CN104797029A - Resonant cavity for verifying wood microwave pretreatment temperature distribution - Google Patents
Resonant cavity for verifying wood microwave pretreatment temperature distribution Download PDFInfo
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Abstract
The invention discloses a resonant cavity for verifying wood microwave pretreatment temperature distribution. The resonant cavity for verifying wood microwave pretreatment temperature distribution comprises a main resonant cavity which is arranged horizontally; at least one fed-in waveguide is arranged on the main resonant cavity in the lateral direction; the main resonant cavity is connected with the fed-in waveguides; the fed-in waveguides are horizontally distributed along the direction from the center of the main resonant cavity to the outside; hollow-out openings are respectively formed in two end surfaces of each fed-in waveguide; the cross section of each fed-in waveguide is rectangular; the length direction of the rectangular cross section of each fed-in waveguide is a horizontal direction; the width direction of the rectangular cross section of each fed-in waveguide is a vertical direction; and the distance from the hollow-out opening of one end, which is far away from the center of the main resonant cavity, of each fed-in waveguide to the center of the main resonant cavity is 1.1 times greater than the length of the rectangular cross section of the fed-in waveguide. The resonant cavity for verifying wood microwave pretreatment temperature distribution has the advantages that wood microwave energy utilization rate is high, microwave energy is dispersed uniformly, temperature distribution uniformity is high, and wood breaking rate is low.
Description
Technical Field
The invention relates to the technical field of wood microwave pretreatment, in particular to a resonant cavity for verifying wood microwave pretreatment temperature distribution.
Background
The area and the storage amount of fast-growing artificial forests in China are at the top of the world, but fast-growing woods generally have the defects of poor permeability, difficulty in drying, later-stage corrosion prevention, flame retardant treatment and the like, so that the high added value utilization of the solid wood is not achieved.
The high-intensity microwave pretreatment is a new technology appearing in the field of wood modification in recent years, and the basic principle of the high-intensity microwave pretreatment is that the high-intensity microwave is utilized to carry out instantaneous treatment on wet wood, so that water in the wood obtains enough energy in a short time, phase change and gas hot-pressing effects are generated, the internal structure of the wood is damaged under the driving of steam expansion power, the fluid migration capacity is improved, and extremely favorable precondition is created for the drying and impregnation treatment of the wood in the later period, even the preparation of new materials.
At present, countries such as the United states, Australia and China have started to try special equipment for microwave pretreatment of high-strength wood, and research the influence rule of microwave pretreatment on the volume expansion rate, permeability and drying rate of the wood. The preliminary research result shows that the optimized high-intensity microwave pretreatment can increase the volume of the wood by more than 10 percent, increase the penetration amount of the preservative by 10 to 14 times, improve the drying rate by 5 to 10 times and obviously improve the drying quality. Even the Australian Melbourne university carries out disassembly and reconstruction treatment on the wood by the technology, and tries to produce novel wood with high permeability and low density and novel wood composite with high strength and high surface hardness. The research opens up a new way for the high-quality utilization of the wood resources of the fast-growing artificial forest.
However, during the wood microwave pretreatment study, researchers found that: after the wood is pretreated by microwave, the distribution of microscopic and macroscopic pores in the wood is not uniform enough, which brings great difficulty to the later-stage impregnation treatment of the wood and the preparation of a new high-performance material. The non-uniformity has a certain relation with the property of the wood and the non-uniformity of the dielectric constant distribution, however, the property of the wood cannot be changed, and only the heating external condition of the wood can be improved, so that the uniformity of the microwave field is improved, and finally, a more ideal wood microwave treatment effect is obtained. The microwave frequency and the microwave heating cavity are the main factors related to the heating condition, and the microwave frequency and the microwave heating cavity jointly determine the temperature distribution of the wood during heating. The microwave frequency for microwave treatment of wood is 0.915Ghz and 2.45Ghz, and the microwave with the frequency of 2.45Ghz is favorable for heating temperature distribution uniformity of wood with thinner thickness, and the frequency is adopted in design. After the frequency is selected, the center of the problem is transferred to the design of the microwave resonant cavity, so how to develop high-efficiency microwave pretreatment equipment by developing the microwave resonant cavity with uniform microwave energy distribution becomes a core and key problem restricting the research and development of the high-strength microwave pretreatment technology of the wood.
