RU2720127C1 - Controlled microwave heating method and device - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: present invention relates to food, chemical and related industries and can be used in controlled treatment of food product with ultrahigh frequency currents. Device for controlled microwave heating of a food product consists of heating chamber (202) with measuring module (205) installed therein, made with possibility of measuring infrared radiation at various sections of the surface of food (201) placed inside heating chamber (202), and control module (204), wherein heating chamber (202) is equipped with microwave field source, wherein measurement module (205) consists of several measuring segments, control module (204) is configured to receive values from each of the segments of the measurement module and control the inclusion of the microwave field source so, that the source was switched on provided that during the last measurement all measured values of infrared radiation on the segments of the measuring module are less than the first monitored value and provided that the difference between the largest and smallest measured values on such segments is less than the second monitored value, and was disconnected if one of said conditions or both conditions are not met.

EFFECT: ensuring uniformity of product heating in microwave field.

14 cl, 3 dwg

Description

Technical field

The present invention relates to the field of food, chemical and related industries and can be used in the controlled processing of a food product by microwave currents (microwave radiation).

State of the art

As you know, a number of microwave ovens are equipped with a contact thermometer to control the heating of the product. A thermometer is placed in the middle of the product, while stopping the process to get a signal that the desired temperature inside the product has been reached. Temperature measurement without stopping the process in this case is impossible, because the thermometer overheats due to induction currents induced by the microwave field in its material. With this control method, surface heating often leads to local overheating and poor product quality. An alternative method is the non-contact measurement of surface temperature using an infrared (IR) sensor, and it is difficult to determine when the desired temperature inside the product is reached. This leads to a decrease in the uniformity of heating, worsens the quality of the resulting product and increases the risks for the safe operation of the equipment.

To date, a common method for controlling the temperature of a material in a microwave chamber is the use of a thermocouple [1]. But this method has several obvious disadvantages. To carry out control, direct contact with the processed object is necessary, which is negative for food products. Secondly, the external EMF is induced on the surface of the thermocouple material, the sensor heats up and the measurement error. As a result, this measurement technique is limited in the range of tasks due to the low reliability and. In 2016, a new method of contact temperature control was proposed and introduced using a U-shaped sealed tube with an injected gaseous medium [2] (RF Patent No. 2607047 of 08/08/2016). Earlier [3, 4], kerosene thermometers were used for these purposes, which could operate in the microwave field with sufficient accuracy. However, they cannot be used to measure the temperature inside the object, in addition, they are inertial. When conducting various studies on microwave processing and drying of grain [5, 6, 7], the temperature of the material was measured using thermocouples, but they were immersed in the product after the termination of the microwave field. Studies show that the rise time of the temperature is not more than 20-60 seconds. The time for temperature equalization after the termination of the microwave, depending on the moisture content of the product, can vary from several minutes to tens of minutes. With such dynamics, the procedure for introducing thermocouples into the studied layer after the termination of the microwave radiation leads to significant distortion of the dynamics and errors of temperature measurement during cooling of the object. It should be noted that the mentioned methods for measuring the temperature of the processed product under microwave exposure were practiced in partially filled microwave zones (in resonator-type installations). In this case, the product occupied a smaller part of the volume of the microwave camera. Therefore, the placement of metal thermocouples in the microwave range led to their burnout.

These disadvantages are inherent in contact measurement methods.

At the same time, there are a number of developments in the field of remote temperature measurement methods, such as the use of remote thermometers and pyrometers. In 2013, it was proposed to use a pyrometer to control the temperature of the processed sample. The basis for the creation of the method was several factors. First of all, it is the presence of energy brightness (intensity) of a heated body. As well as the ability to work with a wide range of temperatures and materials [8]. Using the same principles of non-contact measurement as A. Tkachenko, American inventor Mark Robert, who developed a microwave camera with a thermal imager, presented its solution. The product is quite interesting and may have some prospects in the future, but its high cost makes it useless for widespread use today [9]. In the future, it is possible to use methods of automatic processing of thermograms of a thermal imager for automated decision-making on the state of heating [10-14].

