GB2149486A - Electrical heating appliance for a liquid - Google Patents

Abstract

An electrical heating appliance for a liquid, particularly hot water provider for use in the household, comprises a pipe (210) for conducting the liquid and thermally conductively connected with an electrical heating conductor (212). The pipe comprises an electrically insulating, highly heat-resistant material such as a glass or a ceramic material. The pipe can be thermally conductively connected with a heating plate (202) so as to heat this plate. <IMAGE>

Description

SPECIFICATION Electrical Heating Appliance for a Liquid The present invention relates to an electrical heating appliance for a liquid.

A heating appliance, known from German (Fed.

Rep.) published patent application 26 38 380, is an electric coffee machine with a throughflow heater in the form of a substantially vertical metal pot into the wall of which is cast an electrical pipe heating body.

Also known from German (Fed. Rep.) published patent application 25 45 483 is an electric coffee machine with a throughflow heater which is arranged to extend horizontally below a heating plate and which has a metal water pipe along which an electrical heating element extends. In both cases, the water pipe consisting of metal has the disadvantage that the chemicals employed for decalcification can react with the metal of the pipe and can generate substances harmful to health. In the case of inadequate rinsing after decalcification these substances can pass into the prepared brewed beverage during the next use of the appliance. In the case of water-conducting pipes of aluminium, the problem of pitting exists, which in unfavourable cases can lead to a premature failure of the appliance.Thus, problems of hygiene and fatigue strength arise in the case of these appliances and it would be desirable to reduce or eliminate these problems without undue complications in production.

According to the present invention there is provided an electric heating appliance for a liquid, comprising a pipe which comprises electrically insulating heat-resistant material and which is arranged to conduct a liquid, and an electric heater disposed in thermally conductive connection with the pipe.

Such a pipe is largely resistant to corrosion by the substances usually encountered, so that healthendangering reaction products or material decomposition prejudicing strength may be avoided at the material of the pipe wall.

Preferably, the electrically insulating material, which lies between the electric heater and the inside wall surface of the pipe contacted by the liquid, has a thickness of at least 2 millimetres. As a result, an adequate electrical insulation of the liquid, with which the user can come into contact, against the heater is provided. The protective earthing required in the known appliances with a water pipe of metal is superfluous. In this respect, a reduction in production effort compared with the known appliances is achieved, since assembly steps and components are obviated or a simpler, two-core line as well as a simpler plug are usable in the case of the mains connection line assuming the remaining components of the appliance have appropriate protective insulation.

The pipe can extend substantially horizontally, wherein preferably an upper and/or a lateral region of the pipe circumference is heated, in that an electrical heating conductor is preferably arranged in this region. In the case of the horizontal arrangement of the pipes, for example below a heating plate of an electrical coffee machine, the problem of excessive vapour bubble formation arises and causes uneven water conveying. The conditions are worsened through the mostly unavoidable calcification.The heating of only a lateral and/or upper region of the pipe circumference brings a quite substantial improvement, in part due to the fact that, through one-sided lateral heating, an assymmetry is created; this leads to circulation of the water in the pipe or to helical movement paths of the water in the pipe and thus to a more uniform intermixing of the water, whereby vapour bubble formation due in part to spot overheating is reduced. The heating from above brings about a stronger decoupling between the heating and the water and thereby milder heating of the same due to the vapour bubbles preferentially collecting in the upper region of the pipe in the part conducting the hotter water.The afore-described pipe wall thickness of two or more millimetres leads to a more uniform heat distribution, compared with thinner pipes, during the water heating operation, whereby excessive stresses in the material are avoided. This is particularly important when ceramic material is used, in order to avoid pipe breakages.

In the case of the arrangement of a pipe below a heating plate heated thereby, for example a warming plate of an electric coffee machine, the plate can comprise or consist of an electrically insulating, heat-resistant material such as a glass, a ceramic material or a thermally highly loadable plastics material. This has the advantage that in the case of like or similar materials of pipe and plate, these can be joined through a melted or sintered connection or possibly a good adhesive connection.

