Tunnel oven for microwave heating and cooking foods

The tunnel oven comprises an elongated enclosure connected to an inlet closure and an outlet closure and traversed by a conveyor transporting the food to be cooked. The enclosure is delimited by a wall forming a floor, a wall forming a ceiling, and two side walls of which one is provided with a door giving access to the interior of the enclosure. The enclosure is divided into several successive cooking chambers separated from each other in the upper portion of the latter, each chamber being associated with several different heaters, including microwave heaters. The microwave heaters of each chamber comprise several sources provided with microwave emission members disposed in the wall forming the ceiling of the chamber such that one microwave emission member will be offset relative to a neighboring microwave emission member, in the direction of advance of the food.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to ovens for cooking food for professional 
use and more particularly tunnel ovens for cooking. 
2. Description of the Related Art 
There are known tunnel ovens comprising a generally elongated chamber in 
the form of a parallelepiped of a length of the order of 6 meters which is 
divided into a succession of cooking chambers. This enclosure is at one of 
its ends connected to an inlet closure and at the other to an outlet 
closure. 
The intermediate zones between the chamber and the closures conventionally 
have an incurred shape, the inlet closure being connected to a loading 
zone, while the outlet closure is connected to a discharge zone for the 
foods to be cooked. 
The loading and discharge zones can be connected in a common handling zone, 
such that the installation forms an elongated loop which comes together in 
this handling zone. 
These tunnel ovens operate continuously and their capacity is for example 
about 2500 portions in 7 hours of operation at 250.degree. C., the 
foodstuffs being during cooking contained in trays disposed on carriages 
which move through the tunnel on a conveyor. 
The tunnel ovens are generally provided with different and complementary 
heating means so as to accelerate the cooking and to ensure at the same 
time a good quality of the foods, both as to their nutritional value and 
as to their appearance. 
Thus, the tunnel ovens are preferably provided for simultaneous cooking, 
mixed or separated in function as to the foods to be cooked, with the aid 
of microwaves, pulsed air, steam and infrared radiation. 
These heating modes are selected as a function of the foods to be cooked 
and their individual specifications. Thus, microwaves permit above all 
obtaining the greatest rapidity of cooking, the efficacy of this mode of 
heating being immediate. Steam heating permits avoiding loss of weight and 
also permits preserving the organoleptic properties of certain products 
which otherwise would be changed. 
The pulsed air heating conjointly with other heating modes, if desired 
supplemented by infrared radiation, permits preserving the typical 
advantages of a conventional type of oven, particularly the possibility of 
browning and searing the surface of certain products. 
Each chamber in the series of chambers acts like an oven and is separated 
from the following chamber by a deflector suspended from one wall forming 
the ceiling of the chamber. Each chamber is generally associated with 
several microwave sources, each source being connected to a microwave 
generator by means of a waveguide and empties into the interior of the 
chamber through a microwave emission member in the form of a coupling 
iris, of an antenna or of a slotted guide. 
The microwave emission members within each chamber can be disposed in a 
side wall of the enclosure or in the wall forming the ceiling of the 
latter. They are in a known tunnel oven disposed in the ceiling and 
aligned along a line passing through a transverse plane of the chamber. 
These microwave emission members should be disposed at a certain distance 
from each other to avoid interference phenomena, which would result in the 
microwave emission members not being arranged in an optimum manner 
relative to the trays. 
Each chamber is also associated with a hot air production group comprising 
a turbine, shielded resistances and a deflector grill. This hot air 
production group is mounted to one side of the enclosure in the body of 
the tunnel oven and the deflector grill is integrated into a side wall of 
the enclosure adjacent the corresponding chamber. 
The provision of steam in each chamber is ensured by means of a 
distribution member in the form of at least one injection nozzle which 
projects within the chamber and which is connected to an apparatus for 
steam production. 
Finally, the infrared radiation producing elements are constituted by 
shielded resistances or any other infrared emitter which is suspended in 
each chamber from the wall forming the ceiling of the enclosure. 
SUMMARY OF THE INVENTION 
Each heating mode is controlled separately so as to be able to combine as 
desired with the other heating modes as a function of the foods to be 
prepared. 
The shape of the enclosure as well as the arrangement of the different 
heating means are moreover extremely important for good heat economy and 
to obtain a satisfactory result, not only as to the cooking itself but 
also as to the appearance of the foods. 
To permit cleaning the interior of the tunnel oven, the latter is provided 
with at least one side door pivotally mounted on the body of the tunnel so 
as to give access simultaneously to several cooking chambers. 
The invention has for its object to optimize the power available in each 
individual chamber and to increase the uniformity of heating. 
The invention also has for its object to provide a design for the enclosure 
having an arrangement better adapted to the size of the trays. 
The invention also has for its object to make easier the maintenance of the 
tunnel. 
