GB2448009A

GB2448009A - Liquid heating vessels

Info

Publication number: GB2448009A
Application number: GB0721858A
Authority: GB
Inventors: Robert Henry Hadfield; Peter Hallam Wright; Antonio Martin Gaeta; Michael Collinson
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 2007-03-30
Filing date: 2007-11-07
Publication date: 2008-10-01
Also published as: GB0721858D0

Abstract

A liquid heating appliance comprises a lower liquid vessel 4, an upper liquid vessel 6 that is mountable on the lower vessel and a radiant heater for heating at least the lower vessel. The radiant heater may be at the side (Figure 5), top (Figure 6a, 6b) or bottom (Figure 4) of the lower vessel or there may be a respective heater in each vessel (Figure 7). The heater, such as a halogen heater, may direct visible light into the upper vessel. Alternatively, there may be inductive heating coils. A top heater may be located on a lid of the lower vessel so that the lid conducts heat to the upper vessel. There may be plural heaters at different heights. The vessels may be arranged so that that warm air or steam 5 from the lower vessel is retained in contact with a sidewall of the upper vessel. The lower vessel may include a handle engageable with the upper vessel so as to retain the upper and lower vessels together. The lower vessel may include an electromagnet which exerts an upward force on the removable upper vessel. Additionally, a liquid heating appliance may be controlled in response to detected agitation of the liquid.

Description

Liquid Heating Vessels

Field of the Invention

100011 The present invention relates to liquid heating vessels, and particularly those comprising a lower, electrically heated liquid vessel, an upper liquid vessel and means for heating the upper vessel and the lower vessel.

Background of the Invention

100021 There is a large market in Turkey, and other markets with Turkish influence, for a liquid heating appliance of the type known in English as a Turkish tea maker and in Turkish as caydanlik'. The tea maker comprises a lower electrically heated vessel in the form of a kettle with a lid. The kettle has a water boiling setting and a keep warm setting' which keeps water at a substantially constant temperature at or below boiling. When the water has boiled, it is added to tea leaves in a specially designed teapot which is then placed on top of the kettle in place of the lid. The teapot is kept warm by steam or hot air rising from the kettle, particularly in keep warm mode'. Examples of such tea makers are shown in Turkish patent publications TR 2001/02825 U and TR 2002/01765 U. In larger Turkish tea makers, tea is dispensed from a tap in the teapot, rather than by removing the teapot from the kettle and pouring out the tea.

100031 One problem with tea makers of this type is that the thermal transfer between the kettle and the teapot may be too low, so that the teapot is insufficiently, or inefficiently heated. Another problem is that the combined kettle and teapot is relatively tall and not compact, and is therefore difficult to store or transport. Another problem is that the teapot may be unstable, particularly when full of tea, potentially leading to accidents.

100041 Another problem is that the level of heating required to keep the water at or below boiling may not provide sufficient heat conduction to the teapot. Another problem is that the level of heating required to keep the water at or just below boiling varies with the level of water. Another problem is that it may be difficult to discern the quantity of tea remaining in the teapot.

100051 Another problem is that the level of heating must be controlled to avoid excessive boiling of the water and/or to avoid boiling the tea in the teapot. In Turkish tea makers of the type described herein, it is preferred that the water be kept at a low simmer rather than a full boil; in this way, the water is kept as hot as possible while avoiding wasting energy or excess ambient humidity, and delaying the time until the kettle boils dry. It is known to * 2 provide controls that detect boiling by sensing steam, but such controls are designed to be activated by a full boil.

Statement of the Invention

[0006J According to one aspect of the present invention, there is provided a liquid heating appliance comprising a lower, electrically heated liquid vessel, an upper liquid vessel that is mounted or removably mountable on the lower vessel, and a heater arranged to heat one or both of the lower liquid vessel and the upper liquid vessel. Preferably, the heater is a radiant heater, for example a halogen heater.

100071 The radiation generated by the radiant heater may include light from the visible part of the electromagnetic spectrum, and the radiant heater may be arranged to direct the visible light into the upper vessel such that the level of liquid within the upper vessel is discernible by a user. The visible light may be directed into a space between an inner wall and an outer wall of the upper vessel, and/or into the liquid within the upper vessel. The upper vessel may include at least a transparent or translucent portion arranged such that the visible light can be seen by a user. The visible light may alternatively or additionally be directed into the lower vessel, which may include at least a transparent or translucent portion arranged such that the visible light can be seen by a user. Alternatively, the visible light may be provided by a light source that does not also act as a heater.

(0008J The radiant heater may be positioned in or on a floor or sidewall of the lower vessel.

