High-frequency dielectric heating method

Abstract

To provide a high-frequency dielectric heating method capable of preventing local heating by reducing the concentration of electromagnetic energy at a corner part of a frozen food material even when the frozen food material disposed between electrodes has surface irregularities, and capable of maintaining high heating efficiency of the frozen food material.SOLUTION: There is provided a high-frequency dielectric heating for thawing a frozen food material placed between a pair of electrodes arranged vertically opposite to each other using a high-frequency dielectric heating device including a high frequency power supply that outputs high-frequency power in a MHz band and the pair of electrodes. The method thaws the frozen food material by driving the high-frequency power supply to generate electromagnetic energy between the pair of electrodes in a state in which, with upper surface and lower surface irregularities of the frozen food material being covered with a dielectric body, an upper end of the frozen food material and is substantially flush with an upper end of the dielectric body, and a lower end of the frozen food material is substantially flush with a lower end of the dielectric body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a high-frequency dielectric heating method for thawing frozen food materials by applying a high-frequency electric field. [Background technology]

[0002] Patent Document 1 is known as a document disclosing prior art related to high-frequency dielectric heating. For example, the abstract of this document states that the problem is to "obtain an induction heating device that can prevent localized heating of heated objects such as irregularly shaped foods. Furthermore, it is possible to reduce fluctuations in load impedance between electrodes, thereby enabling the size, cost, and energy conservation of matchers." It also states that the solution is to "provide a high-frequency dielectric heating device according to this invention, which dielectrically heats frozen tuna 6 placed between a pair of opposing high-voltage and earth electrodes 4 and 5 by applying an electric field between the high-voltage and earth electrodes 4 and 5, and the frozen tuna 6 is covered with interposing bodies 8 and 50 having a dielectric constant equal to or greater than that of the frozen tuna 6."

[0003] Furthermore, paragraph 0015 of the same document states, "A deformable second interposing body 50 is interposed between the frozen tuna 6 and the high-voltage electrode 4. This second interposing body 50 is also made of titanium dioxide, which is a high dielectric, and is composed of multiple small spheres 50a with a diameter of 2 to 3 mm packed into a tassel bag 50b made of polyethylene. These small tassel bags 50b are connected in the form of multiple tassels to multiple tassel core ropes 10 hanging down from the high-voltage electrode 4." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent application No. 2004-349116 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in Patent Document 1, multiple clusters of inclusions hanging down from the high-voltage electrode are brought into close contact with the frozen food material, thereby apparently eliminating the uneven shape of the frozen food material, thereby preventing localized heating during high-frequency dielectric heating.

[0006] However, in Patent Document 1, the space between the high-voltage electrode and the frozen ingredients is filled with an intervening body, so much of the electromagnetic energy input into the oven is supplied to the intervening body, thereby reducing the heating efficiency of the frozen ingredients.

[0007] Therefore, the present invention aims to provide a high-frequency dielectric heating method that can reduce the concentration of electromagnetic energy at the corners of the frozen food material, even when the frozen food material placed between electrodes has unevenness, thereby preventing localized heating and maintaining high heating efficiency for the frozen food material. [Means for solving the problem]

[0008] In order to solve the above problems, the high-frequency dielectric heating method of the present invention is a high-frequency dielectric heating method that uses a high-frequency dielectric heating device comprising a high-frequency power supply that outputs high-frequency power in the MHz band and a pair of electrodes arranged opposite each other above and below to thaw frozen food material placed between the pair of electrodes, and in a state in which the upper end of the frozen food material, whose uneven surfaces are covered with a dielectric, is at approximately the same height as the upper end of the dielectric, and the lower end of the frozen food material is at approximately the same height as the lower end of the dielectric, the high-frequency power supply is driven to generate electromagnetic energy between the pair of electrodes and thaw the frozen food material. [Effects of the Invention]