The invention has for its object a tunnel oven for cooking food, comprising 
an elongated enclosure connected to an inlet closure and respectively an 
outlet closure and traversed by a conveyor transporting the foods to be 
cooked, the enclosure being delimited by a wall forming a bottom, a wall 
forming a ceiling and two lateral walls of which one is provided with a 
door giving access to the interior of the enclosure, this enclosure being 
divided into several successive cooking chambers separated from each other 
in the upper portion of the latter, each chamber being associated with 
several different heating means, including microwave means, characterized 
in that the microwave means of each chamber comprise several applicators 
provided with microwave emission members disposed in the wall forming the 
ceiling of the chamber such that a microwave emission member will be 
offset relative to an adjacent microwave emission member, in the direction 
of movement of the food. 
According to other characteristics of the invention: 
at least two adjacent microwave emission members are disposed along a line 
which forms an angle with a plane transverse to the chamber; 
the line is parallel to a diagonal of a tray containing the food to be 
cooked when the tray is located below the microwave emission members; 
all the adjacent microwave emission members are aligned with each other; 
it comprises at least three microwave emission members disposed in a 
triangle; 
at least the side wall opposite that provided with access doors extends, in 
a transverse cross section, along a broken line forming obtuse angles 
alternately projecting outwardly of the enclosure and inwardly toward the 
interior of the latter; 
a projecting angle is disposed in the upper portion of the enclosure and is 
followed by a re-entrant angle which creates a narrowing in the enclosure, 
immediately above the trays; 
a projecting angle is disposed substantially at the level of the conveyor; 
the lateral wall provided with access doors has a shape that is symmetrical 
relative to the opposite wall; 
each chamber is associated with a pulsed hot air production group, and this 
group is integrated into the access door of the enclosure; 
the pulsed hot air production group comprises a turbine, and the air flow 
is directed substantially toward the central axis of the conveyor; 
each chamber is associated with steam distribution means, and the quantity 
of steam distributed decreases from the first chamber to the last; 
the decrease in the quantity of steam is obtained by a decreasing number of 
steam distribution means from one chamber to the next from the first 
chamber to the last; 
the decrease in the quantity of steam is obtained by a decreasing orifice 
diameter of the distribution means for the steam from one chamber to the 
next from the first chamber to the last; 
all the steam distribution means are supplied from a single steam 
generator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The tunnel oven comprises an elongated enclosure 1 comprised by a series of 
cooking chambers 2 which will be described in greater detail below. 
The ends of the enclosure 1 are connected to an inlet closure 3 and an 
outlet closure (not shown in the drawings) having the same structure and 
serving to confine heat energy within the enclosure 1. 
The inlet closure 3 and the outlet preferably have an incurved shape, the 
inlet closure 3 being connected to a loading zone 4, while the outlet 
closure is connected to a discharge zone 5. The loading and discharge 
zones 4, 5 connect and together form a handling zone 6. These elements 
thus form with the enclosure 1 a loop which is closed at the handling zone 
6. 
This loop arrangement has moreover the advantage of reducing the overall 
length of the installation which also with this arrangement is relatively 
large. 
The food to be cooked is in a conventional manner contained in trays 7, 
being disposed on carriages 8 displaced along the rolling track 9 of a 
conveyor 10 which moves through the inlet closure 3, the enclosure 1 and 
out the outlet closure. 
The trays 7 containing the food are thus driven at a convenient and 
constant speed while passing through all the successive cooking chambers 2 
in a closed loop. 
The enclosure 1 is laterally delimited, as shown in FIG. 2, by a wall 
forming a floor 11, a wall forming a ceiling 12 and two side walls 13, 14 
of which one, wall 14, is provided with several access doors 15 to the 
interior of the enclosure 1, in particular for everyday cleaning of the 
latter. 
These access doors 15 are pivotally mounted on the body of the tunnel oven 
and are preferably controlled by a mechanical system which in FIG. 2 is 
shown by an electric jack 16. 
The number of access doors 15 is a function of the number of cooking 
chambers 2; an enclosure 1 provided with eight chambers 2 could for 
example have two access doors 15. 
Each cooking chamber 2 is separated from the following chamber 2 by a plate 
extending vertically from the ceiling 12 and which plate forms a deflector 
17. Such a deflector 17 is also disposed upstream of the first chamber 2 
so as to separate the latter from the inlet closure 3 and another 
downstream of the last chamber 2 so as to separate the latter from the 
outlet closure. 
Each cooking chamber 2 is associated with several different heating means. 
These means permit cooking by microwaves, pulsed air, steam and preferably 
also infrared radiation. 
Thus, each cooking chamber 2 is heated with the aid of several microwave 
applicators, each applicator being connected to a microwave generator (not 
shown). This arrangement is not described because it is quite well known 
per se. 
Each microwave applicator comprises a microwave emission member 18 in the 
form of a coupling iris, an antenna or a slotted guide. 
So as to obtain optimum distribution of the microwaves in each individual 
chamber 2, the microwave emission members 18 are disposed in the wall 
forming the ceiling 12 of the chamber 2 such that each microwave emission 
member 18 will be offset relative to a neighboring microwave emission 
member 18, in the direction of movement of the food or more precisely in 
the direction of movement of the trays 7 containing the food. 
