/or the development of steam bubbles. In particular, the inhibitor 11 may encourage small bubbles to coalesce into larger bubbles soon after formation. The larger bubbles are more resistant to collapsing, which is one of the main causes of noise in water heating vessels. Hence, the inhibitor 11 inhibits bubble collapse and therefore noise. As an alternative or additional effect, the inhibitor 11 may promote stable convection currents, or allow them to flow faster, thus reducing local boiling at the heater 4.

As mentioned above, the present inventors have discovered that certain coatings intended to reduce noise may in fact cause a high-pitched whistling or screaming noise under certain conditions, particularly when very hard water or water with a high mineral content is used. The high-pitched noise typically occurs part way through the heating process, and appears to be caused by the formation of very small bubbles. The high- pitched noise may be prevented by the addition of an inhibitor 11, for example as described below.

Additionally, the present inventors have discovered that the high-pitched noise is generated predominantly from the hottest parts of the element plate 5. Hence, the inhibitor 11 need only be positioned over a part of the element 6, as in the seventh embodiment described below. For example, the inhibitor 11 need only subtend 90° or less of the element plate 5.

Hence, the inhibitor 11 may have a synergistic effect with certain treatments and/or coatings described above: the treatment/coating reduces normal kettle noise, but may create high-pitched noise, which the inhibitor 11 then inhibits. The inhibitor 11 alone may not be able to reduce normal kettle noise.

Furthermore, the present inventors have discovered that this synergistic effect is dependent on the shape and/or configuration of the inhibitor 11. In particular, the inhibitor should encourage bubbles to coalesce, without trapping bubbles so close to the element so as to cause film boiling. A converging surface at a suitable angle is found to perform particularly well; the surface may be at an angle of at least 10° to the horizontal, and the angle may increase with height above the element. The inhibitor 11 may be funnel-shaped, optionally with a horizontal Hp bordering the aperture of the funnel. By way of example, a comparative test was carried out between the following:

Kettle 1: a Kenwood (RTM) 'Stealth' kettle having an underfloor element plate treated with a noise-reduction coating, and a horizontal disruptor with longitudinal slots in the upper surface, circular in plan and fixed onto the element plate; power rating 3.0 kW, max water volume 1.5 1. Kettle 2: a prototype kettle prepared by the applicant, Otter Controls Ltd, having an underfloor element plate treated with a noise-reduction coating of Greblon (RTM) as described herein and having 61.7% binder resin, 10.7% fluoropolymer and 27.6% pigment/filler, and an inhibitor as described below with reference to Figures 22a to 22c; power rating 3.0 kW, max water volume 1.7 1; diffuser plate thickness 2.5 mm.

Kettle 3: convention jug kettle with underfloor element plate, no noise reduction coating or inhibitor, power rating 3.0 kW, water volume 1.7 1.

Each kettle was filled with hard mains water to the maximum recommended volume, and the noise level was measured as a function of time up to boiling. Figure 38a shows the result for the first boiling cycle: kettle 2 is quieter than kettle 1, and both are significantly quieter than the conventional kettle 3. Figure 38b shows the result after fifteen boiling cycles: kettle 1 is now similar to the conventional kettle 3, while kettle 2 is substantially unchanged.

After 15 cycles of heating hard water to boiling, kettle 1 produced an intense, high- pitched whine that started approximately halfway through the heating cycle, falling slowly in pitch and only ceased at boiling. Kettle 2 produced an intermittent, faint, high- pitched hum halfway through the heating cycle, which faded as boiling was approached. The results for kettle 1 are confirmed by independent reviews; for example, a customer review of the Kenwood Miro Brushed Metal Kettle SJM332 (which incorporated the 'Stealth' technology of Kettle 1) available on Amazon.co.uk on 26^th November 2007 reads:

"Was quiet but soon turned noisy! 19 Nov 2007 By Mrs. V. G. Hitchin

I thought this was brilliant when I first bought it 6 months ago, very quiet fast boil. Within two months it turned into a really noisy little beast. I am looking to change already as it is so loud!" As an alternative or additional effect, the inhibitor 11 may create an aesthetically pleasing flow of bubbles within the vessel 1, which may be viewed by the user through a window in the vessel wall 2.