The heating plate and the pipe are then produced as if one piece and have a good heat transfer therebetween. This also makes it possible to, for example, arrange the heating conductor on a surface, alongside the pipe, of the heating plate.

This has the advantage that the conductor, for example a meandering tape extending along the pipe, can be printed onto a planar surface or applied in other manner as coating, which reduces production costs. In addition, a temperature regulator in the current circuit of the conductor can be arranged beside the conductor on a planar surface of the plate. The regulator can be glued to the plate by means of a highly thermally conductive glue, for example a glue containing ceramic powder, or can be pressed resiliently against the heating plate by means of a spring clip which is, for example, anchored at the pipe.

The electrical heating conductor can be arranged at least in part between the pipe and the heating plate, which for example are fused or sintered together, so that it is wholly enclosed and insulated and heats the pipe and the plate simultaneously.

For production reasons, it can be advantageous to use a straight pipe, although, for the creation of hose connections, it would be desirable for the end portions of the pipe to be bent away from the plate.

The pipe can, however, be straight and yet still have hose connections if, for example, the heating plate in the region of the pipe end portions has recesses which, between the outside wall surface of the pipe and the plate, create a space which approximately corresponds to the thickness of the hose wall or is somewhat greater.

In order to make the formation of such recesses possible without unduly weakening the heating plate, the plate can be reinforced in its contact region with the pipe. In the case of a substantial reinforcement which provides a greater thickness of the heating plate in the region of the pipe, it can be sufficient to arrange this thickening to end before the end portions of the pipe so that the pipe end portions project beyond regions of normal thickness of the plate and sufficient space for a hose end drawn over the pipe end portion remains between the plate and the pipe. In place of the thickening, an intermediate member can be used between the plate and the pipe. The intermediate layer can consist of the same material as the pipe or of, for example, metal.The plate can also consist of metal or of one of the materials proposed for the pipe, whereby different combinations with different production advantages or functional advantages are available. An intermediate member of metal affords simple connection possibilities for fastening elements and/or regulators and fuses. An intermediate member of metal has particularly good thermal conductivity, as does a heating plate of metal. Intermediate members and/or heating plates of one of the materials proposed for the pipe offer the advantage of good electrical insulation and, in the case of a similarity or relationship of the materials, the possibility of the creation of good thermally conductive connections. The intermediate member can primarily have the task of heat distribution, while the actual heating plate should have a decorative appearance.

In another preferred embodiment, the end portions of the pipe are so deformed for the formation of hose connectoins as to be clear of the heating plate and to have an oval or generally elliptical cross-section compared with the substantially round cross-section of the rest of the pipe.

The pipe can also have a flattening in the region of its contactwith the heating plate or an intermediate member, i.e. have a substantially straight circumferential portion in order to enlarge the contact zone and thereby the heat transfer and possibly the region, enclosed between the two elements, for accommodation of the heating conductor. Moreover, the pipe can have a planar bearing surface for a regulator in the current circuit of the heating conductor or for a fuse and for this purpose can have a small indented or bent-out wall portion.According to yet another embodiment, the pipe can-as is known from throughflow heaters of aluminium-have a thickened wall thickness over a region of the circumference and along its entire length, which offers the possibility of creating a planar surface for the attachment of the regulator through grinding down a small area at a desired place along the length of the pipe. A cold conductor element can also serve as regulator insofar as the heating conductor itself does not possess a cold conductor regulating characteristic adequate for the desired regulating purposes. A cold conductor regulation can reduce the power, after termination of the water passage, to that required for the heating of the heating plate and thereby eliminate or substantially reduce overheating.