Existing non-contact thermometers, pyrometers, and thermal imagers for use in our invention have disadvantages, namely, a thermometer gives an average value over the entire surface or measures temperature in one local area, while pyrometers and thermal imagers provide excessive detail of the thermal picture of the surface of objects.

In [10–14], experts suggested using methods of automatic processing of thermograms of a thermal imager for automated decision-making about the state of heating, relying on greater detail about the temperature of the heated objects.

Disclosure of the invention

The present invention is based on the technical task of creating a simple and reliable means for carrying out the process of controlled microwave heating of the product.

The technical result achieved by the implementation of the present invention is the uniformity of heating of the product in the microwave field.

In a first aspect of the invention, there is disclosed a method for controlled microwave heating of a food product, in which microwave heating of a food product placed in a heating chamber is carried out, wherein, when microwave heating, the microwave field source is turned on and off and the values of thermal IR radiation from the surface of the food product are measured measuring module, characterized in that the said measuring module consists of several measuring segments, while the measured values of infrared radiation from each of these segments are taken on the control mode the means by which the inclusion of the microwave field source is then controlled so that the microwave field source is turned on, provided that during the last measurement, all measured values of infrared radiation on the segments of the measuring module are less than the first controlled value for infrared radiation and provided that the difference between the largest and smallest measured values of IR radiation in such segments is less than the second controlled value for IR radiation, and was turned off if one of the above conditions or both conditions are not met.

In a second aspect of the invention, there is disclosed a device for controlled microwave heating of a food product, consisting of a heating chamber with a measuring module installed therein, configured to measure infrared radiation at various parts of the surface of the food product placed inside the heating chamber, and a control module, wherein the heating chamber equipped with a microwave field source, characterized in that the measuring module consists of several measuring segments, the control module is configured to receiving values from each of the segments of the measuring module and controlling the switching on of the microwave source so that the microwave source is turned on, provided that during the last measurement all the measured values of infrared radiation on the segments of the measuring module are less than the first controlled value for infrared radiation and provided that the difference between the largest and smallest measured values of IR radiation in such segments is less than the second controlled value for IR radiation, and was disabled if one of the above conditions or both conditions are not met.

Brief Description of the Drawings

The essence of the present invention is illustrated with reference to the drawings, in which:

- figure 1 presents a flowchart of a method of controlled microwave heating of a food product;

- figure 2 presents a block diagram of a device controlled microwave heating of a food product;

- figure 3 presents a graph of the dependence of the heating of the object and the readings of the measuring module from the time of the controlled microwave heating.

Description of preferred embodiments of the invention

Microwave processing of materials demonstrates a large number of promising advantages compared to traditional heating technologies, for example, improved product quality, reduced process time, energy and energy costs due to higher efficiency, reduced environmental pollution and equipment maintenance costs and increased comfort for the user of the microwave device.

In a traditional heating process, heating sources are, for example, heating elements, resistances and infrared rays. Due to temperature radiation and / or convective heat transfer, their energy is transferred to the surface of the material and from there passes into its inner part. The thermal conductivity, adsorption and specific heat of the material determine the heating process. Sensitive materials under certain circumstances do not allow high temperature, and if the material also has poor thermal conductivity, then a long process and overheating of the material are inevitable, therefore, when producing certain products using traditional heating technologies, boundaries are set.

At the disposal of microwave technology, there are mainly 4 frequencies of inductive static measuring systems (frequency for industrial applications, research and medical radio equipment), which may differ from each other depending on the rules of a particular country. The highest frequency indicator is 28,000 or 30,000 MHz, however, the industrial and economical use of such a frequency on a large scale has not yet come into view. The low frequency of 915 MHz has certain technical costs, which only in certain cases justify their application. Household microwave ovens used around the world have an economical “frequency” of 2450 ± 50 MHz.

Microwave heating differs from traditional heating systems due to the fact that heat is directly generated in the volume of the material. In the furnace, dielectric heating of substances containing polar molecules occurs. The electrical component of electromagnetic waves enhances the movement of molecules with a dipole moment, and intermolecular friction leads to an increase in the temperature of the substance. Microwave propagation speed is the speed of light in vacuum or in air. If the microwave source is turned on, it is directly present in the heated body and immediately begins the conversion of energy. With a quick shutdown, the heating process immediately stops. There are no long processes of heating and cooling the furnace. Non-polar materials (for example, air, Teflon, quartz glass) cannot convert energy and, therefore, they do not heat up. Microwaves penetrate these materials, but do not weaken at the same time (without energy conversion). In general, a heated material that is able to carry out energy conversion is considered as “heaters,” since the material itself is a heat source.