The inhibitor 11 may be permanently or removably attached within the reservoir 3, for example by attachment to the lid, wall 2 or element plate 5 of the vessel 1, or to a steam tube, filter or lid provided within the vessel 1. For example, for use in soft water areas where high-pitched noise may not be a problem, the inhibitor 11 may be removed from the vessel 1. The user can use the vessel 1 without the inhibitor 11, and need only attach the inhibitor 11 if the high-pitched noise occurs. The inhibitor 11 may preferably be made of flexible material so that it can be easily inserted into and removed from the vessel 1.

In some embodiments, the inhibitor 11 may be sold or otherwise provided as a discrete article for retrofitting to an existing vessel 1 so as to reduce heating noise. The vessel 1 may have a noise reduction coating or treatment and the inhibitor 11 may be retrofitted to overcome problems associated with using the coating or treatment. Alternatively or additionally, the vessel 1 may have a noise reducing structure of an existing design and the discrete inhibitor 11 may be arranged for fitting to the vessel 1 as a replacement to the existing noise reducing structure.

The inhibitor 11 may be of adjustable dimensions, such as height or diameter, so as to achieve the correct fitting for a specific type of vessel 1, to fine-tune the performance of the inhibitor 11 for different operating conditions, or to facilitate fitting through a narrow opening in the vessel 1. For example, the inhibitor 11 may be provided on an adjustable frame, similar to that of an umbrella but with varying degrees of deployment.

The inhibitor 11 may be made of transparent and/or translucent material; this may make the inhibitor 11 unobtrusive, and allows lighting effects which illuminate the water from below to pass through the inhibitor 11. Furthermore, the flow of steam bubbles may be observed through the inhibitor 11, to enhance the visual effects of the vessel 1. The transparent and/or translucent material may be coloured, preferably in a colour complementary to that of the vessel 1.

The inhibitor 11 may comprise a heat-resistant material such as glass, ceramic or metal such as stainless steel; the inhibitor 11 may then be mounted on the element plate 5 without the need for thermal insulation therebetween. Alternatively, where the inhibitor 11 is made of material that is not heat resistant, the inhibitor 11 may be mounted on the element plate 5 with a thermally insulating portion therebetween, such as one or more thermally insulating feet. Specific embodiments including the inhibitor 11 are described below.

Sixth Embodiment - Funnel Inhibitor

As shown in Figures 17 to 24b, the inhibitor 11 may have the form of a funnel arranged to concentrate the flow of bubbles rising off the electric heater 4 into one or more constricted paths so that the bubbles are more likely to collide and coalesce. The inhibitor 11 is preferably supported a small distance above the heater 4, for example by a support attached to the vessel wall 2. The distance should be great enough to prevent excessive heating of the inhibitor 11 by the heater 4 and to allow water to flow into the inhibitor, but small enough to collect bubbles before they are likely to collapse: a range of 5-15 mm is preferred, but in some circumstances a clearance of as little as 2 mm may used. The inhibitor 11 preferably extends over the hottest parts of the element plate 5, in which local boiling occurs; these are generally those areas closest to or directly above the heater 4. The inhibitor 1 1 may extend radially inwardly from the heater 4.

In the first variant shown in Figure 17, the inhibitor 11 has the form of a funnel that converges upwardly to an aperture 12 through which heated water flows; this constricts the flow of steam bubbles and encourages them to coalesce. Furthermore, bubbles may collect and coalesce on the inner wall of the funnel. The funnel has curved sides that decrease in slope in an outward radial direction from the aperture 12, which may promote either of these effects.

The inhibitor 11 is spaced from the vessel wall 2, to allow cooler water to flow downward towards the heater 4.

In the second variant shown in Figure 18, the inhibitor 11 has an inverted runnel shape relative to the first variant. This arrangement constrains the upward flow of heated water towards the vessel wall 2, while cooler water flows downwards through the aperture 12 in the centre of the funnel. The arrangement may particularly enhance the aesthetic effect, since the bubbles are concentrated towards the vessel wall 2 where they are more easily seen through a window.

