A microwave drying device based on a multi-band magnetron and a drying method using the same
By using a multi-band magnetron microwave drying device, which combines microwave signals in TE10 and TE20 modes, the problems of uneven microwave drying and high energy consumption have been solved, achieving uniform and efficient material drying while reducing energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HENAN UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2026-03-20
- Publication Date
- 2026-07-03
AI Technical Summary
Existing microwave drying technologies suffer from uneven material drying due to uneven microwave field distribution and poor overall control of energy consumption and drying efficiency.
The microwave drying equipment based on multi-band magnetrons combines drying unit, detection unit, control unit and dehumidification unit. It controls microwave signals of different frequency bands simultaneously or on demand through microwave signals in TE10 and TE20 modes, monitors material humidity and temperature in real time, and dynamically adjusts microwave power density and energy output.
It achieves uniformity and quality improvement in material drying, reduces energy consumption and operating costs, and adapts to standardized and automated production of various materials.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of grain drying technology, and particularly relates to a microwave drying device and drying method based on a multi-band magnetron. Background Technology
[0002] Drying is an important physical processing technology for the deep processing of agricultural products. It uses a humidity gradient to promote the release of moisture from the inside of the material to the outside until the gradient disappears, thus achieving the evaporation / removal of moisture. It is a key preservation method for fruits, vegetables, grains, and other products.
[0003] Traditional drying techniques include natural air drying and hot air drying. However, the drawbacks of traditional drying techniques are as follows:
[0004] 1. Natural air drying: It depends on the weather, has low drying efficiency, is prone to contamination and spoilage, takes up space and requires a lot of labor, and the drying effect is uneven. It has been gradually phased out.
[0005] 2. Hot air drying (currently the most widely used method in China): It relies on the convection of hot air for heat exchange, and the heat is conducted from the surface to the inside, which easily leads to burnt outside and damp inside; the surface temperature exceeding 45°C will cause protein denaturation, surface hardening and other quality problems, and will also affect the gluten strength and enzyme activity of flour products; the drying cycle is long (8-12 hours) and the unit energy consumption is high, which does not meet the requirements of low carbon.
[0006] Microwave drying involves emitting electromagnetic waves of a certain power into a cavity via a microwave transmitter. These waves can directly penetrate the material, simultaneously heating its interior and exterior, thus achieving drying. This heating method eliminates the need for a drying medium. Based on the principle of volumetric heating, microwave drying directly stimulates water molecules within the material, enabling rapid heating and evaporation, and shortening drying time. For drying grains, fruits, vegetables, medicinal herbs, and other foods, microwaves can reduce nutrient loss, improve product quality, inhibit shrinkage, reduce microstructural collapse, increase porosity, and enhance rehydration properties.
[0007] Compared with traditional drying technologies, microwave drying has significant advantages such as high efficiency and speed, selective heating, ease of control, and strong heat penetration, effectively avoiding the adverse effects of traditional drying methods on material quality. However, in practical applications, microwave drying still has some problems.
[0008] Existing problems of microwave drying technology:
[0009] 1. Uneven microwave field distribution leads to uneven material drying;
[0010] 2. The overall control of energy consumption and drying efficiency during the drying process is not satisfactory. Summary of the Invention
[0011] The present invention aims to provide a microwave drying device and drying method based on a multi-band magnetron that is easy to use and has good results.
[0012] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a microwave drying device based on a multi-band magnetron, comprising a drying cavity, a drying unit located in the drying cavity, a detection unit, a control unit, a transmission unit, and a dehumidification unit;
[0013] The transmission unit moves through the drying chamber;
[0014] The drying unit includes a magnetron, a waveguide dual-directional coupler, a power divider, a mode converter, a detector, and an attenuator. The magnetron is electrically connected to the waveguide dual-directional coupler. The coupling end of the waveguide dual-directional coupler is connected to the detector and the attenuator in sequence. The electrical signal output end of the attenuator is connected to the signal input end of the control unit. At the same time, the through end of the waveguide dual-directional coupler is connected to the power divider. The first branch end of the power divider is connected to the mode converter. The second branch end of the power divider and the output end of the mode converter simultaneously output microwave signals toward the drying cavity.
