Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1998-08-10
2000-11-28
Pelham, Joseph
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
219439, A47J 3156
Patent
active
061538590
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of international application serial number PCT/GB69/01875, filed Jul. 31, 1996, which claims priority to and the benefit of British application serial number 9515662.6, filed Jul. 31, 1995, and British application serial number 9605345.9, filed Mar. 13, 1996.
The present invention relates to liquid heating vessels, and in particular, but not exclusively, to water heating vessels which may be used to boil water and then maintain the water at a predetermined temperature.
Such vessels are particularly popular in the Far East (where they are called "airpots") where water supplies may not be entirely clean or may be highly chlorinated and where it is therefore desirable to boil the water for a prolonged period (typically 1 to 3 minutes) to sterilise or de-odorise the water. After boiling, the water is kept at a relatively high temperature, usually around 92.degree. C. There is also the requirement that the water in the vessel may be reboiled, for example if it has been standing for some time, or if fresh water is added to the vessel. The vessels are usually sealed and have a lid mounted pump to dispense water from the vessel without the need to open it.
Airpots have two independently controlled heating elements, one for boiling the water and rated, typically, at around 630 W and the other for keeping the boiled water warm, and rated, typically, at about 70W. These elements are independently controlled and are usually formed as belts wrapped around and secured to a lower part of the vessel wall. The element for keeping the water warm may be controlled typically by a thermostat, or electronically. The boiling heating element is sometimes controlled by a bimetallic actuator arranged in the pump or lid of the vessel, the steam path to the actuator and the thermal capacity of the surrounding mechanism introducing a lag from the time water boils in the vessel to the element being switched off. Alternatively the boiling element may be controlled electronically. However, both these arrangements are expensive.
In a first aspect, the present invention seeks to provide an alternative boiling control in a vessel as described above which does not require the sensing of temperature of steam and which will allow a desired boiling time to be achieved, and preferably, at the same time, allow for re-boiling of the water, and which may be reset quickly after its operation in order to allow water in the vessel to be re-boiled relatively soon after boiling, if required.
From a first aspect, therefore, the invention provides a liquid heating vessel having a heating element and base, the base having a sump with a relatively small volume compared to the volume of the vessel as a whole, for containing a relatively small volume of liquid, thermally-responsive means arranged thermally remote from said sump, for interrupting a flow path of electrical energy to the element upon reaching a predetermined temperature, and thermal conduction means arranged between said sump and said thermally responsive means for conducting heat from the sump to the thermally responsive means.
Thus in accordance with the invention, a relatively small volume sump is provided in the base of the heating vessel. This will contain a relatively small volume of liquid which, during heating of the liquid in the vessel will remain relatively isolated from the remaining liquid in the vessel and whose temperature will therefore lag behind that of the main body of liquid. However as heating progresses, convection increases, and as the liquid approaches boiling the liquid in the vessel will become extremely agitated and turbulent, thereby causing the volume of liquid in the sump to be displaced by, or mix with, the main body of liquid. The temperature of the liquid in the sump will then rise rapidly to that of the main body of liquid, so that boiling of the liquid in the vessel can be sensed by the sudden temperature rise of the sump. However in order to provide a desired period of
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patent: 3513292 (1970-05-01), Sano et al.
patent: 5635092 (1997-06-01), O'Neill
patent: 5793020 (1998-08-01), O'Neill
patent: 5897805 (1999-04-01), McClean
Doyle Keith Barrie
Taylor John Crawshaw
Pelham Joseph
Strix Limited
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