A third variant shown in Figure 19 is similar to the first variant, except that the inhibitor 11 includes a flap valve 13 in the aperture 12. The valve 13 is arranged to open when there is sufficient pressure, caused by steam bubbles collecting in the aperture 12, beneath the valve 13. In this way, small bubbles coalesce into large bubbles beneath the valve 13, which intermittently releases the large bubbles.

A fourth variant shown in Figure 20 is similar to the first and third variants, except that the aperture 12 contains a filter 14. The filter 14 provides a surface on which small bubbles may coalesce before passing through apertures in the filter 14. The filter 14 may also collect scale that is deposited out of the water as it is heated, so that scale deposit on the heater 4 is reduced. The filter 14 may be detachable from the inhibitor 11 and is preferably a disposable item that can be replaced by the user before it becomes blocked with scale. Alternatively, the inhibitor 11 may be completely detachable from the vessel 1, to allow cleaning or replacement. The filter 14 may be made of plastic (such as polypropylene), nylon, stainless steel or rubber. The apertures may have the form of a mesh or slots. A fifth variant shown in Figures 21a to 21c is similar to the first variant, but with a much wider aperture 12; the diameter A of the inhibitor 11 is 130 mm, the diameter B of the aperture is 60 mm and the height C of the inhibitor is 20 mm. This led to too many small bubbles being released through the aperture 12 before they had had the opportunity to coalesce. In this embodiment, the periphery of the inhibitor includes an aperture 1 Ia for fitting around a steam tube of a kettle.

A sixth variant, shown in Figures 22a to 22c, is a modification of the fifth variant in that the aperture 12 is bordered by a flat, horizontal annular portion l ib that extends inwardly into the aperture 12; the diameter D of the aperture is thereby reduced to 30 mm. This variant allowed steam bubbles to gather on the underside of the annular portion l ib, coalesce and be released through the aperture 12, thereby significantly reducing noise. The annular portion 1 Ib is significantly above the element plate 5 and is not directly above the heater 4, so that film boiling is avoided.

A seventh variant, shown in Figures 23a to 23c, is modified relative to the fifth variant in that the slope of the sides of the inhibitor 11 is decreased and the diameter B of the aperture 12 is also decreased; the diameter B of the aperture 12 is 30 mm, the diameter

A of the inhibitor 11 is 130 mm and the height C of the inhibitor is 20 mm. However, it was found that the bubbles did not travel easily up the underside of the inhibitor 11 due to the decreased slope, and film boiling began to occur under the inhibitor 11, which reduces heat transfer to the water.

An eighth variant, shown in Figures 24a and 24b, differs from the seventh variant in that the height C of the inhibitor 11 is increased to 35 mm; the diameter B of the aperture 12 remains 30 mm and the diameter A of the inhibitor 11, 130 mm. Hence, the slope of the sides of the inhibitor 11 is sufficient to allow bubbles to rise up and to avoid film boiling.

Various modifications may be applied to any of the variants of the sixth embodiment; for example, as shown in Figures 24a and 24b, slots l ie may be created in the sides of the inhibitor 11, to allow some bubbles to escape from the slots 1 Ic rather than from the aperture 12. As an alternative to slots, other shapes of aperture may be used. In another modification, the underside of the inhibitor 11 may be sufficiently rough to encourage the bubbles to adhere to inhibitor 11 and coalesce before escaping through the aperture 12. The inhibitor may be made of moulded plastic; the mould may be roughened to achieve the required level of roughness for the inhibitor, or the inhibitor may be roughened after forming.