In the process of heating food products in a microwave field, the product, at the initial stage, quickly warms up in the surface layer, the thickness of which depends on the properties of the product and radiation parameters. Further heating throughout the volume depends on the thermal conductivity of the product and the phase transitions occurring in it (for example, ice melting or water evaporation, or protein denaturation), or convective heat and mass transfer by water vapor in the case of bulk products. With intense microwave processing, the flow of thermal energy into the product may not be sufficient to remove heat from the heated surface layers, and the surface will overheat. Since most microwave magnetrons have one level of radiation intensity, the microwave heating process depends only on the on-off cyclogram of the microwave heating source - the magnetron, without the possibility of reducing the heating intensity.

For the purposes of the present invention, a food product is understood to mean a significant group of products of plant or animal origin, used by humans for food or used to improve the taste and aromatic qualities of food products. Such products may be presented by grain, cereals, meat semi-finished products, spices, berries, fruit and herbal raw materials, tea, tea leaves, tea semi-finished products, but are not limited to these examples of food products.

Microwave heating refers to a process in which energy with a frequency from 300 MHz to 300 GHz penetrates into the heated material as an electromagnetic wave with a wavelength in the range from 1 m to 1 mm, and then is converted into heat.

A flowchart illustrating the sequence of operations in the claimed method of controlled microwave heating of a food product is shown in FIG. 1. The method is as follows.

At step 101, the values of thermal IR radiation are measured by the measuring module 204 from the surface of the food product 201 (FIG. 2). The food product 201 can be placed in the microwave heating chamber 202, for example, on a trellised pallet 203 or other suitable supporting static or movable structure made insensitive to heating under the influence of a microwave field. In this case, the food product 201 to be placed may have an arbitrary initial temperature value. For example, the values of infrared radiation in different areas of the product 201 may be less or more in comparison with the controlled values. Also, the values of IR radiation at different parts of the surface of the product 201 may be unevenly distributed. In particular, the food product 201 to be placed can be placed in a package, for example, in a fabric bag, or packaged in small containers, if the food product is presented with tea, it can be tea bags. Preferably, the food product 201 is placed inside the heating chamber so that at least the top layer of the product is completely accessible for measurement by the measuring module 204. The measuring module 204 is a multi-segment structure represented by an infrared temperature sensor, the measuring matrix of which has a resolution of 8 * 8 pixels. The 8 * 8 matrix (64 elements) was selected as the smallest possible for collecting information on the dynamic and topological distribution of heat on the surface, based on the proposition that, to control the operation of the magnetron and effectively prevent local overheating of the product in volume and on the surface, analysis of the distributed over the surface of the dynamics of the parameters of the speed / acceleration of heating-cooling. Preferably, the measuring module 204 is isolated from the influence of the microwave field to prevent its overheating due to the induced by the microwave field tional currents in its material. For this, in particular, the measuring module can be placed in a block isolated from the microwave field made of a metal mesh with a cell width of 1 mm.

At step 102 and step 103, the control module 205 receives the measured values of infrared radiation from each of the segments of the measuring module 204 and sequentially checks the fulfillment of the first and second conditions, in accordance with which they decide on the need to actuate the microwave field source for microwave - heating the food product 201. The source of the microwave field can be represented by one or more coordinated acting magnetrons. Magnetrons can operate at various frequencies from 0.5 to 100 GHz, with capacities from several watts to tens of kilowatts in continuous mode, and from 10 W to 5 MW in pulsed mode. Microwaves enter the microwave heating chamber through a waveguide — a channel with metal walls that reflect microwave radiation.

At step 102, verify compliance with the following conditions:

Tmax <Tctrl, where:

Tmax is the largest value of IR radiation measured on the surface of the food product by any of the segments of the measuring module 204;

Tctrl is the first monitored value.