In the production of a combination of heating plate and water pipe, in which the two elements are firmly connected together, the heating conductor can be applied, for example by a printing or coating technique, onto a planar surface of the heating plate. The pipe is subsequently laid over the heating conductor and the connection of the parts is produced through melting, sintering or gluing. This has the advantage that the heating plate during the mounting of the heating conductor is more easily handled than the pipe and the production effort is thereby reduced.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional view of a first electric coffee machine embodying the invention; Fig. 2 is a sectional view, corresponding to that of Fig. 1, of part of a second coffee machine embodying the invention, showing a through flow heater arranged under a heating plate; Fig. 3 is a cross-section substantially along the line Ill-Ill in Fig. 2; Fig. 4 is a view similar to Fig. 3 but of part of a third coffee machine embodying the invention; Fig. 5 is a view similar to Fig. 3 but of part of a fourth coffee machine embodying the invention; Fig. 6 is a view similarto Fig. 3 but of a part of a fifth coffee machine embodying the invention;; Fig. 7 is a cross-section substantially along the line VIl-VIl in Fig. 6; Fig. 8 is a view similar to that of Fig. 3 but of part of a sixth coffee machine embodying the invention; Fig. 9 is a view similar to that of Fig. 3 but of part of a seventh coffee machine embodying the invention; Fig. 10 is a view similar to that of Fig. 3 but of part of an eighth coffee machine embodying the invention; Fig. 11 is a perspective view of a throughflow pipe and heater in the machine of Fig. 10; and Fig. 12 is a view similarto Fig. 11 but of a modified heater.

Referring now to the drawings, there is shown in Fig. 1 an electrical coffee machine comprising a pedestal housing 2, which is ciosed off downwardly by a base 4 and in a lower region 6 has an opening 8.

The opening is closed off by a heating (or warming) plate 10 of ceramic material abutting a lower rim edge of the opening. Arranged at the underside of the plate 10 is a heating body 12, which heats the plate and the electrical connecting lines of which have been omitted for simplicity. A coffee can 14, on which a coffee filter 16 is placed, stands on the plate 10. An upwardly open fresh water container 20 with a base 22, which has a downwardly projecting outflow stub pipe 24 and through which extends the bore of a rising duct 26 constructed integrally with the base 22, is placed on an upwardly projecting part 18, arranged beside the part 6, of the housing 2.

An overflow pipe 28, with an outflow opening 30 above the filter 16, is placed on the upper end of the rising duct 26. The lower end of the rising duct 26 is connected by means of a downwardly enlarging hose piece 34 with a throug hflow heating device 32 arranged under the base 22 in the heightened part of the housing 2. The device 32 comprises a ceramic pipe 36, which has a wall thickness of 2.2 millimetres and on the outer circumference of which is wound a wire-like heating conductor 38 preferably firmly located by a stoved glazing. The end portions of the pipe 26 are not covered by the conductor, but are resiliently retained in the hose piece 34 and in a drop tube shaped hose piece 40.Above the heated zone and at a spacing from the upper rim, a regulator 42 in the current circuit of the conductor 38 is fastened to the external wall surface of the pipe 36 by means of a glue with good thermal conductivity, for example a glue filled with a ceramic mass.

Figs. 2 and 3 show a heating plate 202 of a coffee machine of other mode of construction with a throughflow heating device 204 fastened at its underside and extending substantially horizontally.

The device 204 in this case additionally heats the plate. The plate 202 has a wall thickness of about 3 millimetres overthe greatest region of its area and in the region of contact with the device 204 has a downwardly projecting portion 206 with a planar underside 208, into which a ceramic pipe 210 of circular cross-section of the device 204 is pressed.

The plate 202 of ceramic material and the pipe 210 are sintered together by common burning, the pipe 210 being coated with a helically extending heating conductor 202 before joining together of these two parts. The terminals for the feed lines as well as the feed lines are, for simplification, omitted from Figs.

2 and 3. The coating ends at a spacing from the pipe ends so that unheated end portions 214 and 216 remain for the connection of a drop duct 218 and a rising duct 220 in the form of silicone hoses. The projection 206 ends, with respect to longitudinal direction of the pipe, somewhat before each end thereof and the plate 202 above the pipe end portions 214 and 216 has recesses 222 and 224 in its base side, which permit the insertion of the hose walls between the pipe end portions and the plate. A regulator 230 in the current circuit of the conductor 212 is glued by means of a thermally conductive glue to the planar surface 208 beside the pipe 210.

In a modification of the embodiment according to Figs. 2 and 3, the ceramic pipe 210 is surrounded above the conductor 212 by a ceramic insulating layer which either extends between the pipe 210 and the plate 202 and is baked together with these into one piece or else extends only around the lower region of the pipe 210 at both sides up to the plate 202 and also somewhat to the side by its end portions on the underside of the projection 206.