Seventh Embodiment - Heater-aligned Inhibitor As shown in Figures 25 to 32b, the inhibitor 11 may have the form of a passage, extending substantially parallel to the element plate 5, in which small bubbles collect and coalesce before escaping from the passage. The passage is preferably aligned substantially above at least a portion of the heating element 6, and may subtend an arc smaller in angle than the heating element 6. In the first variant shown in Figure 25, the inhibitor 11 has the form of an arcuate passage that is rectangular in cross-section and open at the bottom and at each end. The inhibitor is supported a small distance above the element plate 5. The width of the passage is approximately equal to or slightly greater than that of the element 6. The passage extends over substantially less than the length of the element 6. For example, the element 6 may be C-shaped and subtend an angle of 270°, while the passage subtends only 100° or less, or even 90° or less. However, where the element 6 has a different shape other than a C-shape, the passage may conform to that different shape. The passage may be adjustable so as to vary the angle subtended, for example by forming the inhibitor 11 from two or more pieces slidable relative to each other. Bubbles are predominantly formed on 'hot spots' i.e. areas on the element plate 5 that are closest to the element 6, and most particularly those areas that are directly over an intermediate portion of the element 6. The passage is arranged above those areas, so that small bubbles collect in the passage, coalesce, and then escape through the open bottom or end of the passage. The second variant, shown in Figure 26, is similar to the first variant except that the inner side of the passage is open, giving an L-shaped cross-section. The third variant, as shown in Figure 27, is similar to the second variant except that outer side of the passage is open instead of the inner side. These arrangements promote the flow of bubbles respectively inwardly and outwardly of the inhibitor 11. The fourth variant, shown in Figure 28, is similar to the second and third variants except that the passage has neither an inner nor an outer sidewall, and hence is substantially flat in cross-section. Optionally, the upper surface comprises a filter 14 having apertures through which bubbles can escape, as with the filter 14 of the fourth variant of the sixth embodiment. Instead of a filter, larger discrete apertures may be provided in the upper surface. In the fifth variant, shown in Figure 29, the inhibitor 11 extends above the heating element 6 as in the other variants, but comprises a substantially vertically extending arcuate flat strip, on which small bubbles tend to become attached so that they coalesce.

The sixth variant, as shown in Figure 30, is similar to the first variant except that the passage is inclined by a small angle to the plane of the element plate 5 and therefore to the horizontal, so that the open ends of the passage are raised. This concentrates the flow of bubbles through the open ends.

The seventh variant, as shown in Figures 31a and 31b, is similar to the first variant except that the upper surface of the passage includes one of more flap valves 13, which open in response to sufficient pressure caused by bubbles collecting underneath, in a similar way to the valve 13 in the third variant of the sixth embodiment, and as shown in Figure 20.

The eighth variant, as shown in Figures 32a and 32b, is similar to the first variant except that the inhibitor 11 is attached to a spout filter 15 that is arranged to filter water as it is poured out of the spout. Preferably, the spout filter 15 is removable from the vessel 1 with the inhibitor 11, for cleaning by the user.

Eighth Embodiment - Large Area Flat Inhibitor

In the first variant of the eighth embodiment, as shown in Figure 33, the inhibitor 11 is substantially flat and extends substantially parallel to the element plate 5 at a small distance from, or in contact with, the element plate 5. The edge of the inhibitor 1 may be supported at a small distance from the vessel wall 2, or may abut against the vessel wall 2. The inhibitor 11 consists substantially of a filter 14 of similar material to the filter 14 in the other embodiments described above, arranged so that small bubbles collect and coalesce at the filter 14.

The second variant as shown in Figure 34 is similar to the first variant, except that the inhibitor 11 is resiliency deformable so that it can be removed for cleaning or replacement, even through a narrow neck in the vessel 1. Hence, this variant is particularly suitable for vessels 1 that taper upwardly. The vessel wall 2 may include one or more locating members which hold the edge of the inhibitor in position while allowing it to be removed by deformation. The third variant as shown in Figure 35 is similar to the first variant except that the inhibitor 11 is removably attached to the element plate 5 by a suitable fixing, such as a snap fit onto projections on the element plate 5, or bolt fittings with wing nuts. This provides a convenient means of support for the inhibitor 11.

The fourth variant, as shown in Figure 36, is similar to the third variant except that the inhibitor is removably attached to a steam tube 16 provided within the reservoir, for conducting steam to a thermal actuator in the base of the vessel 1.

In the fifth variant, as shown in Figures 37a and 37b, the inhibitor 11 is attached to the lid of the vessel 1, and is removable from the vessel with the lid, as shown in Figure 37b.

