MXPA01010638A - Multi-shelved convection microwave oven - Google Patents

Abstract

An oven, is provided that includes multiple heat transfer means, including convection and microwave heat transfer means. The oven includes a cooking chamber, a blower and at least a shelf disposed within the cooking chamber. The shelf is designed to act as a food support as well as a conduit through which heated air passes into the cooking chamber. The microwave heating means comprises a microwave source and wave guide through which microwaves travel. The wave guide includes a plurality of openings through which microwaves can pass into said cooking chamber. In the preferred embodiment, the openings in the wave guide are positioned to correspond with the predetermined minima or maxima for the microwave wavelength propagating within the wave guide. An electric heating element may also be disposed within the cooking chamber to provide an alternative heating source.

Description

CONVECTION MICROWAVE OVEN WITH MULTIPLE SHELVES FIELD OF THE INVENTION The present invention relates to a multiple rack oven having multiple heating means, including convection, microwave and radiation food heating means.

BACKGROUND OF THE INVENTION The furnace described herein primarily relates to ovens suitable for use in the commercial food service industry such as fast food restaurants, and other food service applications where there is a wide variety in prepared food products, the need for quickly heat food, and space restrictions. Although various furnace designs are known and available for commercial food service applications, there is still a need for an efficient and effective furnace that allows different foodstuffs that require different heat treatment to be cooked simultaneously. So far, single-cavity ovens have been designed which include convection and microwave heat transfer cooking means. Although such furnaces meet the needs of certain commercial food service applications providing rapid cooking and heating, the inability to cook different foods simultaneously with different heating conditions and cooking cycles does not provide the necessary flexibility. In addition, known combination ovens often require mechanical means to stir the microwaves or to move the food product to achieve uniform transfer of heat by microwaves to the food product. The present invention provides an oven that meets a need in the food service industry, since the oven provides fast cooking / heating and the possibility of simultaneously cooking multiple food products under different cooking conditions and cycles. In addition, the ovens of the present invention provide microwave heating means that do not require mechanical stirring of the microwaves or movement of the food products to achieve a substantially uniform distribution of the energy of the microwaves in the cooking cavities of the oven.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a novel food heat treatment system that combines multiple heating means in a single system.

In one aspect of the invention, an oven including a cooking chamber, a fan and a shelf disposed within the cooking chamber is provided. The shelf has a unique design because it has an inlet opening and cavity in fluid communication with the fan, and at least one opening in fluid communication with the cooking chamber through which controlled temperature air can flow into the chamber. cooking chamber for cooking food by convection heating. In an aspect of the invention, the furnace further comprises a microwave heating source for heating food products within said cooking chamber, thereby providing multiple heating methods (convection and microwave). In one aspect of the invention, the microwave heating means includes a microwave source and waveguide through which the microwaves travel. The waveguide includes a plurality of openings through which the microwaves can pass in said cooking chamber. In a preferred aspect of the invention, the openings in the waveguide are positioned to correspond to the predetermined minimum or maximums for the wavelength of the microwaves propagating within the waveguide. That is, the separation of the waveguide openings occurs at multiple of predetermined minimum and / or maximums for the microwaves within the guide generated by the microwave source, most commonly a magnetron.

In one aspect of the invention, a heating element can be mounted within the cooking chamber, providing additional heating means. In a preferred embodiment, a movable reflector stirrer is positioned above the heating element to reflect heat from the heating element to a food product. In another aspect of the invention, the shelf includes a plurality of vents that exit from the top surface of the shelf to hold a food container, thereby allowing air to flow freely beneath the container or the food product. The vents have openings directing temperature controlled air in a direction substantially parallel to the top of the shelf. In a preferred embodiment of the invention, the cooking chamber comprises a first cooking cavity and a second cooking cavity, and includes a first shelf and a second shelf. The first shelf has an inlet opening and cavity in fluid communication with a fan, and the second shelf has an inlet opening and cavity in fluid communication with a fan. In addition, the first and second shelves have at least one opening in fluid communication with the first cooking cavity and second shelf having at least one opening in fluid communication with said second cooking cavity, respectively.