There may be provided a plurality of radiant heaters arranged at respective different heights on the sidewall. The radiant heaters may be selectively switchable to provide varying heating power to the lower vessel. Alternatively, the heating effect of the radiant heaters on the liquid in the lower vessel may vary automatically according to the liquid level, with the liquid being heated predominantly by those heaters that are immersed in the liquid.

100091 The radiant heater may alternatively or additionally be arranged in or around a top portion of the lower vessel, and may be arranged to direct radiant heat in a downward direction into the lower vessel. The upper vessel may be arranged in thermal contact with the radiant heater so as to be warmed by thermal conduction therefrom.

100101 According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower, electrically heated liquid vessel, an upper liquid vessel mounted or removably mountable on the lower vessel, and a heater arranged at a boundary between the upper liquid vessel and the lower liquid vessel so as to heat both the lower liquid vessel and the upper liquid vessel.

100111 According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel, the lower liquid vessel including a first electric heater for heating liquid contained within the lower vessel, and the upper vessel being arranged to be heated by a second electrical heater discrete from the first electrical heater.

Preferably, the second electrical heater is arranged to be switched off or with a reduced power when the upper vessel is removed from the lower vessel.

10012] The second electrical heater may have a lower power rating than the first electrical heater. The second electrical heater may be a self-regulating heater, such as a PTC heater.

100131 According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel, the lower liquid vessel including a plurality of heaters arranged at respective different levels within the lower vessel. The heaters may be self-regulating heaters arranged to provide a high heating power when immersed and a lower heating power when not immersed. The power levels of the heaters may be monitored so as to provide a level indication.

100141 According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel, the lower liquid vessel including an inductive heating coil and the upper vessel including an inductively heatable material arranged to be heated by the inductive heating coil when the upper vessel is mounted on the lower vessel.

100151 According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower, electrically heated liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel in thermal contact therewith, wherein the upper liquid vessel is arranged so that that warm air from the lower vessel is retained in contact with a side wall of the upper vessel.

[00161 In one embodiment, the upper vessel fits at least partially within the lower vessel so that at least part of the sidewall of the upper vessel is located within the lower vessel. In another embodiment, the upper vessel includes a hollow passage open to the lower vessel so that air rising from the lower vessel is trapped within the hollow passage in contact with the sidewall of the upper vessel. The upper vessel may have an outer wall and an inner wall, the hollow passage being formed between the two walls.

j0017] According to another aspect of the present invention, there is provided a liquid heating appliance comprising a lower, electrically heated liquid vessel and an upper liquid S 4 vessel mounted or removably mountable on the lower vessel in thermal contact therewith, wherein the lower vessel includes a handle engageable with the upper vessel so as to retain the upper and lower vessels together.

Brief Description of the Drawings

10018J There now follows, by way of example only, a detailed description of preferred embodiments of the present invention in which: Figures 1 a to 1 e show a Turkish tea maker in a first construction embodiment of the invention, respectively in side view, side view with teapot separated from kettle, cross-sectional view, perspective cut-away view and perspective view; Figures 2a to 2c show a Turkish tea maker in a second construction embodiment of the invention, respectively in perspective view, perspective view with teapot separated from kettle, and cross-sectional partial view; Figures 3a to 3g show a Turkish tea maker in a third construction embodiment of the invention, in perspective view showing in stages a fold-down handle being used to engage a teapot; Figure 4 is a cross-sectional diagram of a Turkish tea maker in a first heating embodiment of the invention; Figure 5 is a cross-sectional diagram of a Turkish tea maker in an alternative first heating embodiment of the invention; Figure 6a is a cross-sectional diagram of a Turkish tea maker in another alternative first heating embodiment of the invention; Figure 6b is a cross-sectional diagram of a Turkish tea maker in another alternative first heating embodiment of the invention; Figure 7 is a cross-sectional diagram of a Turkish tea maker in another alternative first heating embodiment of the invention; Figure 8 is a cross-sectional diagram of a Turkish tea maker in a second heating embodiment of the invention; Figure 9 is a cross-sectional diagram of a Turkish tea maker in an alternative second heating embodiment of the invention; Figure 10 is a cross-sectional diagram of a Turkish tea maker in a third heating embodiment of the invention; and Figure 11 is a cross-sectional diagram of a Turkish tea maker in an embodiment of the invention including a level-sensing device. * 5

Detailed Description of the Embodiments

Tea Maker Construction f0019] In the first embodiment, a Turkish tea maker comprises a kettle I removably mountable on a power base 2 that supplies power to the kettle 1, for example via a cordless electrical connector (not shown) that supplies electrical power to an element (not shown) within the kettle I, or by inductive heating. Preferably, the cordless connector is a 360 cordless connector, allowing free rotation of the kettle I on the base 2. A teapot 3 is arranged to be mounted on top of the kettle I (See Fig. La), from which it can be removed (Fig. Ib) for pouring tea.

