GB2470368A

GB2470368A - A glass kettle with a heating element comprising a film coating of semiconducting material

Info

Publication number: GB2470368A
Application number: GB0908576A
Authority: GB
Inventors: Roger Williamson; Mark Andrew Gagiano
Original assignee: Sagentia Ltd
Current assignee: Sagentia Ltd
Priority date: 2009-05-19
Filing date: 2009-05-19
Publication date: 2010-11-24
Also published as: GB201007922D0; GB0908576D0; GB2470472B; GB2470472A; GB201008094D0; WO2010133824A1

Abstract

The invention relates to a glass kettle comprising a glass vessel 3 for holding water to be heated wherein said kettle has a glass substrate 6 bearing an electrical heating element 5. The element 5 may comprise a substantially transparent film coating of conducting or semiconducting material. In one aspect, the element 5 is provided on an inner surface of a central tube or extrusion (2, Fig.3). In another aspect, a method of controlling electrical power to the kettle comprises forming a semiconductor device comprising a portion of the semiconducting material of the element 5 and using said device to control power. In another aspect, the kettle comprises a substrate having an undulating profile, a level sensor, or a temperature sensor comprising a portion of the layer of semiconducting material.

Description

Kettles

FIELD OF THE INVENTION

This invention relates to electrical kettles.

BACKGROUND TO THE INVENTION

Despite many years of design, there remains a need for improved kettles, in particular with improved energy efficiency and reduced fabrication costs.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provided a glass kettle, the kettle comprising a glass vessel for holding water to be heated; and wherein said kettle has: a glass substrate bearing an electrical heating element.

In some preferred embodiments the heating element comprises a substantially transparent film coating of conducting or semiconducting material, for example doped tin oxide. In preferred embodiments the substrate has an undulating surface profile which descends from a central region of the kettle towards a circumferential edge of a base of the kettle.

In some preferred embodiments the glass vessel and substrate are formed from the same, common piece of glass, and thus in embodiments comprise a continuous piece of glass. Preferably a glass envelope is provided around the glass vessel, to assist in thermal insulation.

In preferred embodiments the electrical heating element comprises a film coating on the outer surface of the glass vessel/substrate (albeit, this may nonetheless be an interior surface of the kettle).

In embodiments the kettle includes a level sensor mounted vertically on an axis of symmetry of the vessel (thus enabling water volume measurements even when the kettle is angled). In preferred embodiments the level sensor is substantially transparent, and thus in embodiments comprises a substantially transparent, for example, a glass substrate over which a substantially transparent conducting or semiconducting film is provided. Conveniently the level sensor comprises a vertical rod or projection suspended within the glass vessel, with the conducting! semiconducting film on the outside (so that it contacts the fluid). The film may be divided into sections and/or provided with electrical connections at intervals to sense the water level.

The invention also provides a method of controlling a kettle by controlling the heat supplied to a heating element of the kettle in response to a sensed water level. A kettle including a control system to implement such a method is also provided.

In a further aspect the invention provides a kettle configured to switch off and/or control power to a heating element of the kettle by detecting a rolling boil by means of a resistive of capacitive level sensor. In this further aspect the invention also provides a kettle including a control system configured to implement such a method.

In a further aspect the invention provides a kettle including a thermal sensor, in particular as described further below, the kettle having an operational mode in which heating is stopped or controlled at a lower temperature than that of boiling water.

Such functionality may be provided additionally or alternatively to that described above, for example as an additional feature in a kettle as described above, especially where a semiconducting film coating is employed (when the layer of semiconductor may be used as the temperature sensor).

In some preferred embodiments the film coating comprises a semi conducting material and a switch for the heating element is fabricated within part of a layer of the same material (either within the heating element itself or as a separate device, for example patterned in a common layer of semiconducting material.

In a still further aspect the invention provides a kettle comprising: a vessel for holding water to be heated; and a central tube or extrusion having, on an inner surface, an electrical heating element comprising a film coating of conducting or semiconducting material.

In embodiments the film maybe vertically divided into separately electrically powerable sections; optionally the central tube or extrusion may further comprise a fluid level sensor. In embodiments the fluid level sensor comprises a coating on an outer surface of the central tube or extrusion (which contacts the fluid); alternatively capacitive sensing may be employed on the inner surface of the central tube or extrusion. In either case the kettle may include a power controller to selectively apply power to one or more of the vertical sections of the heating element in response to a level of fluid sensed by the fluid level sensor.

In embodiments of the kettle the film coating may comprise a semi-conducting oxide, more particularly doped tin oxide, for example antimony tin oxide, fluorine-doped tin oxide or some other substantially transparent conducting doped oxide material. Thus although the use of antimony tin oxide (ATO) film coatings has been found to be especially advantageous due to temperature stability, embodiments of the invention also contemplate substitution of an ATO film coating by a film of a different, electrically conducting material, for example, an alternative substantially transparent conducting oxide film, preferably a tin oxide film, for example Indium Tin Oxide, or a mixture of doped oxides.