In a preferred aspect of this embodiment, microwave heating is provided in the first and second cavities through waveguides, preferably a pair of waveguides associated with each cavity. The preferred waveguide arrangement again provides a waveguide having predetermined minima and maxima, and openings in the waveguide positioned to correspond substantially to the minimum or maximum, thereby providing an efficient and uniform distribution of the waveguide. microwave energy in the cooking cavities along the length of the waveguide. In still another aspect of the invention, the fan that supplies controlled temperature air to the cooking chamber has a discharge opening in its housing through which a portion of the controlled temperature air is discharged from the system. In this arrangement, the furnace further includes an opening for ambient air inlet in fluid communication with the fan, whereby the fan draws air through the inlet opening to replace the discharged air.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of the furnace (configuration of three cavities); Figure 2 is a front view of the interior cooking chamber of the oven (configuration of three cavities); Figure 3 is a front perspective view of the interior cooking chamber and portions of the microwave heat transfer and convection heat transfer systems of the oven (configuration of three cavities); Figure 4 is a front perspective view of the interior cooking chamber and portions of the microwave heat transfer and convection heat transfer systems of the oven (three-cavity configuration); Figure 5 is a front perspective view of the interior cooking chamber and portions of the convection heat transfer system of the oven (three cavity configuration), including the shelf for food products; Figure 6 is a view of the interior cooking chamber showing the electric heating element inside the cooking chamber; Figure 7 is a left side view of the oven, where the left panel of the outer cabinet has been removed to show portions of the convection heating system of the oven (three cavity configuration); Figure 8 is a perspective view of the food shelf that functions as a conduit through which controlled temperature air flows into the oven's cooking chamber; Figure 9A is a perspective view of an alternative embodiment of the shelf; Figure 9B is a cross-sectional view of the alternative embodiment of the shelf shown in Figure 9A; Figure 10 is a perspective view of a grid for product support; Figure 11 is a perspective view of one embodiment of an air supply duct for the convection heat transfer system of the furnace; Figure 12 is a perspective view of a modality "preferred alternative of an air supply duct for the convection heat transfer system of the oven;" Figure 13A is a front view of a filter assembly for filtering the air exiting the cooking chamber; a side view of the filter assembly of Figure 13A; Figure 13C is a schematic representation of the accordion folded filter plate of the filter assembly of Figure 13A; Figure 14 is a side view of a bracket that holds the assembly of filter of figure 13A on the side wall of the interior cooking chamber of the oven; Figure 15 is a schematic representation of a control system for the furnace of the present invention (three cavity configuration); Figure 16 is a perspective view of a configuration of two cavities of the oven; Figure 17 is a partial perspective view of the internal cooking chamber and microwave heating system of the oven (two-cavity configuration); Figure 18 is a perspective view of the microwave heating system of the oven (two-cavity configuration); Figure 19 is a partial perspective view of the oven cooking and configuration chamber with partial discharge of controlled temperature air stream; Figure 20 is a partial perspective view of the ambient air inlet and separation chamber aspects of a preferred embodiment of the two cavity configuration of the oven; and Figure 21 is a perspective view of the reflector stirrer of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The description of the invention provided below is made in relation to the drawings appended thereto. The drawings have been numbered consecutively as Figures 1 to 23. In Figure 1, an embodiment of the furnace 10 of the present invention is shown. The furnace 10 includes an outer cabinet 12 defined by exterior side walls, exterior bottom and top walls and an exterior rear wall. Preferably, said walls are constructed of a stainless steel material. Secured in front of the oven is the door 14 that allows food products to be placed inside and outside the oven. A handle 16 with locking means is secured to the door 14 to allow the door to be secured in a closed position during cooking. The door 14 is designed by known conventional means to prevent microwave leakage of the chamber 18 while the door is closed. With reference to Figures 2-4, 16-17 and 19, the chamber 18 is defined by interior side walls 19 and 21, rear wall 23, upper wall 25 and lower wall 27 (referred to together as the inner walls of the chamber from the oven). Preferably, said interior walls of the furnace chamber are constructed of a stainless steel material. As shown in Figures 1 and 5 (three-cavity oven) and Figures 16-17 and 19 (two-cavity oven), the chamber 18 further comprises a plurality of cooking cavities 18a. In relation to the three-cavity oven of FIGS. 1 to 5, arranged inside the chamber 18 of the oven are upper shelf 20, intermediate shelf 22 and lower shelf 24, preferably constructed of a stainless steel material. The shelves 20 and 22 are mounted movably inside the chamber 18 of the oven, and are located on top of brackets to keep the shelves in position. The lower shelf 24 can rest on the bottom of the oven chamber or, if desired, can also rest on a shelf. Said brackets are generally shown by reference numeral 30, and are secured to the inner side walls of the furnace cavity on