WO1996036197A1

WO1996036197A1 - Lightwave oven using highly reflective surface materials

Info

Publication number: WO1996036197A1
Application number: PCT/US1996/006485
Authority: WO
Inventors: Eugene R. Westerberg; Donald W. Pettibone
Original assignee: Quadlux, Inc.
Priority date: 1995-05-08
Filing date: 1996-05-08
Publication date: 1996-11-14
Also published as: AU5733396A

Abstract

The present invention is a lightwave oven which includes an oven housing enclosing a cooking chamber. A plurality of lamps capable of emitting radiant energy having a significant portion in the visible and near-visible light range of the electromagnetic spectrum are mounted within the housing. Reflecting surfaces such as walls, facets, and/or lamp reflectors are positioned within the oven housing facing the cooking chamber. The reflecting surfaces are at least 88 % reflective (and preferably at least 95 % reflective) of radiant energy falling within the visible and near-visible light range of the electromagnetic spectrum.

Description

LIGHTWAVE OVEN USING HIGHLY REFLECΗVE SURFACE MATERIALS

Related Applications

This application is a continuation-in-part of application Serial No. 08/438,054, filed May 8, 1995, and application Serial No. 08/517,772, filed August 22, 1995, both of which are continuations-in-part of application Serial No. 08/065,802, filed May 21, 1993 and application Serial No. 08/247,029. filed May 20, 1994, both of which were continuations in part of Serial No. 07/738,207, filed July 30, 1991 which was a continuation-in-part of application serial No. 07/350,024, filed May 12, 1989, now U.S. Patent 5,036,179 which was in turn a continuation-in-part of application serial No. 07/195,967, filed May 19, 1988, now abandoned.

Field of the Invention

This invention relates generally to the field of lightwave ovens and particularly to the field of ovens which utilize sources of visible, near-visible, and infra-red radiant energy sources for cooking applications and which are provided to have interior reflecting surfaces which are highly reflective over the visible and near-visible ranges of the electromagnetic spectrum.

Background of the Invention

Lightwave cooking ovens following the present invention and having linear sources of visible, near-visible and infra-red radiant energy are disclosed and described in U.S. Patent No. 5,036,179 and International Application Number PCT US94/05753 which is published under International Publication Number WO 94/28692, each of which are incorporated herein by reference.

Lightwave ovens can use a plurality of lamps, such as quartz-halogen tungsten lamps or equivalent lamps such as quartz arc lamps, or an array of several lamps either operated in unison or selectively operated in varying combinations as necessary for the particular food item sought to be cooked. Typical quartz-halogen lamps of this type can generally provide about between 100 W and 2 kW of radiant energy with a significant portion (i.e., approximately at least 40 %) of the energy in the visible and near visible light range (i.e., approximately 0.4 μm to 1.4 μm) of the electromagnetic spectrum. Each lamp typically operates at 3000 degrees Kelvin and converts electrical energy into black body radiation having a range of wavelengths from approximately 0.4 μm to 4.5 μm with a peak intensity at .965 μm.

These ovens provide high-speed, high-quality cooking and baking of food items by impinging high-intensity visible, near-visible, and infrared radiations onto a food item. The ovens cook the food items within the short periods of time normally found in microwave cooking while maintaining the browning of infrared cooking and the quality of conduction-convection cooking. When food is exposed to a sufficiently intense source of visible, near-visible, and infrared radiation, the food absorbs low levels of visible and near-visible radiation, thereby allowing the energy to penetrate the foodstuff and heat it deeply. The longer infrared radiation does not penetrate deeply but acts as an effective browning agent. These radiation sources are ordinarily positioned above and below the food item, and are typically positioned behind radiation transparent plates mounted inside the oven. These plates can be formed from materials, such as high quality heat-resistant glasses and pyroceramic materials that are transparent to visible, non-visible and infrared radiations. Applicants previously discovered that when the cooking lamps are operated to impinge at least 4 kW of radiant power onto the food, remarkable results in cooking speed and quality are achieved and there is an approximate inverse relationship between cooking time and cooking power. In other words, it was discovered that when in excess of 4 kW is used, cooking time can be decreased by an amount proportionate to an increase in cooking power. Thus, for example, if lamp intensity is increased by 25%, the food will cook approximately 25% faster. This discovery is described in detail in Applicants' International Application Number PCT/US94/05753 which is published under International Publication Number WO 94/28692.