The embodiment according to Fig. 4 comprises a heating plate 402 of a stainless steel, onto the underside of which is pressed an intermediate member 404 of ceramic material, which serves as an assembly and heat transfer component and into the substantially planar underside 406 of which is pressed a ceramic pipe 408 of circular cross-section.

The ceramic pipe does not carry a heating conductor and is baked together with the member 404 through common stoving. A heating conductor 410 is applied by means of printing beside the pipe 408 on the planar underside of the member 404 and by way of this member heats the plate 402 and the pipe 408.

In addition, a regulator in the current circuit of the conductor 410 is disposed beside the pipe 408 and glued onto the planar underside 406 of the member 404. The member 404 ends at a spacing from each end of the pipe 408 so that its end portions jut out freely as in the embodiment of Figs. 2 and 3 so as to provide hose connections. It represents a substantial advantage when resilient hose ends can be drawn over free end portions of the pipe, since connection by means of a resilient plug plugged into the pipe entails a substantial narrowing in crosssection and requires specially shaped ends of the connecting hoses, whereby production effort is increased.In the embodiments according to Figs. 2 to 4, it is possible to use simply manufactured, straight ceramic pipes and to connect simple hose portions to these through external tensioning over the pipe, whereby the production effort altogether is kept low.

The embodiment according to Fig. 5 comprises a heating plate 502 of ceramic material, which has the same thickness of about 3 millimetres over its entire extent, of which only a section is shown. A ceramic pipe 506 is fastened in thermally conductive manner to the underside of the plate 502 by means of a ceramic glue 504. The pipe 506 has an end portion 510 for the connection of a hose 512, which is indicated in dashed lines and so deformed that it possesses an oval cross-section, the longitudinal axis of which extends parallel to the plane of the plate 502. Since the oval end portion 510 is arranged symmetrically to the axis of the annular portion of the pipe 506, it is spaced from the underside of the plate 502, which permits insertion of the wall of the hose 512.The not illustrated other end portion of the pipe 506 is constructed in like manner as the end portion 510 for the connection of a hose. The end portions must have a concave curvature over the entire circumference in order to secure tensioning of the hose wall against the wall of the connecting pipe portion.

The embodiment according to Figs. 6 and 7 possesses a planar heating plate 602 of uniform thickness of a ceramic material, connected to the underside of which is a throughflow heating device 604 by sintering or baking. The device 604 comprises a ceramic pipe 606, which in crosssection has about the shape of a pipe of originally circularly round cross-section which has been pressed flat at one side. The flat wall portion 608 of the pipe 606 lies against the plate 602 and was, before being placed against the plate 602, printed with a heating conductor 610, which extends in meander form along the middle region of the pipe 606 and the turns of which extend downwardly beyond the planar circumferential portion 608 to the righthand side wall of the pipe 606. Circulation of the water in the pipe 606 or helical movement of the water is achieved through this assymmetry in the heating.At one point in the length of the pipe 606 there is a flattening in the form of a depression 612, at which a regulator 614 is fixed by means of a thermally conductive ceramic glue. End portions of the pipe 606 extend beyond the lateral boundary 602 of the plate and possess end portions (not shown) which are enlarged to a circular cross-section and onto which connecting hoses are drawn.

The embodiment according to Fig. 8 possesses an opening 804, against the underside of which is laid a heating plate 806 of stainless steel, in a pedestal housing 802 of an electrical coffee machine. An intermediate member 808, which in cross-section is similar to the letter W, lies against the underside of the plate 806. In the middle region, the member 808 possesses a circularly arcuate portion 810 which in curvature follows the shape of a circular-section ceramic pipe 812 in order to receive heat from the pipe. The pipe 812 is coated in not illustrated manner by a heating conductor helically surrounding it and also possesses an insulating coating so that the conductor is electrically insulated from the member 808, which consists of aluminium.

