DK174056B1 - Method and apparatus for heating media by high frequency electromagnetic waves - Google Patents

Description

in DK 174056 B1

METHOD AND APPARATUS FOR HEATING MEDIA WITH HIGH-FREQUENCY ELECTROMAGNETIC WAVES

5 State of the art

The invention relates to a method of heat treating foodstuffs, especially meat, dairy and vegetable media, as described in the preamble of claim 1.

10

In addition, the invention relates to an apparatus for use in the practice of the method and as set forth in the preamble of claim 8.

15 It is known from a variety of contexts to heat media using microwaves. The different techniques are used for different purposes ranging from drying wood to cooking meat. Most commonly known is the technique of microwave ovens that have become a consumer product.

However, the known techniques have severe disadvantages which are reinforced and are particularly pronounced in connection with economies of scale.

25

From DK patent application no. 4718/86 it is known to continuously feed meat media through guide means, made as a pipe, on which electrodes are mounted on diametrically opposite sides. Before the meat media is allowed into the active zone, the air content is removed by a vacuum pump.

From DK Patent Application No. 1014/91, it is known to pass media through a guide means on which annular electrodes are mounted around the tube two places.

Both of the above methods are associated with certain disadvantages, which become particularly pronounced during large-scale operation. Thus, the depth of penetration, and thus the pipe diameter of the systems, is limited. Further, a problem arises in connection with the electromagnetic field's uniformity as a function of the dielectric properties of the medium.

In addition, a field will also appear on each side of the electrodes which must be derived by means of a grounding or grounding. This grounding or ground connection must necessarily be placed at some distance from the annular electrodes, as these would otherwise be shorted to ground or ground.

This means that a large part of the power of the generator is deposited between the electrodes and the frame. This contributes to providing a very disparate heating or boiling zone, which basically consists of three different zones, namely the primary heating zone between the electrodes and the two secondary heating zones between the electrodes and 20 frames.

Thus, a site-dependent temperature gradient will occur that varies over three areas. This presents problems with heating or boiling of media or materials requiring uniform heating, since in practice it is difficult to compensate for this multi-zone heating during continuous operation. This is also problematic in the case of heating media whose conductivity is temperature dependent, as the depth of penetration is thereby greatly reduced.

The object of the invention is thus partly to achieve a uniform and thus controllable heating or boiling of a medium, and partly to achieve a greater depth of penetration in the medium.

DK 174056 B1 3

This is achieved by the method according to the preamble, which according to the invention is peculiar in that the flow over the secondary conduction paths is wholly or partially controlled by one or more reactants which are connected in series and / or in parallel with the secondary conduction path by means of one or more reactants which are dimensioned so that the secondary conductor path between electrode and frame becomes a vibration circuit with one or more poles, wherein at least one of the poles in the vibration circuit is substantially tuned to resonance at the frequency of the undesired frame current forming the secondary conductor path of an inductive wiring portion, the secondary inductance, between the electrode and the frame, as well as substantially parallel to a capacity, the secondary capacity being substantially tuned so that the oscillation circuit is substantially resonated at the frequency of the HF generator, and the generator is coupled to a compensation coil. , which is essentially aligned so that the spreading capacities f the generator terminals for the frame are brought into resonance with the compensation coil.

20

Advantages of the invention

By controlling the current over the secondary conduit in whole or in part by means of one or more reactances which are connected in series and / or in parallel with the secondary conduit and otherwise carried out, the current flowing between the electrode and the frame is obtained in a simple manner. way can be controlled. Thus, the current in the secondary conduit (s) can be completely controlled.

30

As stated in claim 2, letting the electrical impedance between electrode and frame have at least one pole, at the frequency of the frame current to be eliminated or minimized, it is obtained that the frame current is minimized or eliminated while maintaining the frame connection. . This results in an increased penetration depth, a better heating in DK 174056 B1 4 the primary conduit path. Thus, the invention combines a more uniform field with a field optimization.

As stated in claim 3, to allow the guide member to consist of a tubular body, the cross-section of which may have a shape which is suitable for the medium to be treated, an embodiment is obtained in which it is possible to quickly feed and divert the medium from heating zone.

By, as stated in claim 4, allowing the electrode system to consist of two electrodes connected to an HF generator which is cylindrical or annular and extends around the primary guide means, a way is applied to apply the electromagnetic field in the guide means. which is particularly advantageous in connection with the application of fields in a tubular guide member.

As stated in claim 5, allowing the medium to preheat before the guide means is allowed or before the heating 20 takes place, the heating according to the invention is facilitated by improving the conductivity of the medium before or at the same time heating, which causes the depth of penetration to be increased. This therefore allows the guide means and thus the heated medium to have larger dimensions across the conveyor axis.