Ninth Embodiment - Rotating Inhibitor

In a ninth embodiment, as shown in Figure 39, the inhibitor 11 is rotatably mountable above the element plate 5 by means of a hub portion 1 Id, for example on a projection or spigot on the element plate 5. The inhibitor has a plurality of vanes l ie circumferentially spaced around the hub portion Hd. When the element plate 5 is heated, water and bubbles rise through the vanes 1 Ie, causing the inhibitor 11 to rotate. Bubbles are collected and coalesce on the blades of the vanes 1 Ie before being released through the vanes 1 Ie, thus reducing heating noise.

The rotating vanes l ie also stir the water, thus reducing local boiling and therefore heating noise. Scale deposited on the spigot or projection will be removed by the rotating action of the inhibitor 11, thus reducing the likelihood of jamming.

The rotating inhibitor 11 also produces a pleasing visual effect, particularly when one or more lights are arranged to shine through or reflect off the vanes l ie. There may also be vortex effects visible within the water.

In an alternative, the inhibitor 11 may be rotated by a motor; for example, the inhibitor 11 may include magnetic or magnetisable material, and may be driven by a magnetic rotor under the element plate 5. In another alternative, the water may be rotated by a magnetic or magnetised stirrer separate from the inhibitor 11.

Tenth Embodiment - Compressible Inhibitor

In a tenth embodiment, as shown in Figures 40a to 40c, the inhibitor 11 has the form of a resilient coil that, in an uncompressed state, corresponds in shape to one of the variants of the sixth embodiment i.e. is funnel-shaped. In an alternative, the inhibitor may be formed as a flat coil. The coil can be compressed radially as shown in Figure 40c to allow easy insertion into and removal from a vessel 1, particularly where the vessel 1 has a narrow neck. The cross-section of the coil is L-shaped, such that each pitch of the coil substantially overlaps an adjacent one. Other cross-sections may be alternatively used: for example, an inverted L-shape will encourage bubble to collect in the troughs formed within adjacent pitches of the coil. Other cross-sections such as U, n, I or horizontal sections could be used. Bubbles will coalesce on the underside of the coil and rise up through the aperture 12. A rotational component may be imparted by the coil to the flow of water as it rises up the inside of the inhibitor 11, thus further improving the noise reduction effect, as in the ninth embodiment.

The inhibitor 11 may be sufficiently flexible in the axial direction so as to be extended axially by the pressure of bubbles forming thereunder, thereby elongating the inhibitor 11 and enhancing bubble release as boiling is approached.

Fixing arrangements

Figure 41 shows a modified form of inhibitor 11, for example according to the sixth embodiment, having a plurality of different fixing portions for attachment to different types of vessel 1. Hence, the same form of inhibitor may be used with a plurality of different types of vessel 1 or element plate 5.

As shown in Figure 42a, the inhibitor 11 has a circumferential groove Hf on the underside thereof for fitting onto a projection 5e of the element plate 5.

Further as shown in Figure 42b, the inhibitor 11 has a plurality of perforated projections 1 Ih each of which fit onto a corresponding tag 5f on the element plate 5. The tag 5f projects through the perforation and the end of the tag 5b may be bent laterally so as to secure the inhibitor 11 to the element plate 5; alternatively, if the tab is sufficiently flexible, it may push or click-fit into the perforated projection 1 Ih.

Further as shown in Figure 42c, the inhibitor 11 has a plurality of bayonet projections or tabs 1 Ig that fit under corresponding projections 20 in the side wall of the vessel 1. The inhibitor 11 may be positioned in the base of the vessel 1 and then rotated so that the tabs 1 Ig engage with the projections 20. The projections may be formed as a part of another feature of the vessel 1, such as a water window.

Alternative Embodiments The above embodiments illustrate, but do not limit, the present invention. Alternative embodiments which may occur to the skilled reader on reading the above description may also fall within the scope of the invention.

Claims

I. An electric water heating vessel comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, the upper side having a noise- reduction coating and/or treatment, the vessel further comprising a noise inhibitor arranged above and in proximity to the element plate and extending substantially over the electric heating element, the inhibitor comprising a surface that converges or diverges in an upward direction. 2. The vessel of claim 1, wherein the surface converges in an upward direction.

