RU2126606C1 - Device for microwave processing of dielectric materials - Google Patents

Abstract

FIELD: microwave processing equipment. SUBSTANCE: device has microwave oscillator, chamber, in which load unit, unload unit, fan and ballast absorber are located, waveguide, which output is connected to chamber and input is connected to output of microwave oscillator. Goal of invention is achieved by introduced emitters, additional microwave oscillators, ballast absorbers and waveguides, which outputs are connected to chamber and inputs are connected to outputs of additional microwave oscillators, which are located in plane which is perpendicular to longitudinal axis of chamber in symmetry about this axis in order to provide uniform heating of processed materials on all sides. Ballast absorbers are located on inner surface of chamber walls in opposite to output horns of emitters. In addition size of funnels of horns is reverse proportional to size of chamber walls which are located in opposite to them. Wide walls of opposite side waveguides are perpendicular to one another in points of their connection to corresponding emitters. Output horns of emitters are covered with suppressing insertions which are transparent to radio waves. In addition device has conveyor belt, which is located along its longitudinal axis. EFFECT: uniform heating of processed materials on all sides, exclusion of local overheating. 5 cl, 3 dwg

Description

 The invention relates to the field of electronics, in particular to microwave devices for heat treatment of various bulk, molded materials, products in a stream or in a static mode.

 There are various devices of the waveguide and resonator type for microwave processing of dielectric materials.

 Device / G. S. Knyazhevskaya et al., P. 51 - 52, L., "Mechanical Engineering", 1969 / for microwave heating based on a closed oscillatory system - a rectangular volume resonator - has a resonant heating chamber, which is the final load of the microwave generator, which is connected to the camera through a communication waveguide. The frequency adjustment of this load with the microwave generator is ensured here by the choice of three dimensions of the resonator chamber, when it is a parallelepiped close to a cube, which provides the necessary stability on the frequency axis of the spectrum of the natural frequencies of the resonator chamber at a specific given load.

 The disadvantage of this device is its low efficiency at boot, which differs from the nominal, because in this case, the shift in the resonance frequencies of the camera can be so significant that its frequency matching with the microwave generator is completely violated, this significantly reduces the energy transmitted from the generator to the camera, and the vibrations reflected from the input into the camera cause the microwave generator to self-overheat. In addition, such a device does not provide uniform heating of the material due to numerous standing waves in the chamber volume, which causes local overheating and underheating in the volume of the processed material.

 Known installation for drying materials / avt.svid. N 1522006, MPK4 26 B 3/347, 03/10/08 g /, containing a drying chamber in the form of a working waveguide, equipped with loading and unloading units connected to the chamber of the microwave generator with a communication waveguide, a fan and a receiver-receiver of microwave energy. The unloading unit is made in the form of a tee with a flap valve.

 The disadvantage of the installation is the unsatisfactory uniformity of heating of the processed materials in the waveguide chamber, as well as the high level of spurious radiation into the surrounding space through the loading and unloading units with low unloading of the chamber and in the absence of its loading.

 Of the known devices, the closest in technical essence to the proposed device is a device for microwave processing of bulk materials / ed. testimonial. N 1378089, IPC4 H 05 B 6/64, 04.24.86 g /, containing a microwave generator, a communication device, a camera with loading blocks, discharge blocks, a fan, a ballast absorber located under the bottom of the tray for the processed material, this camera and the communication device is made in the form of waveguides connected together over a wide wall, and the ballast absorber is located opposite the output of the communication device introduced into the camera, the input of which is connected to the output of the microwave generator.

 The disadvantage of this device is the uneven heating of the treated dielectric materials, especially those with low thermal conductivity, in the case when they are processed in a thick layer, due to the one-sided direction of irradiation, as well as overheating of the processed dielectric materials in antinodes of standing waves arising from vibrations reflected from the walls cameras.

 The problem to which the present invention is directed, is such a change in the composition and design of the device in which due to the introduction of emitters, additional microwave generators, ballast absorbers and waveguides and the appropriate relative position of all structural elements: a / ensures uniform heating of the processed material, especially in its thick layers; b) local overheating and underheating of the processed products are eliminated, thereby not only achieving, for example, the required biological stability of the product without the traditional deterioration of its chemical composition, but also accurately metered selective effect on microorganisms and products is realized, and the final effect, for example pasteurization, is achieved when temperature lower than usual.