In embodiments the substrate may be configured to provide a pattern of ridges, bumps or undulations, in particular a pattern which has, in cross-section, a profile which descends from a centre of the kettle towards a circumferential edge of the base. In embodiments the pattern comprises a set of generally concentric ripples, centred about a central, raised portion of the base (substrate). In embodiments the amplitude of the ripples reduces towards the circumferential edge of the base (substrate). Preferably the base of the kettle has a round or oval shape.

In embodiments the electrical heating element, in particular where it comprises a thin film, for example a layer of semiconducting material, may itself be used as a temperature sensor. In this case a signal maybe modulated onto the electrical power, typically DC or low-frequency AC, supplying the heating element, to enable this signal to be detected by demodulation. For example a higher frequency AC signal than a frequency of an AC current providing power for heating the heating element may be employed. Additionally or alternatively a region of the film maybe defined to be dedicated to temperature sensing and being provided with at least one separate electrode connection (optionally sharing one electrode connection with the heating element).

In a kettle as described above an electrical power control device or switch maybe incorporated into a layer semiconducting material forming the heating element itself.

For example by applying a gate electrode over an insulating layer on a portion of the semiconducting layer an FET (Field Effect Transistor) switch maybe fabricated. Such a device may be fabricated in a dedicated, separately defined region of the semiconducting layer or may be incorporated into the heating element, for example extending along the length of an electrode connection to the heating element.

Thus in a further aspect the invention provides a kettle, the kettle comprising: an electrical power input; an electrical heating element, and an electrical power control device electronically connected between said electrical power input and said electrical heating element; whereas said electrical heating element comprises a layer of semiconducting material on a substrate; wherein said electrical power control device is a semiconductor device; and wherein at least a portion of said semiconductor device comprises a portion of said layer of semiconducting material.

In embodiments the portion of the layer of semiconducting material comprising the electrical power control device is connected in series the material defining the electrical heating element, and in embodiments the semiconductor device and heating element may be part of the same, substantially continuous layer of semiconducting material (rather than needing to be defined in a separate, dedicated region of the semiconducting layer).

The device may comprise a diode, in particular a diode using a metal-semiconductor junction. Alternatively p-type and n-type doped regions of the layer maybe employed to fabricate a bipolar transistor. Alternatively, as previously described, an insulated gate FET (or junction FET) maybe fabricated. In general the power controlled semiconductive device comprises an FET, bipolar transistor, IGBT, thyristor, SCR rectifier, TRIAC, or other device. In embodiments the device and heating element and substrate may be substantially transparent.

Suitable materials include, but are not limited to, tin oxide, for example doped with antimony or fluorine, indium tin oxide, and silicon carbide.

In a related aspect the invention provides method of controlling electrical power to the electrical heating element of a kettle comprising a layer of semiconducting material, the method comprising forming a semiconductor device in said semiconducting material comprising said heating element to control said electrical power.

The skilled person will appreciate that the above described features may be provided in different combinations. The features of claim 1 are not essential to aspects of the invention comprising, in particular, one or more of: level sensing; a thermal sensor; a switching mechanism; and a tube heater (as described further later).

Thus in a further aspect the invention provides a kettle as recited in claim 26.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figure 1 shows a schematic illustration of a vertical cross section through an embodiment of a kettle according to the invention; Figures 2a and 2b illustrate an embodiment of a kettle according to the invention incorporating level sensing; and Figure 3 illustrates an embodiment of a kettle according to the invention with an internal tube heater;

DETAILED DESCRPTION OF PREFERRED EMBODIMENTS

Referring first to Figure 1, we will describe an embodiment of a kettle according to the invention.

The kettle makes use of clear thin film resistive coating (ATO) on a glass substrate as the heating element to provide the mechanism for boiling water.

Some benefits which have been identified when using thin film technology (5) as heating mechanism include visibility of the boiling process, energy savings due to improved efficiency due to reduction in heat loss, cost savings in the BOM (bill of materials) and manufacturing process (single-cut blown glass vessel (3) vs. double cut) and no issues with bonding and aligning base plate to main body.

The ridge profile in base (6) increases surface area of thin film heater to improve boiling performance by lowering the peak heating temperature.

Performance can be further improved by the use of a clear outer moulding (1), forming a double skin and air gap (2) to assist thermal insulation. The conical shape with small neck (9) also helps to reduce heat loss through the top surface of the water (4) Electrical connection to the resistive coating is achieved through a central connection (7) and radial connection (8).