As stated in claim 6, only the preheating in or around the region of the medium having the greatest depth of penetration relative to the electrodes is achieved, substantially the same effect as in claim 2, however, using less power during the preheating.

As stated in claim 7, that substantially the entire heating system is encapsulated in a conductive structure, it is achieved that the electromagnetic radiation is substantially eliminated. Likewise, the current displacement present at the HF frequencies used by DK 174056 B1 5 will ensure that there is only current flowing on the inside of the conductive structure. This has an impact on the working environment around the machine, but it also helps to ensure that the various measuring instruments associated with the machine's operation are not disturbed or need to be specially shielded.

The above apparatus for use in the practice of the invention is peculiar in that the secondary wiring path is connected in series and / or in parallel with one or more reactances which are dimensioned so that the secondary wiring path between electrode and frame is a vibration circuit with a or more poles, that at least one of the poles in the oscillation circuit is substantially tuned for resonance at the frequency of the undesirable frame current, that the secondary conduit consists of an inductive conduit, the secondary inductance, between the electrode and the frame, and one in the main case. parallel capacitance, secondary capacitance, which secondary capacitance is substantially tuned so that the oscillation circuit 20 is essentially resonant at the frequency of the HF generator, and that the generator is connected in parallel to a compensation coil which is generally tuned so that the scattering capacities from the terminals of the generator are in resonance with the compensation coil.

25

By connecting in the apparatus in series and / or parallel the secondary current path with one or more reactances, which is dimensioned so that the secondary path between electrode and frame is a vibration circuit with one or more 30 poles, an opportunity for controlling the current is obtained. runs between electrode and frame, and the power output in the primary and secondary zones can be regulated without significant undesired power loss, and by at least one of the poles in the oscillation circuit being substantially tuned to resonance 35 at the frequency of the undesired frame current, a minimization or elimination of frame current and further, DK 174056 B1 6 achieves the greatest possible power output in the heating zone without significant power loss outside the primary boiler heating zone. Finally, a simple and inexpensive embodiment of the invention is obtained, as it requires a minimum of 5 external components and their adjustment by allowing the secondary current path to consist of an inductive wiring portion, the secondary inductance, between the electrode and the ground, and a substantially parallel coupled capacity, the secondary capacity. , which secondary capacity in the main case is tuned so that the parallel oscillation circuit is essentially resonant at the frequency of the HF generator.

As stated in claim 9, the secondary current conduction path to frame consists of a tubular electrode formed in an electrically conductive material, a well-defined current conduction path to the frame having well-defined inductive properties is obtained. Further, the tube electrode shields the electromagnetic field.

By as stated in claim 10, in parallel or partially coupling the secondary current path with a capacitor such that the secondary current path constitutes a parallel oscillation circuit, a simple embodiment is obtained by which one can easily adjust or eliminate the frame current.

As stated in claim 11, an adaptation capacitance exhibiting an electrode-medium capacitance and a capacitance between the electrode and the oscillation circuit is provided between the electrodes and the oscillating circuits, an opportunity is obtained to be able to do so by means of this adaptive capacitance. an adjustment of the penetration depth and an adjustment of the power deposition between the electrodes.

By, as stated in claim 12, allowing the fitting capacitance to consist of a gap between the electrode and the secondary pipe part which is suitably filled by a dielectric, for example air, a practical embodiment of an adaptation capacitance is obtained, as well as a greater depth of penetration of the electric field is obtained from the end portions or end plates of the electrodes in the medium.

As stated in claim 13, inserting external adaptation capacitances provides a simple and well-defined possibility of adaptation. Thus, there are significant advantages with regard to sizing the adaptive capacitances, as these are very well defined in that the temperature of the capacitances at external location relative to the electrodes is relatively low and constant, since their temperature will not fluctuate with the temperature of the electrodes. . This 15 brings additional operating benefits, minimizing the risk of impact. Further, it is advantageous that the capabilities of any impact do not cause a breakdown of the heating or cooking wall.

As stated in claim 14, extending an elongated electrically conductive structure from the connection points of the wires to the electrodes over the primary pipe portion and encircling a smaller portion of its length, the field extending into the primary pipe portion is symmetrical. . This causes no cold zones to appear in the primary tube. Namely, a discrete capacitance across the secondary tube portion will cause a uniform charge density on the tubular electrode, which current density is greatest in the area around the capacitance terminals. However, the extended tube portion toward the primary tube portion will cause the charge density to distribute homogeneously over the extended tube portion, thereby providing a uniform symmetrical field into the primary tube portion.