 To solve this problem, in a known installation for microwave processing of dielectric materials containing a microwave generator, a camera with a loading unit, an unloading unit, a fan and a ballast absorber, a waveguide whose output is inserted into the camera, and the input is connected to the output of the microwave generator, according to the invention, emitters, additional microwave generators, ballast absorbers and waveguides are introduced, the outputs of which are introduced into the chamber, and the inputs are connected to the outputs of additional microwave generators, the outputs of all waveguides are connected to the inputs of the respective emitters, which are located in a plane perpendicular to the axis of the chamber, are axisymmetric (with counter-directed exit openings), and ballast absorbers on the inner surface (side, upper and lower) of the chamber walls.

 The dimensions of the output openings of the emitters are made inversely proportional to the corresponding dimensions of the opposite chamber walls.

 The wide walls of the opposing waveguides with the emitter inputs are mutually perpendicular.

 The output openings of the emitters are drowned out by radio-transparent inserts.

 The installation can be equipped with a (radiolucent) vibration-chute or belt conveyor, which is located along the longitudinal axis of the chamber.

 The combination of these features provides an increase in the integral and local processing uniformity, which is confirmed by the analytical justification given below.

As an indicator of the integral uniformity of heating, we determine the ratio of the specific power density of microwave oscillations in the least heated layer of the processed material to its density in the most heated layer. Consider, for example, when the flow of processed products, like the camera, has a rectangular section and transverse dimensions h and g, which are approximately three times smaller than the corresponding dimensions of the camera body H and G / this will simplify the calculations /, the installation is equipped with 4 microwave generators, 4 waveguides, 4 emitters, which are located one on each side of the camera in one plane perpendicular to the axis of the camera, symmetrically about this axis (and have opposite directions openings). The flow of processed products is equidistant from opposite sides of the camera body. Let the power of each generator of the proposed camera is 4 times less than the power of the microwave generator according to the prototype. For a prototype with similar overall dimensions, the least heated layer is the lower layer, remote from the waveguide output at a distance l ^p = h + h = 2h, for the proposed installation, this is the inner, middle layer, at a distance from the output opening of the upper and lower emitters, equal to l $\genfrac{}{}{0ex}{}{\text{u}}{\text{i}}$ = h + h / 2 = 1.5h; i = 1.2 and at a distance from the output aperture of the side emitters, equal to l $\genfrac{}{}{0ex}{}{\text{u}}{\text{i}}$ = g + g / 2 = 1.5g; i = 3, 4. The most heated layer in the prototype is the upper one / at a distance h from the output aperture of the emitter /, for the proposed installation - the upper and lower, lateral left and lateral right / at a distance of respectively h and g /.

 To calculate the power flux density at the surface of the processed material, we specify the values of the radiation pattern width in the planes of electric and magnetic tension.

В предлагаемой установке с продольным размером L /L-длина камеры/ ширина луча согласована с шириной потока согласованных материалов. Поэтому для изобретения необходимо записать:
для верхнего, например, рупорного излучателя, с размерами выходного раскрыва

2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{1}}$ = 2 arctg L/2H ; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{1}}$ = 2 arctg G/2H ; (2)
для нижнего излучателя с размерами выходного раскрыва

2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{2}}$ = 2 arctg G/2H ; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{2}}$ = 2 arctg L/2H ;
для левого бокового излучателя с размерами раскрыва

получается
2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{3}}$ = 2 arctg L/2G ; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{3}}$ = 2 arctg H/2G ;
для правого излучателя с размерами раскрыва

ширина луча во взаимоперпендикулярных плоскостях равняется
2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{4}}$ = 2 arctg H/2G ; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{4}}$ = 2 arctg L/2G .
Площадь горизонтального сечения луча в камере прототипа у верхнего слоя потока материалов, т.е. на удалении h от выходного раскрыва волновода согласно /1/ равняется
S^П= 2h·tgθ^П·2h·tgφ^П≃ 3,3h².
Следовательно, при мощности СВЧ-генератора прототипа, равной P, плотность потока мощности в этом сечении равна

Для предлагаемой установки с размерами G=3g; H=3h; L и мощностью каждого из СВЧ-генераторов, равной P/4, плотности потока мощности при поперечных размерах потока g и h согласно /2 - 5/ равны:
у верхнего и нижнего слоев

у бокового левого и бокового правого слоев

Определим значение электрической напряженности поля в верхнем слое /на поверхности/ материала, считая, что локальное электромагнитное поле можно рассматривать как плоскую волну, а волновое сопротивление среды равно W=120 Ом. При этом для устройств по прототипу и изобретению получим

Электрическая напряженность поля в наименее прогреваемом слое может быть определена с учетом коэффициента Г'' затухания волны в материале с учетом пути, пройденного волной в обрабатываемом материале,