The most frequently adopted method for optimally designing the microwave resonant cavity is a computer simulation technology, and in order to ensure the reliability of a simulation result, the simulation temperature of a computer needs to be compared with an actual test result, the simulation precision of the model is verified, the model is corrected, and finally, an optimized mathematical model and the size parameters of the microwave resonant cavity are obtained. In addition, the resonant cavities with different feeding modes have great influence on the microwave energy utilization rate of the wood, the temperature distribution uniformity, the wood breakage rate and the like, and the wood microwave pretreatment conditions of the resonant cavities with different feeding modes during the comparative analysis test are required. At present, a traveling wave heater is a common microwave heating resonant cavity, namely, an oblique feed-in waveguide is arranged on a rectangular resonant cavity, and the design is mainly based on the requirements of safety aspects such as processing amount, ignition prevention, microwave leakage prevention and the like, so that the heating uniformity is not sufficiently researched. Since the wood is moving in the cavity, the uniformity of heating throughout the wood depends on the cross-section. Although the traveling wave heater microwaves can be absorbed by the wood through multiple reflections, the temperature distribution over the cross section of the wood is not improved. Because the microwave energy of the traveling wave heater is relatively concentrated at the feed inlet, localized high temperatures produce wood breakage rates. Although the traveling wave heater has a high microwave energy utilization rate, the temperature distribution uniformity is not good, the wood breakage rate is high, and the traveling wave heater is not the best choice.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems in the prior art, the resonant cavity for verifying the wood microwave pretreatment temperature distribution is high in utilization rate of wood microwave energy, uniform in microwave energy dispersion, good in temperature distribution uniformity and low in wood breakage rate.
In order to solve the technical problems, the invention adopts the technical scheme that:
a resonant cavity for verifying wood microwave pretreatment temperature distribution comprises a horizontally arranged main resonant cavity, at least one feed-in waveguide is arranged on the lateral side of the main resonant cavity, the main resonant cavity is communicated with the feed-in waveguide, the feed-in waveguide is horizontally arranged along the direction from the center of the main resonant cavity to the outside, and two end faces of the feed-in waveguide are hollow openings.
Preferably, the cross section of the feed waveguide is rectangular, the length of the rectangle is arranged along the horizontal direction, the width of the rectangle is arranged along the vertical direction, and the distance L from the hollowed-out opening at one end of the feed waveguide far away from the center of the main resonant cavity to the center of the main resonant cavity is greater than 1.1 times of the length of the rectangle.
Preferably, the main resonant cavity and the feed-in waveguide are both rectangular, the number of the feed-in waveguides is one, and the feed-in waveguide is arranged on one side surface of the main resonant cavity. Further, the length and the width of the main resonant cavity are both 0.197m and the height is 0.155m, and the length and the width of the rectangle of the cross section of the feed waveguide are 0.0953m and 0.0546 m.
Or preferably, the main resonant cavity and the feed-in waveguides are both rectangular, the number of the feed-in waveguides is two, and the two feed-in waveguides are respectively and symmetrically arranged on the side surface of the main resonant cavity. Further, the length and width of the main resonant cavity are both 0.197m and the height is 0.155m, and the length and width of the rectangle of the cross section of the feed waveguide are 0.0953m and 0.0546 m.
Or preferably, the main resonant cavity is cylindrical, the feed waveguides are rectangular, the number of the feed waveguides is three, and the three feed waveguides are arranged on the side surface of the main resonant cavity in central symmetry. Further, the diameter of the main resonant cavity is 0.197m, the height is 0.155m, and the length of the rectangle of the cross section of the feed waveguide is 0.0953m and the width is 0.0546 m.
Or preferably, the main resonant cavity is cylindrical, the feed waveguides are rectangular, the number of the feed waveguides is four, and the four feed waveguides are arranged on the side surface of the main resonant cavity in central symmetry. Further, the diameter of the main resonant cavity is 0.197m, the height is 0.155m, and the length of the rectangle of the cross section of the feed waveguide is 0.0953m and the width is 0.0546 m.
The resonant cavity for verifying the temperature distribution of the microwave pretreatment of the wood has the following advantages: the resonant cavity for verifying the wood microwave pretreatment temperature distribution comprises a horizontally arranged main resonant cavity, at least one horizontally arranged feed-in waveguide is arranged on the side of the main resonant cavity, the main resonant cavity is communicated with the feed-in waveguide, the feed-in waveguide is horizontally arranged along the direction outwards from the center of the main resonant cavity, and two end faces of the feed-in waveguide are hollowed-out openings.