[0009] According to the high-frequency dielectric heating method of the present invention, even if the frozen food material placed between the electrodes has unevenness, it is possible to reduce the concentration of electromagnetic energy at the corners of the frozen food material, thereby preventing localized heating and maintaining high heating efficiency for the frozen food material. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 1, viewed from the front. [Figure 2] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 2. [Figure 3] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 3. [Figure 4] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 3. [Figure 5] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 4. [Figure 6] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 5. [Figure 7] FIG. 10 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 6. [Figure 8] FIG. 13 is a front view of the vicinity of the electrodes of the high-frequency dielectric heating device of Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the high-frequency dielectric heating method of the present invention will be described in detail with reference to the drawings. Although each drawing has coordinate axes pointing up, down, left, and right, these are directions set for the convenience of explanation, and all of the embodiments described below are not limited to the directions of these axes. [Example]

[0012] FIG. 1 is a schematic diagram showing the electrodes and their vicinity in a high-frequency dielectric heating device 1 used in carrying out the high-frequency dielectric heating method of Example 1, viewed from the front. As shown here, the high-frequency dielectric heating device 1 has a high-frequency power supply 11, a high-voltage electrode 12, and a ground electrode 13. The high-frequency power supply 11 is a power supply that outputs high-frequency power in the MHz band, such as 13.56 MHz, 27.12 MHz, or 40.68 MHz, which is an ISM band. The high-voltage electrode 12 is an electrode electrically connected to the high-frequency power supply 11, and the ground electrode 13 is an electrode connected to earth (grounded). The two electrodes are installed facing each other in a vertical direction. Furthermore, a frozen food material 2 (e.g., a block of meat) covered with plastic wrap or the like is placed above the ground electrode 13, and sheet-like dielectric materials 3 are placed above and below the frozen food material 2.

[0013] The dielectric 3 in this embodiment is a flexible sheet that eliminates the appearance of unevenness on the surface of the frozen food material 2, and is made by wrapping an encapsulating substance 3a in a thin film 3b. Here, the encapsulating substance 3a is a highly fluid substance with a relative dielectric constant equivalent to that of the frozen food material 2 (for example, ±10%), and is, for example, a liquid such as water, or fine beads formed by adding a coagulant to a liquid such as water. The thin film 3b is, for example, a highly flexible plastic film made from polyethylene, polyvinylidene chloride, or the like.

[0014] When carrying out the high-frequency dielectric heating method of this embodiment, first, a sheet-shaped dielectric material 3 having the same shape as the frozen food material 2 when viewed from above is selected and spread out flat. Then, the frozen food material 2 is placed on the spread dielectric material 3, and another dielectric material 3 is placed on top of the frozen food material 2. This results in the entire top and bottom surfaces of the frozen food material 2 being covered with the dielectric material 3. Next, the frozen food material 2 sandwiched between the dielectric materials 3 is placed between the high-voltage electrode 12 and the earth electrode 13, and the high-frequency power supply 11 is driven to generate electromagnetic energy between the electrodes, thawing the frozen food material 2 by dielectric heating.

[0015] Here, since the dielectric 3 of this embodiment is configured such that a highly fluid encapsulating substance 3a is wrapped in a highly flexible thin film 3b, the dielectrics 3 arranged above and below the frozen food material 2 deform due to the weight of the frozen food material 2 and the dielectrics 3 themselves, following the uneven shape of the upper and lower surfaces of the frozen food material 2, and come into close contact with the frozen food material 2. At this time, the thinnest parts of the upper and lower dielectrics 3 become as thin as the film thickness of the thin film 3b (for example, 1 mm), so by using the dielectric 3 of this embodiment, it is possible to easily form a mass that is as thick as the frozen food material 2, has a uniform dielectric constant, and has few unevenness.

[0016] According to the principle described above, the top and bottom surfaces of the frozen food material 2 in this embodiment are covered with the dielectric 3 in a shape that conforms to the material's shape, eliminating apparent corners and preventing localized heating during thawing. Furthermore, the amount (thickness) of the dielectric 3 present in the region between the high-voltage electrode 12, the frozen food material 2, and the ground electrode 13 is minimized, making it possible to maintain high heating efficiency for the frozen food material 2. In a high-frequency dielectric heating device 1 that heats by applying a high-frequency electric field to opposing electrodes, electromagnetic energy is incident on the surfaces of the frozen food material 2 that, in principle, face the high-frequency electrode or the ground electrode 13. Therefore, minimizing the amount of dielectric 3 present near these surfaces (in this embodiment, the top and bottom surfaces of the frozen food material 2) significantly contributes to preventing a decrease in heating efficiency.

