GB2137060A - Radiant-Energy Heating and/or Cooking Apparatus - Google Patents

Abstract

Radiant-energy heating and/or cooking apparatus includes a unit which utilizes a high temperature heater 11, such as a tungsten filament, and a reflector 14 for directing radiant energy toward a cooking surface. A layer of visible-wavelength radiation absorbing material 18 is provided between the radiant-energy source and the cooking surface, to reduce visible-wavelength radiation viewable by an apparatus system user, while substantially transmitting radiation in at least the near-infrared-wavelength region to foodstuffs to be cooked. The layer of absorbing material may be iron oxide. <IMAGE>

Description

SPECIFICATION Radiant-Energy Heating and/or Cooking Apparatus It is well known to provide combination conductive-energy and radiant-energy foodstuffcooking apparatus having a heater positioned below a radiation-transmissive coverplate. For example, the cooking apparatus 1 shown in Figure la of the accompanying drawings uses a heat-insulative block 2, typically fabricated of a ceramic material, into which channels 3 are formed in a meander pattern, to contain a heating-energy-producing heating coil 4. The energy from heating coil 4 is transmitted through a radiation-transmitting coverplate 5. Thus, when coil 4 is energised by connecting the coil ends 6 to a suitable power source, food-heating energy is provided to a cooking utensil (not shown) adjacent to the exterior coverplate surface 5a.

Another cooking apparatus 8 shown in Fig. 1 b uses a thin-film or foil resistance element 9 below a radiation-transmissive coverplate 5'. In a manner similar to apparatus 1, heating energy is introduced into foodstuffs placed above the coverplate exterior surface 5a' when heating element leads 6', are connected to a power source.

A heating source typically supplies energy at both infrared and visual wavelengths. Prior art cooking units have operated at relatively low temperatures, typically not greater than 14000K, because visual discomfort to the cook may occur if higher temperatures are used. Because of the relatively low operating temperatures, far infrared-wavelength energy is absorbed by the coverplate 5 or 5' to cause the coverplate to rapidly reach very high temperatures. At such low operating temperatures, (e.g. 14000K), the specific power density MeR in the heating coil 4 or 9 is relatively low and there is appreciable energy provided in the far-infrared region, i.e.

radiation having a wavelength greater than about 2.6 microns, further increasing the coverplate temperature. The coverplate is therefore highly susceptible to breakage due to the extreme thermal shock which occurs whenever spillage occurs in the cooking process.

In accordance with the present invention there is provided radiant-energy heating and/or cooking apparatus comprising means for generating radiant energy including infrared and visible wavelengths, means defining a surface at which at least the infrared radiation is provided for heating and/or cooking purposes, and means disposed between the heating means and the surface for reducing the amount of visible wavelength radiation available at the surface.

The invention advantageously enables a radiant-energy cooking apparatus to operate at significantly higher temperatures to provide a higher percentage of energy in the food-cooking near-infrared region, while reducing the additional visual wavelength energy produced as a result of operating at higher temperatures. The visiblewavelength radiation is preferably reduced by absorption.

In a preferred embodiment of the invention, the heating means is a tungsten filament tube positioned substantially at the focus of an infrared reflecting means. The visual-wavelength energy-absorbing means is preferably a layer of iron oxide. The absorbing layer can be positioned about the heating tube or across the open mouth of the infrared reflector, and intercepts the visual radiation prior to the radiant energy encountering a coverplate. A plurality of the heating tubereflector-visible-wavelength absorber (or spectral bandstop filter) units may be placed in an array beneath at least one coverplate, to define a total surface from which the foodstuff-heating infrared radiation is emitted.

By way of example only, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figures la and 1 b are perspective views of prior art cooking apparatus; Figure 2 is a perspective view of a radiantenergy heating and/or cooking apparatus embodying the invention; and Figure 2a is a graph illustrating the relationship between sp.ecific energy density and radiation wavelength for various heating means temperatures.

Referring now to Figure 2, out novel radiantenergy heating and/or cooking apparatus 9 utilises a radiant-energy producing means 11, such as a tungsten filament and the like. The filament is preferably enclosed within a tube 12 of a material which is substantially transmission of at least infrared wavelengths in the range from about 1.0 micrometers to about 3.0 micrometers.