By, as stated in claim 15, allowing the capacitive reactance to be a tubular capacitor encircling the entire pipe portion, a uniform and homogeneous charge density is obtained at the terminals of the capacitor. This will again produce a uniform symmetric field into the primary pipe portion, and thus no cold zones in the same, without the use of an extended joint-5 structure.

By providing a preheating mechanism as set forth in claim 16, for media whose dielectric properties are temperature dependent, the flow path can be "predetermined" by the heat zone (s) created in the medium.

By as stated in claim 17, allowing the external components to be mounted on the primary guide tube, a particularly advantageous embodiment is obtained, since for different products 15 different types of guide tubes which are specifically adapted to the products concerned will be necessary. This, in turn, will cause the guide tube to change its properties and to recalibrate the system. By installing fully dimensioned components that fit the guide pipe used, it is achieved that the apparatus can be switched very quickly from one production to another.

Drawing 25

An example of the prior art, as well as two embodiments of the invention will be described in more detail in the following section with reference to the drawing, in which: 1 shows a known heating apparatus, and FIG. 2 shows an embodiment of an apparatus according to the invention.

35 DK 174056 B1 9

Description of the Examples In FIG. 1 shows a known heating pipe, where the voltage generator 1 is connected via wires 7, 8 to electrodes 2, 5 3. The electrodes 2, 3 are placed as ring electrodes outside of an electrically non-conducting pipe 4. Two ground electrodes 5, 6 are connected to ground or frame via frame connections 11, 12.

The medium to be heated is passed through the tube in the direction of the arrow.

10

In operation, the apparatus will act in that an electromagnetic field is applied over the electrodes 2, 3 by means of the generator 1. The electromagnetic field will proceed in principle in two ways, namely in a primary zone A between the two electrodes and in two secondary zones B between electrodes and grounding electrodes. As can be seen, this means that there are three heating zones, which, before mentioned, causes some disadvantages in several compounds. Thus, a portion of the current applied to the medium in the tube for ground or ground 20 runs over the secondary zones.

In FIG. 2 shows an embodiment according to the invention, in which the field and current in the secondary conduit path are virtually eliminated or at least adjusted to a level suitable for the specific arrangement.

The exemplary embodiment shown is preferably intended for heating and cooking meat media, but there will be nothing to prevent other foodstuffs such as dairy and vegeable products from being heat treated according to the invention in a similar manner.

The meat medium is fed in the direction of the arrow through an electrically insulating tube 4. The tube is held by holding means 9, 10.

35

A generator 1 is connected via conduits 7, 8 to tubular electrodes 20, 22 on the outside of the tube via fitting capacities 24, 25 and connection points 27, 28 on the leading edge of the tubular electrodes. Above the terminals of the generator, a compensation coil 25 is connected which compensates 5 for parasitic capacitances between the terminals and the frame. The tubular electrodes 20, 22 are directly connected to the frame via frame connections 11, 12.

Two capacities 21, 23 are each connected in parallel across one of the 10 electrodes 20, 22. Each electrode acts between the lead connection and the frame as a wiring path which is primarily inductive. The capacities 21, 23 are therefore tuned such that the two oscillation circuits consisting of the capacitance 21 and the tubular electrode 20, as well as the capacitance 23 and the tubular electrode 22, are both in resonance or in the region of resonance. Thus, no appreciable current will flow between connection point 28 and frame 12, as well as between connection point 27 and frame 11.

20 This means that the field inside the pipe is no longer in several different zones, but concentrates in the primary zone A. Thus, the heating in the primary zone A is more efficient, because the generator can put more power into the primary zone as there is no going power lost in the secondary zones.

25 Further, it is associated with the advantage that the medium is not "preheated" in the secondary zone before it reaches the primary zone. This is very important in connection with cooking or heating media whose dielectric properties are temperature dependent, the preheating of the secondary zone of FIG. 1 is not very concentrated and only manages to heat the boundary layer against the pipe. This means that when it reaches the primary zone, the medium has a heated surface.

35 Thus, the current flowing in the meat as a function of the applied field would prefer to run on the surface of the medium, since the impedance on the surface is smallest. This thus provides a kind of negative feedback which is overcome in the embodiment shown in FIG. 2, the medium first being exposed to a field as it enters the primary zone.

5

At the leading edges of the tubular electrodes 20, 22, two elongated electrically conductive structures 29, 30. extend directly electrically to the tubular electrodes 20, 22.

10

These cause the charge density, and thus the field into the primary pipe portion, to be homogeneous, with the charges distributed uniformly all around the guide tube 4 on these electrically conductive structures 29, 30. If cylindrical capacities 21, 23 which is symmetrically positioned around the tubular electrodes 20, 22, the elongated electrical conductive structures may be omitted, such capacitances per se will cause a homogeneous charge density all around the tube 4.

