GB2202418A

GB2202418A - Porous ceramic support for electric heating element

Info

Publication number: GB2202418A
Application number: GB08705974A
Authority: GB
Inventors: Mikolaj Zienkowicz
Original assignee: VULCAN REFRACTORIES Ltd
Current assignee: VULCAN REFRACTORIES Ltd
Priority date: 1987-03-13
Filing date: 1987-03-13
Publication date: 1988-09-21
Also published as: GB8705974D0

Abstract

A heater (10) to provide heat by both radiation and convection comprises a mounting plate (11) of a porous ceramic material on or in which a heating element (12) is mounted. A blower (16) may assist air flow through the porous ceramic material to provide heat by convection. A cover (17, 18) may cover the heating element (12) or the mounting plate (11) if the ambient conditions are hostile to the element (12), in the latter case the cover (18) likewise being of porous ceramic material. The ceramic may be alumina, alumina-silicate or silicon carbide. The heating element may be an open coil or sheathed in steel or ceramic. <IMAGE>

Description

HEATER This invention relates to heaters, and in particular to heaters of the type comprising a heating element mounted on a mounting plate.

Conventionally such mounting plates are of a ceramic material so as to withstand the temperature of the heating element which is mounted thereon. However such heaters, although providing satisfactory radiant heating, provide very little heat output by way of convection or conduction.

It is an object of the present invention to provide a heater of the aforementioned type in use of which heating is effected both by radiation and, to a greater extent than heretofore, by convection.

The invention provides a heater having a heating element mounted on a mounting plate, characterised in that the mounting plate is formed of a porous. ceramic material.

Preferably the heating element is an electrical element, and it may be an open coil element. The element may have a sheath therearound and said sheath may be of stainless steel or ceramic material. Alternatively a cover plate of a porous ceramic material may be located to overlie said mounting plate with said element disposed therebetween.

The heater may also comprise blowing means operable to blow air through said mounting plate and any cover plate provided thereon.

Preferably said porous ceramic material has a porosity of between 30% and 70%, and may be of aluminasilicate, fused alumina or silicon carbide or other temperature resistant material to withstand the operating conditions.

The heater may be adapted to operate at a heating power of between 10 and 100 watts/in2, and may operate at between 10 and 20 watts/in2 for drying applications.

One embodiment of heater in accordance with the invention will now be described with reference to the accompanying drawing in which: Fig. 1 is a plan view of the heater, Fig. 2 is a section on line 2-2 of Fig. 1, and Fig. 3 is a side view of the heater perpendicular to the view of Fig. 2.

Referring now to the figures there is shown a heater 10 comprising a mounting plate 11 and an element 12. The element 12 is located in a zig-zag array within a groove 13 of such a configuration formed in the plate 11. The plate 11 is of a ceramic material, which is both heat and chemically resistant, and is formed to have a porosity of between 30% and 70%. Such porosity may be provided by forming the plate of granules, the size of which determine the porosity of the plate 11.

Alternatively the plate may be formed having "burn-out" materials evenly distributed therein, such that heat or chemicals may be used to remove the "burn-out" materials and thereby leave the plate 11 with the required porosity. The plate 11 may be formed of aluminasilicate for lower operating temperatures. Other temperature resistant materials, for example fused alumina, silicon carbide or the like, may be used for higher operating temperatures. The element 12 is an open coil electrical element which lies in the groove 13 and whose ends or tails 15 pass through holes 14 provided in the plate 11 adjacent opposed corners thereof.

The element tails are to be connected to a suitable source of electrical power. The element 12 may be a nickel-chrome-aluminium spiral for operating temperatures of up to 12750C but may be of other suitable materials for higher operating temperatures if required. The layout of the groove 13 provides a substantially even heating distribution over the entire surface of the plate 11. However, other groove configurations may be provided if a variation of heating level over the surface of the plate 11 is desired. The element 12 provides a radiant heat source and the passage of air through the porous plate 11 provides a source of heating by connection. This may occur naturally, particularly if the plate 11 is disposed in a horizontal or near horizontal position, but may be enhanced by means of an enforced air flow created by a blower device 16 shown diagrammatically in Fig. 2.

The element 12 may be uncovered if the atmosphere in which it operates is not hostile to it and a high radiation component of heating is required. If however the atmosphere is hostile, e.g. corrosive due to the presence of sulphur dioxide, the element 12 may have a sheath 17 therearound of for example stainless steel or ceramic material. Alternatively a cover 18, shown in dashed lines in Figs. 2 and 3, may be provided to overlie the plate 11, the cover 18 and the plate 11 being of similar porous ceramic material.

As a further alternative the element 12 may be embedded in the material of the plate 11.

Conveniently the plate 11 is square in plan view and may be for example 2ft square although other dimensions and planforms may be used if desired.

With the present heater the heating element serves to provide radiant heat in addition to the heating of-any air or gas passing therethrough. In addition adjacent heaters of the present type may be located adjacent each other and may have different heating capacities so that a varying heating distribution across a heater assembly may be achieved if required. Such an arrangement is difficult to achieve with the purely gaseous heaters used heretofore.

The element 12 may be switched on intermittently to burn-off any deposits formed on the plate 11 and/or cover 18.

Claims

lo A heater having a heating element mounted on a mounting plate, characterised in that the mounting plate is formed of a porous ceramic material.
2. A heater according to claim 1 wherein said heating element is an electrical heating element.
3. A heater according to claim 2 wherein said heating element comprises an open coil element.
4. A heater according to claim 3 or any claim dependent thereon wherein said heating element is a nickel-chrome-aluminium spiral element.
5. A heater according to claim 4 adapted to operate at a temperature of up to 12750C.
6. A heater according to any one of claims 1 to 5 wherein said heating element has a sheath therearound.
7. A heater according to claim 6 wherein said sheath is of stainless steel.
8. A heater according to claim 6 wherein said sheath is of ceramic material.
9. A heater according to any one of claims 1 to 5 comprising a cover plate of a porous ceramic material located to overlie said mounting plate with said element disposed therebetween.
10. A heater according to any one of claims 1 to 9 comprising blowing means operable to blow air through said mounting plate and any cover plate provided thereon.
11. A heater according to any one of claims 1 to.10 wherein said porous ceramic material has a porosity of between 30% and 70%.
12. A heater according to claim 11 wherein said mounting plate is formed of granules.
13. A heater according to claim wherein said mounting plate'is formed of a material having "burn-out" materials evenly distributed therein and which may be removed therefrom by heat or chemical action.
14. A heater according to any one of claims 1 to 13 wherein said ceramic material is alumina silicate.
15. A heater according to any one of claims 1 to 13 wherein said ceramic material is fused alumina.
16. A heater according to any one of claims 1 to 13 wherein said ceramic material is silicon carbide.
17 A heater according to any one of claims 1 to 16 adapted to operate at a heating power of between 1.55 and 15.5 watts/sq.cm.
18. A heater according to claim 17 adapted to operate at a heating power of between 1.55 and 3.1 watts/sq.cm.
19. A heater according to any one of claims 1 to 18 wherein said heating element is located in a zig-zag array within a groove of such configuration formed in said mounting plate.
20. A heater according to any one of claims 1 to 18 wherein said heating element, is embedded in the material of said mounting plate.
21. A heater according to any one of claims 1 to 20 wherein said mounting plate is substantially square in plan view.
22. A heater according to claim 21 wherein said mounting plate is substantially 61 cms square in plan view.
23. A heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.