It was also previously understood that forming the interior walls of the food chamber from reflective materials improves uniformity of cooking. This is because the visible and infrared waves from the radiation sources impinge directly on the food item and are also reflected off the reflective surfaces and onto the food item from many angles.

It has now been further discovered that radiant powers in excess of 4 kW are not needed in many situations if the oven is provided with reflective interior walls and other surfaces which exhibit extremely high levels of reflectivity in the visible and near-visible ranges of the electromagnetic spectrum. In other words, the type of high speed cooking previously exhibited by lightwave ovens is also exhibited, without a loss in quality, even when substantially lower radiant powers are used, so long as the lightwave ovens are equipped with reflecting surfaces such as walls, facets, and lamp reflector housings that are highly reflective over the visible and near-visible light range of the electromagnetic spectrum. Further improvements in cooking efficiency may be achieved through minimization of the effects of components inside the oven which absorb radiant energy emitted by the lamps. An object of the present invention is therefore to optimize oven performance by improving oven wall reflectivity and by minimizing use of absorptive materials.

Summary of the Invention The present invention is a lightwave oven which includes an oven housing enclosing a cooking chamber. A plurality of lamps capable of emitting radiant energy having a significant portion in the visible and near-visible light range of the electromagnetic spectrum are mounted within the housing. Reflecting surfaces such as walls, facets, and/or lamp reflectors are positioned within the oven housing facing the cooking chamber. The reflecting surfaces are at least 88% reflective (and preferably at least 95% reflective) of radiant energy falling within the visible and near-visible light range of the electromagnetic spectrum. The reflecting surfaces are preferably formed on the interior walls of the oven, but the reflecting surfaces may also be reflector housings within which the lamps are housed or other components such as facets designed to reflect radiant energy towards food positioned within the cooking chamber.

Description of the Drawings

Fig. 1 is a perspective view of an oven according to the present invention. Fig. 2 is a front plan view of a first embodiment of an oven according to the present invention, in which the door has been removed for purposes of clarity.

Fig. 3 is an exploded view of an oven interior cavity of the oven of Fig. 2. Fig. 4 is a perspective view of an interior cavity of a second embodiment of an oven according to the present invention.

Fig. 5 is a cross-section view of the interior cavity of Fig. 4 taken along the plane designated 4-4 in Fig. 4.

Fig. 6 is a perspective view of an interior cavity of a third embodiment of an oven according to the present invention.

Fig. 7 is a graph showing oven efficiency as a function of wall reflectivity for a lightwave oven.

Detailed Description of the Invention

Three embodiments of ovens according to the present invention will be described. Each of the embodiments includes the features shown in Fig.l. Referring to Fig. 1, an oven 10 according to the present invention is comprised generally of an oven housing 12 and a door 14. Door 14 may be provided with a window 16 formed of heat resistant glass or pyroceramic material. •

Referring to Fig. 2, a first embodiment of an oven 10a according to the present invention includes a cooking chamber 18a, a circular grill 20a mounted within the chamber 18a, and radiant energy sources (preferably lamps 22a, 24a) mounted above and below the grill.

The energy for cooking is supplied by the upper and lower lamps 22a, 24a. The lamps are preferably quartz-halogen tungsten lamps which are capable of producing approximately between 100 W and 2 kW of radiant energy with a significant portion of the light energy in the visible and near-visible range (i.e., approximately 0.4 μm to 1.4 μm) of the spectrum. Each lamp typically operates at 3000 degrees Kelvin and converts electrical energy into black body radiation having a range of wavelengths from approximately 0.4 μm to 4.5 μm with a peak intensity at .965 μm. When illuminated, the lighted portion of a preferred lamp has a length of approximately 6-10 inches.

In the preferred embodiment, there are four upper lamps 22a and three lower lamps 24a. By appropriately selecting the lateral spacing between the lamps relative to the food, even cooking can be achieved over the entire surface. This is accomplished by rotating the food item using the rotatable grill 20a and by arranging the lamps such that during the cooking cycle all regions of the food surface receive equivalent amounts of energy from the lamps.