100201 As shown in Figure lc, the teapot 3 has a double-walled construction: tea is contained within a vessel 6 having an inner wall 7, around which is arranged an outer wall 8 of the teapot. A hollow space 9 is formed therebetween with an open bottom so that hot air andlor steam 5 rising from the warm or boiling liquid 4 in the kettle passes into the hollow space 9, and thereby warms the inner wall 7 of the teapot. The arrangement is shown in cutaway perspective in Figure Id, while Figure le shows the complete arrangement in perspective, by way of comparison.

1] In a second embodiment, the teapot 3 is of single-walled construction, having only inner wall 7. In this embodiment, the teapot 3 fits within the kettle 1, which thereby effectively forms the outer wall. As shown in Figure Ia, the teapot 3 has an upper rim 10 that abuts the top of the kettle I, effectively forming a lid of the kettle. This arrangement makes the combined kettle and teapot more compact and stable.

100221 As shown in Figure 2c, hot air and/or steam 5 rises up into a space 9' between the wall 7 of the teapot and the upper section of the wall of the kettle I, thereby keeping the teapot 3 warm.

100231 In a variant of the second embodiment, the teapot 3 is arranged so that it can rest either on top of or within the kettle, depending on the relative rotational orientation. This may be achieved by having a non-circular opening in the top of the kettle, with a shape that conforms to the teapot 3 only in one or more relative orientations, for example a square opening into which a cuboidal teapot fits.

100241 In the third embodiment, the kettle I has a handle 11 formed of two halves I la, 1 lb which can be folded down horizontally on respective sides of the top of the kettle, as shown in Figures 3a to 3c. The kettle 1 has a lid 12 that can be removed and replaced by a teapot 3 that fits on top of the kettle, as shown in Figure 3d. The two halves of the handle 11 are then * 6 folded up vertically so that they retain the teapot 3 therebetween, as shown in Figures 3e and 3f. In particular, the handle 13 and spout 14 of the teapot 3 may be retained between the two halves ha, hib of the handle 11, which may be locked together by a catch or other locking means (not shown). In this way, the teapot 3 is held securely on top of the kettle I and the tea maker is easily transportable. The teapot may also have a folding handle.

100251 Features of the different embodiments may be combined together: for example, the kettle I of the first or second embodiment may be provided with a handle II as in the third embodiment, to secure the teapot 3 to the kettle 1.

Heating Method -Radiant Heater (00261 In a first heating embodiment of the invention, heating power is provided by one or more halogen heaters or other radiant heaters, preferably which also emit visible light.

[00271 In the embodiment shown in Figure 4, a halogen heater 22 is provided in a base section 20 of the kettle 1, so as to heat the water 4 by means of infrared radiation. Some of the infrared radiation passes through the water 4 and is incident on the inner wall 7 of the teapot 3 so as to keep tea warm within the vessel 6. In this way, the heating of the teapot 3 is not reliant on convection of hot air or steam from the kettle I. As an additional advantage, the teapot 3 may be preheated by the halogen heater 22 while the water 4 is heated up to boiling.

100281 An advantage of halogen heaters is that they generate visible light as well as infrared; the visible light serves to illuminate the water 4 so as to provide an easy visual indication of the level of the water 4, visible for example through a window in the side wall of the kettle 1. In the present embodiment, the visible light may also illuminate the teapot 3.

For example, in a case where at least a part of the inner wall 7 and a corresponding part of the outer wall 8 are transparent or translucent, the level of tea in the teapot 3 may be easily seen. A particularly advantageous lighting effect may be achieved by illuminating the space 9 between the inner wall 7 and the outer wall 8 in this way, where the teapot is arranged as in the embodiment of Figure 1. The base of the vessel 6 may be transparent or translucent so that visible light passes into the tea, thereby producing a lighting effect which may be seen through transparent or translucent parts of the side wall of the teapot 3, or through its spout.

This lighting effect is not purely aesthetic, but allows the strength of the tea to be discerned.

100291 Alternatively, the halogen heater 22 may be positioned in or on a sidewall of the kettle I so as to irradiate the contents laterally. In an alternative embodiment shown in * 7 Figure 5, a plurality of halogen heaters 22a-n are mounted in this way, in an array that extends in a substantially vertical direction up the sidewall.