Advantageously, filament 11, which may be a helically-coiled filament having its direction of elongation positioned along the linear center line of cylindrical tube 12, will be operated at a temperature between about 20000K and about 30000 K, and preferably at a temperature of about 26000K. The heating tube is mounted, by means not shown but well known to the art, with the filament 11 substantially at the focus of a reflector 1 4. Reflector 1 4 serves to collect and concentrate at least the infrared-wavelength radiant energy toward an open mouth region 1 4a of the reflector.A coverplate 1 6 is placed across the entire reflector mouth region 1 4a; the coverplate can be fabricated of any material which is substantially transparent to radiation in the near-infrared spectrum, which materials include glasses (such as germanium glass, chemically-treated plate glass and the like), quartz and similar materials. Thus, almost all of the radiation produced by filament 11 is directed toward reflector mouth 14a and the coverplate 1 6 thereover. This radiant energy includes the desired near-infrared energy for foodstuff cooking and also includes undesirable visible-wavelength energy.

In accordance with the invention, a visualwavelength light filtering means 1 8 is interposed between the radiant-energy source (filament 11) and the exterior surface 1 6a of the cover plate.

Thus, radiant energy of visible wavelengths is substantially absorbed within the apparatus 10, and the visible-wavelength radiation level capable of impinging upon the cooking unit user is attenuated. The visible-wavelength light absorber 18 may be a planar layer 1 8a interposed between the reflector mouth area 14a and the coverplate 16; advantageously, planar layer 1 8a may be fabricated upon the coverplate interior surface 1 6b. If.coverplate 1 6 is to be removable (for cleaning and the like purposes), layer 1 8a can be a separate member, separately mounted across reflector mouth 1 4a. Alternatively, a layer 1 8b of visual-wavelength absorbing material may be fabricated upon the exterior surface 1 2a of the heating means tube 12.Layer 1 8a or 1 8b can be fabricated of any material having a substantially higher absorption of radiant energy in the visiblewavelength region (from about 0.4 microns to about 0.7 microns), and a substantially lesser absorption, or attenuation, of radiant energy in the near-infrared wavelength region (from about 1 micron to about 3 microns). The absorber can also be a red-transmissive material, such as a glass and the like, formed into a separate member or distributed in another element, e.g. in the tube 12. One material found to be particularly useful for visible-wavelength energy absorption, in layer 1 8a or 1 8b, is iron oxide. The iron oxide can be applied by the method described and claimed in co-pending application Serial No.

322,421, filed November 18, 1981, assigned to the assignee of the present application and incorporated herein in its entirety by reference. In that application, the production of an iron oxide coating, of any desirable thickness, by spraying an alcoholic soluton of ferric chloride upon a hot surface (as might be provided by operation of filament 11 for some time prior to the actual spraying of the ferric chloride-alcohol solution) is described and claimed. The use of an iron oxide coating is particularly advantageous in that most of the blue and green visible-wavelength radiation is absorbed while infrared-wavelength radiation is efficiently transmitted.This allows a portion of the red visible-wavelength radiation to be transmitted through the absorbing layer 18 and, subsequently, through coverplate 16, whereby the user views the coverplate as having a somewhat dull red color, indicative of the apparatus being energized.

It should be understood that tube 12 may be dispensed with and the filament 11 placed within a hermetically-sealed container bounded by the reflecting means 14 and the coverplate 1 6. It should also be understood that other heating means may be utilized and may have shapes other than the linearly-extended filament shown.

In particular, meander-line filaments may be utilized, having a mean center line which may be a curve in either two- or three-dimensional space, as required for the particular end use. Similarly, additional units of the heating means 11-reflector means 14-visualfilter7ng means~18~cornbination can be utilized in a single apparatus 10, as shown by the additional reflectors 14', filament 11 '/protective tubes 12', associated spectral filtering means 18' and coverplates 16' (all shown in broken line) disposed leftwardly and rightwardly with respect to the unit shown in solid line in Figure 2.When a plurality of heating units are utilized, individual coverplates 1 6 and 1 6' may also be utilized, or the totality of coverplates may be formed into a unitary member defining a surface above which is an area upon which, or a volume within which, foodstuffs can be cooked. It should also be understood that thermal insulation may be used about the exterior of apparatus 10 as required. Apparatus 10 need not be utilized only for the heating or cooking of foodstuffs, but can be utilized for any task requiring irradiation of at least one object with infrared radiation.