[0015] The detection unit includes an infrared temperature sensor and an infrared humidity sensor. The signal output terminals of the infrared temperature sensor and the infrared humidity sensor are respectively connected to the signal input terminal of the control unit. The control unit outputs signals to control the operation of the drying unit, the transmission unit and the dehumidification unit.
[0016] The drying chamber is equipped with a material inlet and a material outlet. The transmission unit includes a conveyor belt that enters the drying chamber from the material inlet and exits the drying chamber from the material outlet. Microwave suppressors are installed at both the material inlet and the material outlet.
[0017] It also includes a pulse power source. The control unit sends commands to the pulse power source, and the pulse power source outputs pulse energy according to the commands. The pulse energy provides power to the magnetron.
[0018] The magnetrons are at least two, and multiple magnetrons are connected in parallel.
[0019] The microwave drying method based on a multi-band magnetron using the above-mentioned microwave drying apparatus comprises the following steps in sequence:
[0020] Step 1: Select fresh materials as the objects to be dried;
[0021] Step 2: Spread the material evenly on the conveyor belt;
[0022] Step 3: The conveyor belt carries the fresh material into the drying chamber; the drying unit operates to dry the material.
[0023] Step 4: The drying process is carried out using TE.10 The mode performs microwave drying on the material in the middle region of the drying chamber, while employing TE... 20 The method involves drying wheat on both sides of the cavity;
[0024] Step 5: During the drying process in step 4, the detection unit monitors the humidity change of the material in the drying chamber in real time. When the detection unit detects that the humidity of the material in the drying chamber reaches the preset drying standard, it feeds back to the control unit, and the control unit controls the drying process to complete.
[0025] Step 6: After the drying process is completed, the conveyor belt will carry the material out of the drying chamber and collect the grain.
[0026] During the drying process in step 4, the control unit outputs a signal to start the dehumidification device, which then discharges the hot and humid air from the drying chamber.
[0027] During the drying process in step 4, the humidity value of the material is monitored. The control unit receives the humidity value and, based on this,
[0028] When the moisture content is 30%, the microwave power density is 790~810w / kg;
[0029] With a moisture content of 22% to 30%, the power density decreases by 50 to 70 W / kg for every 2% reduction in moisture content.
[0030] With a moisture content of 16-22%, the power density decreases by 80-90 W / kg for every 2% reduction in moisture content.
[0031] With a moisture content of 12-16%, the power density decreases by 95-105 W / kg for every 2% reduction in moisture content.
[0032] The output signal ensures that the microwave power density within the drying cavity meets the requirements.
[0033] In step 5, when the material temperature exceeds the maximum threshold, the control unit outputs a signal to the pulse power source to reduce the output energy of the pulse power. The material layer thickness is 5-10 cm.
[0034] The moisture content of fresh materials is 20%-30% at the initial moisture content.
[0035] The beneficial effects of the present invention through the above technical solutions are as follows:
[0036] 1. The microwave drying equipment described in this invention has a simple structure and is easy to operate. Through the combined application of the drying unit, detection unit, dehumidification unit and control unit, and the use of a multi-band magnetron, it is suitable for simultaneous transmission of multi-band microwave signals or for controlling the individual transmission of different frequency band microwave signals as needed, and can accurately adapt to the drying needs of different materials.
[0037] 2. Infrared temperature and humidity sensors monitor and provide accurate feedback on the humidity of materials during the drying process in real time, preventing material deformation caused by excessive temperature.
[0038] 3. The control unit actively adjusts power parameters in real time based on feedback data, combining high intelligence, process coordination, and wide applicability;
[0039] 4. This device simultaneously achieves standardized and automated production, and is easy to modify based on the existing equipment architecture, with good scalability, and is suitable for drying various materials.