Drawings
Fig. 1 is a schematic perspective view of a first embodiment of the present invention.
FIG. 2 is a graph of a simulated temperature profile of a wood surface when heated using an embodiment of the invention.
FIG. 3 is a simulated temperature profile of a central section of wood when heated using an embodiment of the invention.
Fig. 4 is a schematic perspective view of a second embodiment of the present invention.
FIG. 5 is a graph of a simulated temperature profile of a wood surface when heated using example two of the present invention.
Fig. 6 is a simulated temperature distribution plot of a central section of wood when heated using example two of the present invention.
Fig. 7 is a schematic perspective view of a third embodiment of the present invention.
Fig. 8 is a simulated temperature profile of a wood surface when heated using example three of the present invention.
Fig. 9 is a simulated temperature profile of a central section of wood when heated using example three of the present invention.
Fig. 10 is a schematic perspective view of a fourth embodiment of the present invention.
FIG. 11 is a graph of a simulated temperature profile of a wood surface when heated using an embodiment of the invention four.
Fig. 12 is a simulated temperature profile of a central section of wood when heated using an embodiment of the invention four times.
Detailed Description
The first embodiment is as follows:
as shown in fig. 1, the resonant cavity for verifying the temperature distribution of wood microwave pretreatment in the present embodiment includes a main resonant cavity a arranged horizontally, at least one feed-in waveguide is arranged laterally of the main resonant cavity a, the main resonant cavity and the feed-in waveguide are communicated with each other, the feed-in waveguide is arranged horizontally along a direction outward from a center of the main resonant cavity a, and both end surfaces of the feed-in waveguide are hollow openings. Referring to fig. 1, this embodiment represents a wood material placed at the center of the main cavity a as W.
As shown in fig. 1, the cross section of the feed waveguide is rectangular, the length of the rectangle is arranged along the horizontal direction, the width of the rectangle is arranged along the vertical direction, the distance L (see the mark in fig. 3) between the hollowed-out opening at one end of the feed waveguide far away from the center of the main resonant cavity a and the center of the main resonant cavity a is greater than 1.1 times of the length of the rectangle, and based on the above dimensions, the microwave matching between the structure, the dimension and the frequency of the main resonant cavity a and the feed waveguide in the group of resonant cavities can be realized, wherein the structure, the dimension and the frequency of the microwave are 2.; it goes without saying that the above-described structure can also be adapted by the person skilled in the art as desired to other frequencies of microwaves for heating wood, for example microwaves with a frequency of 0.915Ghz, etc.
In this embodiment, the main cavity a has a cylindrical shape, the feeding waveguides have a rectangular parallelepiped shape, the number of the feeding waveguides is four (see B, C, D, E in the figure), and the four feeding waveguides B, C, D, E are arranged on the side surface of the main cavity a in a central symmetry manner. It should be noted that, in order to achieve uniform distribution of microwave, the wood W is placed at the center of the main cavity a, and the specific shape of the main cavity a and the shape of the wood W are corresponding, so that the wood W in this embodiment is a cylinder (as shown in fig. 1).
In this embodiment, the diameter of the main resonant cavity a is 0.197m, the height is 0.155m, the length of the rectangle of the cross section of the feed waveguide is 0.0953m, and the width is 0.0546m, based on the above dimensions, the matching between the structure and the dimension between the main resonant cavity a and the feed waveguide in the group of resonant cavities of the microwave and the microwave can be realized; and the dimensions of the resonant cavity A and the feed waveguide B, C, D, E are smaller, and the feed of the main resonant cavity A and the feed waveguide are overlapped in the center of the main resonant cavity A, so that the central energy of the main resonant cavity A is higher, and therefore, the heat can be prevented from being accumulated at the feed inlet, and the heating of the wood is more uniform.
In this embodiment, the distance between the hollow opening at the end of the feed waveguide far from the center of the main cavity a and the center of the main cavity a is 0.1485m, which is greater than 1.1 times the length of the rectangle (0.0953m × 1.1 ═ 0.10483 m).
In addition, in the present embodiment, a temperature measuring hole is provided at the top of the main resonant cavity a, so that a temperature measuring sensor can be inserted. During the experiment, the temperature distribution of the wood W during microwave treatment is measured in an optical fiber sensing temperature measurement or infrared temperature measurement mode, the temperature distribution can be compared and analyzed with a simulation result, the microwave heating temperature distribution of the wood with different resonant cavities is verified, the reason of the temperature difference between the simulation result and the experiment is analyzed, and a model is improved so as to simulate and predict the temperature distribution more accurately.
