RU2257018C2 - Microwave commercial oven - Google Patents

Abstract

FIELD: industrial appliances.

SUBSTANCE: device has heating chamber, on outer side of upper and side walls of which L-shaped portion of rectangular wave guide, short-circuited at an end, is mounted for transferring energy from microwave generator to one-dimensional non-equidistant antenna-exciter of circle-polarized field in heating chamber, in form of four strip antennae of identical characteristics of circular polarization AB₁, AB₂, AB₃, and AB₄ with non-common-mode feeding, distance between AB₁ and AB₂, and AB₃ and AB₄ is equal to 45 mm, and between AB₂ and AB₃ - 39 mm, antennae are mounted inside heating chamber on its upper wall and through coaxial-wave subs are connected to rectangular wave guide section. Each strip antenna contains disk emitter, which through metallic rods is connected at the center to central conductor of coaxial exit of coaxial-wave subs and at distance of 4/5 of radius of metallic disk - to metallic screen plate, which is mounted on outer conductors of all four coaxial-wave subs through circular apertures in screen plate with rigid non-detachable mechanical connection and good galvanic contact along whole perimeter of outer conductor of coaxial output of coaxial-wave subs. Screen plate does not touch upper wall of heating chamber and is a portion of each strip antenna. Disk emitters of strip antennae are positioned in plane, parallel to upper wall of heating chamber.

EFFECT: higher efficiency, broader functional capabilities.

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Description

Technical field

The invention relates to microwave equipment, in particular to electric heaters using the energy of the microwave field, and is intended for heat treatment of food products in catering.

State of the art

A microwave oven is known, which is a device for heating food products with microwave field energy, comprising a heating chamber equipped with a door, a microwave generator located in a removable housing of an electronic unit having a common working wall with a heating chamber, and a radiation module installed in a working wall connection hole heating chamber for inputting microwave energy. The radiation module contains a segment of a coaxial line that is connected to a radiator of conductive material, and a metal ring adjacent to the inner surface of the working wall of the heating chamber along the perimeter of the communication hole with an electromagnetic seal around its perimeter (see, for example, Pat. RF No. 2124278, H 05 B 6/64, 1998). The communication hole is made in the side wall of the chamber and is filled with radiolucent material. The emitter is installed in the recess of the guide element made of a material that conducts electromagnetic waves and is connected by a jumper. With the guide element is connected with the possibility of galvanic contact ring. The radiation module and the guiding element are fixed on the rack and located in the housing of the electronic unit (outside the heating chamber), made in the form of a tray facing its open end to the outer surface of the wall of the heating chamber in which the communication hole is made. The open end of the housing of the electronic unit is connected to a metal frame along its outer perimeter. The metal frame is detachably connected with the possibility of galvanic contact to the outer surface of the wall of the heating chamber in which the communication hole is made, and is provided with a recess made along the perimeter of the frame in which the electromagnetic seal is placed.

The main disadvantage of this device is its low efficiency, due to the uneven distribution of the electromagnetic field inside the heating chamber. As the measurements showed, the uniformity of the distribution of microwave energy in the heating chamber is 46–48%, and the efficiency (efficiency) does not exceed 50%. This leads to uneven heating of the products, poor quality of their processing.

The closest technical solution to the invention is a commercial microwave oven, which is a device for processing food products with microwave energy, comprising a heating chamber equipped with a door, a microwave generator located in the side compartment of the microwave oven outside the heating chamber, a segment of a L-shaped rectangular short-circuited at the end a waveguide mounted on the outer side of the upper and side walls of the heating chamber, an electromagnetic field excitation module in the heating chamber , which is a metal dipole antenna, rigidly mechanically and electrically connected in the center with a hollow thin-walled metal cylinder, whose upper end is immersed inside a rectangular short-circuited at the end segment of a rectangular short-circuited at the end of a rectangular waveguide, through a common communication hole in the upper wall of the heating chamber waveguide for transferring energy from the microwave generator to the heating chamber, and a fan installed in the side compartment of the microwave oic furnace for generating an air flow directed from the air duct radiotransparent dielectric and metal causes forced rotation of the dipole antenna of the magnetron and cooling (see., e.g., Commercial Microwave Oven RCS10MPS, US, AMANA. Owner's Manual Code No. 12668501 A, 2001). On the opposite wide wall of the horizontal section of the rectangular waveguide short-circuited at the end of the segment, a matching metal pin is mounted coaxially with the rotating antenna with a galvanic contact. In the communication hole, a thin-walled metal cylinder is encircled by a dielectric ring providing a suspension of the metal dipole antenna and allowing its forced rotation.