This desired result is most readily accomplished by positioning the lamps asymmetrically with respect to the midline of the horizontal cooking area (i.e. the midpoint between the front and back or left and right sides of the oven cavity). The asymmetrical configurations of lamps may be selectively illuminated depending on the size of the food item sought to be cooked and its ability to absorb visible light. Because different food types will be capable of absorbing different amounts of energy, a configuration of this type would be particularly helpful when, for example, a dish containing various foods is positioned on the grill for cooking. One example of the asymmetrical spacing of the lamps is shown in published International Application Serial No. PCT/US94/05753. It should be appreciated, however, that many other configurations are available and that, for example, it may be desirable to position all of the upper and/or lower lamps on one side of the midline in order to reduce the amount of absorbent pyroceramic material (see plates 52, 54 in Fig. 3) within the oven.

The oven 10a is formed of an internal housing 26a which is mounted within an external housing 28. Interior housing 26a includes bottom and top walls 30a, 31a, and side walls 32a extending between the bottom and top walls 30a, 31a. Rectangular openings 34, 35 are formed in bottom and top walls 30a, 31a, respectively.

Each side wall 32a is comprised of a substantially vertical wall portion 36 and, at the top, an angled portion 38 which extends towards the interior of the oven. In one embodiment, angled portion 38 is angled approximately 45° downwardly from the vertical plane occupied by vertical wall portion 36.

Triangular metal flaps 40 extend outwardly of the angled portions 38, such that when the interior housing 26 is fitted inside the external housing 28 the flaps 40 lie parallel to the door 14 (Fig. 1) of the oven 10a. The angled portions 38 of side walls 32a create, in combination with the top panel 31a and vertical portions 36 of side walls 32a, faceted edges for the oven interior surface. Each "facet" is comprised of three surfaces, each of which extends from its neighboring surface(s) by approximately 135°. These facets are believed to improve oven efficiency by as much as 8% by (1) decreasing the overall surface area of the oven; and (2) allowing portions of the radiant energy which would otherwise become lost through many "bounces" in the corner regions to be re-directed towards the food location with fewer bounces or, in many cases, with a single bounce. An added benefit of the facets is that they are easier to clean than cubic comers.

Many alternative oven shapes or faceting configurations may be conceived which direct reflected light towards the food location. For example, all corners and edges within the oven may be beveled, or the oven may have a spherical or cylindrical shape or many small facets formed into the oven walls. Referring to Fig. 3, a back wall 42a of the oven chamber extends vertically from the bottom Wall 30a to the top wall 31a of the chamber.

An upper reflector housing 44, and a lower reflector housing 46 are each mounted within the oven. Each has an inward-facing side which is formed of Alanod aluminum having a mirrored surface and having a reflectivity of at least approximately 88-90%. Upper reflector housing 44 is positioned such that its inward facing side is positioned to face downwardly above opening 35 at the top of the interior housing 26a, while lower reflector housing 46 is positioned such that its interior facing side faces upwardly through opening 34 in bottom wall 30a.

Vents 48 are formed in front and rear sides of the reflector housings 44, 46 to permit the escape of heated air, which is subsequently pulled out of the oven via an exhaust tube (not shown).

The laterally positioned sides of reflector housings 44, 46 include slots 50 through which the ends of the lamps 22a, 24a extend. The lamps 22a, 24a are mounted within the oven to receive power in a conventional manner.

Two radiation transparent plates 52 and 54 are mounted inside the oven. These plates isolate the cooking chamber from the radiant lamps, making the oven easier to clean. These plates can be formed from materials, such as high quality heat-resistant glasses and pyroceramic materials, that are transparent to visible, non-visible and infrared radiations.

The upper transparent plate 52 is positioned below the upper lamps 22a such that it covers opening 35 at the top of the interior housing 26a and, in effect, closes the lamps 22a within the reflector housing 44. The lower transparent plate 54 is positioned above lower lamps 24a such that it covers opening 34 in bottom wall 30a and, in effect, closes the lamps 24a within the reflector housing 46.

Because the pyroceramic material absorbs radiation emitted by the lamps and reflected from within the oven, it is desirable to minimize the total area of pyroceramic material in order to maximize the oven's efficiency. Minimizing the area of pyroceramic material maximizes the area of reflective surfaces that can be made in the oven, and thereby enables a greater portion of the radiation to reflect off of the more highly reflective reflector and wall material rather than being absorbed by the pyroceramic plates. As described above, positioning the lamps towards one side (or towards the front or back) of the oven, rather than arranging the lamps across the entire top or bottom of the oven, helps to minimize the amount of absorptive pyroceramic material in the oven. Positioning the lamps individually behind individual, and thus narrower, pyroceramic plates, can also help to minimize the amount of pyroceramic material in the oven. Less absorptive window materials may also be used to improve the efficiency of the oven. Each pyroceramic plate is approximately 10.5 inches x 13.8 inches in size (the upper and lower walls 210, 21 1 are approximately 18 inches square).