In order to verify the temperature distribution uniformity of the embodiment, the embodiment adopts finite element analysis software COMSOLMUTIPhysics to carry out simulation, in the simulation calculation, wood with the water content of 20% is selected, and the thermal conductivity coefficient lambda of the wood is 0.14 x (1-0.72 x (25-T)/100) [ w/(m DEG C)](T is the temperature at that time), the specific heat C is 2130 ^ (1+ T/100) ^0.2(J/kg ℃), the density ρ is 427(kg/m3), the dielectric constant is 2.94-0.21J, and the initial temperature T is0At 15 ℃, TE10 waves are fed in the microwaves, the frequency is 2.45GHz, and the single-port feeding power is 1.5 kw. To calculate the temperature of each point of the wood, the wood is divided into a plurality of tiny parts, the energy and temperature relationship of each part is studied respectively (of course, the heat transfer with the rest parts needs to be considered), and then the results of each step are integrated together, thereby completing the whole calculation, which is the basic idea of finite element analysis. In the simulation calculation of this embodiment, the specific heat and the thermal conductivity of the wood vary with the temperature, and the temperature varies with time, so the specific heat, the thermal conductivity and the temperature are all functions of time, and if it is ensured that the three are values at the same time, the calculation time division of each step must be quite small, which is obviously very complicated and unnecessary. The calculation method can be adopted, firstly, the temperature of the wood is assumed to be unchanged in a short period of time, so that the specific heat and the heat conductivity coefficient are also constants, the energy absorbed by the wood in the period of time can be calculated by using the two constants, the temperature change of the wood is simultaneously solved, and the new temperature value is substituted into the specific heat and the heat conductivity coefficient to continue the cycle calculation until the preset time is calculated.
In the embodiment, finite element analysis software COMSOL Multiphysics is adopted to simulate and verify the temperature distribution of wood microwave pretreatment, and when the temperature distribution of wood microwave pretreatment is simulated and verified, an electromagnetic field and microwave energy distribution model and a heat transfer model for calculating heat transfer in the wood need to be established.
One) establishing an electromagnetic field and microwave energy distribution model:
in the theoretical simulation of the high-strength microwave heating process, when the electromagnetic field and the temperature field distribution condition in the wood W arranged in the main resonant cavity A are simulated, in order to simplify analysis and theoretical calculation, the following reasonable assumptions are firstly made on the heating model of the wood W: 1. the initial temperature and the water content of the wood W are uniformly distributed; 2. the volume of the wood W is kept unchanged in the microwave heating process; 3. the cylindrical wood W is coaxial with the main resonant cavity A; 4. the heat exchange between the wood surface and the air satisfies the boundary conditions of convection and heat transfer.
According to the Maxwell equation system, the electromagnetic field distribution in the wood in the microwave heating process satisfies the formulas (1) to (4).
In the formulae (1) to (4),which represents the strength of the electric field,which represents the intensity of the magnetic induction,which is indicative of the strength of the magnetic field,it is shown that the current density is,represents a potential shift, pcWhich represents the density of the free charge,it is shown that the operation of calculating the divergence is performed,indicating a rotation calculation. Wherein,σ is the conductivity, and is the dielectric constant, and μ is the permeability.
The distribution of the electromagnetic field inside the wood W can be calculated according to the formulas (1) to (4). In the embodiment, the microwave excitation source adopts a time-harmonic electromagnetic fieldFilm, i.e. electric field strengthAnd the intensity of the magnetic fieldThe values of (A) are:wherein,indicates the electric field intensityThe amplitude of the vibration of the vehicle,indicating the strength of the magnetic fieldI denotes an imaginary unit, ω denotes an angular frequency, and t denotes time. Magnetic induction intensityAnd electric displacementCan be expressed as electric field intensityAnd the intensity of the magnetic fieldThe functions are specifically shown in formulas (5) and (6).
In the formulae (5) and (6),it is shown that the calculation of the rotation degree is performed,indicates the electric field intensityThe amplitude of the vibration of the vehicle,indicating the strength of the magnetic fieldI denotes an imaginary unit, ω denotes an angular frequency, μ denotes a magnetic permeability, σ denotes a wire coefficient, denotes a dielectric constant, 'denotes a real part of a complex dielectric constant,' denotes an imaginary part of a complex dielectric constant,*is a complex dielectric constant of the dielectric ceramic,*can be expressed as*＝′+i″。
Formula (7) is obtained from formulae (5) and (6) (Ayappa, 1997).