[0040] 5. The microwave drying method described in this invention adopts a multi-mode, actively controlled microwave drying method. Different modes are used to dry materials in different areas of the drying chamber, which can effectively avoid problems such as uneven heating of materials and damage to quality, improve drying efficiency and quality, and reduce energy consumption and operating costs. Attached Figure Description
[0041] Figure 1 This is a schematic diagram of the microwave drying equipment described in this invention;
[0042] Figure 2 This is a block diagram illustrating the principle of the drying unit.
[0043] Figure 3 This is a schematic diagram of the mode conversion system structure;
[0044] Figure 4 for Figure 3 Sectional view;
[0045] Figure 5 For TE 10 Model electric field distribution diagram,
[0046] Figure 6 For TE 20 Model electric field distribution diagram;
[0047] Figure 7 For TE 10 Pattern and TE 20 Temperature field distribution diagram of the combined effects of the models;
[0048] Figure 8 This is a schematic diagram showing the change in power density with water content;
[0049] Figure 9 For TE 10 Model wheat drying uniformity coefficient;
[0050] Figure 10 The uniformity coefficient of wheat drying in multiple modes;
[0051] Figure 11 Figure 1 shows the uniformity coefficient of wheat microwave drying at different power levels.
[0052] 1-Input port flange, 2-Output port flange, 3-Feed waveguide housing, 4-First transition waveguide housing, 6-Second transition waveguide housing, 5-Mode converter, 7-Transmission belt, 8-Drying chamber, 9-Drying unit, 10-Dehumidification unit. Detailed Implementation
[0053] Example 1: A microwave drying device based on a multi-band magnetron, such as... Figures 1-4 As shown, it includes a drying chamber 8, a drying unit 9, a detection unit, a control unit, a transmission unit, and a dehumidification unit 10.
[0054] The drying chamber 8 is equipped with a material inlet and a material outlet. A transmission unit moves through the drying chamber 8. In this embodiment, the transmission unit includes a horizontally placed conveyor belt 7 located at the bottom of the drying chamber 8, which carries and transports the material. The conveyor belt 7 enters the drying chamber 8 from the material inlet and exits the drying chamber 8 from the material outlet. Microwave suppressors are installed at both the material inlet and the material outlet. The internal absorbing material or multi-section waveguide structure attenuates leaked microwave signals, ensuring that microwave energy is concentrated on the material and preventing microwave leakage from harming operators or surrounding equipment.
[0055] The dehumidification unit 10 is used to remove moisture from the drying chamber 8, in conjunction with the drying of the material. In this embodiment, a centrifugal fan is used as the dehumidification unit. The centrifugal fan can extract the hot and humid air from the drying chamber, improving drying efficiency. During use, the control unit can control the operation of the centrifugal fan. Controlling the operation of the centrifugal fan through the control unit is a mature existing technology, and this embodiment does not involve any improvement to this solution.
[0056] The control unit includes a PLC controller, which can receive electrical signals and output signals to control the operation of the transmission unit, drying unit 9 and dehumidification unit 10 based on the received electrical signals.
[0057] The drying unit 9 includes a pulse power source. The control unit sends commands to the pulse power source, and the pulse power source outputs pulse energy according to the commands. The pulse energy provides power to the magnetron. The control unit changes the commands sent to the pulse power source, thereby changing the energy of the pulse power source and thus changing the power of the magnetron. In this embodiment, the control unit outputs a signal to the pulse power source, thereby changing the output power of the pulse power source. This is a mature existing technology, and the specific implementation method can use existing technology, which will not be described in detail in this embodiment.
[0058] In this embodiment, the drying unit 9 also includes a magnetron, a waveguide dual directional coupler, a power divider, a mode converter, a detector, and an attenuator.
[0059] The magnetron is used to generate the microwave signals required for microwave drying. Magnetrons suitable for different frequency bands are selected to enable simultaneous transmission of multiple frequency band microwave signals or to control the individual transmission of different frequency band microwave signals as needed. Since materials often operate in low-frequency mode during drying, the different frequency bands in this embodiment are chosen to adapt to different drying scenarios and broaden the application range. For example, a low-frequency band is used to dry materials thicker than 10cm, while a high-frequency band is used to dry materials approximately 1cm thick.
