US3663798A

US3663798A - An infrared heating surface

Info

Publication number: US3663798A
Application number: US852609A
Authority: US
Inventors: Thomas O P Speidel; Edward E Trotter; Paul K Shefsiek
Original assignee: Thermo Electron Corp
Current assignee: Thermo Fisher Scientific Inc
Priority date: 1969-08-25
Filing date: 1969-08-25
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: NL7012583A; CA925915A; GB1282656A

Abstract

A heating or cooking system which includes an infrared heating source disposed below a surface transparent to infrared radiation which is directed upwardly through the surface. The surface may be maintained at a cool temperature by circulating air beneath the surface as radiation is passed through it. The heat source includes a resistance element for generating infrared radiation operated in an inert environment and a reflector to direct the infrared radiation toward and through the surface.

Description

United States Patent Speidel et al.

[151 3,663,798 1 May 16, 1972 AN INFRARED HEATING SURFACE Inventors: Thomas 0. P. Speidel, Bedford; Edward E.

Trotter, Holliston; Paul K. Shefsiek, Acton, all of Mass.

Thermo Electron Corporation, Waltham, Mass.

Filed: Aug. 25, 1969 Appl. No.: 852,609

Assignee:

US. Cl ..2l9/464, 219/343, 219/347, 219/354, 219/461, 219/553, 313/315, 338/237 Int. Cl. ..H0lb 3/44, H0lb 3/74, H01c 1/02 Field ofsearch ..219/343,347, 461,464, 354, 219/553, 349; 252/502; 313/315; 338/237 References Cited UNITED STATES PATENTS 7/1935 Braselton ..219/553 X 10/1968 Jacobs ....219/464 X 7/1898 Quidas ....219/347 X 6/1952 Wilcox ..2l9/461 6/1954 Dobbins..... ....2l9/347 4/1966 Whiteford ..2l9/343 X FOREIGN PATENTS OR APPLICATIONS 834,815 12/1938 France ..219/354 OTHER PUBLICATIONS Metal Progress, May 1959, pp. 1 15, l 16 (Handbook) Electrical Engineers Handbook, Electric Power, pp. 15- 10, 13, 21; 4th Ed., John Wiley & Sons, lnc., New York, NY. 1958) King ..2l9/343 X Bassett ..219/464 Primary ExaminerR. F. Staubly Armrney-Kenway, Jcnney & Hildreth [57] ABSTRACT A heating or cooking system which includes an infrared heating source disposed below a surface transparent to infrared radiation which is directed upwardly through the surface. The surface may be maintained at a cool temperature by circulating air beneath the surface as radiation is passed through it. The heat source includes a resistance element for generating infrared radiation operated in an inert environment and a reflector to direct the infrared radiation toward and through the surface.

14 Claims, 3 Drawing Figures Patented May 16, 1972 FIG. 2'

Jill;

INFRARED HEATING SURFACE This invention relates generally to radiation heating devices and more particularly to an arrangement for directing radiant heat through a surface while maintaining the surface at a cool temperature. Although the invention is probably best suited for use in a cooking range, it may be employed in a wide variety of heating applications.

When the invention is employed in a cooking range a number of advantages are obtained over conventional gas or electric ranges. Among these advantages is that the cooking surface is completely flat and the heat source is below and completely covered by the cooking surface. Because the flat, uninterrupted surface constitutes the top of the range, cleaning is simplified. Additionally, location of the heat source completely below the cooking surface eliminates hazards presented by the normally exposed heat sources of conventional ranges, the cooking surface remaining relatively cool. Also, of course, the flat, uncluttered top of the range presents a pleasing and attractive appearance.

Conventional cooking ranges utilize heat conduction or convection techniques. For example, electric stoves employ resistance elements which are exposed directly at the cooking surface of the range. These resistance elements are relatively slow in thermal response and considerable time is necessary to bring the element to a desired temperature or simply to change the temperature. When such heating elements are shut off, they remain dangerously hot for some time presenting a hazard to the user. With my invention, on the other hand, thermal response to control changes is rapid and accurate. For example, the heating elements employed in conventional cooking ranges are relatively massive and it is not uncommon for such elements to reach full thermal output only after a delay of the order of 1 minute or more. The time required to cool down or to change the temperature of these massive elements similarly is prolonged. In contrast, my invention employs heating elements which can be brought to full heating output within two or three seconds and which may also be cooled fully within a similar short time.

It is among the primary advantages of the invention that the cooking surface may be maintained at a low temperature and may even be cool to the touch even while in operation. This not only minimizes the danger of injury, as noted above, but facilitates cleaning because foods spilled accidentally on the cooking surface will not burn.