FIG. 1 shows a first arrangement of the microwave emission members 18 
according to which these members 18 are disposed along a line A--A which 
forms an angle .alpha. with a transverse plane B--B of the chamber 2. 
FIG. 4 associates this first embodiment with microwave emission members 
18A, 18B and 18C. This arrangement is equivalent to the arrangement of the 
applicators 18D, 18B, 18E. FIG. 4 moreover shows several modifications of 
the arrangement of the microwave emission members 18. 
According to a preferred modification, the line A--A along which are 
disposed the microwave emission members 18 is parallel to the diagonal of 
a tray 7 containing the foods to be cooked when the tray 7 is located 
below these microwave emission members 18. 
The microwave emission members can 18, when they are three in number, be 
disposed so as to form a triangle as shown by the arrangement of the 
microwave emission members 18A, 18B and 18D, or else 18C, 18B and 18E, the 
apex of this triangle being directed in the direction of movement of the 
trays 7 respectively or in the opposite direction. 
FIG. 4 also shows a modification with five microwave emission members 18A, 
18B, 18C, 18D and 1BE of which four are disposed in the regions of the 
corners of the ceiling 12 of the chamber 2 and one is disposed at the 
center. Preferably, all the microwave emission members 18 are disposed 
along lines parallel to the diagonals of the tray 7 when the latter is 
located in the cooking chamber 2. 
Each cooking chamber 2 is also associated, as shown in FIG. 3, with a 
pulsed air production group 19 comprising resistances 20, a turbine 21 
driven by an electric motor 22 and a deflector grill 23 directed toward 
the interior of the chamber 2. 
Contrary to the known tunnel ovens in which the pulsed air production 
groups are disposed in a fixed lateral wall, these groups 19 are according 
to the invention integrated into the access doors 15 toward the interior 
of the enclosure 1, which makes them easily accessible for maintenance. 
Moreover, the axis of the turbine 21 is directed substantially toward the 
central axis of the conveyor 10, which ensures that a portion of the 
pulsed air is directed directly against the food contained in the tray 7, 
while another portion of the air passes below the tray 7 and is then 
returned by the opposite side wall of the enclosure. This arrangement has 
the effect of establishing a continuous hot air circulation around the 
tray 7. 
More generally, and also with other air heating means as for example gas, 
it is the flow of hot air propelled by the turbine 21 which is directed 
toward the central axis of the conveyor 10. 
Each cooking chamber 2 is moreover associated with steam distribution means 
in the interior of the chamber 2. These means comprise nozzles 24 opening 
into the enclosure, with at least one nozzle 24 for each cooking chamber 
2. 
These nozzles 24 are arranged in the upper portion of the chambers 2, but 
their placement is not important for the distribution of steam within the 
corresponding chamber 2. 
According to the invention, all nozzles 24 are supplied from a single steam 
generator (not shown). Steam is led from the generator toward the nozzles 
24 by a conduit 25 forming a ramp extending parallel to the enclosure, 
above the latter. 
The quantity of steam distributed in the cooking chambers 2 decreases from 
the first chamber 2 to the last so as to optimize the efficiency of this 
manner of heating, the quantity of steam distributed being proportional to 
the temperature of the foods to be cooked which increases from the inlet 
toward the outlet of the enclosure. 
According to a first modification, this decrease of the quantity of steam 
distributed in each successive chamber 2 is obtained by a decreasing 
number of nozzles 24 from one chamber 2 to the next. 
According to a second modification, this decrease of the quantity of steam 
distributed in each successive chamber 2 is obtained by a decreasing 
diameter of the orifices of the nozzles 24 from one chamber 2 to the next. 
It is naturally also possible to combine these two modifications. 
So as better to brown and sear the surface of certain products, each 
chamber 2 can moreover preferably be provided with infrared radiation 
producing elements constituted by shielded electrical resistances 26 
suspended at a suitable height in each chamber 2 from the ceiling 12 of 
the chamber 12. 
So as better to distribute on the one hand the microwaves emitted by the 
generators and on the other hand to improve the circulation of the hot air 
propelled by the groups 19 in the chambers 2, at least the side wall 13, 
opposite the wall 14 provided with the access doors 15, but if desired 
also this latter wall 14, extends, in a transverse cross section, along a 
broken line forming obtuse angles alternately projecting outwardly of the 
enclosure and inwardly of the latter. 
Thus, to better distribute the microwaves, such a projecting angle 27 is 
disposed in the upper portion of the enclosure and is followed by a 
re-entrant angle 28 which creates a narrowing in the enclosure, 
immediately above the trays 7. 
Another projecting angle 29 is disposed substantially at the level of the 
conveyor 10, which angle 29 has the effect of improving the circulation of 
air about the trays 7 driven by the conveyor 10. 
The side wall 14 provided with the access doors 15 can preferably have a 
shape which is symmetrical relative to the opposite side wall 13. 
There is thus obtained a tunnel oven in which the thermal efficiency is 
optimized and whose maintenance is facilitated due to the arrangement of 
the groups 19 for the production of hot air.