In the formula (7), the reaction mixture is,it is shown that the operation of calculating the divergence is performed,denotes the electric field intensity, k is a dielectric property parameter of wood W, denotes the dielectric constant, ` denotes the real part of the complex dielectric constant, ` denotes the imaginary part of the complex dielectric constant,*is a complex dielectric constant of the dielectric ceramic,*can be expressed as*And ═ i ″. The electric field distribution in the wood W can be obtained by solving the formula (7). In this embodiment, the wood dielectric constant is assumed to be constant along the electric field direction, so the first term of equation (7) is zero, and equation (8) can be simplified.
In the formula (8), the reaction mixture is,it is shown that the operation of calculating the divergence is performed,denotes the electric field intensity, and k is the dielectric property parameter of wood W. The dielectric property parameter k of the wood W is expressed by the following formulas (9) to (11).
k＝α+iβ (9)
In the expressions (9) to (11), i represents an imaginary unit, f represents a microwave radiation frequency, c represents an optical velocity, tan represents a wood loss factor, and' represents a real part of a complex permittivity. The expression of the wood loss factor tan is shown in formula (12).
In the formula (12), 'denotes a real part of complex permittivity, and' denotes an imaginary part of complex permittivity.
In simulating the electric field distribution in the wood W, equation (8) is solved by the boundary conditions of the following equations (13) and (14).
In the formulae (13) and (14), n represents a surface normal unit vector,electric field strength indicating air boundary positionThe amplitude of the vibration of the vehicle,electric field intensity indicating boundary position of woodThe amplitude of the vibration of the vehicle,indicates nullMagnetic field strength at gas boundary positionThe amplitude of the vibration of the vehicle,magnetic field strength indicating boundary position of woodWherein subscript 1 represents air and subscript 2 represents wood.
The expression (14) can also be expressed as the electric field intensity by the expression shown in the expression (15)As a function of (c).
In the formula (15), the reaction mixture is,indicates the electric field intensityThe amplitude of the vibration of the vehicle,indicating the strength of the magnetic fieldI denotes the imaginary unit, μ0Denotes the medium permeability and ω denotes the angular frequency.
The solution of equation (8) consists of two oppositely propagating wave functions as shown in equation (16).
E＝A1eikr+B1e-ikr (16)
In the formula (16), E represents an electric field, i represents an imaginary unit, k represents a wave number, r represents a radius, A1And B1The boundary parameters determined by the boundary condition equations (13) and (14) are shown, respectively. According to the solved electric field E in the wood W, the Poynting theorem can be applied to solve the energy density Q of the electromagnetic field at any position in the wood W as shown in the formula (17), so that the establishment of an electromagnetic field and microwave energy distribution model is completed.
In the formula (17), Q represents the electromagnetic field energy density at any position in the wood W, ω represents the angular frequency,0is a dielectric constant in vacuum, denotes the dielectric constant, "denotes the imaginary part of the complex dielectric constant,*is a complex dielectric constant of the dielectric ceramic,*can be expressed as*＝′+i″，Which represents the strength of the electric field,indicates the electric field intensityComplex conjugation of (a).
And II) establishing a thermal migration model.
The microscopic heat balance inside the wood W during microwave pretreatment can be described by formula (18) (Ayappa, 1997).
In the formula (18), ρ represents the density of wood, CPDenotes the specific heat of wood, kTWhich represents the thermal conductivity of the wood material,expression solutionDivergence calculation, T denotes temperature and Q is the electromagnetic field energy density within the wood.
The boundary conditions of formula (18) are shown in formulas (19) and (20).