In accordance with the invention the continuous cooking surface is formed from a special glass or other material which is transparent to infrared radiation. Infra red heat sources are located below and are covered completely by the cooking surface. The heat sources include resistance heating elements which are sealed within envelopes also constructed from a material transparent to infrared radiation through which necessary electrical leads are sealed. The atmosphere within the envelopes is inert to retard deterioration or oxidation of the resistance elements, thus increasing their useful life. The heat sources include reflectors which direct substantially all of the radiation toward and through the cooking surface. The cooking surface and envelopes may be cooled by an air stream which is blown continuously along the underside of the cooking surface and about the envelopes. This maintains the surface temperature of the cooking surface and envelopes at a relatively low level.

Itis among the general objects of the invention to improve radiation heaters and more particularly to provide an improved cooking range in which the cooking surface may be maintained at a cool temperature even while the device is in operation.

Also among the objects is to provide a cooking range in which the heating elements are unexposed thus reducing the likelihood of danger to the user.

A further object of the invention is to provide a cooking range having a rapid thermal response to temperature controls.

An additional object of the invention is to provide a cooking range having a top cooking surface which may be cleaned easily and which requires minimal maintenance.

Another object of the invention is to provide a radiation heating arrangement of simple and economical construction.

Other objects and advantages of the invention will be apparent from the following detailed description of the invention with reference to the accompanying drawings wherein:

FIG. 1 is a perspective view of a range, partially broken away, in which the invention is employed;

FIG. 2 is a side elevation, in section, through the top of the range; and

FIG. 3 is an enlarged sectional view of the invention as seen from the plane 33 of FIG. 2.

FIG. 1 shows a range of generally conventional appearance, but which includes a cooking arrangement constructed in accordance with the invention. The range includes a control panel 10 which is located at the top rear but which may be at any convenient position. The range top, indicated generally by the reference character 12, is supported on the frame of the stove at a level suitable for a typical user. The range top 12 includes a baseplate 14 which supports a number of radiation units 16. A cooking surface 18 is spaced above and parallel to the baseplate 14 to support cooking utensils over the radiation units. The spaced lateral edges of the baseplate l4 and cooking surface 18 are enclosed by side plates 20 which may be formed integrally with the side panels of the range itself. As described more fully below, the baseplate l4, cooking surface 18, and side walls 20 define a flow channel to guide coolant air along the underside 22 of the cooking surface 18 and along the radiation units 16. In some installations, a separator 24 extending from the baseplate 14 to the underside of the cooking surface 18 has proven useful for more effective cooling.

The cooking surface 18 preferably is formed from glass such as Vycor, Pyrex, Cervit, Hercuvit, sapphire, ceramic, quartz, or other material which is substantially transparent to infrared radiation but substantially opaque, or at least translucent, to visible radiation emitted by the radiation units 16. Such visible radiation contributes little to the heating function and may detract from the appearance of the range. The smooth, continuous range top 12 is not only aesthetically appealing but may be cleaned with minimal effort.

Each of the radiation units 16 is formed from one or more radiant tubes 26, as best seen in FIG. 2. The individual radiant tubes 26 include a high temperature heating element or filament 28 formed from materials such as tungsten, silicon carbide, graphite rope, or other similar material, heated by its resistance to the flow of electrical currents. The filament 28 is isolated and hermetically sealed within an envelope 30 and appropriate electrical leads are sealed through the envelope for electrical connection of the filament to a power source through the controls on the panel 10. The sealed connections between the leads of the filament 28 may also provide support for the filament 28 in a desired position within the envelope 30. The envelope is manufactured from a material which is substantially transparent to infrared radiation such as quartz, sapphire, Vycor, borosilicate glass or similar materials. To protect the filament from high temperature oxidation, the envelope 30 may be evacuated or filled with an inert gas. Evacuation is preferred because heat conduction or convection occurs in an inert gas and optimum low temperatures are not attained.

Each of the radiant tubes 26 is provided with a reflector 32 arranged to direct substantially all of the emitted infrared radiation upwardly toward the cooking surface 18. The reflector preferably is formed directly upon the internal surface of the envelope 30 and may consist of a thin coat of aluminum or gold. Other arrangements may be employed, for example, the reflective coating may be located about the outside surface of the envelope 30 or a separate reflector may be provided below the radiant tube. The upper half of each radiant tube, however, should be unobstructed to define a window through which substantially all of the emitted infrared radiation may pass upwardly toward cooking surface 18. The electrical connections to the ends of the filament 28 may also serveas physical supports for the filaments 28 to hold them juxtaposed to their associated reflector surfaces 32. Although the radiant tubes are shown as being cylindrical in shape, they may be constructed in toroidal, pancake or spiral configurations. The cylindrical radiant tubes 26 may be supported by insulating brackets 34 secured to the baseplate 14.