From the middle portion 810 of the member 808 and keeping a spacing from the underside of the plate 806, lateral cheeks 814 and 816 extend substantially radially to the pipe axis and obliquely upwards to the plate 806, where they pass over into flanges 818 and 820 lying against the plate 806. A thermally conductive paste or glue can be introduced in the region of the flanges 818 and 820 between the member 808 and the plate 806 for improvement of the heat transfer. A thermaliy conductive paste or glue can also be introduced between the pipe 812 and the middle part 811 of the member 808. That cheek 816 of the member 808 which is closer to one side wall 830 of the pedestal housing 802 can have an opening which serves for the reception of a mounting bolt of a regulator 832.The cheek 814 remote from the wall 830 has an elongate opening 834, in which is engaged a hook-shaped end portion 836 of a resilient spring clip 838 of steel. The spring clip is guided below the pipe 812 and, adjacent the wall 830, has a forked end 840, which is guided in a slide element 842 to be displaceable substantially in the longitudinally direction of the clip 838 and parallel to the plate 806. The slide element 842 is firmly secured by a screw to the underside of a post 844 projecting downwardly beside the plate 806.

During assembly, the hook-shaped end portion 836 of the hook is hooked into the opening 834 of the member 808 and bent around the underside of the ceramic pipe 812 in that the end 840 with the slide element 842 is secured to the post 844. The clip 838 hoids not only the member 808 and the pipe 812 in close contact with each other, but also by way of the pipe 812 presses the intermediate member 808 against the plate 806 and this against the rim of the opening 804.

In the embodiment according to Fig. 9, a pedestal housing 902 of an electrical coffee machine has an opening 904, against the rim of which is laid a heating plate 906. The plate 906 is held in its place by means of spring clasps 908, which bear on the one hand against the plate and on the other hand on the edge of an opening 910 of a mounting rib 912 projecting downwardly in the interior of the housing 902 laterally of the plate and which press the plate resiliently against the rim of the opening 904 and against an annular seal 914 surrounding this. The plate 906 consists of a ceramic material and has a uniform thickness of about 4 millimetres over the largest part of its extent.Projecting downwardly from the plate is an enlargement 916, which forms a ceramic pipe in that a channel 918 of circular cross-section is present in the enlargement, the axis of which channel extends parallel to the surface of the plate 906. At one side of the channel 918, the enlargement 916 possesses a projection 920 with a planar surface 921 which is parallel to the surface of the plate and on which is printed a meandering heating conductor tape. The tape as a whole extends parallel to the channel 918 and the individual heating paths thereof, with the exception of the connecting paths, extend transversely to the channel 918.The surface 921 carrying the conductor 922 lies at a height between the axis and the uppermost boundary of the channel 918 and the outside wall surface of the enlargement 916 is arranged so that, in the region of the projection 920, it does not follow the inside wall of the channel 918 but instead, starting from about midway between the axis and the lowermost boundary of the channel 918, extends tangentially to the wall of the channel 918 and obliquely upwards towards the surface 921.

As a result, heat is preferentially supplied to the lefthand side of the channel 918 by reason of the greater thermally conductive cross-sectional area and the proximity to the conductor 922. This asymmetrical heating of the channel 918 leads to a circulation of the water in spiral movements in the channel 918 and effects a reduction in the steam generation or otherwise allows a high temperature of the prepared brewing water without too much steam being generated. In modification of the illustrated embodiment, the lefthand outside wall surface of the enlargement 916 has a prolongation 950, drawn in broken lines, up to a place 960 of normal wall thickness of the plate 906, in which case the projection 920 beside the channel 918 is superfluous. The conductor in this case is applied to the surface 950 orto the downward extension thereof, as indicated by dotted lines 964. Since this surface extends obliquely to the vertical direction, it is easily accessible for application of the conductor 964 by, for example, a printing tool.

In Fig. 10, the heating pipe is designated by 301 and the heating plate by 302. It can be seen that the pipe is in thermally conductive contact, over a relatively large area of the pipe, directiy with the plate 302. The plate can, of course, be arranged to be even more effective by use of several heating pipes which are fastened as uniformly as possible at the underside ofthe plate.

An embodiment in which the heating element extends helically around the entire external circumference of the pipe 301, is illustrated in Fig.