t＝0，T＝Tini，0≤r≤R (19)
t＞0， <math>
<mrow>
<mo>-</mo>
<msub>
<mi>k</mi>
<mi>T</mi>
</msub>
<mfrac>
<mrow>
<mo>∂</mo>
<mi>T</mi>
</mrow>
<mrow>
<mo>∂</mo>
<mi>r</mi>
</mrow>
</mfrac>
<mo>=</mo>
<mi>h</mi>
<mrow>
<mo>(</mo>
<mi>T</mi>
<mo>-</mo>
<msub>
<mi>T</mi>
<mi>a</mi>
</msub>
<mo>)</mo>
</mrow>
<mo>+</mo>
<msub>
<mi>L</mi>
<mi>vap</mi>
</msub>
<msubsup>
<mi>k</mi>
<mi>m</mi>
<mo>'</mo>
</msubsup>
<mrow>
<mo>(</mo>
<msub>
<mi>C</mi>
<mrow>
<mi>w</mi>
<mo>,</mo>
<mi>s</mi>
</mrow>
</msub>
<mo>-</mo>
<msub>
<mi>C</mi>
<mi>equi</mi>
</msub>
<mo>)</mo>
</mrow>
<mo>,</mo>
</mrow>
</math> r＝R (20)
In the formulae (19) and (20), T represents time, T represents temperature, and T representsiniDenotes the initial temperature of the wood, kTDenotes the thermal conductivity of the wood, h is the coefficient of thermal conductivity in the wood, TaIndicating the initial temperature of air, LvapIs the heat of vaporization of water, k'mIs the water exchange coefficient, Cw,sIs the surface water content of the wood CequiIn order to balance the moisture content with air, R is the radius of the cylindrical wood W.
Finally, the simulated temperature distribution graph of the surface of the wood W when heated by using the resonant cavity of the present embodiment is obtained through simulation calculation of the finite element analysis software COMSOL Multiphysics, as shown in fig. 2, and in the right-side temperature comparison schematic bar, the lower limit value is 29.641 degrees celsius, and the upper limit value is 99.657 degrees celsius. As can be seen in fig. 2, the microwave energy is mostly absorbed by the central area of the wood W. Therefore, a representative central section of the wood W is selected as a subject to be studied, and the simulated temperature profiles of the central section of the wood W are individually extracted to obtain the simulated temperature profiles shown in fig. 3, where the lower limit value of the right-side temperature contrast graph is 29.641 degrees celsius and the upper limit value thereof is 98.43 degrees celsius.
Example two:
the basic structure of this embodiment is the same as that of the first embodiment, and the main differences are as follows: the number of feed waveguides differs.
As shown in fig. 4, the number of the feed waveguides in this embodiment is three (see B, C, D in the figure), and three feed waveguides B, C, D are arranged on the side of the main cavity a in central symmetry.
The present embodiment uses finite element analysis software COMSOL Multiphysics for simulation, and establishes an electromagnetic field and microwave energy distribution model and a heat transfer model for calculating heat transfer inside the wood material, which are identical to those in the first embodiment. Finally, the simulated temperature distribution of the surface of the wood W when heated by using the resonant cavity of the present embodiment obtained through simulation calculation of the finite element analysis software COMSOL Multiphysics is shown in fig. 5. As can be seen in fig. 5, the microwave energy is mostly absorbed by the central area of the wood W. Therefore, a representative central cross section of the wood W is selected as a subject to be studied, and the simulated temperature distribution map of the central cross section of the wood W is individually extracted to obtain a simulated temperature distribution map as shown in fig. 6.
Example three:
the basic structure of this embodiment is the same as that of the first embodiment, and the main differences are as follows: the shape of the main cavity a, the number of fed waveguides, are different. Also, in general, the wood W is placed at the center of the main cavity a, and in order to achieve uniform distribution of the microwave, the shape of the wood W is related to the shape of the main cavity a, for example, the shape of the wood W in the embodiment is a rectangular parallelepiped, unlike the shape of the wood W in the first embodiment which is a cylinder.
As shown in fig. 7, the main cavity a and the feeding waveguides in this embodiment are rectangular, the number of the feeding waveguides is two (see B, C in the figure), and the two feeding waveguides B, C are respectively and symmetrically disposed on the side of the main cavity a, that is: the feed waveguide B is disposed on one side surface of the main cavity a, and the feed waveguides C are symmetrically disposed on the other side surface of the main cavity a opposite to the aforementioned side surface.
In this embodiment, the length and width of the main cavity a are 0.197m and the height is 0.155m, and the length of the rectangle of the cross section of the feed waveguide is 0.0953m and the width is 0.0546 m.
In this embodiment, finite element analysis software COMSOL Multiphysics is used for simulation, and when an electromagnetic field and microwave energy distribution model and a thermal migration model for calculating heat transfer inside the wood are established, because the shape of the wood W in this embodiment is a cuboid (different from the cylinder in the first embodiment), boundary conditions in the electromagnetic field and microwave energy distribution model and the thermal migration model are slightly different, but the basic principle of modeling is the same as that in the first embodiment, and therefore, the description is not repeated here. Finally, the simulated temperature distribution of the surface of the wood W when heated by using the resonant cavity of the present embodiment obtained through simulation calculation of the finite element analysis software COMSOL Multiphysics is shown in fig. 8. As can be seen in fig. 8, the microwave energy is mostly absorbed by the central area of the wood W. Therefore, a representative central cross section of the wood W is selected as a subject to be studied, and the simulated temperature distribution map of the central cross section of the wood W is individually extracted to obtain a simulated temperature distribution map as shown in fig. 9.