100301 The halogen heaters 22a-n may be selectively or individually switchable. In one example, substantially all the heaters 22a-n are energised for the heating mode, but only some of the heaters are energised for the keep warm mode. The level of the water 4 is generally lower when keep warm mode is required, since some of the water will have been poured out into the teapot 3, so that only lower ones of the heaters are energised. In another example, the heaters 22a-n are switched according to the detected level of the water 4, with only heaters below the water level being energised. Alternatively, only two halogen heaters 22 may be provided, with both heaters switched on for heating mode and only the lower heater switched on for keep warm mode.

[00311 Alternatively, the halogen heaters 22a-n may be switchable only as a group. In that case, heaters that are not immersed will still radiate heat, but may reach an equilibrium temperature while radiating less heat than the immersed heaters, by virtue of the lack of cooling from the water 4. The internal side wall of the kettle may be reflective so as to direct infrared radiation back to the heaters andlor the water 4.

[00321 Alternatively, the halogen heater(s) may be positioned towards the lop of the kettle and arranged to direct infrared radiation downwardly into the water 4. In the embodiment shown in Figure 6a, the heater 22 is positioned on the underside of the teapot 3 or in a lid of the kettle, where the lid is not removable when the teapot 3 is mounted on the kettle 1.

Waste heat from the heater 22 is conducted into the vessel 6 of the teapot, thereby keeping warm both the tea in the teapot 3 and the water 4 within the kettle 1. Where the heater 22 is positioned on the underside of the lid, the lid may provide a hotplate on which vessels other than the teapot 3, such as a coffee pot, may be kept warm. The lid also allows the kettle I to function while the teapot 3 is removed.

100331 The power output of the heater 22 may be varied automatically according to the detected level of the water 4 andlor the tea. The voltage provided to the heater 22 may be stepped down from mains voltage to a low voltage, such as I 2V. Advantageously, the low voltage can be safely conducted to the top of the kettle, for example through an electrical connection in the sidewall or the handle.

100341 In an alternative embodiment shown in Figure 6b, a halogen heater 22 is arranged towards the top of the kettle 1, so as to direct heat downwards at an oblique angle. Infrared radiation striking the side wall of the kettle may be reflected towards the bottom of the kettle 1. The sidewalls may have a reflective surface so as to reflect infrared radiation. The bottom * 8 surface and/or lower parts of the sidewall of the kettle 1 may have an infrared absorbing surface. In this way, the heating effect of the heater 22 is directed towards the bottom or lower parts of the kettle 1.

0035] Alternatively or additionally, the halogen heater 22 may be arranged to direct infrared radiation upwards towards a sidewall which reflects the radiation towards the teapot 3. The bottom surface of the teapot may be of a material that absorbs the radiation, or reflects the radiation back into the kettle 1.

[0036J In another alternative, there may be provided discrete heaters 22 for the kettle 1 and the teapot 3. In the embodiment shown in Figure 7, there is provided a first heater 22a positioned in a base portion 20 of the kettle I, as in the embodiment of Figure 4, and a second heater 22b positioned on the underside of the teapot 3 or in a lid of the kettle I and arranged to direct radiant or conducted heat onto the teapot 3 and/or into the vessel 6 of the teapot 3. The second heater 22b is controlled independently of the first heater 22a so as to keep tea in the vessel 6 hot, but below boiling. The power level of the second heater 22b may be controlled according to the detected level and or temperature of tea within the vessel 6. Where the heater 22 is provided in the teapot 3, an electrical contact is made between the kettle I and the teapot 3 when mounted thereon. There may be provided an electrical contact track around the rim of the kettle 1, which makes contact with a contact portion of the kettle regardless of the relative orientation of the teapot 3 and the kettle 1. In other words, a low-voltage 360 connector may be provided between the kettle I and the teapot 3.

100371 As an alternative to the halogen heater(s) 22, another electrically powered combined heat and light source may be provided, such as a high-power LED array.

Heating Method -Self-Regulating Heater 100381 In a second heating embodiment of the invention, the heater(s) comprise one or more self-regulating heaters. In one preferred embodiment, the heater or heaters comprise one or more PTC (positive temperature coefficient) resistors, and particularly resistors that exhibit a sharp rise in resistance at a critical temperature. The critical temperature is selected to coincide with the heated liquid being at a temperature just below boiling.

100391 In a specific embodiment shown in Figure 8, a first PTC heater 22a heats the water 4 in the kettle 1, while a second PTC heater 22b heats tea in the vessel 6. The first PTC heater 22a may be operable to heat the water 4 to boiling, whereupon the critical temperature is reached and the first PTC heater 22a operates as a keep warm heater. Alternatively, another * 9 conventional heater may be provided to heat the water 4 up to boiling; this is advantageous where it is not practicable to provide a high-power PTC heater as the first FTC heater 22a.

