WO2007132160A1

WO2007132160A1 - Radiant electric heater

Info

Publication number: WO2007132160A1
Application number: PCT/GB2007/001611
Authority: WO
Inventors: Kevin Ronald Mcwilliams
Original assignee: Ceramaspeed Limited
Priority date: 2006-05-11
Filing date: 2007-05-02
Publication date: 2007-11-22
Also published as: GB0610118D0

Abstract

A radiant electric heater comprises a base layer (3) of thermal and electrical insulation material and an upstanding peripheral wall (9) of thermal insulation material extending around a peripheral region of the base layer to define an undivided elongate region on the base layer. First and second radiant heating means (5, 7) are supported relative to the base layer (3) and are positioned at opposite ends of the undivided elongate region so as to define on the base layer first and second heated regions at each end thereof with a region (19) therebetween in which no heating means is present.

Description

RADIANT ELECTRIC HEATER

This invention relates to a radiant electric heater and more particularly relates to a radiant electric heater in which at least two radiant electric heating elements are positioned in spaced relationship on a common base of thermal insulation material.

It is known, for example from GB-A-1 558 543, to provide cooking apparatus which incorporates a complex arrangement of heating regions such as two circular heating regions with a waisted region filling the space between the two circular regions. Such an arrangement gives rise to an elongate heated area which is useful for elongate cooking utensils such as fish kettles.

When such an arrangement is incorporated into a radiant heater for a smooth top cooker, such as of glass ceramic material, in which a radiant heating element is supported relative to a base of thermal and electrical insulation material, the three heating elements are supported on a common base of insulation material and are surrounded by a peripheral wall of thermal insulation material and separated from each other by suitably shaped, e.g., curved, walls of thermal insulation material. The use of walls of thermal insulation material in this manner is known, for example from GB-A-2 044 057.

There is a problem associated with such heaters in that the heaters are expensive to manufacture and tend to be uneconomic for appliance manufacturers to incorporate into smooth top cookers. There is, therefore, a need for such a heater which provides two separate heating elements together with a means for heating the smooth top in the region between the two heating elements so as to provide suitable heating for elongate utensils such as fish kettles. It is therefore an object of the present invention to provide a radiant electric heater for a smooth top cooker which overcomes or at least ameliorates the above disadvantage.

According to the present invention there is provided a radiant electric heater comprising:

a base layer of thermal and electrical insulation material;

an upstanding peripheral wall of thermal insulation material extending around a peripheral region of the base layerto define an undivided elongate region on the base layer;

first and second radiant heating means supported relative to the base layer and positioned at opposite ends of the undivided elongate region so as to define on the base layer first and second heated regions at each end thereof with a region therebetween in which no heating means is present; and

means for energising the first and second radiant heating means independently of each other.

At least a part of the peripheral wall may be separate from the base layer. Alternatively, the peripheral wall may be integral with the base layer.

The base layer may be supported in a metal dish.

A ridge may be formed in the base layer, the ridge extending at least partly across the heater in the region in which no heating means is present, the ridge being lower than the peripheral wall. A corresponding ridge may be formed in the metal dish whereby the thickness of the base layer remains substantially constant. The base layer may comprise a microporous thermal and electrical insulation material.

The base layer may be formed as a single piece of insulation material.

The heating means may be selected from corrugated ribbon and helically coiled wire heating elements.

The region in which no heating means is present may be in the form of a waisted region between the first and second heating means. The waisted region may be narrower in a central region thereof than in end regions thereof.

The heater may include a thermal limiting device for each of the radiant heating means. Each thermal limiting device may include a temperature sensing probe which extends at least partly across the respective radiant heating means.

A low wall, having a height less than the height of the peripheral wall, may run around the boundary between each of the first and second heating means and the region in which no heating means is present.

The present invention also relates to a cooking appliance including a heater as hereinbefore defined and a smooth cooktop, the heater bearing against the underside of the smooth cooktop. The cooktop may comprise glass ceramic material.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a plan view of one embodiment of a radiant electric heater according to the present invention; - A -

Figure 2 is a cross-sectional view of the heater shown in Figure 1 and includes a smooth cooktop of a cooking appliance;

Figure 3 is a cross-sectional view on a larger scale of part of a modified radiant electric heater according to the present invention;

Figure 4 is a cross-sectional view of a further modification of the heater shown in Figure 3;

Figure 5 is a diagrammatic plan view of another embodiment of a radiant electric heater according to the present invention; and

Figure 6 is partial cross-sectional view, on a larger scale, of part of the heater shown in Figure 5 together with a smooth cooktop of a cooking appliance.

The radiant electric heater shown in Figures 1 and 2 comprises a metal dish 1 containing a base layer 3 of thermal and electrical insulation material, such as microporous thermal and electrical insulation material. The dish 1 is elongate in shape with rounded ends and the base layer 3 of insulation material is formed in the base in a single piece.

Two radiant electric heating means in the form of heating elements 5, 7, for example of corrugated ribbon or helically coiled wire form, are arranged in a circular configuration relative to the base layer 3 (that is, the base layer 3 is common to both heating elements), one at each end of the elongate dish 1 to provide first and second heated regions such that the heating elements are spaced apart. Where corrugated ribbon is used, the ribbon may be mounted on edge and embedded partially in the base layer 3, for example by way of a plurality of legs extending from the ribbon. Alternatively, where helically coiled wire is used, the wire may be arranged in grooves and secured to the base layer

3 by means of staples or the like. In the embodiment of Figures 1 and 2 the base layer 3 is substantially planar between the two heating elements 5, 7 so a flat waisted region 19 of base insulation material lies between the two heating elements. The flat waisted region is narrower in a central region thereof than in the end regions thereof.