[0060] The core of changing the microwave frequency band is to replace the magnetron with one corresponding to the frequency band. Using a high-frequency magnetron will output high-frequency microwaves, and using a low-frequency magnetron will output low-frequency microwaves. If it is necessary to output both high-frequency and low-frequency microwaves simultaneously, a multi-magnetron configuration can be used, with high-frequency and low-frequency magnetrons installed separately.
[0061] Users can replace the magnetron with one of different frequency bands according to their own drying needs, thereby meeting their drying requirements.
[0062] The device uses multiple magnetrons; in this embodiment, two magnetrons are used. The two magnetrons can use the same frequency band or different frequency bands. For example, when drying materials, both magnetrons can use the low-frequency band simultaneously.
[0063] It is important to note here that the two magnetrons are connected in parallel. Of course, for expansion purposes, three or four magnetrons can also be used in this embodiment, simply by adding appropriate waveguide dual directional couplers, power dividers, mode converters, detectors, and attenuators.
[0064] In this embodiment, each magnetron is electrically connected to a waveguide dual-directional coupler. The coupling ends of the waveguide dual-directional coupler are connected to a detector and an attenuator in sequence. The coupling amount of the waveguide coupler is only required to meet the detection requirements, and the specific coupling amount is not limited. The electrical signal output end of the attenuator is connected to the control unit. At the same time, the through end of the waveguide dual-directional coupler is connected to a power divider. The first branch end of the power divider is connected to a mode converter. The second branch end of the power divider and the output end of the mode converter simultaneously output microwave signals toward the drying cavity 8.
[0065] When working, the magnetron generates TE. 10 Microwave signal in mode, TE 10The microwave signal in the mode undergoes "directional transmission + signal sampling" through a waveguide dual directional coupler. The waveguide dual directional coupler couples out a certain amount of microwave signal and transmits it to the detector and attenuator. The waveguide dual directional coupler extracts the forward-transmitted microwave power component and feeds it into the detector and attenuator. The detector and attenuator process the microwave signal, converting the power signal into a quantizable electrical signal. The attenuator outputs an electrical signal to the control unit. The control unit monitors the microwave power based on the received signal. During use, the control unit determines whether the microwave power value meets the set value based on the received power signal.
[0066] When in use, the waveguide dual directional coupler suppresses the coupling output of reverse power to avoid signal crosstalk from interfering with the monitoring accuracy.
[0067] During implementation, the through-hole of the waveguide dual directional coupler continuously transmits the remaining microwave signal to the power divider. The microwave signal then travels through the power divider to the mode converter, which converts the microwave signal to its TE (transmission frequency). 10 Mode conversion to TE 20 The mode is transmitted to the drying chamber 8 for drying. Simultaneously, another channel of the power distributor directly transmits the microwave's TE signal. 10 The mode is transmitted to drying chamber 8, where it undergoes microwave drying, thereby achieving TE. 10 and TE 20 Both modes perform drying operations simultaneously within the drying chamber 8.
[0068] In this embodiment, to accommodate the installation of the mode converter, a feed waveguide housing 3 is installed outside the drying cavity 8. The front end of the feed waveguide housing 3 is provided with an input flange 1, which is connected to the housing of the power divider. The first branch of the power divider is connected through the input flange 1. The feed waveguide housing 3 contains a waveguide cavity, and the first branch of the power divider inputs the microwave signal into the waveguide cavity through the input flange 1. The rear of the feed waveguide housing 3 is sequentially connected to a first transition waveguide housing 4 and a second transition waveguide housing 6. Both the first transition waveguide housing 4 and the second transition waveguide housing 6 also contain waveguide cavities for microwave transmission.
[0069] A mode converter 5 is installed between the first transition waveguide housing 4 and the second transition waveguide housing 6. The waveguide cavity inside the first transition waveguide housing 4 is directly connected to the microwave input port of the mode converter 5, and the microwave output port of the mode converter 5 is directly connected to the waveguide cavity of the second transition waveguide housing 6. An output flange 2 is connected to the waveguide cavity of the second transition waveguide housing 6. The output flange 2 is connected to the wave inlet of the drying cavity 8 and is used to oriented the wave inlet of the drying cavity 8 toward the inside of the drying cavity 8.