Level sensing The thin film resistive coating can also be used to create an invisible' level sensor as part of a low voltage circuit (12) on a transparent inner tube (11). The axial sensor enables incremental water volume readings (13) when the kettle is angled during the filling process (Fig2B).

This can be linked to an audible or visual indicator on the device.

There is also the possibility to use this level sensor in conjunction with a switchable heat source, optimising the power density according to the water level required versus surface area.

The level sensing is conducted using resistance or capacitive sensing. Further by using either capacitive or resistive sensing, it is possible to detect a rolling boil due to the large bubbles of steam causing a dramatic change in the relative capacitance or resistance of the water. This can then be used to shut down the kettle instead of using a steam pipe and /or bi-metallic strip.

Thermal sensor Typical thin film coatings are intrinsic semiconductors. For example, SiC and tin oxide are both semiconductors with large band gaps (typically 3.2eV). By doping the semiconductor can be made to be n-type or p-type. Typically, impurities make the thin film an n-type semiconductor. For example, ATO is an n-type semiconductor.

However p-type semiconductors can also be produced.

Typical thin film materials hence have a reversible resistance -temperature characteristic and thus the heating element itself can be used as a thermal sensor to measure the temperature of the heating element or substrate. Alternatively, a separate area of thin film which does not constitute part of the heating element, but placed on the same substrate close to the element can be used to measure the temperature using a separate low voltage/low cunent circuit. The area can be manufactured using a masking process when the main heating element is being created.

It is preferred to detect the resistance change using a low voltage / low current so that the sensitivity is improved and the semiconductor is not saturated, hence a separate area for thermal detection is preferred rather than using the bulk element itself. Should the bulk element need to be used, then a high frequency signal multiplexed on to the DC or low frequency AC bias can be used to detect variation in resistance, without the requirement to measure high voltages or currents.

The thermal sensor can also be used to detect the boiling point of the water rather than using a steam tube and/or bi-metallic strip, which has a longer reaction time due to thermal coupling. The thermal sensor can also be used to stop heating at lower temperatures which is required for making drinks other than black tea: coffee, green tea and so forth.

Switching mechanism In embodiments the heating elements are required to be switched on and off. This may achieved using a manual switch, a relay or a solid state switching device, generally separated from the heating element itself. However this can add extra cost to the overall system.

Hence, it is desired to create a system by which the heating element switch is included within the heating element. Given that the thin film technology is a semiconductor, it is possible to create at the same time as the heating element different types of semiconductor switch or rectifier. In particular, one can produce a FET device by overlaying a thin insulator, such as mica or silicon dioxide on top so an area of the thin film element (typically where the current enters or leaves the element). On top of the insulator a metallisation layer is created to which a voltage can be applied to switch the element. Further devices are possible: for example, at the metal -thin film junction a Schottky diode is created, further using n-type and p-type variants of silicon carbide or tin oxide it is possible to create a rectifying diode or bipolar transistor. Because the material can withstand high temperatures, there is no need for a heat sink and any heat losses are directly used in the heater, thus increasing efficiency as well as reducing cost. Many of these devices can be transparent and hence can be used within the kettle to switch the elements to provide different heating levels and control.

Internal tube heater In Fig 3, one can see that by introducing a glass or ceramic (alumina oxide) tube or extrusion (2) connected through the base of the kettle (1), central to the water source, the thin film resistive coating can be used as a heating element for boiling water within the body of the liquid. This allows for increased surface area of the heat source and thus maximising contact area with the water. Any heat is delivered straight to the water source and minimises thermal loses to any external influences. The heating cycle of the vertical heater along with the profile of the internals of the water reservoir allows for the optimisation of toroidal flow characteristics in heating the water and therefore improves the performance of the water heating by reducing the effective surface area of water in contact with an energy loosing surface until the final stages of boiling. This effect also minimises noise levels from the heating water during the boiling process, since this mechanism promotes the steam bubbles imploding within the body of water rather than on the surface. This mechanism, hence, improves efficiency.

To optimise the effects, the heater element can be sectioned (6) with electrodes (5) at increments up the length of the tube allowing switching of power (see Switching mechanism) dependent on water level (4) (see Level sensing section -sensing coating is on exterior of tube element (3)). i.e. if only partially full, all power may substantially only be directed to the bottom section of the heating tube, thus minimising redundant heating by the remainder of the heating element. The tube method can also use the switching methods and capacitive / resistive sensing described above.