где f - частота колебаний СВЧ-генератора;
ε₀(μ₀) - электрическая /магнитная/ постоянная;
ε′- относительная диэлектрическая проницаемость материала;
tgδ - тангенс угла потерь в материале.For the prototype, they are known to be determined by the dimensions of the opening of the waveguide, for example

In the proposed installation with a longitudinal dimension, the L / L-chamber length / beam width is consistent with the flow width of the matched materials. Therefore, for the invention it is necessary to write:
for the top, for example, a horn emitter, with the dimensions of the output opening

2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{1}}$ = 2 arctan L / 2H; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{1}}$ = 2 arctg G / 2H; (2)
for lower emitter with output opening dimensions

2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{2}}$ = 2 arctg G / 2H; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{2}}$ = 2 arctan L / 2H;
for left side radiator with aperture dimensions

it turns out
2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{3}}$ = 2 arctg L / 2G; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{3}}$ = 2 arctg H / 2G;
for the right radiator with openings

beam width in mutually perpendicular planes equals
2θ $\genfrac{}{}{0ex}{}{\text{u}}{\text{4}}$ = 2 arctg H / 2G; 2φ $\genfrac{}{}{0ex}{}{\text{u}}{\text{4}}$ = 2 arctg L / 2G.
The horizontal cross-sectional area of the beam in the prototype chamber at the upper layer of the material flow, i.e. at a distance h from the output aperture of the waveguide according to / 1 / equals
S ^P = 2h · tgθ ^P · 2h · tgφ ^P ≃ 3.3h ² .
Therefore, with the power of the microwave generator of the prototype equal to P, the power flux density in this section is

For the proposed installation with dimensions G = 3g; H = 3h; L and the power of each of the microwave generators equal to P / 4, the power flux density at the transverse dimensions of the flow g and h according to / 2 - 5 / are equal:
at the upper and lower layers

at the lateral left and lateral right layers

We determine the value of the electric field strength in the upper layer / on the surface / material, assuming that the local electromagnetic field can be considered as a plane wave, and the wave resistance of the medium is W = 120 Ohms. Moreover, for devices of the prototype and invention we obtain

The electric field strength in the least heated layer can be determined by taking into account the attenuation coefficient G ″ of the wave in the material, taking into account the path traveled by the wave in the processed material,

where f is the oscillation frequency of the microwave generator;
ε ₀ (μ ₀ ) - electric / magnetic / constant;
ε′- relative dielectric constant of the material;
tanδ is the loss tangent in the material.

Следовательно, искомые удельные плотности мощности /т. е. плотности мощности, диссипируемые в единице объема материала) согласно /9/ и /11/ для прототипа равняются
P $\genfrac{}{}{0ex}{}{\text{П}}{\text{max}}$ = ε′tgδ·(E $\genfrac{}{}{0ex}{}{\text{П}}{\text{max}}$ )²; P $\genfrac{}{}{0ex}{}{\text{П}}{\text{min}}$ = ε′tgδ·(E $\genfrac{}{}{0ex}{}{\text{П}}{\text{min}}$ )²; (12)
для предлагаемой камеры

В предлагаемой установке минимальные удельные плотности мощности складываются в виде

Таким образом, искомые показатели равномерности прогрева материалов согласно /10 - 14/ при g ≃ h равняются:
для прототипа
γ_П= P $\genfrac{}{}{0ex}{}{\text{П}}{\text{min}}$ /P $\genfrac{}{}{0ex}{}{\text{П}}{\text{max}}$ = exp[-2Г″h];
для предлагаемой установки

Пример. g = h = 0,3 м; ε′= 77; tgδ = 0,015.
Найти: γ_П, γ_u
Решение. Г'' = 3,3;
γ_П= exp(-2•3,3•0,3) ≃ 0,14.

Вывод. Предлагаемая установка в типовых условиях функционирования имеет показатели интегральной равномерности обработки продукции, в семь раз более высокий, чем у прототипа.In this case, the electric field strengths at g ≅ h, given that the least heated layer of the proposed installation is located on the axis of the material flow, we calculate in the form

Therefore, the desired specific power densities / t. e. power densities dissipated per unit volume of material) according to / 9 / and / 11 / for the prototype are
P $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ = ε′tgδ · (E $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ ) ² ; P $\genfrac{}{}{0ex}{}{\text{P}}{\text{min}}$ = ε′tgδ · (E $\genfrac{}{}{0ex}{}{\text{P}}{\text{min}}$ ) ² ; (12)
for the proposed camera

In the proposed installation, the minimum specific power densities are added as

Thus, the required indices of uniformity of heating of materials according to / 10 - 14 / for g ≃ h are:
for prototype
γ _P = P $\genfrac{}{}{0ex}{}{\text{P}}{\text{min}}$ / P $\genfrac{}{}{0ex}{}{\text{P}}{\text{max}}$ = exp [-2G ″ h];
for the proposed installation

Example. g = h = 0.3 m; ε ′ = 77; tanδ = 0.015.
Find: γ _П , γ _u
Decision. G '' = 3.3;
γ _P = exp (-2 • 3.3 • 0.3) ≃ 0.14.