[00401 A second FTC heater 22b is positioned so as to conduct heat into the vessel 6, and is operable to keep tea warm within the vessel 6. The second PTC heater 22b may be provided around a rim of the top of the kettle I. Alternatively, the second FTC heater 22b may be provided in the teapot 3, which in this case makes an electrical contact with the kettle I for example as described above.

100411 In another specific embodiment shown in Figure 9, the water 4 within the kettle I is heated by plurality of PTC heaters 22a-n arranged at different levels along a side wall of the kettle 1. Those PTC heaters that are immersed are cooled to below their critical temperature and therefore provide a high heating output at least until the water 4 reaches boiling point, while those that are not immersed quickly reach their critical temperature and provide a low heating output. In this way, the combined heating power of the PTC resistors 22a-n adjusts automatically to the level of the water 4.

(00421 in this embodiment, the PTC resistors 22a-n act as a level sensor, and this effect may be used to provide a level output for use in an electronic control or level indicator, by detecting which of the FTC resistors are above their critical temperature, for example by measuring the voltage drop across each resistor.

(0043j A similar arrangement of PTC resistors may be provided within the vessel 6.

Alternatively, a single PTC resistor may be provided under the floor of the vessel, as in the embodiment of Figure 8.

(00441 As an alternative to a PTC heater, there may be provided a trace heating wire which may or may not be self-regulating.

Heating Method -Inductive Heater (0045J In a third heating embodiment of the invention, heating power is provided by one or more inductive heaters. In the embodiment shown in Figure 10, an inductive coil 22 is provided around the rim of the kettle 1; the inductive coil 22 is connected to an AC frequency converter (not shown) for converting AC mains power to a suitable frequency for induction heating. At least a portion of the vessel 6 comprises inductively heatable material, such as ferromagnetic or ferrimagnetic material, preferably iron or steel, such as stainless steel. The floor and/or sidewalls of the vessel 6 may have a core of such inductively heatable material, with one or more surface layers or coatings resistant to corrosion while allowing thermal conduction from the core into the vessel 6. Preferably, the inductively * 10 heatable portion of the teapot 3 fits within the inductive coil so as to provide high inductive coupling. When the teapot 3 is removed from the kettle, the inductive heating effect is automatically removed.

100461 Alternatively, the inductively heatable material may be provided on the top of the kettle, for example as a hotplate on which the teapot 3 or other vessels may rest.

100471 The power level of the inductive heater(s) may be controlled according to the detected temperature of the tea within the vessel 6. Alternatively, the inductively beatable material may be selected to have a Curie temperature that is reached when the contents of the vessel reaches the desired temperature. In this case, the heating power is self-regulating.

Reduced Friction Teapot 100481 The inductive coil 22 may act as an electromagnet, and the teapot 3 may include diamagnetic or electrically conductive material such that the electromagnet applies an upward force on the teapot 3, so as to reduce the effective weight of the teapot 3 and therefore its friction against the kettle 1. Advantageously, this may reduce the friction between the teapot 3 and the kettle 1, allowing the teapot 3 to be turned more freely relative to the kettle I. If sufficient power is applied to the coil, the teapot 3 may be made to levitate from the kettle 1, depending on the weight of the teapot 3; this may provide a visual indication of how much tea is in the teapot. Means for stabilizing the teapot 3 may be provided; the stabilizing means may be magnetic, electromagnetic, or mechanical. Such stabilizing means may be used to centre the teapot 3 relative to the kettle 1, with or without the provision of an upward force. The upward force may be provided by an electromagnet that does not act as an inductive coil.

Additional Heating Features 100491 In any of the above embodiments in which the teapot is not heated directly by its own heater 22, heat may be conducted from the kettle 1 to the teapot 3 by means of a thermal bridge. The thermal bridge may be in thermal contact with the heater 22 of the kettle I and/or with the water 4 within the kettle 1. Hence, instead of relying on hot air or steam convection to warm the teapot 3, thermal conduction is used by means of the thermal bridge.

100501 The kettle 1 and/or teapot 3 may be insulated so as to achieve the desired thermal equilibrium when the keep warm heater(s) is/are energised. For example, the kettle I may be thermally insulated so that heat escapes predominantly from the teapot 3, or vice versa. In * 11 this way, a single heater 22 may keep both the water 4 and the tea at the required temperature. In one specific example, the water 4 is kept warm by means of a heater 22 in thermal contact with the teapot 3, by means of thermal insulation of the kettle 1 or teapot 3 and/or by means of the arrangement of the heater, for example as shown in Figure 6.

100511 The teapot may include a heat diffusing plate in the base of the vessel 6, to ensure uniform heating of tea and avoid localised boiling, which is detrimental to the flavour of the tea.

Heating Control 100521 In any of the above embodiments in which heating is not self-regulating, the power output of the heater(s) may be controlled according to the level of water or tea to be heated.