opposite sides of the walls of the cavity. By providing removable shelves, they can be cleaned more easily. With reference to figures 2, 5 and 8, the shelves 20, 22 and 24 will be described in greater detail. Each shelf is designed not only to support a food product, but is also designed as a conduit through which gas (preferably air) of controlled temperature (eg, heated) passes and provides convection heating to food products within each cavity 18a of the oven. As shown in the figures referred to above, each shelf has an upper portion 31, a lower portion 32, side portions 34 and 36, rear portion 38 and front portion 40, which define the cavity 41 of the shelf. The front portion 40 is disposed within the furnace chamber, adjacent to the side wall 19 of the interior chamber of the furnace. In addition, the front wall 40 of each shelf has openings 42 and 44 through which controlled temperature air can pass in the cavity 41 of the shelf. After the controlled temperature air is disposed in the shelf cavity, the air then passes through the openings 52 in ventilation grilles 50, which project from the upper portion 31 of each shelf. Vent grilles 50 are located in separate areas and allow air to exit through openings in the ventilation grilles in a direction substantially parallel to the upper portion of the shelf, at least as it initially comes out of a ventilation grille 50. The openings in the vents 50 are best seen in Figures 5 and 8, and are represented by the reference numeral 52. When controlled temperature gases leave the openings 52 in the oven cavity, the food products arranged within the cavity of the furnace are heated by heat transfer by convection. An advantage of openings with vents projecting from the shelf is that when a tray or other food container is placed on the shelf, the heated air travels freely under the tray and between the vents, providing a Very effective convection heat transfer. In an alternative mode of shelf design, the vents are inverted and do not project from the top of the shelf, but rather project into the shelf cavity. In this configuration, the ventilation grilles function as paddles within the shelf cavity. Although this configuration does not allow air to flow freely under a food tray disposed over the openings, a wire rack 900 (FIG. 10) may be placed on the shelf to raise the food container (or food) from the surface top of the shelf, thereby providing a satisfactory convective heat transfer. In yet another alternative embodiment of the shelf shown in Figures 9A and 9B, the top surface of the shelf 31a has vertically extending projections 50a, depressed areas or surfaces 46 and openings 48 disposed in the depressed areas. The arrows shown in Figure 9B generally outline the direction of the air traveling in the cavity 41a of the shelf and through the openings 48. Like the ventilation grid configuration (not inverted) described above, an advantage of the shelf design represented in Figures 9A and 9B, is that when a tray or other food container is placed on the shelf, the heated air travels freely under the tray and between the ventilation grilles, providing a more effective convection heat transfer. Controlled temperature air is supplied on each shelf by fan assemblies 60 (figure 4). As shown in Figure 4, each fan assembly 60 comprises a fan housing 64, a fan wheel 66 and an arrow 68 operably connected to a motor which rotates each fan wheel. In the preferred embodiment of the invention, each fan wheel is rotated by a single axis 68 which is operably connected to motorized means. It has been found that a one-tenth horsepower engine is suitable. It has also been found that a fan wheel of the forward inclined type is suitable. The air is extracted in the fan housing, and is arranged in tapered (conical) ducts 62 which, as shown, are disposed between the side wall of the cabinet and the side wall 19 of the furnace chamber. In Figure 4, specific reference numbers are provided only with respect to the tapered conduit which is in fluid communication with the lower shelf. However, the characteristics of the lower fan and duct assemblies are essentially identical to the upper and intermediate duct and fan assemblies, and therefore the descriptions for the latter are not repeated. As shown in Figure 4, each tapered conduit has a proximal end 162 and a distal end 168. An entry opening is provided at the proximal end, where the temperature controlled gas from the fan 60 enters the conduit (i.e. the inlet opening 164 is in fluid communication with the fan assembly associated with the conduit). In addition, each tapered conduit 62 has an elongated opening 70 in the bottom wall facing inwardly, and also a plurality of holes 72. As shown in this embodiment, the holes 72 and the elongate openings 70 are formed in the side wall 19. of the chamber 18 of the furnace (Figure 12), the rest of the duct 62 being formed by two tapered side walls and an upper wall. Controlled temperature gases entering each conduit 62 exit through openings 72 in the respective cavities of the furnace to heat the food product contained within said cavities. Further, as shown, a portion of the air entering each conduit 62 also exits through the opening 70 and flows respectively into the cavities 18a of the shelves 20, 22 and 24. In other words, each tapered conduit feeds a separate shelf (20, 22, 24), and also feeds controlled temperature air through holes 72 above each shelf (20, 22, 24). Accordingly, as described above, heat transfer by convection is achieved by the present furnace design through holes located in the side wall of the furnace cavity above each shelf, and also through the shelves themselves to through the ventilation grilles arranged on the upper portion of each shelf. In an alternative arrangement, the furnace would not include holes 72 and, therefore, all heated gas would flow from the conduits 62 in the shelf associated