Example four:
the basic structure of this embodiment is the same as that of the first embodiment, and the main differences are as follows: the shape of the main cavity a, the number of fed waveguides, are different. The shape of the wood W in this embodiment is different from that of the embodiment.
As shown in fig. 10, in this embodiment, the main cavity a and the feeding waveguide are both rectangular parallelepiped in shape, the number of the feeding waveguides is one (see B in the figure), and the feeding waveguide B is disposed on one side surface of the main cavity a.
In this embodiment, the length and width of the main cavity a are 0.197m and the height is 0.155m, and the length and width of the rectangle of the cross section of the feed waveguide B are 0.0953m and 0.0546 m.
In this embodiment, finite element analysis software COMSOL Multiphysics is used for simulation, and when an electromagnetic field and microwave energy distribution model and a thermal migration model for calculating heat transfer inside the wood are established, because the shape of the wood W in this embodiment is a cuboid (different from the cylinder in the first embodiment), boundary conditions in the electromagnetic field and microwave energy distribution model and the thermal migration model are slightly different, but the basic principle of modeling is the same as that in the first embodiment, and therefore, the description is not repeated here. Finally, the simulated temperature distribution of the surface of the wood W when heated by using the resonator according to the present embodiment obtained through simulation calculation of the finite element analysis software COMSOL Multiphysics is shown in fig. 11. As can be seen in fig. 11, the microwave energy is mostly absorbed by the central area of the wood W. Therefore, a representative central cross section of the wood W is selected as a subject to be studied, and the simulated temperature distribution map of the central cross section of the wood W is individually extracted to obtain a simulated temperature distribution map as shown in fig. 12.
By combining the simulated temperature distribution diagram of the surface of the wood W and the simulated temperature distribution diagram of the central section of the wood W in the first to fourth embodiments, it can be known that the microwave energy in the first to fourth embodiments is relatively dispersed on the wood W and is not concentrated at the feed inlet, so that the wood breakage rate caused by local high temperature can be effectively reduced, and the rules of the influence of various feed modes on the wood microwave energy utilization rate, the temperature distribution uniformity and the wood breakage rate can be effectively analyzed. Furthermore, for the one-port feeding manner (microwave is concentrated on one side of the wood) in the fourth embodiment, the two-port feeding manner in the third embodiment enables the microwave energy to be distributed symmetrically, further, the three-port feeding manner in the second embodiment enables the microwave energy to be distributed more uniformly, and the four-port feeding manner in the first embodiment enables the microwave energy to be distributed most uniformly relatively, so it can be determined that the more the number of the horizontally arranged feeding waveguides arranged laterally of the main resonant cavity a is, the higher the utilization rate of the microwave energy of the wood is, the more the microwave energy is uniformly dispersed, the better the temperature distribution uniformity is, and the lower the wood breakage rate is.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.
Claims (10)
1. A resonant cavity for verifying wood microwave pretreatment temperature distribution is characterized in that: the feed-in waveguide type resonant cavity comprises a main resonant cavity which is horizontally arranged, at least one feed-in waveguide is arranged on the lateral side of the main resonant cavity, the main resonant cavity is communicated with the feed-in waveguide, the feed-in waveguide is horizontally arranged along the direction from the center of the main resonant cavity to the outside, and two end faces of the feed-in waveguide are hollow openings.
2. The resonant cavity for verifying temperature distribution of microwave pretreatment of wood according to claim 1, wherein: the cross section of the feed-in waveguide is rectangular, the length of the rectangle is arranged along the horizontal direction, the width of the rectangle is arranged along the vertical direction, and the distance L from the hollowed-out opening at one end of the feed-in waveguide far away from the center of the main resonant cavity to the center of the main resonant cavity is larger than 1.1 times of the length of the rectangle.
3. The resonant cavity for verifying the temperature distribution of microwave pretreatment of wood according to claim 2, wherein: the main resonant cavity and the feed-in waveguide are both rectangular, the number of the feed-in waveguides is one, and the feed-in waveguide is arranged on one side surface of the main resonant cavity.