The level may be detected by means of a level sensor as described for example in our earlier applications GB0709164.8 and GBO7I 1752.6, the contents of which are incorporated herein by reference. In particular, the power output for a keep warm function may be controlled according to the detected level.

100531 The keep warm mode of the kettle I may be entered after the heating mode is terminated, for example in response to detection of boiling. Alternatively, the keep warm mode may be switched independently of the heating mode. Heating in keep warm mode may be regulated by controlling the power level of the heater, or by pulsing the heater on and off with a duty cycle that is varied so as to achieve the desired average level of heating.

Periodically, such as after a predetermined number of cycles, the heating mode may be entered again to bring the water back to boiling andthe keep warm mode is then entered once more.

(00541 In those embodiments where a keep warm heater is provided for the teapot 3, the keep wann heater may switched off, or its power level reduced, when the teapot 3 is removed from the kettle. This may be achieved by a contact switch on or around the lid 12, or by other methods as described above.

[00551 The kettle 1 may be provided with a control that detects when the water 4 has reached a low simmer and/or a full boil; the keep warm mode may then be entered, or heating may be terminated altogether. In keep warm mode, a timer may be set such that heating mode is entered periodically, such as every 2 minutes, so as to bring the water up to the boil or simmering point. The control monitors the agitation of the water, which is indicative of simmering. Preferably, once the keep warm mode is entered, the control * 12 continues to monitor the agitation of the water, and reduce or eliminate the keep warm heating when a simmer is detected.

100561 In this way, a steam sensor is no longer essential; this may be advantageous, because condensation in the control may be avoided, and the cost of a steam sensor need not be incurred. A thermostat may also be provided to detect when the water has cooled below a minimum threshold, such that the keep warm mode needs to be entered. However, it is preferable that the heat input during keep warm mode is varied to match the heat loss from the water 4, such that cycling of the thermostat is avoided.

100571 In one embodiment, the agitation is monitored by a water level detector that is sensitive to small, rapid fluctuations of the water level as the water becomes agitated. In another embodiment, the agitation is monitored by an acoustic sensor that detects the characteristic sound of water reaching boiling point, such as the reduction in heating noise caused by a reduction in the collapse of steam bubbles within the water as the water reaches boiling.

100581 One example of the water level sensor, as shown in Figure 11, is a distance-measuring device 23 situated at or around the top of the kettle I. The device may be a laser or ultrasonic distance measuring device. The device 23 accurately measures fluctuations in the absolute distance to the water surface, and the control detects when the fluctuations exceed a predetermined level. The predetermined level may vary dependent upon the amount of water in the vessel, which may also be determined by the device according to the absolute distance to the water surface.

[00591 The distance-measuring device 23 may be positioned substantially on the central vertical axis of the kettle 1, as shown in Figure 11, so that the accuracy of the water level accuracy measurement is not dependent upon the kettle 1 being vertical. Alternatively, there may be provided a plurality of distance measuring devices at different positions, so as to compensate for the angle of the kettle 1. The distance measuring device(s) may be used to accurately measure the level of water during filling at the tap, when the kettle 1 is likely to held at an angle. Alternatively, the distance-measuring device may be positioned outside the water reservoir of the kettle, and may be directed at the water surface through a window.

100601 Another example of a water level sensor comprises a capacitive level sensor array positioned around the perimeter of the kettle 1, either within or outside the water reservoir.

Such an array may also be used to measure the water level when the kettle 1 is at an angle.

100611 A power source, such as a battery or capacitor, may be provided in the kettle 1 so as to provide power to the water level sensor when the kettle 1 is removed from the power base S 13 2. Preferably, the power source is rechargeable and is recharged when the kettle body I is connected to the power base 2.

10062) At least some of the level sensor or sensing techniques described above may be used to detect the level or volume of liquid in a liquid heating vessel on or before commencement of a heating operation, to determine whether the liquid level is above a predetermined maximum and/or below a predetermined minimum level; if not, the heating operation may be inhibited, or an indication given to the user. In this way, unsafe operation of the vessel may be prevented.

100631 At least some of the level sensor or sensing techniques described above may be used to detect the level or volume of liquid in a liquid heating vessel while the vessel is being filled. A warning indication may be made to the user when a predetermined maximum level has been exceeded. In the case of the tea maker described above, the kettle I may include a rechargeable power source so that the control may perform level detection when the kettle I is removed from the base 2. The predetermined level may be set by the user, for example by 1 5 means of a user interface. Preferably, this setting may be changed even when the kettle I is removed from the base 2. If the predetermined level is exceeded, the user interface 11 may give the user the option to change to a higher level and continue filling, or empty out some of the water until the current level is reached. The kettle I could be prevented from being heated is the water level is above or below a predetermining level, or if the kettle I is on a sloping surface.