11. The heating element 304 is applied by a screen printing process as a paste consisting of, for example, tungsten and aluminium oxide. Contact surfaces 306 for conducting current to the heating element 304 are disposed at both ends of the pipe 301. The heating element 304, with the exception of the contact surfaces 306, is insulated by a layer 305 consisting of, for example, aluminium oxide. The pipe is so fastened, for example by means of clamps, to the heating plate 302 that the planar surface 303 has direct contact with the plate.

Connecting contacts are clamped to the contact surfaces 306 and suitable hoses are drawn over the ends of the pipe in order to be able to conduct the water through the pipe. After heating, the water rises in known manner in the rising pipe and is finally conducted over the coffee powder in a filter.

Illustrated in Fig. 12 is an embodiment which, from the aspect of safety, is even more suitable, since the heating element in this case does not come into contact with the metallic heating plate. In this embodiment, a meandering heating element 704 is printed onto the curved surface of the pipe 701, whilst its planar surface 703, which later comes into contact with the plate, remains completely free of the metallic conductor. Designated by 706 are contact surfaces against which electrical contacts are clamped in order to conduct the current to the heating element. The fastening and the mounting of the hoses takes place as described above in connection with Fig. 11.

To keep the liquid in a vessel standing on the plate at a constant temperature, it is necessary to attach a regulator to the plate or the pipe so as to switch off the current feed when the liquid has reached a desired temperature and to switch the current on again when the temperature has fallen below a certain minimum value. It is, however, also possible to produce the heating element not from a metal, which has only a weakly inclined positive coefficient of temperature, but from a cold conductor material, the characteristic of which extends more steeply so that the resistance increases with increasing temperature in such a manner that the desired temperature of the liquid can be maintained even without a regulator.

It is also possible for part of the rising pipe to consist of a heating pipe of that kind, which leads to a further reduction in dead time, which in any case is already short in this manner of heating, as well as to a frequently desired increase in the brewing temperature. Through this additional heating part, heat transfer to the liquid can be effected more favourably. However, care would have to be taken in such an arrangement that this part of the heating is switched off when the water has run complete!y through the rising pipe.

The afore-described heating devices have the advantage that the heat transfer from the pipe to the heating plate is so improved that relatively little energy is needed in order to keep the liquid heated by the plate at a constant target temperature. It is particularly advantageous to lay the heating element in meander form around the pipe so that the planar surface is free of the heating element.

Thus, the danger of a conductive connection of the heating element to metallic plate is avoided.

Moreover, the insulating layer on the planar surface or on the entire heating element can be dispensed with.

Claims (42)

1. An electric heating appliance for a liquid, comprising a pipe which comprises electrically insulating heat-resistant material and which is arranged to conduct a liquid, and an electric heater disposed in thermally conductive connection with the pipe.

2. An appliance as claimed in claim 1, wherein the pipe material is one of glass and ceramic material.

3. An appliance as claimed in either claim 1 or claim 2, wherein the pipe material is disposed between the heater and the inside wall surface of the pipe and has a thickness of at least two millimetres.

4. An appliance as claimed in any one of the preceding claims, comprising a heating plate disposed in thermally conductive connection with and heatable by the pipe.

5. An appliance as claimed in claim 4, wherein the plate comprises an electrically insulating heatresistant material.

6. An appliance as claimed in claim 4, wherein the plate material comprises one of glass, a ceramic material and a plastics material.

7. An appliance as claimed in either claim 5 or claim 6, wherein the pipe material and plate material are the same as or similar to each other and are fused or sintered together.

8. An appliance as claimed in any one of claims 4 to 6, wherein the pipe and the plate are glued together.

9. An appliance as claimed in any one of claims 4 to 8, wherein the heater is arranged at least in part between the pipe and the plate.

10. An appliance as claimed in any one of claims 4 to 6, comprising an intermediate member of thermally conductive material arranged between the plate and the pipe.

11. An appliance as claimed in claim 10, wherein the material of the intermediate member is one of ceramic material and aluminium.

12. An appliance as claimed in either claim 10 or claim 11, wherein the heater is arranged on the intermediate member and alongside the pipe.

