Radiant electric heater

Abstract

A radiant electric heater comprises a dish-shaped enclosure ( 1 ) formed of a first thermal insulation material and having a base ( 3 ) and a peripheral wall ( 5 ) and at least one upwardly-extending protrusion ( 7 ) formed in the base and defining a channel ( 9 ) in the base within the peripheral wall. A layer ( 11 ) of a second thermal insulation material, having greater thermal insulation properties than the first thermal insulation material, is provided in the channel. A radiant electric heating element ( 13 ) is supported on or in the layer of the second thermal insulation material.

1 . A radiant electric heater comprising:
 a dish-shaped enclosure ( 1 ) formed of a first thermal insulation material and having a base ( 3 ) and a peripheral wall ( 5 ) and at least one upwardly-extending protrusion ( 7 ) formed in the base and defining a channel ( 9 ) in the base within the peripheral wall;   a layer ( 11 ) of a second thermal insulation material, having greater thermal insulation properties than the first thermal insulation material, provided in the channel; and   a radiant electric heating element ( 13 ) supported relative to the layer of the second thermal insulation material.   
     
     
         2 . A heater as claimed in  claim 1 , wherein the upper level of the upwardly-extending protrusion ( 7 ) is not higher than the upper level of the peripheral wall ( 5 ). 
     
     
         3 . A heater as claimed in  claim 2 , wherein the upper level of the upwardly-extending protrusion ( 7 ) is lower than the upper level of the peripheral wall ( 5 ). 
     
     
         4 . A heater as claimed in  claim 1 , wherein the layer ( 11 ) of the second thermal insulation material is substantially annular in configuration, extending between the upwardly-extending protrusion ( 7 ) and the peripheral wall ( 5 ). 
     
     
         5 . A heater as claimed in  claim 1 , wherein the layer ( 11 ) of the second thermal insulation material is in the form of a narrow track which corresponds to the course of the heating element ( 13 ). 
     
     
         6 . A heater as claimed in  claim 1 , wherein the first thermal insulation material comprises a highly porous inorganic material which incorporates a high proportion of silicon dioxide. 
     
     
         7 . A heater as claimed in  claim 6 , wherein the first thermal insulation material is selected from an expanded sheet silicate, highly porous volcanic material, siliceous fossil earth, or plant ash, or cementitious materials, and mixtures thereof. 
     
     
         8 . A heater as claimed in  claim 7 , wherein the highly porous inorganic material is vermiculite. 
     
     
         9 . A heater as claimed in  claim 1 , wherein the first thermal insulation material includes a binder. 
     
     
         10 . A heater as claimed in  claim 9 , wherein the binder is present in an amount in the range from 0.01 to 40 percent by weight. 
     
     
         11 . A heater as claimed in  claim 10 , wherein the binder is present in an amount in the range from 10 to 30 percent by weight. 
     
     
         12 . A heater as claimed in  claim 9 , wherein the binder is selected from an aqueous phosphate solution, a silicophosphate, an alkali metal water glass, or a silica sol, and mixtures thereof 
     
     
         13 . A heater as claimed in  claim 1 , wherein the second thermal insulation material is compacted microporous thermal insulation. 
     
     
         14 . A heater as claimed in  claim 13 , wherein the microporous thermal insulation material comprises:
 30 to 100 weight percent microporous, finely divided metal oxide;   0 to 50 weight percent opacifier;   0 to 50 weight percent reinforcing fibre;   0-15 weight percent inorganic binder.   
     
     
         15 . A heater as claimed in  claim 14 , wherein the finely divided metal oxide is silica and/or alumina. 
     
     
         16 . A heater as claimed in  claim 14 , wherein the finely divided metal oxide is present in a range from 50 to 90 percent by weight. 
     
     
         17 . A heater as claimed in  claim 14 , wherein the opacifier is selected from titanium dioxide, ilmenite, silicon carbide, iron oxide, chromium dioxide, zirconium oxide, manganese dioxide, zirconium silicate and mixtures thereof. 
     
     
         18 . A heater as claimed in  claim 14 , wherein the opacifier is present in a range from 20 to 50 percent by weight. 
     
     
         19 . A heater as claimed in  claim 14 , wherein the reinforcing fibre is selected from glass wool, glass fibres, aluminosilicate fibres, rock wool, ceramic fibres, and mixtures thereof. 
     
     
         20 . A heater as claimed in  claim 14 , wherein the reinforcing fibre is present in a range from 5 to 20 percent by weight. 
     
     
         21 . A heater as claimed in  claim 14 , wherein the inorganic binder is present in a range from 0 to 2 percent by weight. 
     
     
         22 . A heater as claimed in  claim 1 , wherein the heating element ( 13 ) comprises a corrugated ribbon heating element partially embedded edgewise in the layer ( 11 ) of the second thermal insulation material. 
     
     
         23 . A heater as claimed in  claim 1 , wherein the heating element ( 13 ) comprises a coiled heating element secured to the layer ( 11 ) of the second thermal insulation material. 
     
     
         24 . A heater as claimed in  claim 23 , wherein the coiled heating element ( 13 ) is secured to the layer ( 11 ) of the second thermal insulation material by means of staples.