The main disadvantage of this device is its low efficiency. As the results of testing the microwave oven RCS10MPS (US, AMANA) showed, depending on the mass, volume and location of the processed product inside the heating chamber, the uniformity coefficient of electromagnetic energy distribution is variable and takes values from 40% to 64%, and the efficiency from 38% up to 51%. This leads to poor quality food processing, additional energy costs. During operation, the microwave oven is unstable to vibration and shock.

Disclosure of invention

The main objective of the invention is to increase the efficiency of the microwave oven by increasing the uniformity of the distribution of microwave energy inside the heating chamber, increasing the efficiency and stabilizing the heat treatment of food products.

The stated technical problem is solved in a microwave oven containing a microwave field excitation module located inside the heating chamber, and a microwave generator installed outside the heating chamber, as well as an L-shaped rectangular waveguide, one end of which is short-circuited, installed on the outer surface of the upper and side walls of the heating chamber and the other is connected to the output of the microwave generator, while in the upper wall of the heating chamber and in the adjacent wall of the horizontal section of the L-shaped rectangular of the waveguide made reciprocal communication holes. According to the invention, the microwave field excitation module is made in the form of a non-equidistant antenna array formed by two pairs of identical strip antennas of a circularly polarized field, mounted on the upper wall of the heating chamber and connected to a horizontal section of an L-shaped rectangular waveguide by means of coaxial waveguide adapters according to the number of strip antennas of a circularly polarized field . Moreover, coaxial waveguide adapters are installed in the aforementioned communication holes in adjacent walls of the heating chamber and the horizontal section of the L-shaped rectangular waveguide. Each of the strip antennas of a circularly polarized field contains a disk emitter having a central hole for connecting a corresponding coaxial waveguide adapter to the central conductor, and a peripheral hole for connecting to a metal screen. A metal screen is installed between the microwave field excitation module and the upper wall of the heating chamber with a gap relative to the latter and connected to the external conductor of each of the aforementioned coaxial waveguide adapters.

In addition, according to the invention, the central holes of the disk emitters are located on a conditional line parallel to the longitudinal axis of symmetry of the horizontal section of the L-shaped rectangular waveguide, and the peripheral holes of the disk emitters are offset from the conditional line.

It is advisable that the central and peripheral openings of the disk emitter are connected to the central conductor of the corresponding coaxial waveguide adapter and to the metal shield, respectively, by means of metal pins.

The invention allows to obtain a highly uniform distribution of the energy of the microwave field inside the heating chamber, to practically eliminate the dependence of the efficiency of the microwave oven on the volume, mass and location of the processed product in the heating chamber and to ensure the stability of heat treatment of products during long-term cooking.

Numerous experimental studies have been conducted of a prototype microwave oven, for example, based on RCS10MPS (US, AMANA) without a rotating platform made according to the invention, having a heating chamber with dimensions 241 × 343 × 400 mm. As a result of research, the values of the coefficient of uniformity of distribution of microwave energy were obtained 94%, efficiency 62%. Moreover, changes in the uniformity of energy distribution and efficiency for different volumes, masses and locations of the processed product did not exceed 2-4%. The use of a four-element non-equidistant antenna in the microwave oven provided stable excitation of 29 spatial harmonics.

Brief Description of the Figures

Figure 1 presents a schematic illustration of a microwave oven; figure 2 - disk emitter.

The best embodiment of the invention

The microwave oven (see figure 1) contains a casing 1 for protection and shielding, inside which there is a heating chamber 2, equipped with a door (not shown in the drawings), in which a non-equidistant antenna array is formed, formed by two pairs of identical strip antennas 3 of a circularly polarized field, and compartment 4, in which the microwave generator 5 is installed.

An L-shaped rectangular waveguide 6 is installed on the outer surface of the upper and side walls of the heating chamber 2, one end of which is short-circuited and the other, open, is electrically connected to the microwave generator 5 through the waveguide-resonator adapter 7. In the upper wall of the heating chamber 2 and in the adjacent with it the wall of the horizontal section of the L-shaped rectangular waveguide 6 is provided with communication mating holes for transmitting the energy of the microwave generator 5 to the strip antennas 3. In the aforementioned communication holes (not shown in the drawings dstavleny) set identical in structure and electrical parameters coaxial-waveguide adapters on the number of stripline antennas 3, i.e. four coaxial-waveguide adapters, each of which is formed by a metal pear-shaped coupling element 8, mounted in a Teflon sleeve (not shown in the drawings), passing into the central conductor 9 of the coaxial line and matched using a metal pin 10, and an external conductor 11 in the form of a metal sleeve galvanically and mechanically permanently connected around the perimeter through a communication hole with the wall of the horizontal section of the L-shaped rectangular waveguide 6. The outer conductor 11 of each of the of the wave-waveguide adapters is galvanically connected to the screen 12 made in the form of a metal plate and is rigidly fixed in the corresponding hole of the screen 12. The screen 12 is detachably connected to the upper wall of the heating chamber 2 through a metal fastening plate rigidly mechanically and galvanically connected to it 13. Access to strip antennas 3 is closed by a radio-transparent screen 19.