13. An appliance as claimed in any one of claims 4 to 9, wherein the heater is arranged on the plate and alongside the pipe.

14. An appliance as claimed in any one of claims 4 to 9, wherein the plate is provided in the region of each end portion of the pipe with a recess accommodating a portion of a respective hose receiving the associated pipe end portion.

15. An appliance as claimed in any one of claims 4 to 9, wherein the plate is provided with a portion of increased thickness defining a projection bearing against the pipe, end portions of the pipe extending outwardly of the projection.

16. An appliance as claimed in any one of claims 10 to 12, wherein the pipe is substantially straight and end portions thereof project outwa rdiy of the intermediate member.

17. An appliance as claimed in any one of claims 10 to 12, wherein the pipe is substantially straight and the intermediate member is provided with a recess in the region of each end portion of the pipe.

18. An appliance as claimed in any one of claims 4 to 17, wherein the cross-section of the pipe is oval at its end portions and round at its portion between the end portions, the major axis of the oval crosssection extending substantially parallel to the plane of the plate.

19. An appliance as claimed in any one of claims 4 to 9, 14 and 15, wherein the pipe has a flattened portion bearing against the plate.

20. An appliance as claimed in any one of claims 10 to 12,16 and 17, comprising a heating regulator arranged beside the pipe and disposed in thermally conductive connection with the intermediate member.

21. An appliance as claimed in any one of claims 4 to 9, 14, 15 and 19, comprising a heating regulator arranged beside the pipe and disposed in thermally conductive connection with the plate.

22. An appliance as claimed in any one of claims 1 to 19, comprising a heating regulator disposed in thermally conductive connection with the pipe.

23. An appliance as claimed in claim 22, wherein the regulator is connected to the pipe at a position spaced from the heater.

24. An appliance as claimed in either claim 22 or claim 23, wherein the regulator is connected to the pipe by a thermally conductive glue.

25. An appliance as claimed in any one of claims 22 to 24, wherein the regulator is connected to the pipe at a flattened portion thereof.

26. An appliance as claimed in any one of claims 4 to 6, wherein the pipe and the plate are formed integrally with each other.

27. An appliance as claimed in claim 26, wherein the heater is mounted on a mounting portion in the region of a junction of the plate and the pipe.

28. An appliance as claimed in any one of the preceding claims, wherein the pipe extends substantially horizontally and the heater is arranged on at least one of an upper and a lateral outer circumferential surface portion ofthe pipe.

29. An appliance as claimed in claim 4, wherein the appliance is a tea or coffee machine and the pipe is connected to a rising duct for supplying water to a filter, the heating plate being arranged to support a vessel for a prepared beverage to be kept heated.

30. An appliance as claimed in claim 29, wherein the pipe is of part-circular cross-section and bears at a longitudinally extending planar surface thereof againstthe plate, the heater comprising an electrical conductor which is helically wound around the pipe to extend across the planar surface and which is covered by a layer of insulating material.

31. An appliance as claimed in claim 29, wherein the pipe is of part-circular cross-section and bears at a longitudinally extending planar surface thereof against the plate, the heater comprising an electrical conductor which extends on a meandering path around the pipe apart from the planar surface.

32. An appliance as claimed in claim 31, wherein the conductor is covered by a layer of insulating material, the planar surface being free of such layer.

33. An appliance as claimed in any one of claims 29 to 32, wherein part of the rising duct comprises a tube of glass or ceramic material, a respective heating element being arranged at the outer surface of the tube.

34. An appliance substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

35. An appliance substantially as hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.

36. An appliance substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

37. An appliance substantially as hereinbefore described with reference to Fig. 5 of the accompanying drawings.

38. An appliance substantially as hereinbefore described with reference to Figs. 6 and 7 of the accompanying drawings.

39. An appliance substantially as hereinbefore described with reference to Fig. 8 of the accompanying drawings.

40. An appliance substantially as herein before described with reference to Fig. 9 of the accompanying drawings.

41. An appliance substantially as hereinbefore described with reference to Figs. 10 and 11 of the accompanying drawings.

42. An appliance substantially as hereinbefore described with reference to Fig. of the accompanying drawings.