My invention effects heating by radiation and does not rely on conduction or convection techniques. Because the cooking surface 18 is substantially transparent to the infrared radiation it is heated only to a slight degree, substantially all of the emitted radiation being absorbed by the cooking utensil resting atop the cooking surface. The slight heating of the cooking surface 18 is caused by absorbed visible radiation as well as the small amount of absorbed infrared radiation. To further ensure that the cooking surface 18 remains at a relatively cool temperature, the blowers 36 which draw cool, ambient air through an inlet 38 and direct it through the flow chamber 40 defined by the baseplate 14, cooking surface 18 and side plates 20. The blower 36 is located at the front of the range and may be covered by a shield 42 in the bottom of which the inlet opening 38 is formed. An outlet port 44 is formed at the rearward end'of the flow chamber 40 and may be formed in part by the upstanding rear edge of the baseplate 14. The outlet port 44 preferably leads to exhaust vents 46 at the top rear of the range. Thus, cooling air passes in intimate heat-transferal contact with the underside 22 of the cooking surface 18 and about the external surface of the radiant tubes 26 carrying excess heat generated by the absorbed radiation away from the cooking surface. The cooking top thus operates at such a low temperature that it may be touched with the bare hands and foods spilled on the cooking surface do not adhere.

In the preferred embodiment, shown in the drawings, the separator 24 divides the flow chamber 40 into two sections, each section including two separate radiation units 16. One of the blowers 36 is associated with each section of the flow chamber. This arrangement is advantageous in that if the radiation units 16 within one of the chamber section are not in use, the blower 36 associated with those unused units 16 need not be operated. The other blower 36, associated with the channel section in which the radiation units 16 are operated, draws the cool, ambient air only through that section of the flow chamber 40, the flow of air being guided by the separator 24. Additionally, the output of the blower 36 may be varied directly with the output of their associated radiation units 16. This may be accomplished by connecting the blower motors in a conventional arrangement, not shown, in circuit with the temperature controls 11 for the radiation units 16 so that as the output of the radiation units is increased the output of their associated blowers 36 similarly will be increased.

It should be understood that the foregoing description is intended to be merely illustrative of my invention and that other embodiments and modifications will be apparent to those skilled in the art without departing from its spirit. For example, the infrared transparent surface has been described as a generally flat plate which is desirable when the invention is employed in a cooking range, but it may assume other shapes when utilized in other heating applications.

Having thus described my invention what I desire to claim and secure by Letters Patent is:

l. A heating unit comprising:

a. means forming a range-type surface from a material which is relatively transparent to infrared radiation;

b. a plurality of elongated tubes positioned closely adjacent said surface substantially along a plane parallel to the plane of said surface and adapted to emit infrared radiation, each of said tubes including a high temperature graphite electrical resistance element and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element;

c. reflector means closely adjacent said resistance element and said surface on the side of said resistance element opposite said surface for directing radiation from said resistance element toward said surface; and

d. means for directing a relatively cool gas to flow along said surface forming means and about at least a portion of said envelope in heat conductive relation thereto to maintain said surface and at least said portion of said envelope at a relatively cool temperature during emission of said radiation.

2. A heating unit as defined in claim 1 wherein said means for directing said relatively cool gas comprises:

means defining a flow channel about said envelope, said flow channel being defined in part by said surface forming means; and

blower means in communication with said flow channel for generating said flow of relatively cool gas.

3. A heating unit according to claim 1 wherein said surface comprises a cooking surface for supporting food and food utensils, said cooking surface being on the side of said surface forming means opposite said elongated tubes.

4. A heating unit according to claim 3 wherein said cooking surface defines a plurality of cooking zones having a plurality of said elongated tubes positioned closely adjacent each zone.