[0070] Meanwhile, the second branch of the power divider is also connected to the inlet of the drying cavity 8.
[0071] The magnetron generates TE under the action of a pulsed power source. 10 The microwave signal in the mode enters a waveguide dual directional coupler, from which a portion is coupled out for the control unit to detect microwave power; the other portion enters a power divider, where it is split into two paths. One path goes to a mode converter, where it is converted into a TE signal. 20 The microwave signal of the mode, and another TE 10 The microwave signal is output from the power divider, and the output is still TE. 10 Mode microwave signal, ultimately, TE 10 Mode microwave signal and TE 20 The microwave signal of the mode is sent into the drying chamber together to dry the material.
[0072] The detection unit includes an infrared temperature sensor and an infrared humidity sensor. The signal output terminals of the infrared temperature sensor and the infrared humidity sensor are respectively connected to the signal input terminal of the control unit. As is known above, the control unit is a PLC. The PLC receives the signals from the infrared temperature sensor and the infrared humidity sensor and obtains temperature and humidity data based on the received signals. This is a mature existing technology, and this embodiment does not involve any improvement in this regard. At the same time, its implementation method will not be described in detail.
[0073] This embodiment also uses TE. 10 and TE 20 Two modes of microwave signals are used to dry materials, compared to simple TE. 10 mode or TE 20 This mode provides better and more thorough drying, because of the TE... 10 Microwave signals in the mode such as Figure 5 As shown, the electric field mainly acts on the middle region, thus its drying effect on the sides is poor; while TE 20 Patterns, such as Figure 6 As shown, its electric field mainly acts on the two sides, and its drying effect on the middle is poor; while the combined TE 10 and TE 20 If there are two modes, such as Figure 7 As shown in the figure, the temperature field distribution during wheat drying indicates that the drying effect is more significant.
[0074] This invention uses TE 10 and TE 20 The dual-mode drying of materials yields better results compared to a single-mode drying because the multi-mode process involves a more uniform temperature field. Figure 5 , 6 As shown in Figures 7 and 8.
[0075] This invention discloses a microwave drying device based on a multi-band magnetron. It has a simple structure and is easy to operate. Through the combined application of drying unit 9, detection unit, dehumidification unit 10 and control unit, the multi-band magnetron is used to realize the simultaneous transmission of multi-band microwave signals or the individual transmission of different frequency band microwave signals as needed. It can accurately adapt to the drying needs of different materials and has a good drying effect.
[0076] This embodiment also discloses a microwave drying method based on a multi-band magnetron using the above-mentioned microwave drying apparatus, the method comprising the following steps in sequence:
[0077] Step 1: Select fresh material as the object to be dried; the moisture content of the fresh material should be 20%-30% at its initial moisture content.
[0078] Step 2: Spread the material evenly on conveyor belt 7; the material thickness should be 5-10 cm.
[0079] Step 3: Conveyor belt 7 carries fresh material into drying chamber 8; drying unit 9 operates to dry the material;
[0080] Step 4: The drying process is carried out using TE. 10 The microwave signal of the mode performs microwave drying treatment on the material in the middle area of the drying chamber 8, while using TE 20 The microwave signal of the mode dries the wheat on both sides of the drying chamber 8;
[0081] Step 5: During the drying process in Step 4, the detection unit monitors the humidity changes of the material in the drying chamber 8 in real time. When the detection unit detects that the humidity of the material in the drying chamber 8 has reached the preset storage standard, it feeds back to the control unit. The control unit outputs a signal to the pulse signal source, which stops generating energy to the magnetron. The magnetron then stops emitting microwave signals, and the drying process ends at this point. Note that the storage standards vary for different materials. This embodiment does not limit the specific standards; the storage standards for different materials are mature existing technologies.