L00641 Any of the above construction embodiments may be combined with any of the heating embodiments, except where they are obviously incompatible.

100651 The embodiments described above are illustrative of rather than limiting to the present invention. Alternative embodiments apparent on reading the above description may nevertheless fall within the scope of the invention. * 14

Claims

Claims 1. A liquid heating appliance comprising a lower liquid vessel,

an upper liquid vessel that is mounted or removably mountable on the lower liquid vessel, and a radiant heater arranged to heat either or both of the lower liquid vessel and the upper liquid vessel.
2. The appliance of claim I, wherein the radiant heater is arranged to heat both the lower liquid vessel and the upper liquid vessel.
3. The appliance of claim 1 or claim 2, wherein the radiant heater is arranged to generate light in the visible spectrum.
4. The appliance of claim 3, arranged to direct the visible light into the upper vessel.
5. The appliance of claim 4, wherein the upper vessel includes at least a transparent or translucent portion arranged such that the visible light can be seen therethrough.
6. The appliance of any one of claims 3 to 5, arranged to direct the visible light into the lower vessel which includes at least a transparent or translucent portion arranged such that the visible light can be seen by a user.
7. A liquid heating appliance comprising a lower liquid vessel, an upper liquid vessel that is mounted or removably mountable on the lower vessel, and a radiant heater positioned in or on a sidewall of the lower vessel.
8. The appliance of claim 7, comprising a plurality of radiant heaters arranged at respective different heights on the sidewall.
9. The appliance of claim 8, wherein the radiant heaters are selectively switchable to provide varying heating power to the lower vessel.
10. The appliance of claim 8, wherein the heating effect of the radiant heaters on the liquid in the lower vessel varies automatically according to the liquid level within the lower vessel.
11. A liquid heating appliance comprising a lower liquid vessel, an upper liquid vessel that is mounted or removably mountable on the lower vessel, and a radiant heater positioned in or around a top portion of the lower vessel, and arranged to direct radiant heat in a downward direction into the lower vessel. * 15
12. The liquid heating appliance of claim 11, wherein the upper vessel is arranged or arrangeable in thermal contact with the radiant heater so as to be warmed by thermal conduction therefrom.
13. A liquid heating appliance comprising a lower liquid vessel, an upper liquid vessel mounted or removably mountable on the lower vessel, and a heater arranged at a boundary between the upper liquid vessel and the lower liquid vessel so as to heat both the lower liquid vessel and the upper liquid vessel.
14. The appliance of claim 13, wherein the heater is a radiant heater arranged to heat the lower vessel by thermal radiation and the upper vessel by thermal conduction.
15. A liquid heating appliance comprising a lower liquid vessel, an upper liquid vessel having a lid and a heater arranged to heat the lid by thermal conduction, and an upper liquid vessel mountable on the lid so as to be warmed thereby.
16. The appliance of claim 15, wherein the heater is arranged to heat liquid within the lower liquid vessel.
17. The appliance of claim 15, wherein the lid comprises inductively heatable material, and the lower liquid vessel includes means for inductively heating the lid.
18. A liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel that is mounted or removably mountable on the lower vessel, the lower liquid vessel including a first electric heater for heating liquid contained within the lower vessel, and the upper vessel being arranged to be heated by a second electric heater discrete from the first electrical heater.
19. The appliance of claim 18, wherein the second electrical heater is arranged to be switched off or with a reduced power when the upper vessel is removed from the lower vessel.
20. The appliance of claim 18 or claim 19, wherein the second electrical heater is a self-regulating heater.
21. The appliance of claim 20, wherein the second electrical heater is a PTC heater.
22. The appliance of any one of claims 18 to 21, wherein the second electrical heater is located within the upper vessel, the appliance including an electrical connector between the lower vessel and the upper vessel. * 16
23. The appliance of claim 22, wherein the electrical connector is a 3600 electrical connector.
24. A liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel that is mounted or removably mountable on the lower vessel, the lower liquid vessel including a plurality of heaters arranged at respective different levels within the lower vessel.
25. The liquid heating appliance of claim 24, wherein the heaters are self-regulating heaters arranged to provide a high heating power when immersed and a lower heating power when not immersed.
26. The liquid heating appliance of claim 25, including means for monitoring the power levels of the heaters and for providing a level indication in dependence thereon.
27. A liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel, the lower liquid vessel including an inductive heating coil arranged to heat the upper vessel.
28. The appliance of claim 27, wherein the lower vessel includes an inductively heatable material which is in thennal contact with the upper vessel when the upper vessel is mounted on the lower vessel.