Each of the circularly polarized field strip antennas 3 comprises a disk radiator 14 (see FIG. 2) having a central hole 15 for connecting a corresponding coaxial waveguide adapter to the central conductor 9, and a peripheral hole 16 for connecting to a metal screen 12 that is installed between the module excitation of the microwave field and the upper wall of the heating chamber 2 with a gap relative to the latter and connected to the external conductor 11 of each of the aforementioned coaxial waveguide adapters. The central hole 15 of each disk radiator 14 is connected to the central conductor 9 of the corresponding coaxial-waveguide adapter by means of a metal pin 17. The peripheral hole 16 of each disk radiator 14 is connected to the screen 12 by means of a metal pin 18. Through-screen holes 12 are provided for installing the pins 18 ( not shown in the drawings) allowing rotation of the disk radiator 14 around its axis. The strip antennas 3, i.e., the microwave field excitation module, are rigidly fixed in the heating chamber 2 by means of pins 17 and 19.

The Central holes 15 of all disk emitters 14 are located on a conditional line parallel to the longitudinal axis of symmetry of the horizontal section of the L-shaped rectangular waveguide 6. The peripheral holes 16 of all disk emitters 14 are offset relative to the conditional line.

Assemble the microwave as follows.

First, four coaxial-waveguide adapters are installed in the communication holes, mechanically fixed by a screen 12, which is rigidly detachably fixed using two mounting plates 13. Then, strip antennas 3 are installed, which excite a circularly polarized field in the heating chamber 2, the distances between the symmetry axes of the first and second antennas 3, as well as the third and fourth are equal to 45 mm, the distance between the axis of symmetry of the second and third antennas is 39 mm For this, each disk radiator 14 is connected with a metal pin 17 with a central conductor 9 of the corresponding adapter and metal pin 18 with a screen 12 in which a through hole is made allowing rotation of the disk radiator 14 around its axis by an angle of 3 to 10 degrees. The offset of the said peripheral holes 16 relative to the conditional line on which the central holes 15 are located is determined in the process of tuning the antenna array to ensure maximum power transmission from the microwave generator 5 to the load. Setting the excitation module is carried out in the following order. First, the first strip antenna 3 is tuned in when three other antennas 3 and short-circuited adapters are disconnected 7. The load in the heating chamber is a vessel with 1 dm ^{3 of} water. The greatest power corresponds to the shortest boiling time of water in the vessel. Then the remaining strip antennas 3 are tuned in the same way.

A microwave works in a known manner.

The tests carried out on a prototype commercial microwave oven without a rotating platform made according to the invention showed its high efficiency in comparison with known objects of a similar purpose. As a result of the test, it was found that the coefficient of uniformity of energy distribution inside the chamber reaches 94%, efficiency - 62%, while ensuring the stability of these parameters when changing the volume, mass and location of the processed product in the heating chamber.

Sources of information

1.US, Commercial Microvave Oven RCS10MPS, Owner's Manuel Code 12668501 A, 2002 (www.amana-commercial.com).

2. RU, patent No. 2124278, class. H 05, 6/64, 1998.

3. Veins B.C. Measuring ponderomotive microwave converters. Theory and application. Kharkov, “Vishka school”, 1989, 135 pp.

Claims (1)

A microwave oven, which is a device for processing food products with microwave energy, comprising a heating chamber equipped with a door, a microwave generator located in the side compartment of the microwave oven outside the heating chamber, a L-shaped segment of a rectangular waveguide mounted on the outside of the upper and side wall of the heating chamber, a fan located in the side compartment of the microwave oven to cool the magnetron and remove vapors from the working chamber, distinguishing I mean that it is equipped with a microwave field exciter in the working chamber, which is a one-dimensional non-equidistant array of 4 with identical characteristics of strip antennas, emitting a circularly polarized electromagnetic field, which is installed inside the heating chamber on its upper wall, each of the 4 strip antennas through coaxial the waveguide transition is connected to a horizontal segment of a short-circuited at the end of the L-shaped rectangular waveguide for transferring energy from the microwave generator to the chambers , the strip antenna emitting a circularly polarized field contains a metal disk radiator connected through metal conductive pins in the center to the central conductor of the coaxial output of the coaxial waveguide transition and at a point 4/5 of the radius of the metal disk radiator to the metal shield plate installed on the outer conductor of the coaxial segment of each of the 4 coaxial waveguide junctions with mechanical and galvanic contact over the entire outer diameter of the outer conductor of the coaxial segment of the coaxial waveguide transitions, not touching the upper wall of the heating chamber and which is part of the strip antennas.

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