The value of Tctrl can be set by the user. Exceeding this value is undesirable when heating food product 201.

At step 103, verify compliance with the following conditions:

Tmax - Tmin <ΔTctrl, where

Tmin is the smallest value of IR radiation measured on the surface of the food product by any of the segments of the measuring module 204;

ΔTctrl is the second monitored value.

The ΔTctrl value can be set by the user. This value reflects the largest allowable difference between the values of IR radiation in different parts of the surface of the food product 201, i.e. the most acceptable uneven heating. Exceeding ΔTctrl is also undesirable when heating food 201.

In particular, when controlling the switching on of the microwave source, the readings of those measuring segments on which the measured values are constant, i.e. do not change over time. This may occur if the supporting surface on which the product 201 is placed, which is not heated by the microwave field, falls into the area accessible for measurement by the measuring module 204.

At step 104, the magnetron is turned on, and this is turned on only if, when sequentially checking the conditions at steps 102 and 103, both conditions are satisfied.

If the food product is heated unevenly, then when the Tctrl or ΔTctrl value is reached, go to step 105, where the magnetron is turned off to prevent local overheating, which will damage the product 201 or its parts. Despite the fact that both conditions for the controlled values of Tctrl and ΔTctrl may be unfulfilled at the same time, it will be sufficient to turn off the magnetron if at least one of these values is reached when the food product 201 is heated.

When conducting microwave heating, the control module 205 takes values from the measuring module 204 with a certain frequency to interrupt or resume the microwave heating process. So, when you turn on the magnetron in step 104 or turn it off in step 105, the entire heating cycle is repeated, starting from step 101. The interaction between the modules 204 and 205 can be provided in automatic mode. Microwave heating can be completely stopped when a certain condition is met, the observance of which is checked on the control module 204. For example, such a condition can consist in reaching a certain value for the frequency of switching on / off the microwave source: if its frequency decreases, then microwave heating stop completely. In addition, other conditions may be provided for exiting the microwave heating cycle, for example, reaching a predetermined time for microwave heating.

In the disclosed invention, there is no need to calibrate the IR sensors of the measuring module 204 to a real temperature scale to measure the absolute temperature values on the surface of objects. To illustrate this principle, FIG. 3 presents graphs of the temperature of the object versus the time of controlled microwave heating, recorded by autonomous thermometers (round “tablet” sensors without emf induction) located in the center (curve 301 in FIG. 3) and in the extreme zone (curve 302 in FIG. 3) of the heated object, as well as the highest value of Tmax among the readings recorded by segments of the measuring module 204 (curve 303 in FIG. 3). It should be noted that the readings of autonomous sensors-thermometers are not available during the entire cycle of microwave heating, the data are unloaded after each process step.

Microwave heating was carried out for 15 minutes. In the first minute of heating, the temperature in the center of the heated object was 30 ° С, at the edge of the heated object - 25 ° С. After 15 minutes of heating, the temperature increased stepwise, as can be seen from the constant temperature in some areas. At the fifteenth minute of heating, the temperature in the center of the heated object is 83 ° C, at the edge of the heated object is 78 ° C. At the same time, the maximum value of IR radiation among the elements of the multi-segment measuring module 204 ranged from 25 to 45 units.

In all cases, it is enough to carry out 2-3 technological tests to determine the control values of Tctrl and ΔTctrl for each type of food product, while placing 2 autonomous thermometers in the center and in the extreme zone of the object to control the actual temperature reached. Subsequently, the values of Tctrl and ΔTctrl obtained from the readings of the multi-segment measuring module 204 are used in the technological map of the microwave processing of a food product of this type without the use of stand-alone thermometers located in the heated object.

As a result, a device was created on the principle of a microwave oven with a non-contact temperature measurement system based on an IR sensor with an 8 * 8 matrix, without the need for a complex and expensive thermal imager system and algorithms that operate with complex parameters such as localization / speed / acceleration of heating-cooling . The algorithm for analyzing the readings of the IR sensor matrix and the magnetron control circuit based on this algorithm proposed in the claimed method for controlled microwave heating of a food product showed that it is possible to create a microwave heating device with high energy efficiency and increased control during heat treatment without using the technology of “inverter microwave ovens” " In principle, it should be noted that the developed algorithm operates with only two parameters calculated on the basis of the readings of the IR sensor matrix — the largest value and the difference between the largest and smallest values among the matrix elements. The proposed monitoring and control operations ensure uniform heating of the object throughout the volume without local overheating, which was confirmed by the placement of temperature sensors, "tablets" in different parts of the heated objects. As a result, a convenient device was obtained that can solve the heat treatment problem more efficiently in comparison with solutions known from the prior art.