3. The vessel of claim 2, wherein the surface converges towards an aperture in the inhibitor.

4. The vessel of any one of claims 1 to 3, wherein the surface is angled at at least 10° to the horizontal. 5. The vessel of any one of claims 1 to 4, wherein the slope of the surface of the inhibitor increases in an upward direction.

6. The vessel of any one of claims 1 to 5, wherein the surface includes one or more apertures therein.

7. The vessel of any one of claims 1 to 6, wherein the inhibitor is funnel- shaped with a substantially central aperture.

8. The vessel of claim 7, wherein the surface of the inhibitor decreases in slope adjacent the substantially central aperture.

9. The vessel of claim 8, wherein the surface of the inhibitor is substantially horizontal adjacent the aperture. 10. The vessel of any one of claims 1 to 9, wherein the underside of the surface is sufficiently rough as to promote adhesion of steam bubbles thereto.

II. The vessel of any one of claims 1 to 10, wherein the inhibitor is flexible so as to facilitate removal thereof from the vessel.

12. The vessel of any one of claims 1 to 11, wherein the inhibitor comprises transparent or translucent material.

13. The vessel of any one of claims 1 to 12, wherein the inhibitor comprises heat-resistant material. 14. The vessel of claim 13, wherein the inhibitor is mounted directly on the element plate.

15. The inhibitor of any one of claims 1 to 13.

16. The vessel of any one of claims 1 to 14, wherein the noise-reduction coating is hydrophobic. 17. The vessel of claim 16, wherein the noise-reduction coating comprises a resin component.

18. The vessel of any one of claims 1 to 14, 16 or 17, wherein the element plate has a heat diffusion layer for diffusing heat from the heating element to the underside of the element plate, wherein the heat diffusion layer is substantially thicker than the element plate.

19. The vessel of claim 18, wherein the diffusion layer is at least 2 mm thick.

20. An electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element and at least one thermal sensor in thermal contact therewith, the upper side having a noise reduction coating and/or treatment above the element and the at least one thermal sensor, and an area substantially free of the noise reduction coating and/or treatment.

21. The heater of claim 20, wherein an area of the coating and/or treatment above the element and the at least one thermal sensor is substantially continuous.

22. The heater of claim 20, wherein the coating and/or treatment is provided in discrete areas above the element and the at least one thermal sensor.

23. The heater of any one of claims 20 to 22, wherein the area substantially free of the noise reduction coating and/or treatment includes an area at the periphery of the element plate.

24. The heater of any one of claims 20 to 23, wherein the area substantially free of the noise reduction coating and/or treatment includes an area at the centre of the element plate.

25. The heater of any one of claims 20 to 23, wherein the noise reduction coating and/or treatment extends over an area at the centre of the element plate. 26. The heater of any one of claims 20 to 25, wherein the coating and/or treatment is arranged over only a portion of the heating element.

27. The heater of claim 26, wherein the heating element is a sheathed heating element and the portion is an intermediate portion of the sheathed heating element. 28. The heater of any one of claims 20 to 27, wherein the noise reduction coating and/or treatment is provided intermittently above the element and the at least one thermal sensor.

29. The heater of any one of claims 20 to 27, wherein the noise reduction coating and/or treatment is provided continuously above the element and the at least one thermal sensor.

30. An electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, the upper side having both a surface treatment and a surface coating that are not congruent. 31. The heater of claim 30, wherein an area of the upper side is provided with the surface treatment but is substantially free of the surface coating.

32. The heater of claim 30 or claim 31, wherein an area of the upper side is provided with the surface coating but is substantially free of the surface treatment.

33. The heater of any one of claims 30 to 32, wherein an area of the upper side is provided with the surface coating and the surface treatment.

34. The heater of any one of claims 20 to 33, including a heat diffusion layer for diffusing heat from the heating element to the underside of the element plate, wherein the heat diffusion layer is substantially thicker than the element plate.

35. An electric water heating vessel including an electric heating element and a structure arranged to promote coalescence of steam bubbles rising from the electric heating element. 36. The vessel of claim 35, wherein the structure comprises a funnel arranged to concentrate a flow of steam bubbles through an aperture in the funnel.

37. The vessel of claim 36, wherein the aperture includes a valve for releasing the steam bubbles through the aperture in response to pressure exerted by the bubbles. 38. The vessel of claim 36, wherein the aperture includes a filter.