The interior surfaces of the interior housing 26 preferably have highly reflective surfaces. Walls 30a, 31a, 32a 42a, and the door 12a preferably have inner surfaces of a highly reflective material, such as highly polished (mirrored) Alanod aluminum, which is at least approximately 88-90% reflective over the portion of the electromagnetic spectrum in which the lamps emit radiation (approximately .4 μm to 4.5 μm).

In the shown embodiment of the present invention, interior housing 26 has a vertical interior height of 7.38 inches (i.e. measuring from the top panel 31a to the bottom wall 30a). The height of vertical wall portion 36 is 5.25 inches and angled portion 38 is approximately 3 inches from the top of vertical portion 36 to its upper edge.

The circular grill 20a (Fig. 2) is comprised of a grid of small diameter metallic bars. A mechanism for rotating the grill 20s may be of the type shown and described in published International Application Serial No. PCT US95/05784.

The oven of the first embodiment exhibits a cooking efficiency of approximately 25 - 30%. An interior cavity 26b of a second embodiment of an oven 10b according to the present invention is shown in Fig. 4. The interior cavity 26b is bounded by side walls 32b, a rear wall 42b, bottom and top walls 30b, 31b and the door (see door 14 Fig. 1). The oven interior cavity is approximately 15.5 inches wide (between side walls 32b), 10.5 inches high (between top and bottom walls 31b, 30b), and 14 inches deep (between door 14 and rear wall 42b). A grill (not shown but see grill 20c in Fig. 6) is positioned within the cooking chamber 18b.

Upper and lower lamps 22b, 24b extend from the upper and lower corners, respectively, of side walls 32b. There are preferably four upper lamps and four lower lamps, all of which are oriented towards the center of the oven cavity. The lamps are preferably 250 W quartz-halogen lamps. During a typical cooking operation, the lamps are operated to emit approximately 1500 - 1850 W of radiant power into the oven.

The oven walls 30b, 31b, 34b, 42b are lined with Everbright 95, a highly polished specular (i.e., mirrorlike) silver which is coated with a plastic film to prevent tarnishing. Everbright 95 is commercially available from Alcoa, Inc. The interior surface of the door 14 is preferably also lined with the same material. The lamps may additionally be positioned within reflectors of the type described with respect to the first embodiment and/or facets of the type shown in Fig. 2. Such facets and/or reflectors may also be made from Everbright 95 or a similarly reflective material.

This material is approximately 95 % reflective over the visible and near visible light range of the electromagnetic spectrum. In other words, 95 % of the radiant energy within the range of 0.4 - 1.4 μm which strikes the reflecting surface at a given moment reflects off of that surface, while the remaining 5 % of the radiant energy within that range is absorbed by the reflecting surface. This material is further beneficial in that has increased reflectivity (approximately 97 - 98%) at wavelengths of up to approximately 2 μm and so it is highly reflective of radiant energy falling within the infra-red region of the electromagnetic spectrum, as well. The oven of the second embodiment, when operated at 110V, 15 A, exhibits a cooking efficiency of approximately 48 %.

An interior housing 26c of a third embodiment of an oven 10c according to the present invention is shown in Fig. 6.

Like the previously described interior housings, the interior housing 26c includes walls 30c, 31c, 32c and 42c and a door (see door 14 in Fig. 1). The oven cavity is approximately 10 inches wide

(between side walls 32c), 14 inches high (between top and bottom walls 31c, 30c), and 13 inches deep (between the door 14 and rear wall 42c). A grill 20c is positioned within the cooking chamber 18c.

Upper and lower lamps 22c, 24c extend from diagonally opposing upper and lower corners, respectively, of side walls 32c. There are preferably two upper lamps and two lower lamps, all of which are oriented towards the center of the oven cavity in a manner similar to that shown in Fig. 5 with respect to the second embodiment. The lamps are preferably 500 W quartz-halogen lamps. During a typical cooking operation, the lamps are operated to emit approximately 1500 - 1850 W of radiant power into the oven.