The list of items in the drawings

101 The step of measuring the temperature values on the surface of the food product 102 The step of verifying compliance with the first condition "Tmax <Tctrl" 103 The step of verifying compliance with the second condition "Tmax - Tmin <ΔTctrl" 104 The step of turning on the magnetron 105 Magnetron Shutdown Step 201 Food product 202 Microwave heating chamber 203 Grate pan 204 Control module 205 Measuring module 206 Magnetron 207 IR radiation 301 The temperature curve in the center of the heated object 302 Temperature curve in the extreme zone of the heated object 303 Curve of Tmax values recorded by the measuring module

List of sources

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Claims (14)

1. A method of controlled microwave heating of a food product, in which microwave heating of the food product placed in the heating chamber is carried out, while the microwave source is turned on and off by microwave heating and the values of thermal IR radiation from the surface of the food product are measured by a measuring module, characterized in that the said measuring module consists of several measuring segments, while the measured values of infrared radiation from each of these segments are taken on the control module, with which then They are turned on by turning on the microwave field source so that the microwave field source is turned on, provided that during the last measurement all the measured values of infrared radiation on the segments of the measuring module are less than the first controlled value for infrared radiation and provided that the difference between the largest and smallest the measured values of infrared radiation in such segments are less than the second controlled value for infrared radiation, and was disabled if one of the above conditions or both conditions are not met. 2. The method according to claim 1, in which the food product is placed inside the heating chamber so that at least the top layer of the product is completely accessible for measurement by the measuring module. 3. The method according to claim 1, in which when controlling the inclusion of a microwave source, the readings of those measuring segments in which the measured values are constant in time are excluded. 4. The method according to claim 1, in which the first controlled value is a user-set value of infrared radiation, the excess of which is undesirable when heating the food product. 5. The method according to claim 1, in which the second controlled value is a user-set value for the difference between the smallest and largest values of infrared radiation in different parts of the surface of the food product, and exceeding this difference is undesirable when heating the food product. 6. The method according to claim 1, in which complete microwave heating of the food product, depending on the frequency of inclusion of the source of the microwave field. 7. A device for controlled microwave heating of a food product, consisting of a heating chamber with a measuring module installed in it, configured to measure infrared radiation at different parts of the surface of the food product placed inside the heating chamber, and a control module, while the heating chamber is provided with a microwave source fields, characterized in that the measuring module consists of several measuring segments, the control module is configured to receive values from each of the segments of the measuring module and controlling the inclusion of the microwave field source so that the microwave field source is turned on, provided that during the last measurement all the measured values of infrared radiation on the segments of the measuring module are less than the first controlled value for infrared radiation and provided that the difference between the largest and smallest measured values of infrared radiation in such segments is less than the second controlled value for infrared radiation, and was disabled if one of the above conditions or both conditions are not met. 8. The device according to claim 7, in which the source of the microwave field is represented by one or more coordinated acting magnetrons. 9. The device according to claim 7, in which the measuring module is isolated from exposure to a microwave field. 10. The device according to claim 7, in which each measuring segment of the measuring module is represented by an infrared temperature sensor. 11. The device according to claim 10, in which the measuring matrix of infrared sensors has a resolution of 8 * 8 pixels. 12. The device according to claim 7, in which the first monitored value for infrared radiation is a user-set value, the excess of which is undesirable when heating the food product. 13. The device according to claim 7, in which the second controlled value is a user-set value for the difference between the smallest and greatest values in different parts of the surface of the food product, and exceeding this difference is undesirable when heating the food product. 14. The device according to claim 7, in which the control module is additionally configured to automatically complete microwave heating, depending on the frequency of switching on the microwave source.

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