Output. The proposed installation in typical operating conditions has indicators of integral uniformity of product processing, seven times higher than that of the prototype.

 As an indicator of the local uniformity of processing, we choose the ratio of the specific power density dissipated in the processed material at the nodes of the standing wave in the working volume of the chamber to the specific power density in the antinodes of this wave.

 Without cumbersome calculations, without large errors, it can be argued that in the prototype device this indicator is noticeably less than unity / in practice, the indicator does not exceed 0.3; when special measures are taken, for example, with the use of dissectors, it is achievable 0.8 / due to the inevitable reflection of microwave oscillations from the walls of the camera body, folding in phase or out of phase with the incident wave. In the proposed installation, there are no reflections from the walls and only the incident wave energy dissipates in the material. Therefore, the desired indicator of local uniformity of processing is approximately equal to unity, that is, higher than in the device of the prototype, even when applying special measures.

 The implementation of the output openings of the emitters with dimensions inversely proportional to the corresponding dimensions of the opposite walls of the chamber, allows you to concentrate the incident radiation of each of the microwave generator on the processed material and maximize the power of each microwave generator.

 The implementation of the wide walls of the opposing waveguides in the places of their connection with the emitters mutually perpendicular leads to orthogonal polarization of the electromagnetic waves incident on the processed material from the opposite side. Therefore, even in the critical mode, when there is no processed material, the leakage of the electromagnetic wave incident from the opposite side through the emitter and waveguide into the microwave generator is excluded, which eliminates the mutual overheating of microwave generators.

 Closing the output openings and emitters (radiolucent) inserts prevent moisture, dust and particles of the processed material from entering the waveguides and microwave generators, which leads to an increase in the stability and reliability of microwave generators.

 The location of ballast absorbers on the inner surface (lateral, upper and lower) of the chamber walls leads to the exclusion of reflections from the chamber walls, to the exclusion of the formation of standing waves, and, therefore, eliminates local overheating of the processed material, reduces the likelihood of spurious radiation through the loading and unloading blocks, and neutralizes the dependence of the setting frequency of the working chamber on the degree of its load and, therefore, firstly, increase the share of useful energy of the microwave generator, and secondly, it eliminates the presence of standing waves in waveguides, which significantly reduces the risk of self-overheating of the microwave generator, i.e. increases the operational reliability of the installation.

 Equipping the installation with (radiotransparent) vibration-chute or belt conveyor, which is located inside the chamber along its longitudinal axis, allows for continuous supply of the processed material to the working area of the chamber and unloading of the processed material, which leads to a significant increase in the productivity of the installation.

 In FIG. 1, 2 shows a General view of the proposed installation for microwave processing of dielectric materials with different types of conveyors, FIG. 3 is a section in the plane A in FIG. 2.

 Installation / Fig. 1, 3 / comprises a chamber 1, with loading units 2 located therein, an unloading unit 3, a fan 4; Microwave generators 5, 6, 7, 8 / G5, G6, G7, G8 /, waveguides 9, 10, 11, 12 with corresponding emitters 13, 14, 15, 16, ballast absorbers 17, 18, 19, 20. Installation equipped with vibration-tray / Fig. 1 / or tape / Fig. 2 / by a conveyor 21 / shown by a dotted line / located inside the chamber along its longitudinal axis. The emitters 13, 14, 15, 16 are muffled by radiolucent liners / not conventionally shown in the drawing /.

 The outputs of the microwave generators 5, 6, 7, 8 are connected to the inputs of the waveguides 9, 10, 11, 12. Their outputs the waveguides are connected to the respective emitters 13, 14, 15, 16.

 The emitters 13, 14, 15, 16 are located in a plane perpendicular to the longitudinal axis of the chamber 1, symmetrically relative to this axis, with the possibility of simultaneous comprehensive uniform heating of the processed materials. Ballast absorbers 17, 18, 19, 20 are located on the inner surface of the walls of the chamber 1 opposite the output openings of the respective emitters 13, 14, 15, 16.

 The wide walls of the opposing waveguides 9 and 11, 10 and 12 at their junctions with the emitters 13, 14, 15, 16 are mutually perpendicular.