[0082] Step 6: After the drying process is completed, the control unit outputs a signal to make the conveyor belt 7 work. The conveyor belt 7 carries the material out of the drying chamber 8, and finally the grain is collected.
[0083] During the drying process in step 4, the control unit outputs a signal to activate the dehumidification device, which removes moisture from the drying chamber 8. To control power consumption, an infrared humidity sensor collects humidity signals from the drying chamber and transmits these signals to the control unit. When the control unit detects that the humidity level in the drying chamber reaches 60%-70%, it outputs a signal to activate the dehumidification device, which operates for 1 minute at a time, starting every 2-3 minutes. This embodiment employs intermittent activation to reduce power consumption and improve dehumidification efficiency.
[0084] Meanwhile, during the drying process, an infrared temperature sensor continuously collects the material's temperature signal. When the material temperature reaches the maximum threshold, the control unit outputs a signal to reduce the microwave power entering the drying chamber, preventing the temperature from continuing to rise and causing material denaturation. Note that different materials can withstand different maximum temperatures; this is existing technology, and this embodiment limits the maximum temperature.
[0085] During the drying process in step 4, the humidity and temperature values of the material are monitored, and the microwave signal within the drying chamber 2 is ensured to meet certain conditions based on the output signal from the control unit. Specifically, this involves the TE signal generated by the multi-band magnetron. 10 The microwaves in the mode are partly fed directly into the drying chamber, and partly converted into TE signals by a mode converter. 20 The microwave signal of the mode then enters the drying chamber, TE 10 Microwave and TE modes 20 When microwave drying is used to dry the material in the middle and side areas of the drying chamber, the detection unit detects the humidity and temperature values of the material in the drying chamber and transmits the detected temperature and humidity values to the control unit. The control unit compares the received signals with the drying standard. If it is determined that the humidity values meet the drying standard, the control unit outputs a signal to end the drying process.
[0086] During operation, the waveguide dual directional coupler transmits the coupled microwave signal to the detector and attenuator. The detector and attenuator convert the microwave power into an electrical signal, which is then transmitted to the control unit. Based on the received electrical signal, the control unit determines whether the microwave power has reached the set value. If not, the control unit increases the pulse energy output by the pulse energy source, thereby increasing the microwave power. Otherwise, it remains unchanged.
[0087] The control unit determines whether the microwave power has reached the set value by: the infrared humidity sensor constantly collects the humidity signal of the material and transmits the collected humidity signal, i.e. the water content, to the control unit. The control unit outputs a signal based on Figure 8 to change the microwave power density.
[0088] For ease of understanding, the information from image 8 has been extracted and presented as follows:
[0089] When the moisture content is 30%, the microwave power density is 790~810w / kg;
[0090] With a moisture content of 22% to 30%, the power density decreases by 50 to 70 W / kg for every 2% reduction in moisture content.
[0091] With a moisture content of 16-22%, the power density decreases by 80-90 W / kg for every 2% reduction in moisture content.
[0092] With a moisture content of 12-16%, the power density decreases by 95-105 W / kg for every 2% reduction in moisture content.
[0093] This invention discloses a microwave drying method based on a multi-band magnetron. It employs different modes to dry materials in different areas of the drying chamber, which can effectively avoid problems such as uneven heating and quality damage, improve drying efficiency and quality, and reduce energy consumption and operating costs.
[0094] Example 2 differs from Example 1 in that fresh wheat is used as the material to be dried. Three drying methods are employed during the drying process: one is the method described in this example, and another uses only TE. 10 Microwave drying of the same mode served as control group 1; control groups 2, 3, 4, and 5 also used TE at the same time. 10 and TE 20 Two modes of microwave signals, but a single power value is used for drying throughout.
[0095] By comparing control group 1 with this embodiment, it is proven that TE 10 Pattern and TE 20 Combining the two modes can achieve better drying results.
[0096] By comparing control groups 2, 3, 4, and 5 with this embodiment, the influence of power on the drying effect is demonstrated.