29. The appliance of claim 27, wherein the upper vessel includes an inductively heatable material arranged to be heated by the inductive heating coil when the upper vessel is mounted on the lower vessel.
30. The appliance of claim 28, wherein the upper vessel includes an inductively heatable portion arranged to fit within the inductive coil.
31. The appliance of any one of claims 27 to 30, including means for controlling the power level of the inductive coil according to a detected temperature within the upper vessel.
32. The appliance of any one of claims 27 to 31, wherein the inductively heatable material has a Curie temperature selected such that the heating of the upper vessel is self-regulated so as to prevent boiling within the upper vessel.
33. A liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel removably mountable on the lower vessel, the lower liquid vessel including an electromagnet and the upper vessel having a composition such that the electromagnet exerts an upward force on the upper vessel.
34. A liquid heating appliance comprising a lower liquid vessel and an upper liquid vessel mounted or removably mountable on the lower vessel, the lower liquid vessel including a heater for heating the lower vessel, and a thermal bridge for heating the upper vessel by thermal conduction.
35. An appliance according to any one of claims I to 34, wherein said heater, or at least one of said heaters, is a keep warm heater.
36. An appliance according to any one of claims I to 34, wherein said heater, or at least one of said heaters, is a primary heater.
37. A liquid heating appliance comprising a lower liquid vessel, an upper liquid vessel that is mounted or removably mountable on the lower vessel, and a light source arranged to illuminate the upper liquid vessel.
38. The appliance of claim 37, arranged to direct light from the light source into the upper liquid vessel.
39. The appliance of claim 38, wherein the upper vessel includes at least a transparent or translucent portion arranged such that the visible light can be seen therethrough.
40. The appliance of any one of claims 37 to 39, arranged to direct the light into the lower vessel which includes at least a transparent or translucent portion arranged such that the visible light can be seen by a user.
41. A liquid heating appliance including a control for controlling liquid heating by detecting agitation of the liquid and reducing or eliminating liquid heating when the detected agitation meets predetermined criteria.
42. The appliance of claim 37, including a level detector arranged to detect said agitation by detecting fluctuations of the liquid level.
43. The appliance of claim 42, wherein the level detector is arranged to detect said liquid level, the predetermined criteria being dependent on the detected level.
44. The appliance of claim 42, wherein the level detector comprises a distance measurement device.
45. The appliance of claim 44, wherein the distance measurement device is a laser measurement device. * 18
46. The appliance of claim 44, wherein the distance measurement device is an ultrasonic measurement device.
47. The appliance of claim 42, wherein the level detector comprises a capacitative level detector.
48. The appliance of any one of claims 42 to 47, wherein the level detector is arranged to compensate for tilting of the appliance.
49. The appliance of claim 37, including an acoustic detector arranged to detect said agitation by detecting a predetermined acoustic characteristic of the liquid as it is heated.
50. A liquid heating vessel comprising a lower, electrically heated liquid vessel and an upper liquid vessel that is mountable on the lower vessel in thermal contact therewith, wherein the upper liquid vessel is arranged so that that warm air or steam from the lower vessel is retained in contact with a sidewall of the upper vessel.
51. The liquid heating vessel of claim 50, wherein the upper vessel fits at least partially within the lower vessel so that at least part of the sidewall of the upper vessel is located within the lower vessel.
52. The liquid heating vessel of claim 51, wherein the upper vessel has an upper rim forming a lid for the lower vessel.
53. The liquid heating vessel of claim 51 or claim 52, wherein the upper vessel is arranged to rest on top of the lower vessel or to fit therein, according to the relative rotational orientation thereof.
54. The liquid heating vessel of claim 50, wherein the upper vessel comprises an inner wall and an outer wall having a space therebetween open to the lower vessel so that hot air rising from the lower vessel is retained in the space in contact with the inner wall.
55. The liquid heating vessel of any one of claims 50 to 54, wherein the lower vessel includes a handle engageable with the upper vessel so as to retain the upper and lower vessels together.
56. A liquid heating vessel comprising a lower, electrically heated liquid vessel and an upper liquid vessel that is mountable on the lower vessel in thermal contact therewith, wherein the lower vessel includes a handle engageable with the upper vessel so as to retain the upper and lower vessels together.
57. The liquid heating vessel of claim 56, wherein the handle comprises first and second parts moveable together so as to retain at least a part of the upper liquid vessel therebetween.
58. The liquid heating vessel of any one of claims 50 to 57, wherein the lower vessel is removably mountable on a power base for supplying power to the lower vessel for heating liquid contained therein.
59. A liquid heating appliance substantially as herein described with reference to andlor as shown in the accompanying drawings.