4. A resonant cavity for verifying the temperature distribution of microwave pretreatment of wood according to claim 3, wherein: the length and width of the main resonant cavity are both 0.197m and the height is 0.155m, and the length and width of the rectangle of the cross section of the feed waveguide are 0.0953m and 0.0546 m.
5. The resonant cavity for verifying the temperature distribution of microwave pretreatment of wood according to claim 2, wherein: the main resonant cavity and the feed-in waveguides are both rectangular, the number of the feed-in waveguides is two, and the two feed-in waveguides are symmetrically arranged on the side face of the main resonant cavity respectively.
6. The resonant cavity for verifying temperature distribution of microwave pretreatment of wood according to claim 5, wherein: the length and width of the main resonant cavity are both 0.197m and the height is 0.155m, and the length and width of the rectangle of the cross section of the feed waveguide are 0.0953m and 0.0546 m.
7. The resonant cavity for verifying the temperature distribution of microwave pretreatment of wood according to claim 2, wherein: the main resonant cavity is cylindrical, the feed-in waveguides are cuboid, the number of the feed-in waveguides is three, and the three feed-in waveguides are arranged on the side face of the main resonant cavity in a centrosymmetric mode.
8. The resonant cavity for verifying temperature distribution of microwave pretreatment of wood according to claim 7, wherein: the diameter of the main resonant cavity is 0.197m, the height is 0.155m, and the length of the rectangle of the cross section of the feed waveguide is 0.0953m and the width is 0.0546 m.
9. The resonant cavity for verifying the temperature distribution of microwave pretreatment of wood according to claim 2, wherein: the main resonant cavity is cylindrical, the feed-in waveguides are rectangular, the number of the feed-in waveguides is four, and the four feed-in waveguides are arranged on the side face of the main resonant cavity in a centrosymmetric mode.
10. The resonant cavity for verifying temperature distribution of microwave pretreatment of wood according to claim 9, wherein: the diameter of the main resonant cavity is 0.197m, the height is 0.155m, and the length of the rectangle of the cross section of the feed waveguide is 0.0953m and the width is 0.0546 m.
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| CN105338677A (en) * | 2015-11-25 | 2016-02-17 | 四川大学 | Pipeline type industrial microwave heating device |
| CN105357791A (en) * | 2015-12-15 | 2016-02-24 | 南京三乐微波技术发展有限公司 | Microwave transmission system used for microwave heating system |
| CN105818234A (en) * | 2016-03-16 | 2016-08-03 | 中南林业科技大学 | Multi-cavity multi-port quickly-replacing wood microwave pretreatment device and application method thereof |
| CN107308895A (en) * | 2017-06-09 | 2017-11-03 | 四川大学 | A kind of thermostatic type microwave continuous flow reactor |
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| CN110000691A (en) * | 2019-04-27 | 2019-07-12 | 林丽芳 | A kind of solid wood board wire-drawing frame that timber processing is wound with electric resonance solution tide |
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| CN105338677B (en) * | 2015-11-25 | 2019-01-15 | 四川大学 | Duct type industrial microwave heating device |
| CN105338677A (en) * | 2015-11-25 | 2016-02-17 | 四川大学 | Pipeline type industrial microwave heating device |
| CN105357791A (en) * | 2015-12-15 | 2016-02-24 | 南京三乐微波技术发展有限公司 | Microwave transmission system used for microwave heating system |
| CN105818234A (en) * | 2016-03-16 | 2016-08-03 | 中南林业科技大学 | Multi-cavity multi-port quickly-replacing wood microwave pretreatment device and application method thereof |
| CN107308895A (en) * | 2017-06-09 | 2017-11-03 | 四川大学 | A kind of thermostatic type microwave continuous flow reactor |
| CN107308895B (en) * | 2017-06-09 | 2019-12-24 | 四川大学 | Constant-temperature microwave continuous flow reactor |
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| CN110000691A (en) * | 2019-04-27 | 2019-07-12 | 林丽芳 | A kind of solid wood board wire-drawing frame that timber processing is wound with electric resonance solution tide |
| CN112229146A (en) * | 2020-10-20 | 2021-01-15 | 西安电子科技大学 | Drying control method, system and equipment for microwave drying, simulation optimization and application |
| CN112229146B (en) * | 2020-10-20 | 2022-05-03 | 西安电子科技大学 | Drying control method, system and equipment for microwave drying, simulation optimization and application |
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Application publication date: 20150722 |