[0097] The drying method described in this embodiment is as follows: First, fresh wheat is spread flat on a conveyor belt;
[0098] The conveyor belt introduces fresh wheat into the drying chamber;
[0099] The drying and dehumidification units begin to operate.
[0100] To make a direct comparison of the effects, the wheat in control group 2 was simulated with the same moisture content as the wheat in example 2, starting from 2%.
[0101] The control unit controls the drying unit to generate TE 10 The microwave signal; the power divider will divide a portion of the TE 10 The microwave signal of the mode is directly transmitted to the drying cavity; the power divider transmits another part of the TE signal. 10 The microwave signal of the mode is transmitted to the mode converter, which then converts the TE signal into a signal. 10 The microwave signal of the mode is converted into TE 20 Mode, TE 20 The microwave signal of the mode enters the drying chamber, along with TE 10The microwave signals of the mode are used together for drying. The control unit constantly monitors the temperature and humidity values of the central area and the two sides of the drying chamber. The microwave power density is adjusted according to the received humidity value. After working for a period of time, it is found that the temperature and humidity values of the wheat in the central area and the two sides meet the set conditions. The control unit outputs a signal to stop the drying unit and the dehumidification unit.
[0102] Control group 1:
[0103] The working process is as follows: First, fresh wheat is spread evenly on the conveyor belt;
[0104] The conveyor belt introduces fresh wheat into the drying chamber;
[0105] The drying and dehumidification units begin to operate.
[0106] The control unit controls the drying unit to generate TE 10 After the microwave signal is continuously applied for a set time, the control unit outputs a signal to stop the drying unit and the dehumidification unit from working.
[0107] To better represent the drying effect of wheat after microwave heating, this embodiment introduces a uniformity coefficient to characterize the drying uniformity of wheat after microwave heating. A higher uniformity coefficient value indicates better drying uniformity. In this embodiment, the uniformity coefficient of wheat during the drying process is as follows: Figure 10 As shown, the uniformity coefficients of wheat in control group 1 and control group 2 are as follows: Figure 9 As shown.
[0108] from Figure 9 and Figure 10 It is evident that wheat drying using the method described in this invention results in a higher uniformity coefficient and a better drying effect.
[0109] Control group 2:
[0110] The working process is as follows: First, fresh wheat is spread evenly on the conveyor belt;
[0111] The conveyor belt introduces fresh wheat into the drying chamber;
[0112] The drying and dehumidification units begin to operate.
[0113] The control unit controls the drying unit to generate microwave signals, TE 10 Pattern and TE 20 Simultaneously, a microwave signal of the mode enters the drying chamber, at a power of 200W. The control unit continuously monitors the temperature and humidity values in the central region. After 30 seconds of operation, it is found that the temperature and humidity values of the wheat in the central region meet the set conditions. Subsequently, the control unit controls the drying unit to generate a microwave signal, TE. 10 Pattern and TE20 The microwave signal of the mode enters the drying chamber at the same time. At this time, the given microwave power value is 200W. After working for 30 seconds, the control unit determines that the temperature and humidity values of the wheat in both sides meet the set conditions based on the received signal. Subsequently, the control unit outputs a signal to stop the drying unit and the dehumidification unit from working.
[0114] The difference between control group 3 and control group 2 is that in TE 10 and TE 20 In this mode, the microwave power is 300W.
[0115] The difference between control group 4 and control group 2 is that in TE 10 and TE 20 In this mode, the microwave power is 400W.
[0116] The difference between control group 5 and control group 2 is that in TE 10 and TE 20 In this mode, the microwave power is 500W.
[0117] Figure 11 The uniformity coefficient of microwave heating of wheat under Example 2 and Control Groups 2, 3, 4 and 5 is given.
[0118] from Figure 11 It can be seen that the method described in Example 2 achieves the best uniformity in microwave heating of wheat, meaning this microwave heating drying method can obtain better grain drying results. It also demonstrates that multiple modes, with power following the temperature, can achieve better drying effects.