5. A heating unit comprising:

a. means forming a range-type cooking surface having a plurality of cooking zones for supporting food and food utensils, said zones being formed from material which is relatively transparent to infrared radiation;

b. a plurality of elongated tubes adapted to emit infrared radiation positioned closely adjacent each of said cooking zones along the side of said surface forming means opposite said cooking surface and substantially along a plane parallel to the plane of said cooking surface, each of said tubes including a high temperature electrical resistance element and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element, said resistance element being capable of producing radiation for heating material adjacent said cooking surface, to a temperature level sufficiently high to excessively heat at least a portion of said envelope;

c. reflector means closely adjacent said resistance element and said cooking surface on the side of said resistance element opposite said cooking surface for directing radiation from said resistance element toward said cooking surface; and

d. means for directing relatively cool gas about said portion of said envelope in heat conductive relation thereto during emission by said resistance element of sufi'rcient radiation to excessively heat said envelope.

6. A heating unit according to claim 5 wherein said elongated tubes each comprise a graphite resistance element.

7. A heating unit according to claim 6 wherein said graphite resistance element comprises graphite rope.

8. A heating unit according to claim 5 wherein said envelope encloses an inert environment for said resistance element.

9. A unit for cooking foods comprising:

a. means forming a range-type surface for supporting food and food utensils, said surface defining a plurality of cooking zones relatively transparent to infrared radiation;

b. a plurality of elongated tubes for emitting infrared radiation positioned closely adjacent each of said zones along the side of said surface forming means opposite the side upon which food and utensils are supportable, substantially along a plane parallel to the plane of said surface, each of said tubes including a high temperature electrical resistance element and a hermetically sealed borosilicate glass envelope transparent to infrared radiation enclosing said element, said resistance elements being capable of producing infrared radiation sufficient to establish a temperature level at said zones for cooking food material, said infrared radiation being sufficient to excessively heat said envelope;

c. reflector means closely adjacent said resistance elements and said surface on the side of said resistance elements opposite said surface for directing radiation from said resistance elements toward said surface;

d. means forming a flow channel about said envelopes, said flow channel being defined in part by a portion of said surface forming means; and

e. means for directing a relatively cool gas through said channel in heat conductive relation to said envelopes and along at least said portion of said surface forming means for removing heat from said envelopes and said portion of said surface forming means during emission by said resistance element of sufficient radiation to cook food material supported at said cooking zone.

10. A cooking unit according to claim 9 wherein a plurality of said elongated tubes is positioned adjacent each of said cooking zones.

11. A cooking unit according to claim 9 wherein each of said elongated tubes comprises a graphite electrical resistance element 12. A cooking unit according to claim 11 wherein said graphite electrical resistance element comprises graphite rope.

13. A heating unit comprising:

a. means forming a surface from material which is relatively transparent to infrared radiation;

b. elongated source means positioned closely adjacent said surface substantially along a plane parallel to the plane of said surface and adapted to emit infrared radiation, said source means including a high temperature electrical resistance element of graphite rope and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element, said resistance element being capable of producing radiation for heating material adjacent the side of said surface forming means opposite said source means to a temperature level sufficiently high to excessively heat at least a portion of said envelope;

d. means for directing relatively cool gas about said portion of said envelope in heat conductive relation thereto during emission by said resistance element of sufficient radiation to excessively heat said envelope.

14. A unit for cooking foods comprising:

a. means forming a surface for supporting food and food utensils, said surface defining a plurality of cooking zones relatively transparent to infrared radiation;

b a plurality of elongated tubes for emitting infrared radiation positioned closely adjacent said zones along the side of said surface forming means opposite the side upon which food and utensils are supportable, substantially along a plane parallel to the plane of said surface, each of said tubes including a high temperature electrical resistance element of graphite rope and a hermetically sealed borosilicate glass envelope transparent to infrared radiation enclosing said element, said resistance elements being capable of producing infrared radiation sufficient to establish a temperature level at said zones for cooking food material, said infrared radiation being sufficient to excessively heat said envelopes;

e. means for directing a relatively cool gas through said channel in heat conductive relation to said envelopes and along at least said operation of said surface forming means for removing heat from said envelopes and said portion of said surface forming means during emission by said resistance element of sumcient radiation to cook food material supported at said cooking zone.

Claims

1. A heating unit comprising: a. means forming a range-type surface from a material which is relatively transparent to infrared radiation; b. a plurality of elongated tubes positioned closely adjacent said surface substantially along a plane parallel to the plane of said surface and adapted to emit infrared radiation, each of said tubes including a high temperature graphite electrical resistance element and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element; c. reflector means closely adjacent said resistance element and said surface on the side of said resistance element opposite said surface for directing radiation from said resistance element toward said surface; and d. means for directing a relatively cool gas to flow along said surface forming means and about at least a portion of said envelope in heat conductive relation thereto to maintain said surface and at least said portion of said envelope at a relatively cool temperature during emission of said radiation.