An upstanding peripheral wall 9 of thermal insulation material extends around the internal periphery of the metal dish 1 and has an overall elongate shape with rounded ends. The peripheral wall extends around the two heating elements 5, 7 and may be separate from, or integral with, the base layer 3.

Two thermal limiting devices 11 extend from the periphery of the heater and each includes a temperature probe 13 which extends at least partly across the respective heating element and a switch head 15. Each heating element 5, 7 is connected to a separate terminal block 17 mounted on the external periphery of the metal dish 1. In use, the terminal blocks 17 are connected to power control means (not shown) which is adapted to energise the two heating elements 5, 7 independently of each other.

Because the base layer 3 is substantially planar and there is no wall between each of the heating elements 5 and 7, the heat from the two heating elements is able to heat a smooth cooking surface 21 , for example of glass ceramic material, of a cooking appliance not only in the region above the respective heating element, but additionally in the waisted region 19. Although, when only one heating element 5 or 7 is required, there may be some loss of heat from the heating element to a region above the waisted region 19 and to a region above the other heating element, it has been found in practice the loss is not significant and can be compensated for by increasing the power rating of the energised heating element. On the other hand, cost savings are significant because no heating element is required in the waisted region, no curved dividing walls are required between each heating element and the waisted region, and because only two heating elements are provided rather than three the cost of an associated controller is also reduced. The cooktop may be marked so as to define two circular cooking zones for receiving substantially circular cooking utensils and a waisted cooking zone between the two circular zones so as to define a continuous elongate cooking zone on the cooking surface for elongate cooking utensils such as fish kettles.

The radiant electric heater according to the present invention may be modified in a number of ways to reduce the loss of heat when only one heating element 5 or 7 is required. For example, as shown in Figure 3, a ridge 23 of thermal and electrical insulation material may be provided in the base layer 3 between the two heating elements 5, 7 and extending at least partly across the width of the heater, the ridge having sloping sides and extending partially, but not entirely, from the plane of the base layer towards the underside of the cooking surface 21. The ridge 23 has the effect of reflecting incident radiation towards the underside of the cooktop 21 of the appliance in the area of the waisted region 19 rather than allowing such radiation to pass to the region above the other heating element. Where a ridge 23 is provided, it may be desirable to provide a corresponding ridge in the underside of the metal dish 1 such that the base layer 3 remains at constant thickness and density.

Alternatively, as shown in Figures 5 and 6, a low wall 25 may be formed in the base layer of thermal and electrical insulation material around the periphery of each of the heating elements 5, 7 between the heating elements and the waisted region 19. Such a low wall 25 effectively prevents a significant proportion of direct radiation from one of the heating elements passing to the region of the other of the heating elements, while not substantially affecting the passage of radiation to the cooktop 21 above the waisted region 19.

Claims

1. A radiant electric heater comprising:

a base layer (3) of thermal and electrical insulation material;

an upstanding peripheral wall (9) of thermal insulation material extending around a peripheral region of the base layer (3) to define an undivided elongate region on the base layer;

first and second radiant heating means (5, 7) supported relative to the base layer and positioned at opposite ends of the undivided elongate region so as to define on the base layer first and second heated regions at each end thereof with a region (19) therebetween in which no heating means is present; and

means (17) for energising the first and second radiant heating means independently of each other.

2. A heater as claimed in claim 1 , characterised in that at least a part of the peripheral wall (9) is separate from the base layer (3).

3. A heater as claimed in claim 1 , characterised in that the peripheral wall (9) is integral with the base layer (3).

4. A heater as claimed in any preceding claim, characterised in that the base layer (3) is supported in a metal dish (1 ).

5. A heater as claimed in any preceding claim and including a ridge (23) formed in the base layer (3) and extending at least partly across the heater in the region (19) in which no heating means is present, the ridge being lower than the peripheral wall (9).

6. A heater as claimed in claim 5 when dependent on claim 4, characterised in that a corresponding ridge is formed in the metal dish (1 ) whereby the thickness of the base layer (3) remains substantially constant.

7. A heater as claimed in any preceding claim, characterised in that the base layer (3) comprises a microporous thermal and electrical insulation material.

8. A heater as claimed in any preceding claim, characterised in that the base layer (3) is formed as a single piece of insulation material.

9. A heater as claimed in any preceding claim, characterised in that the heating means (5, 7) is selected from corrugated ribbon and helically coiled wire heating elements.

10. A heater as claimed in any preceding claim, characterised in that the region (19) in which no heating means is present is in the form of a waisted region between the first and second heating means (5, 7).

11. A heater as claimed in claim 10, characterised in that the waisted region (19) is narrower in a central region thereof than in end regions thereof.

12. A heater as claimed in any preceding claim and including a thermal limiting device (11) for each of the radiant heating means (5, 7).

13. A heater as claimed in claim 12, characterised in that each thermal limiting device (11 ) includes a temperature sensing probe (13) which extends at least partly across the respective radiant heating means (5, 7).

14. A heater as claimed in any preceding claim, characterised in that a low wall (25), having a height less than the height of the peripheral wall (9), runs around the boundary between each of the first and second heating means (5, 7) and the region (19) in which no heating means is present.

15. A cooking appliance including a heater as claimed in any preceding claim and a smooth cooktop (21 ), the heater bearing against the underside of the smooth cooktop.

16. A cooking appliance as claimed in claim 15, wherein the cooktop (21) comprises glass ceramic material.