[0017] As described above, according to the high-frequency dielectric heating method of this embodiment, even if the frozen food material placed between the electrodes has unevenness, it is possible to reduce the concentration of electromagnetic energy at the corners of the frozen food material, thereby preventing localized heating and maintaining high heating efficiency for the frozen food material. [Example]

[0018] 2 is a schematic diagram showing the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 2 as viewed from the front. Below, explanations of parts that are substantially the same as those of Example 1 will be omitted, and differences will be mainly explained.

[0019] In Example 1, two dielectrics 3 were used to seemingly eliminate unevenness at the top and bottom of the frozen food material 2, but in this example, one dielectric 3 larger than the dielectric 3 in Example 1 is used to seemingly eliminate unevenness all around the frozen food material 2. Therefore, in this example, the frozen food material 2 is packed in the following manner.

[0020] That is, in the high-frequency dielectric heating method of this embodiment, first, the frozen food material 2 is placed on the dielectric material 3 spread out flat, and the dielectric material 3 is folded appropriately so that the entire peripheral surface of the frozen food material 2 is covered with the dielectric material 3. Thereafter, the frozen food material 2 covered with the dielectric material 3 is placed between the high-voltage side electrode 12 and the earth side electrode 13, and the high-frequency power supply 11 is driven to perform heating.

[0021] 2 shows an example in which the end of the dielectric 3 is folded toward the upper surface of the frozen food material 2, but it is also possible to fold it upside down. That is, the dielectric 3 may first be placed along the upper surface of the frozen food material 2, and then folded toward the lower surface of the frozen food material 2 to cover the frozen food material 2 with the dielectric 3.

[0022] As described above, according to this embodiment, not only are the unevenness on the top and bottom surfaces of the frozen food material 2 eliminated, but the unevenness on the side surfaces is also apparently eliminated, thereby reducing the concentration of electromagnetic energy at the corners around the entire circumference of the frozen food material 2, preventing localized heating, and maintaining high heating efficiency for the frozen food material. [Example]

[0023] 3 and 4 are schematic diagrams showing the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 3 as viewed from the front. Below, explanations of parts that are substantially the same as those of Example 2 will be omitted, and differences will be mainly explained.

[0024] In this embodiment, resin hooks 3c and snap buttons 3d are fixed to the ends of the dielectric 3, and the frozen food material 2 is wrapped in a dielectric 3 having substantially the same shape as the dielectric 3 of Example 2, and the hooks 3c and snap buttons 3d are fitted together to maintain the wrapped state of the frozen food material 2. This improves the positional stability of the dielectric 3, and reduces the risk of the dielectric 3 slipping off the frozen food material 2 during operation of the device. [Example]

[0025] 5 is a schematic front view of the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 4. Below, explanations of parts that are substantially the same as those of Example 2 will be omitted, and differences will be mainly explained.

[0026] In this embodiment, a belt 3e is wound around the outer periphery of the dielectric 3 which encases the frozen food material 2. When operating the device, the frozen food material 2 is wrapped in the dielectric 3, and then the belt 3e is appropriately wound around the outer periphery of the dielectric 3 before being placed between the electrodes. In this configuration, as in Example 3, the positional stability of the dielectric 3 is improved, reducing the risk of the dielectric 3 slipping off the frozen food material 2 during operation of the device. The belt 3e may be a rubber belt or a string. [Example]

[0027] 6 is a schematic diagram of the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 5, viewed from the front. Below, explanations of parts that are substantially the same as those in the above-mentioned examples will be omitted, and differences will be mainly explained.

[0028] While the dielectric 3 in the above-described embodiments was an encapsulating substance 3a wrapped in a thin film 3b, the dielectric 3 in this embodiment does not use a thin film 3b. In other words, the dielectric 3 in this embodiment is the encapsulating substance 3a itself. Therefore, in this embodiment, the dielectric 3 (encapsulating substance 3a) is used in a state where it is contained in a resin container 4. Specifically, a small amount of the dielectric 3 (encapsulating substance 3a) is first placed in the container 4, and then the frozen food material 2 is placed in the container 4. Then, the dielectric 3 (encapsulating substance 3a) is added until the top end of the dielectric 3 (encapsulating substance 3a) and the top end of the frozen food material 2 are approximately flush with each other. This makes it possible to eliminate the appearance of unevenness in the frozen food material 2 even when the encapsulating substance 3a itself is used as the dielectric 3. Note that, at this time, pretreatment such as covering the frozen food material 2 with a plastic film may be performed to prevent direct contact between the frozen food material 2 and the encapsulating substance 3a.