39. The vessel of claim 35, wherein the structure is arranged to concentrate a flow of steam bubbles towards the wall of the vessel.

40. The vessel of claim 35, wherein the structure comprises a passage generally conforming to at least a part of the heating element and arranged above the element to collect the steam bubbles.

41. The vessel of claim 40, wherein the passage has one or more open ends.

42. The vessel of claim 41, wherein the passage is inclined upwardly towards the one or more open ends.

43. The vessel of any one of claims 40 to 42, wherein the passage is substantially open towards the heating element.

44. The vessel of any one of claims 40 to 43, wherein the passage has one or more open sides.

45. The vessel of any one of claims 40 to 44, wherein the passage includes a filter.

46. The vessel of any one of claims 40 to 45, wherein the passage includes a valve for releasing the steam bubbles from the passage in response to pressure exerted by the bubbles.

47. The vessel of claim 35, wherein the structure includes a surface generally conforming to at least a part of the heating element and arranged above the element such that steam bubbles coalesce thereon.

48. The vessel of claim 35, wherein the structure comprises a substantially horizontal filter arranged above the heating element.

49. The vessel of claim 35, wherein the structure is rotatably mounted within the vessel.

50. The vessel of claim 49, wherein the structure is arranged to be rotated by the action of the bubbles on the structure.

51. The vessel of claim 50, wherein the structure comprises a plurality of vanes.

52. The vessel of claim 49, wherein the structure is arranged to be rotated by a motor.

53. The vessel of claim 52, wherein the structure is magnetically coupled to the motor.

54. The vessel of claim 35, wherein the structure comprises a coil.

55. The vessel of claim 54, wherein the coil is radially compressible. 56. The vessel of claim 54 or claim 55, wherein the coil is arranged to promote rotational flow.

57. The vessel of any one of claims 54 to 56, wherein the coil is axially extendible by the action of the bubbles thereon.

58. The vessel of any one of claims 35 to 57, wherein the structure is resiliently deformable to facilitate removal from the vessel.

59. The vessel of any one of claims 35 to 58, wherein the structure is removably attachable to a part of the vessel.

60. The vessel of claim 59, wherein the structure comprises a plurality of different fixing arrangements.

61. The vessel of claim 59, wherein the structure is attached to a removable spout filter. 62. The vessel of claim 59, wherein the part of the vessel comprises a steam tube.

63. The vessel of claim 59, wherein the part of the vessel comprises an element plate.

64. The vessel of claim 59, wherein the part of the vessel comprises a lid. 65. The vessel of any one of claims 35 to 64, wherein the structure comprises transparent or translucent material.

66. The vessel of any one of claims 35 to 65, wherein the structure comprises heat-resistant material.

67. The vessel of claim 66, wherein the structure is mounted directly on the element plate.

68. The vessel of any one of claims 35 to 67, wherein the structure is adjustable in one or more dimensions.

69. The structure of any one of claims 35 to 68.

70. A method of reducing heating noise in an electric water heating vessel including an electric heating element, comprising providing in the vessel the structure of claim 69.

71. The method of claim 70, including providing the structure as a replacement to an existing noise reducing structure.

72. The method of claim 70 or 71, wherein the electric heating element comprises an element plate having a noise reduction coating or treatment thereon.

73. An electric water heating vessel including an electric heating element and a passage generally conforming to at least a part of the heating element and arranged above the element to collect the steam bubbles.

74. An electric water heating vessel including an electric heating element and a surface generally conforming to at least a part of the heating element and arranged above the element such that steam bubbles coalesce thereon.

75. The vessel of any one of claims 35 to 74, wherein the electric heating element is arranged on the underside of an element plate, and at least part of the upper surface of the element plate includes a noise reduction coating and/or treatment.

76. An electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, and a heat diffusion layer for diffusing heat from the heating element to the underside of the element plate, wherein the heat diffusion layer is substantially thicker than the element plate.

77. The electric water heater of claim 76, wherein the ratio of the diameter of the diffusion layer to the thickness thereof is less than approximately 50.