 The sizes of the output openings of the emitters 13, 14, 15, 16 are inversely proportional to the corresponding dimensions of the opposite walls of the chamber 1.

 The proposed device operates as follows.

 Microwave generators 5, 6, 7 and 8 generate electromagnetic oscillations of a certain frequency and power / for example, their frequency is 2450 MHz, and the power is 1.5 kW /. These electromagnetic vibrations through the waveguides 9, 10, 11, 12 and the corresponding emitters 13, 14, 15, 16 enter the chamber 1. The placement of the emitters 13, 14, 15, 16 in the chamber 1 and the choice of their sizes according to the invention allows the microwave energy to be concentrated generators in the working area of chamber 1, where the processed material is fed by conveyor 21, loaded into chamber 1 through loading unit 2 and discharged from chamber 1 through unloading unit 3. Ballast absorbers 17, 18, 19, 20 exclude reflection of microwave waves of each from microwave generators and the formation of standing in Waves in chamber 1. Fan 4 is used to extract vapors from chamber 1.

In the waveguides 9, 10, 11, 12, the wave H _{01 is used} , the electric vector of which is known to be perpendicular to the wide side of the waveguide. Therefore, the mutual perpendicularity of the wide walls of the opposing waveguides 9 and 11, 10 and 12 eliminates the "leakage" of the electromagnetic wave incident from the opposite side of the chamber 1 into the microwave generators 6, 7, 8, 5.

 The design of the loading unit 2 and the unloading unit 3 prevents spurious radiation of microwave oscillations through the loading / unloading window / in the chamber 1 both when it is fully loaded and when there is no processed material. The loading / unloading window / is, for example, a transverse waveguide / Fig. 1 / or a gateway with a three-blade rotor / Fig. 2 /.

 Microwave heating of the processed material in the considered example is carried out simultaneously on four sides by an energy flow, the longitudinal and transverse dimensions of which coincide with the corresponding dimensions of the processed material flow. The movement of the material flow to the unloading unit 3 / Fig. 1 / is carried out using / radiotransparent / vibration-chute conveyor 21 due to inertial forces in the process of vibration of the tray, articulated on a rocking chair to the walls of the chamber 1, or using a tape tape / radiotransparent / conveyor 21 / Fig. 2 /.

 The proposed installation provides comprehensive uniform heating of the processed materials, while eliminating local overheating in the entire volume of the processed material and underheating of the material at the bottom of the tray / conveyor belt /.

In addition, the proposed installation provides:
the ability to process materials in a stream at a safe level of power flux density through loading units 2 and unloading 3 at idle, and in the operating mode due to ballast absorbers 17, 18, 19, 20 located on the inner, side, upper and lower walls of the chamber 1 and excluding reflections from its walls; pairwise mutually perpendicular arrangement of waveguides 9, 10, 11, 12 prevents mutual overheating of microwave generators 6, 7, 8, 5; radiolucent liners prevent moisture and dust from entering them when processing the flow of materials;
independence of the share of useful energy of microwave generators 6, 7, 8, 5 from the degree of loading of the camera, because ballast absorbers 17, 18, 19, 20 neutralize the resonance properties of chamber 1;
high operational reliability of microwave generators 6, 7, 8, 5, because there are no standing waves in waveguides 9, 10, 11, 12, self-overheating and failure of microwave generators 6, 7, 8, 5 are therefore excluded.

Claims (5)

 1. Installation for microwave processing of dielectric materials, containing a microwave generator, a camera with a loading unit, an unloading unit, a fan and a ballast absorber, a waveguide whose output is introduced into the camera, and the input is connected to the output of a microwave generator, characterized in that emitters, additional microwave generators, ballast absorbers and waveguides are introduced into it, the outputs of which are introduced into the chamber, and the inputs are connected to the outputs of additional microwave generators, the outputs of all waveguides are connected to the inputs of the corresponding teachers who are located in a plane perpendicular to the longitudinal axis of the chamber, symmetrically about this axis with the ability to provide simultaneous, comprehensive, uniform heating of the processed materials, and ballast absorbers are located on the inner surface of the chamber walls, opposite the output openings of the emitters.  2. Installation according to claim 1, characterized in that the dimensions of the output openings of the emitters are inversely proportional to the corresponding dimensions of the opposite walls of the chamber.  3. The installation according to claim 1, characterized in that the wide walls of the opposing waveguides at their junctions with the respective emitters are mutually perpendicular.  4. Installation according to claim 1, characterized in that the output openings of the emitters are muffled by radiolucent liners.  5. Installation according to claim 1, characterized in that it is equipped with a conveyor, which is located inside the chamber, along its longitudinal axis.

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