[0029] This configuration also makes it possible to provide a high-frequency dielectric heating device 1 that can reduce the concentration of electromagnetic energy at the corners of the frozen food material 2, prevent localized heating, and maintain high heating efficiency for the frozen food material. [Example]

[0030] 7 is a schematic diagram of the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 6, viewed from the front. Below, explanations of parts that are substantially the same as those of Example 2 will be omitted, and differences will be mainly explained.

[0031] In this embodiment, a matching box 14 configured by appropriately combining capacitors and inductors is provided between the high frequency power supply 11 and the high voltage side electrode 12. By using this matching box 14 to match the output impedance of the high frequency power supply 11 with the load impedance, the heating efficiency of the frozen food material 2 can be further improved. [Example]

[0032] 8 is a schematic diagram of the vicinity of the electrodes of the high-frequency dielectric heating device 1 of Example 7, viewed from the front. Below, explanations of parts that are substantially the same as those of Example 2 will be omitted, and differences will be mainly explained.

[0033] In this embodiment, a balanced-unbalanced converter 15 is provided between the high-frequency power supply 11 and the electrodes. This balanced-unbalanced converter 15 has the function of dividing the power supplied from the high-frequency power supply 11 into two systems of power with approximately symmetrical positive and negative polarities, and applies symmetrical electric fields to the upper electrode 16 and the lower electrode 17. With this configuration, the upper electrode 16 and the lower electrode 17 operate approximately symmetrically to impart energy to the frozen food material 2, making it possible to further reduce uneven heating of the frozen food material 2.

[0034] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment. [Explanation of symbols]

[0035] 1. High frequency dielectric heating device 11 High frequency power supply 12 High voltage electrode 13 Earth electrode 14 Matching box 15 Balance-to-unbalance converter 16 Upper electrode 17 Lower electrode 2 Frozen ingredients 3 Dielectrics 3a Inclusion substances 3b thin film 3c hook 3D snap button 3e belt 4 containers

Claims

1. A high-frequency dielectric heating method for thawing a frozen food material placed between a pair of electrodes using a high-frequency dielectric heating device including a high-frequency power source that outputs high-frequency power in the MHz band and a pair of electrodes arranged opposite to each other above and below, comprising: A high-frequency dielectric heating method characterized by driving the high-frequency power source to generate electromagnetic energy between the pair of electrodes and thawing the frozen food material, with the unevenness of the upper and lower surfaces of the frozen food material covered with a dielectric so that the upper end of the frozen food material is at approximately the same height as the upper end of the dielectric and the lower end of the frozen food material is at approximately the same height as the lower end of the dielectric.

2. The high-frequency dielectric heating method according to claim 1, A high-frequency dielectric heating method, characterized in that the dielectric is a highly fluid encapsulating substance having a relative dielectric constant equivalent to that of the frozen food material, wrapped in a flexible thin film.

3. 3. The high-frequency dielectric heating method according to claim 2, A high-frequency dielectric heating method, characterized in that the dielectric material is a sheet covering the entire upper surface of the frozen food material and a sheet covering the entire lower surface of the frozen food material.

4. 3. The high-frequency dielectric heating method according to claim 2, A high-frequency dielectric heating method, characterized in that the dielectric is a sheet that can wrap the entire periphery of the frozen food material.

5. 5. The high-frequency dielectric heating method according to claim 4, A high-frequency dielectric heating method characterized in that the dielectric maintains the frozen food material 2 wrapped in it by fitting a resin hook or snap button provided at the end.

6. 5. The high-frequency dielectric heating method according to claim 4, The high frequency dielectric heating method is characterized in that the dielectric maintains a state in which the frozen food material 2 is wrapped by wrapping a belt around the outer periphery.

7. The high-frequency dielectric heating method according to claim 1, A high-frequency dielectric heating method, characterized in that the dielectric is a highly fluid substance placed in a resin container and having a dielectric constant equivalent to that of the frozen food material.

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