78. The electric water heater of claim 76 or claim 77, wherein the ratio of the thickness of the diffusion layer to that of the element plate is greater than approximately 4.

79. The electric water heater of any one of claims 76 to 78, wherein the thickness of the diffusion layer is greater than 3 mm.

80. The electric water heater of any one of claims 76 to 79, wherein the thickness of the diffusion layer is greater than 3.9 mm. 81. The electric water heater of any one of claims 76 to 80, wherein the element plate comprises a central, substantially planar portion under which the electric heater extends, and the diffusion layer extends beyond the central portion.

82. The electric water heater of claim 81, wherein the diffusion layer has a radially inner planar portion, and a peripheral portion that extends out of the plane of the planar portion.

83. The electric water heater of claim 82, wherein the peripheral portion of the diffusion layer extends away from the element plate.

84. The electric water heater of claim 82, wherein the peripheral portion of the diffusion layer extends towards the element plate.

85. The electric water heater of any one of claims 82 to 84, wherein the peripheral portion is substantially continuous around the periphery of the diffusion layer.

86. The electric water heater of any one of claims 76 to 85, including a noise reduction layer on the upper side of the element plate.

87. The electric water heater of any one of claims 76 to 86, wherein at least a portion of the surface of the upper side of the element plate is roughened by a surface treatment.

88. An electric water heater comprising an element plate having an upper side for contacting water and an underside having an electric heating element in thermal contact therewith, wherein the upper side is roughened by a surface treatment. 89. The electric water heater of claim 87 or 88, wherein the surface treatment is formed by at least one of abrasion, roughening, scouring, etching and blast finishing.

90. The electric water heater of claim 87 or 88, wherein the treatment is formed by grit blasting. 91. The electric water heater of any claims 87 to 90, wherein the surface roughness of said at least one portion is in the range 0.5 - 4 Ra.

92. The electric water heater of any one of claims 87 to 91, wherein another portion of the upper side of the element plate, not above the heating element, is substantially free of the surface treatment.

93. The electric water heater of any one of claims 92, wherein the surface treatment is applied substantially only to a portion of the upper side of the element plate above the heating element.

94. The electric water heater of any one of claims 87 to 91, wherein the surface treatment is applied to a plurality of discrete portions on the upper side of the element plate.

95. The electric water heater of any one of claims 88 to 92, wherein the surface treatment is applied directly to the surface of the element plate.

96. The electric water heater of any one of claims 88 to 92, wherein the surface of said upper side comprises a noise reduction layer to which the surface treatment is applied.

97. The electric water heater of claim 86 or claim 96, wherein the noise reduction layer is resin-based.

98. The electric water heater of claim 97, wherein the noise reduction layer includes 50-65% resin component.

99. The electric water heater of claim 97 or 98, wherein the noise reduction layer includes a non-stick component.

100. The electric water heater of claim 99, wherein the non-stick component comprises 10-20% of the composition of the noise reduction layer. 101. The electric water heater of any one of claims 97 to 100, wherein the noise reduction layer includes one or more fillers or pigments.

102. The electric water heater of claim 101, wherein the average particle size of the one or more fillers or pigments is less than 20 microns.

103. The electric water heater of claim 1, 86 or 96, wherein the noise reduction layer comprises glass or ceramic material.

104. The electric water heater of claim 103, wherein the noise reduction layer is formed by a sol-gel process.

105. The electric water heater of any one of claims 20 to 34 or 76 to 104, further including a circumferential seal around the periphery of the element plate, for sealing against a wall of a water heating vessel.

106. A water heating vessel having an electric water heater according to any one of claims 20 to 34 or 76 to 105.

107. The water heating vessel of claim 106, including an inhibitor.

108. The water heating vessel of claim 107, wherein the inhibitor is arranged to promote coalescence of steam bubbles rising from the electric water heater.

109. The vessel according to any one of claims 1 to 11, 16, 35 to 64, 73 to 75, and 106 to 108, including a motorised stirrer.

110. The vessel of claim 109, wherein the stirrer is magnetically coupled to a motor.

111. An electric water heater substantially as herein described with reference to the accompanying drawings. 112. An electric water heating vessel substantially as herein described with reference to the accompanying drawings.