In embodiments the element may be switched by TRIAC switching, with differential choke filtering (for example, a differential mode filter of 1 8mH) for EMC capability.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS: 1. A glass kettle, the kettle comprising a glass vessel for holding water to be heated; and wherein said kettle has: a glass substrate bearing an electrical heating element.
2. A glass kettle as claimed in claim 1 wherein said heating element comprises a substantially transparent film coating of conducting or semiconducting material.
3. A glass kettle as claimed in claim 2 wherein said film coating comprises doped tin oxide.
4. A glass kettle as claimed in any preceding claim wherein said substrate has an undulating surface profile which descends from a central region of said kettle towards a circumferential edge of a base of said kettle.
5. A glass kettle as claimed in any preceding claim wherein said glass vessel and said glass substrate are formed from a common piece of glass.
6. A glass kettle as claimed in claim 5 wherein said glass vessel and substrate have an inner region for holding said water and wherein said electrical heating element is fabricated on an outer surface of said glass vessel and substrate.
7. A glass kettle as claimed in any preceding claim further comprising a glass envelope around said glass vessel.
8. A glass kettle as darned in any preceding claim further comprising a level sensor mounted vertically on an axis of symmetry of said vessel.
9. A glass kettle as claimed in any preceding claim further comprising a level sensor, wherein said level sensor is substantially transparent.
10. A kettle as claimed in any preceding claim wherein said substrate bears a layer of semiconducting material, wherein said heating element is formed from said semiconducting material, and wherein said kettle includes a temperature sensor comprising a portion of said layer of semiconducting material.
11. A kettle as claimed in any preceding claim further comprising: an electrical power input; and an electrical power control device electronically connected between said electrical power input and said electrical heating element; wherein said electrical heating element comprises a layer of semiconducting material on said substrate; wherein said electrical power control device is a semiconductor device; and wherein at least a portion of said semiconductor device comprises a portion of said layer of semiconducting material.
12. A kettle comprising: a vessel for holding water to be heated; and a central tube or extrusion having, on an inner surface, an electrical heating element comprising a film coating of conducting or semiconducting material.
13. A kettle as claimed in claim 12 wherein said film is vertically divided into separately electrically powerable sections.
14. A kettle as claimed in claim 12 or 13 further comprising a fluid level sensor comprising; a second film coating of conducting or semiconducting material on an outer surface of said central tube or extrusion.
15. A kettle as claimed in claim 13 or 14 comprising fluid level sensor and a power controller to electrically apply power to one or more of said separately electrically powerable sections of said heating element film responsive to a level of fluid sensed by said fluid level sensor
16. An electric kettle comprising: an electrical power input; an electrical heating element, and an electrical power control device electronically connected between said electrical power input and said electrical heating element; wherein said electrical heating element comprises a layer of semiconducting material on a substrate; wherein said electrical power control device is a semiconductor device; and wherein at least a portion of said semiconductor device comprises a portion of said layer of semiconducting material.
17. An electric kettle as claimed in claim 16 wherein said portion of said layer of semiconducting material is electronically connected in series with a portion of said layer of semiconducting material defining said electrical heating element.
18. An electric kettle as claimed in claim 17 wherein said portion of said layer of semiconducting material of said semiconductor device and said portion of said layer of semiconducting material defining said electrical heating element comprise a substantially continuous region of said layer of semiconducting material.
19. An electric kettle as claimed in claim 16, 17 or 18 wherein said electrical heating element has at least one electrode and wherein said electrical power control device is fabricated in a said portion of said layer of semiconducting material adjacent said electrode.
20. An electric kettle as claimed in any one of claims 16 to 19 wherein said electrical power control device has a metal electrode connection and comprises a diode formed between said metal electrode and said layer of semiconducting material.
21. An electric kettle as claimed in any one of claims 16 to 20 wherein said layer of semiconducting material includes both p-type and n-type doped regions and wherein said electrical power control device comprises a bipolar transistor.
22. An electric kettle as claimed in any one of claims 16 to 21 further comprising a gate electrode over said portion of said layer of semiconducting material of said semiconductor device, and an insulator between said gate electrode and said layer of semi conductivity material, and wherein said electrical power has a metal electrode connection and comprises a field effect transistor.
23. An electric kettle as claimed in any one of claims 16 to 22 wherein said layer of semiconducting material comprises tin oxide or silicon carbide.
24. An electric kettle as claimed in any one of claims 16 to 25 wherein said substrate and said layer of semiconducting material on said substrate are substantially transparent.
25. A method of controlling electrical power to an electrical kettle comprising a layer of semiconducting material, the method comprising forming a semiconductor device in said semiconducting material of said heating element, and using said semiconductor device to control said electrical power.
26. A kettle having a substrate bearing an electrical heating element, the kettle further comprising one or more of: i) said substrate has an undulating surface profile which descends from a central region of said kettle towards a circumferential edge of a base of said kettle; ii) a level sensor mounted vertically on an axis of symmetry of said vessel; iii) a level sensor, wherein said level sensor is substantially transparent; iv) a substrate bearing a layer of semiconducting material, wherein said heating element is formed from said semiconducting material, and wherein said kettle includes a temperature sensor comprising a portion of said layer of semiconducting material.