with the conduit. Referring to Figures 4 to 7, openings 90 for return of air are provided in the side wall 19 within each cooking cavity 18a for the return of gas from each cooking cavity to the fans 60. By providing return passages of air inside each cavity 18a, each cavity can function as a separate convection oven, thus allowing the cooking of different foods at different temperatures and in different cycles. In an alternative embodiment of the invention (Figures 13 AC and 14), the air return openings 90 can be covered by a filter assembly 300 mounted to the side wall 19 by a bracket 302 or other known means to prevent particles from food, grease and other materials escape from the cooking cavity through the return openings. A preferred filter assembly 300 is shown in FIGS. 13 AC and 14, and comprises a filter frame 304 that holds a perforated metal plate 306 that is folded into an accordion shape, thereby providing a greater surface area on the which the return air passes before leaving the cooking chamber through the return openings. The temperature of the air or gas circulated can be controlled by any known means. A suitable means for heating and controlling the air temperature is by the well known electric heating rods 80 (i.e., Calrod) (Figure 7) or a "gas burner" (not shown). The heating rods 80 can be arranged in any suitable position. In the preferred embodiment, the heating rods are placed as shown in Figure 7, in the return air path for the furnace. Figure 7 shows only a heating rod placed between the upper and intermediate conduits 62 in the area between the side wall of the outer cabinet and the side wall 19 of the cavity. Preferably, a heating element is located upstream of each conduit 62 through openings 82, as shown in Figure 7. • Regarding the tapered conduit design, conduit 62 can have a constant taper from the end proximal 162 to distal end 168 as shown in Figures 3-5 and 7, or may have multiple degrees of tapering as shown by dashed lines in Figure 11. As shown in Figure 11 and denoted by the crossed interrupted lines, conduit 62 may have a The double taper configuration, which has been found to provide uniform air flow from the orifices along the length of the conduit. More particularly, in the configuration of the double taper of the duct 62, said duct has a first horizontal tapered portion 160 adjacent the proximal end 162 and inlet opening 164 (i.e. where the fan air enters the duct), and a second horizontal tapered portion 166 adjacent the distal end 168. As shown, the first horizontal tapered portion 160 has a greater taper angle than the second horizontal tapered portion 166 having a lower slope. Preferably, the first horizontal tapered portion 160 extends approximately one quarter to one half the length of the conduit. The degree of taper in the first and second horizontal tapered portions may vary. Preferably, the first horizontal tapering portion decreases 2.54 cm for each 2.54 cm to 7.62 cm in length, and the second horizontal tapering portion decreases 2.54 cm for each 17.78 cm to 40.64 cm in length. By providing a double taper, it has been found that air is distributed more evenly along the length of the conduit from the proximal end 162 to the distal end 168. In a more preferred embodiment of the conduit 62 shown in Figure 12, said conduit does not it only includes the double taper horizontally along its length as described above, but also includes a vertically tapered portion 170 adjacent the proximal end 162 to further improve the air flow in the conduit and the even distribution of heated air in the conduit. oven chamber along the length of the duct. After the controlled temperature air enters the oven cavity 18a through the holes (optionally) described above and the shelves, the air is returned to the fan housing through the return openings 90 in the side wall 19 of the furnace cavity (ie, the wall of the cavity adjacent to each conduit 62 (see Figures 2-5). The air returning through the openings 90 is heated by the heating element 80 before it enters. to the fan housing, wherein the heated air is again circulated in the oven cavity through the conduits 62. Optionally, an electrical heating element 101 (eg, Calrod heating elements), can also be arranged adjacent to the upper part of the oven cavity to provide means for roasting food products disposed on the upper shelf (see figures 1, 2 and 6). in means for heating food products by means of microwave energy. In one embodiment of the invention shown in Figures 2 and 3, microwaves are disposed in the oven cavity through microwave openings 200 formed in the side wall 21 of the oven cavity. The side wall 21 is disposed opposite the side wall 19 of the oven cavity. As shown in the preferred embodiment, there are three series of openings 200, each being assisted by a separate magnetron assembly 210. The type (ie, energy) of magnetron used is a matter of choice, and is based on selection factors well known It was found that the use of 2450 MHz magnetrons is adequate in the embodiment shown in Figures 16 to 18. In the embodiment shown in Figures 2 and 3, each magnetron 210 feeds microwaves into and through a conduit 212 associated with the assembly. of the particular magnetron and through the openings 200 and in the furnace cavity. The openings 200 and the structure 202 of the duct are arranged so that a more uniform supply of microwaves is provided within the oven cavity. A preferred configuration for the openings 200 is shown in the figures. Other configurations can also be determined, and these will vary according to the design and dimensions of the cooking cavity. As shown in the figures, each cavity 18a has its own independent microwave source (ie, magnetron assemblies). In this way, heating of food products arranged in different cavities at different rates and in different cycles can be provided, separately controlling each magnetron.