2. A heating unit as defined in claim 1 wherein said means for directing said relatively cool gas comprises: means defining a flow channel about said envelope, said flow channel being defined in part by said surface forming means; and blower means in communication with said flow channel for generating said flow of relatively cool gas.

5. A heating unit comprising: a. means forming a range-type cooking surface having a plurality of cooking zones for supporting food and food utensils, said zones being formed from material which is relatively transparent to infrared radiation; b. a plurality of elongated tubes adapted to emit infrared radiation positioned closely adjacent each of said cooking zones along the side of said surface forming means opposite said cooking surface and substantially along a plane parallel to the plane of said cooking surface, each of said tubes including a high tempErature electrical resistance element and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element, said resistance element being capable of producing radiation for heating material adjacent said cooking surface, to a temperature level sufficiently high to excessively heat at least a portion of said envelope; c. reflector means closely adjacent said resistance element and said cooking surface on the side of said resistance element opposite said cooking surface for directing radiation from said resistance element toward said cooking surface; and d. means for directing relatively cool gas about said portion of said envelope in heat conductive relation thereto during emission by said resistance element of sufficient radiation to excessively heat said envelope.

9. A unit for cooking foods comprising: a. means forming a range-type surface for supporting food and food utensils, said surface defining a plurality of cooking zones relatively transparent to infrared radiation; b. a plurality of elongated tubes for emitting infrared radiation positioned closely adjacent each of said zones along the side of said surface forming means opposite the side upon which food and utensils are supportable, substantially along a plane parallel to the plane of said surface, each of said tubes including a high temperature electrical resistance element and a hermetically sealed borosilicate glass envelope transparent to infrared radiation enclosing said element, said resistance elements being capable of producing infrared radiation sufficient to establish a temperature level at said zones for cooking food material, said infrared radiation being sufficient to excessively heat said envelope; c. reflector means closely adjacent said resistance elements and said surface on the side of said resistance elements opposite said surface for directing radiation from said resistance elements toward said surface; d. means forming a flow channel about said envelopes, said flow channel being defined in part by a portion of said surface forming means; and e. means for directing a relatively cool gas through said channel in heat conductive relation to said envelopes and along at least said portion of said surface forming means for removing heat from said envelopes and said portion of said surface forming means during emission by said resistance element of sufficient radiation to cook food material supported at said cooking zone.

11. A cooking unit according to claim 9 wherein each of said elongated tubes comprises a graphite electrical resistance element.

12. A cooking unit according to claim 11 wherein said graphite electrical resistance element comprises graphite rope.

13. A heating unit comprising: a. means forming a surface from material which is relatively transparent to infrared radiation; b. elongated source means positioned closely adjacent said surface substantially along a plane parallel to the plane of said surface and adapted to emit infrared radiation, said source means including a high temperature electrical resistance element of graphite rope and a hermetically sealed borosilicate glass envelope relatively transparent to infrared radiation enclosing said resistance element, said resistance element being capable of producing radiation for heating material adjacent the side of said surface forming means opposite said source means to a temperature level sufficiently high to excessively heat at least a portion Of said envelope; c. reflector means closely adjacent said resistance element and said surface on the side of said resistance element opposite said surface for directing radiation from said resistance element toward said surface; and d. means for directing relatively cool gas about said portion of said envelope in heat conductive relation thereto during emission by said resistance element of sufficient radiation to excessively heat said envelope.

14. A unit for cooking foods comprising: a. means forming a surface for supporting food and food utensils, said surface defining a plurality of cooking zones relatively transparent to infrared radiation; b. a plurality of elongated tubes for emitting infrared radiation positioned closely adjacent said zones along the side of said surface forming means opposite the side upon which food and utensils are supportable, substantially along a plane parallel to the plane of said surface, each of said tubes including a high temperature electrical resistance element of graphite rope and a hermetically sealed borosilicate glass envelope transparent to infrared radiation enclosing said element, said resistance elements being capable of producing infrared radiation sufficient to establish a temperature level at said zones for cooking food material, said infrared radiation being sufficient to excessively heat said envelopes; c. reflector means closely adjacent said resistance elements and said surface on the side of said resistance elements opposite said surface for directing radiation from said resistance elements toward said surface; d. means forming a flow channel about said envelopes, said flow channel being defined in part by a portion of said surface forming means; and e. means for directing a relatively cool gas through said channel in heat conductive relation to said envelopes and along at least said operation of said surface forming means for removing heat from said envelopes and said portion of said surface forming means during emission by said resistance element of sufficient radiation to cook food material supported at said cooking zone.