Referring now to Figure 2a, radiation wavelength A is plotted with increasing value along an abscissa 21, and is scaled in micrometers. Spectral power density MeR is plotted along major ordinate 22 and is scaled in units of 105W/(m2,um). The relative amplitude of visual-wavelength light V(A) is plotted along a minor ordinate 23. A curve 25 (shown in broken line) is referenced to minor ordinate 23 and indicates the relative sensitivity of human vision.

A family of solid-line curves 27a--279 illustrate the relative power density, referred to major ordinate axis 22, of radiation produced by a source operating at temperatures from 20000 K (curve 27a) through a temperature of 32000K (curve 27g) in 2000 K increments. A broken-line curve 29 illustrates the wavelength at which peak power density occurs with respect to filament temperature.Another broken-line curve 30, at about 2.6 micrometers wavelength, indicates the wavelength above which is found infrared radiation which does not substantially pass through typical coverplates; it is desirable to have the majority of infrared radiation occurring below line 30, and it is also desirable to have the peak power density curve 29 occur at a wavelength greater than about 1.0 micrometers, for the particular filament temperature utilized, to maximize the proportion of near-infrared radiation available. Similarly, the area under visible-light curve 25, of a selected radiation curve 27, should be as small as possible. It will be seen that filament temperatures between about 20000K and about 30000 K, meet these requirements. The higher temperatures are somewhat preferred, as the higher power density MeR values thereat can provide significant reduction in heating means material costs. This cost reduction must be balanced by the additional visible-wavelength radiation at higher operating temperatures; a -preferred temperature of about 26000K (curve 27d) is believed to be the best compromise at this time.

Claims (17)

1. Radiant-energy heating and/or cooking apparatus comprising: means for generating radiant energy at at least infrared and visible wavelengths; means for defining a surface at which at least the infrared-wavelength radiation is to be provided for cooking purposes; and means disposed between said heating means and said surface for reducing the amount of visible-wavelength radiation available at said surface.

2. The apparatus of claim 1, further comprising means disposed about said heating means for directing substantially all of at least said infraredwavelength radiation through said surface.

3. The apparatus of claim 2, wherein said reducing means includes a layer visiblewavelength radiation absorbing material.

4. The apparatus of claim 3, wherein said absorbing material absorbs at least blue and green visible light.

5. The apparatus of claim 4, wherein said material is iron oxide.

6. The apparatus of claim 2, wherein said heating means is a filament disposed within said reflecting means.

7. The apparatus of claim 6, wherein said heating means further includes a member enclosing said filament.

8. The apparatus of claim 7, wherein said reducing means is fabricated upon said enclosing member.

9. The apparatus of claim 8, wherein said filament has an elongated linear shape; said enclosing member is a tube of radiationtransmissive material formed about said filament; and said directing means is a parabolic trough having said filament disposed along the focus thereof.

10. The apparatus of claim 6, wherein said filament has an elongated linear shape; said directing means is a parabolic trough having said filament disposed along the focus thereof; and said reducing means is a layer of a material, absorbing radiant energy in the visiblewavelength spectrum, extending across a mouth region of said trough.

11. The apparatus of claim 1, wherein said heating means operates at a temperature between about 2000 K and about 30000 K.

12. The apparatus of claim 11, wherein said heating means operates at a temperature of about 26000K.

13. The apparatus of claim 1, further including at least one additional heating means, located upon the same side of said surface as said heating means; and additional reducing means positioned between said surface and said at least one additional heating means.

14. The apparatus of claim 13, further comprising additional directing means cooperating with said additional heating means to cause substantially all of the infrared-wavelength radiation from said additional heating means to pass through said surface.

1 5. The apparatus of claim 13, wherein said surface is a two-dimensional surface.

1 6. The apparatus of claim 13, wherein said surface is a three-dimensional surface defining a volume in which at least one object can be heated by the infrared-wavelength radiation passing through said surface.

17. Radiant-energy heating and/or cooking apparatus substantially as herein described with reference to Figure 2 of the accompanying drawings.