A schematic representation of the heating controls for the embodiment of Figures 1 to 5, is shown in Figure 15. In a preferred embodiment of the invention shown in Figures 16 to 20 (two-cavity design), power is supplied magnetron microwave 410 in each oven cavity 18a through a pair of waveguides 400, 402 (ie, ducts) disposed above each cavity. In this way, each cavity 18a has its own independent microwave source. Each waveguide includes a plurality of openings 404, preferably slots, through which the microwaves travel in the cooking cavity. The slots 404 are spaced apart to provide a substantially uniform distribution of the microwaves along the length of the waveguide. Specifically, the slots are spaced approximately at multiples of the minimum or maximum calculated for the microwaves generated by the microwave source, i.e., the magnetron. The minima and maxima for a particular magnetron and waveguide are calculated by known means. Microwave minimums and maximums for various microwave wave and waveguide designs can also be easily determined by referring to tables published by magnetron suppliers such as Continental Microwave & Tool Co., Inc., Hampton, New Hampshire. As shown, the slots 404 are preferably arranged at angles relative to the length of waveguides that run generally back and forth from each cavity. In addition, as shown in Figures 17 and 18, fan assemblies 500 are preferably provided to cool the magnetrons 410 during operation. In a preferred embodiment of the invention, alternative reflector shakers 600 are disposed above the heating elements in the upper part of the heating chamber 18 to reflect heat from the heating element towards the lower part of the shelf. Preferably, the agitators are made of a material that also reflects the microwaves, so that improved agitation of the microwaves is achieved, thereby promoting uniformity of cooking. A suitable material of the agitator is stainless steel. As shown, the reflecting agitator 600 is operably connected to the support 602 which is moved by the link 604, which in turn is connected to a transmission link 606 driven by the motor 608. In the embodiment of the invention shown in FIG. 16 to 20, it should be noted that the chamber 18 comprises two cooking cavities 18a, and that two doors 700 are used to seal the oven. Another feature of one embodiment of the invention provides for the discharge of a portion of the controlled temperature cooking air from the fan housing. Referring to Figures 17 to 19, a discharge opening 702 is shown in the fan housing 64 through which a portion of the controlled temperature gas is discharged from the furnace by means of chimneys (or ducts) 704. The air discharge of the system causes ambient air to be extracted through the inlet opening 706 disposed at the rear of the furnace. Ambient air is then removed in separation chamber 708 disposed between the upper and lower cavities 18a. The air from the separation chamber 708 is then removed through the openings 710 towards the upper and lower fan assemblies 60, which are in fluid communication with the separation chamber. The discharge air flow and the ambient air flow in the system are shown by arrows in Figures 19 and 20. The location of the separation chamber between the oven cavities is particularly advantageous, since the heat of Cooking cavities heat the air in the separation chamber, thus functioning as a heat exchanger to preheat the ambient air. Figures 11 and 16 generally show the control panel (or controller) 450 for the embodiments described herein. Preferably, the controller 450 has the ability to control the microwave heating energy and the cooking cycle times, and is capable of being programmed for particular food cooking applications. Also, it is also preferable that the controller 450 controls the convective heat transfer aspects of the invention (e.g., fans 60 and heating elements) and the reflector agitators described above.