Claims
1. A microwave drying apparatus based on a multi-band magnetron, characterized by: It includes a drying chamber, a drying unit located within the drying chamber, a detection unit, a control unit, a transmission unit, and a dehumidification unit; The transmission unit moves through the drying chamber; The drying unit includes a magnetron, a waveguide dual-directional coupler, a power divider, a mode converter, a detector, and an attenuator. The magnetron is electrically connected to the waveguide dual-directional coupler. The coupling end of the waveguide dual-directional coupler is connected to the detector and the attenuator in sequence. The electrical signal output end of the attenuator is connected to the signal input end of the control unit. At the same time, the through end of the waveguide dual-directional coupler is connected to the power divider. The first branch end of the power divider is connected to the mode converter. The second branch end of the power divider and the output end of the mode converter simultaneously output microwave signals toward the drying cavity. The detection unit includes an infrared temperature sensor and an infrared humidity sensor. The signal output terminals of the infrared temperature sensor and the infrared humidity sensor are respectively connected to the signal input terminal of the control unit. The control unit outputs signals to control the operation of the drying unit, the transmission unit and the dehumidification unit.
2. The multi-band magnetron-based microwave drying apparatus of claim 1, wherein: The drying chamber is equipped with a material inlet and a material outlet. The transmission unit includes a conveyor belt that enters the drying chamber from the material inlet and exits the drying chamber from the material outlet. Microwave suppressors are installed at both the material inlet and the material outlet.
3. The microwave drying equipment based on a multi-band magnetron as described in claim 2, characterized in that: It also includes a pulse power source. The control unit sends commands to the pulse power source, and the pulse power source outputs pulse energy according to the commands. The pulse energy provides power to the magnetron.
4. The microwave drying equipment based on a multi-band magnetron as described in claim 3, characterized in that: The magnetrons are at least two, and multiple magnetrons are connected in parallel.
5. A microwave drying method based on a multi-band magnetron using the microwave drying apparatus of claim 4, characterized in that: The method includes the following steps in sequence: Step 1: Select fresh materials as the objects to be dried; Step 2: Spread the material evenly on the conveyor belt; Step 3: The conveyor belt carries the fresh material into the drying chamber; the drying unit operates to dry the material. Step 4: The drying process is to use TE 10 mode to dry the material in the middle area of the drying cavity, while TE 20 mode is used to dry the wheat on both sides of the cavity. Step 5: During the drying process in Step 4, the detection unit monitors the humidity change of the material in the drying chamber in real time. When the detection unit detects that the humidity of the material in the drying chamber reaches the preset drying standard, it feeds back to the control unit, and the control unit controls the drying process to complete. Step 6: After the drying process is completed, the conveyor belt will carry the material out of the drying chamber and collect the grain.
6. The microwave drying method based on a multi-band magnetron as described in claim 5, characterized in that: During the drying process in step 4, the control unit outputs a signal to start the dehumidification device, which then discharges the hot and humid air from the drying chamber.
7. The microwave drying method based on a multi-band magnetron as described in claim 6, characterized in that: During the drying process in step 4, the humidity value of the material is monitored. The control unit receives the humidity value and, based on this, When the moisture content is 30%, the microwave power density is 790~810w / kg; With a moisture content of 22% to 30%, the power density decreases by 50 to 70 W / kg for every 2% reduction in moisture content. With a moisture content of 16-22%, the power density decreases by 80-90 W / kg for every 2% reduction in moisture content. With a moisture content of 12-16%, the power density decreases by 95-105 W / kg for every 2% reduction in moisture content. The output signal ensures that the microwave power density within the drying cavity meets the requirements.
8. The microwave drying method based on a multi-band magnetron as described in claim 7, characterized in that: In step 5, when the material temperature exceeds the maximum threshold, the control unit outputs a signal to the pulse power source to reduce the output energy of the pulse power.
9. The microwave drying method based on a multi-band magnetron as described in claim 8, characterized in that: The material should be laid to a thickness of 5-10 cm.
10. The microwave drying method based on a multi-band magnetron as described in claim 9, characterized in that: The moisture content of fresh materials is 20%-30% at the initial moisture content.