The oven walls and the door are formed of 0.6 inch thick Spectralon, a PTFE polymer which is commercially available from Lab Sphere, Inc.. Spectralon in this thickness is a highly diffuse (rather than specular) material which is approximately 98% reflective over the visible and near visible ranges of the electromagnetic spectrum.

The oven of the third embodiment, when operated at 110V, 15 A, exhibits a cooking efficiency of approximately 60 %. Fig. 7 is a graph showing oven efficiency as a function of wall reflectivity for a lightwave oven.

The calculations were made based on two identical reflectivity tests performed on a 7.5 inch diameter, 1.5 inch high Pyrex dish filled with water. The absorptivity of the dish of water was approximately .7 (i.e., it was approximately 70 % absorptive of radiant energy striking it). The dish was positioned approximately 2 inches below the center of the oven.

The plots of the two tests are shown superimposed on one another, with one plot shown in solid lines and the other in dashed lines. This graph illustrates the differences in cooking efficiency which are exhibited when foods of identical thicknesses and absoφtivity are cooked in lightwave ovens which have identical dimensions and components but which differ only in the reflectivity of their wall materials. As can been seen, for reflectivities below approximately 88%, cooking efficiency increases gradually with reflectivity. However, when wall materials having reflectivities above 88% are used, the slope of the curve increases significantally, indicating significant increases in oven efficiency. The present invention is described in relation to three embodiments but is limited only in terms of the language of the appended claims. For example, other highly reflective wall materials may be substituted for the various reflective surface materials described, and forms of reflecting surfaces in addition to the facets, lamp reflectors, and walls described herein may also be used without deviating from the scope of the present invention.

Claims

We claim:

I. A lightwave oven comprising: an oven housing enclosing a cooking chamber; a plurality of radiant energy sources mounted within the oven, the radiant energy sources for emitting radiant energy having a significant portion in the visible and near-visible light range of the electromagnetic spectrum; and reflecting surfaces within the oven housing and facing the cooking chamber, wherein the reflecting surfaces are at least 88% reflective of radiant energy falling within the visible and near-visible light range of the electromagnetic spectrum.

2. The lightwave oven of claim 1 wherein the reflecting surfaces are formed of a diffuse material.

3. The lightwave oven of claim 1 wherein the reflecting surfaces are formed of a specular material.

4. The lightwave oven of claim 1 wherein the reflecting surfaces are at least 95% reflective of radiant energy falling within the visible and near-visible light range of the electromagnetic spectrum.

5. The lightwave oven of claim 1 wherein the oven housing includes walls and wherein the reflecting surfaces include the housing walls.

6. The lightwave oven of claim 1 wherein the radiant energy sources include lamps mounted within reflector housings and wherein the reflecting surfaces include the reflector housings.

7. The lightwave oven of claim 1 wherein the oven housing includes a plurality of corners, and wherein the radiant energy sources include lamps positioned at at least a portion of the comers.

8. The lightwave oven of claim 7 wherein the lamps are oriented diagonally to direct radiant energy towards a center region of the oven.

9. A method of cooking food comprising the steps of: (a) providing an oven having an oven interior and reflecting surfaces facing the oven interior;

(b) positioning a food item in the oven interior;

(c) generating radiant energy having a significant portion in the visible and near-visible light range of the electromagnetic spectrum;

(d) impinging at least a first portion of said radiant energy onto the food item; and (e) reflecting at least a second portion of said radiant energy from the reflecting surfaces such that at least 88% of the radiant energy which has a significant portion in the visible and near-visible light range of the electromagnetic spectrum and which strikes the reflecting surfaces is reflected by said surfaces.

10. The lightwave oven of claim 9 wherein step (a) includes the step of providing an oven having reflecting surfaces which are formed of a diffuse material.

I I . The lightwave oven of claim 10 wherein step (a) includes the step of providing an oven having reflecting surfaces which are formed of a specular material. 12. The lightwave oven of claim 1 1 wherein step (e) includes τeflfefcfirtg**at leasf a secβnH'portioji of said radiant energy from the reflecting surfaces such that at least 95% of the radiant energy which has a significant portion in the visible and near-visible light range of the electromagnetic spectmm and which strikes the reflecting surfaces is reflected by said surfaces.