The present invention is not limited to the examples illustrated above, and it is understood that one skilled in the art would be able to use substituents and equivalents without departing from the present invention.

Claims (25)

NOVELTY OF THE INVENTION CLAIMS •

1. A furnace, characterized in that it comprises: a cooking chamber; a fan; at least one shelf disposed within said cooking chamber, said shelf (at least one) having an inlet opening and cavity in fluid communication with said fan, said shelf having at least one opening in fluid communication with

Said cooking chamber through which controlled temperature gases can flow in said cooking chamber; and at least one opening for return of air in said chamber in fluid communication with the fan to return said controlled temperature gases to said fan. 2. The oven according to claim 1, characterized 15 furthermore because it comprises a microwave heating source for heating food products within said cooking chamber.

3. The oven according to claim 1, further characterized in that it comprises a microwave source and waveguide through which said microwaves travel, said waveguide having a 20 plurality of openings through which said microwaves can pass in said cooking chamber.

4. The furnace according to claim 3, further characterized in that said microwaves traveling in said waveguide have a predetermined minimum and maximum wavelength and maximums, said openings in said waveguide being positioned to correspond substantially with said minimums. or maximums.

5. The furnace according to claim 1, further characterized in that it comprises a heating element inside said chamber.

6. The oven according to claim 5, further characterized in that it comprises a movable stirrer located above said heating element, said stirrer being able to reflect heat from said heating element to said shelf (at least one).

7. The oven according to claim 6, further characterized in that said stirrer is constructed of a microwave reflector material.

8. The oven according to claim 1, further characterized in that said shelf (at least one) has an upper surface and a plurality of ventilation grilles emerging from said upper surface to hold a food container above said surface higher.

9. The furnace according to claim 8, further characterized in that said opening (at least one) in said shelf (at least one) is configured to project said temperature-controlled gases in a direction that is substantially parallel to said upper surface of said shelf.

10. The oven according to claim 1, further characterized in that said cooking chamber comprises a first cooking cavity and a second cooking cavity, and said shelf (at least one) comprises a first shelf and a second shelf, said first shelf having an inlet opening and cavity in fluid communication with a fan, and said second shelf having an inlet opening and cavity in fluid communication with a fan, said first shelf having at least one opening in fluid communication with said first cooking cavity, and said second shelf having at least one opening in fluid communication with said second cooking cavity.

11. The oven according to claim 10, further characterized in that it comprises a first microwave heating source for heating food products inside said first cooking cavity, and a second microwave heating source for heating food products within said oven. second cooking cavity.

12. The oven according to claim 10, further characterized in that it comprises: a first microwave source and a first waveguide through which the microwaves travel, said first waveguide having a plurality of openings through which said microwaves can pass in said first cooking cavity; and a second microwave source and a second waveguide through which the microwaves travel, said second waveguide having a plurality of openings through which said microwaves can pass in said second cooking cavity.

13. The furnace according to claim 12, further characterized in that it comprises: a third microwave source and a third waveguide through which the microbrowns travel, said third waveguide having a plurality of openings through which said microwaves can pass in said first cooking cavity; and a fourth microwave source and a fourth waveguide through which the microwaves travel, said fourth waveguide having a plurality of openings through which said microwaves can pass in said second cooking cavity.

14. The furnace according to claim 12, further characterized in that said microwaves traveling in said first waveguide have a predetermined minimum and maximum wavelength and maximums, said openings in said first waveguide being positioned to correspond substantially with minimum or maximum sayings; and said microwaves traveling in said second waveguide having a predetermined minimum and maximum wavelength and maximums, said openings in said second waveguide being positioned to correspond substantially with said minimum or maximum.

15. - The furnace according to claim 13, further characterized in that said microwaves traveling in said first waveguide fc have a wavelength and predetermined minima and maxima, said openings in said first waveguide being positioned to correspond substantially with minimum or maximum sayings; said microwaves traveling in said second waveguide having a predetermined wavelength and minimums and maximums, said openings in said second waveguide being positioned to substantially correspond to said minimums or maximums; said microwaves that 10 travels in said third waveguide have a predetermined minimum and maximum wavelength and maximums, said openings in said third waveguide being positioned to substantially correspond to said minimum or maximum; and said microwaves traveling in said fourth waveguide having a wavelength and predetermined minima and maxima, said 15 openings in said fourth waveguide being positioned to substantially correspond to said minimum or maximum.

16. The furnace according to claim 10, further characterized in that it comprises at least one opening for return of air in said first cooking chamber in fluid communication 20 with a fan for returning said controlled temperature gases to said fan, and at least one opening for return of air in said second cavity in fluid communication with a fan to return said controlled temperature gases to said fan.

17. - The furnace according to claim 1, further characterized in that said fan comprises a fan housing having a discharge opening through which a portion of said controlled temperature air is discharged from said fan housing, said furnace comprising further an opening for ambient air inlet in fluid communication with a second chamber disposed between said first and second cooking cavities, said second chamber being in fluid communication with said fan, wherein said fan extracts air from said second chamber.

18. A thermal treatment apparatus, characterized in that it comprises: a thermal treatment chamber; a fan in fluid communication with said chamber for circulating temperature controlled air in said chamber; a shelf disposed within said chamber, said shelf comprising: an upper portion having an upper surface facing upwards; said upper portion having a plurality of openings through which air that is circulated by said fan can pass; and a cavity below said upper portion through which air that is circulated by said fan can pass.

19. The heat treatment apparatus according to claim 18, further characterized in that it comprises a microwave heating source for heating food products within said chamber.

20. - The heat treatment apparatus according to claim 18, further characterized in that it comprises a microwave source and waveguide through which said microwaves travel, said waveguide having a plurality of openings through which said microwaves they can pass in said cooking chamber.

21. The heat treatment apparatus according to claim 20, further characterized in that said microwaves traveling in said waveguide have a predetermined minimum and maximum wavelength and maximums, said openings in said waveguide being located to substantially correspond with said minimums or maximums.

22. The heat treatment apparatus according to claim 18, further characterized in that said openings are in the form of ventilation grilles emerging from said upper surface to hold a food container.

23. The oven, further characterized in that it comprises: a cooking cavity defined by a door and a plurality of walls; said cooking cavity having a length, width and height; a first microwave source to produce microwaves; a first waveguide having a length that traverses said length or said width of said cooking cavity; said first waveguide providing a conduit through which said microwaves travel; said first waveguide having a plurality of grooves along the center line of its length through which said microwaves can pass in said cooking cavity.

24. - The oven according to claim 23, further characterized in that it comprises: a second microwave source and a second waveguide through which the microwaves travel, said second waveguide having a length that traverses said length or said width of said cooking cavity; said second waveguide providing a conduit through which the microwaves of said second microwave source travel; said second waveguide having a plurality of openings along its length through which said microwaves can pass in said cooking cavity.

25. The oven according to claim 24, further comprising a fan that circulates heated air in said cooking cavity. -? ua - ^ ..-: »,.; " or*. ge * f-: JMBiaS &., -....