20

Claims (17)

A method of heat treating foodstuffs, especially meat, dairy and vegetable media, which is conveyed in a substantially non-conductive guide member (4) and wherein the heating is obtained by applying the medium to an electric field with a given frequency by means of electrodes (2, 3, 20, 22. disposed on the surface of the guide member (4) and thus not in physical contact with the medium, the medium delimited by the guide member (4) constituting a primary conduction path between the electrodes (2, 3; 20, 22), wherein at least two of the electrodes are further connected to ground or ground over two or more secondary conduits, characterized in that the current across the secondary conduits is wholly or partially controlled by one or more reactances which are connected in series and / or parallel to the secondary conduit by one or more reactants which are dimensioned so that the secondary conduit between electrode (2, 3; 20, 22) and frame (11, 12) becomes a svingni circuit 20 with one or more poles, wherein at least one of the poles of the oscillation circuit is substantially tuned for resonance at the frequency of the undesired frame current, that the secondary conductor path is formed by an inductive conductor, the secondary inductance, between the electrode and the ground, 25 is coupled with a capacity, the secondary capacity being substantially tuned so that the oscillation circuit is substantially resonated at the frequency of the HF generator (1) and that the generator (1) is connected in parallel with a compensation coil (26) which is substantially tuned, so that spreading capacities -30 ne from the clamps (11, 12) of the generator (1) are brought into resonance with the compensation coil. Method according to claim 1, characterized in that the electrical impedance between electrode (2, 3; 20, 35 22) and frame (11, 12) is produced by at least one pole, at the frequency of the frame current to be eliminated or min. - DK 174056 B1 will be eliminated. Method according to claim 1 or 2, characterized in that the guide member (4) is formed by a tubular body (4), the cross-section of which is in a shape suitable for the medium to be treated. Method according to any one of claims 1-3, characterized in that the electrode system consists of two electrodes (2, 3; 20, 22) connected to an HF generator (1), which electrodes are formed as cylinders. or rings and placed around the primary guide member (4). Process according to any one of claims 1-4, characterized in that the medium is preheated before the guide means (4) is allowed or before the heating takes place. Method according to any one of claims 1 to 5, characterized in that the preheating is carried out only in or around the region of the medium which has the greatest penetration depth relative to the electrodes (2, 3; 20, 22). 25 Process according to any of the preceding claims 1-6, characterized in that substantially the entire heating system is encapsulated in a conductive structure with properties such as a Faraday cage. 30 Apparatus for use in the practice of the method of heat treating foodstuffs, in particular meat, dairy and vegetable media, wherein the heating is obtained by applying to the medium an electric field at a given frequency by means of electrodes, which apparatus has one or more heating or boiling zones in a guide member DK 174056 B1 (4), which is defined by walls with a low or no dielectric loss, which walls have an inner side which is facing and arranged to possibly enter into contact with the medium and an outer surface having electrodes (2, 3; 5, 6; 20, 5 22) connected to one or more HF generators (1), wherein at least two of the electrodes (5, 6) is connected to ground or ground over a secondary conduit, characterized in that the secondary conduit is connected in series and / or in parallel with one or more reactances dimensioned so that the secondary conduit between electrode (2, 3; 20, 22 ) and frame (11, 12) are one oscillation circuit with one or more poles, at least one of the poles in the oscillation circuit is substantially tuned to the frequency of the unwanted frame current, that the secondary conduit path consists of an inductive conduit, the secondary inductance, between electrode and frame, and a substantially parallel coupled capacity, secondary capacity, which secondary capacity is substantially tuned so that the oscillation circuit is essentially resonant at the frequency of the HF generator (1) and that the generator (1) is connected in parallel with a compensation coil (26) is tuned so that the spreading capacities from the terminals of the generator (1) to the frame (11, 12) are in resonance with the compensation coil. Apparatus according to claim 8, characterized in that the secondary conduit path to the frame consists of a tubular electrode (20, 22) formed in an electrically conductive material, extending between leads (7, 8) and frame (11, 12). 30 Apparatus according to any one of claims 8-9, characterized in that the secondary wiring path is connected wholly or partially in parallel with a capacitor (21, 23) and constitutes a vibration circuit. 35 Apparatus according to any one of claims 8-10, characterized in that an adaptive capacitance extending between the oscillating circuit and the electrode is inserted between the electrode and the electrode and between the electrode and the medium. 5 Apparatus according to claim 11, characterized in that the adaptive capacitance consists of a gap between the electrode and the secondary pipe part which is suitably filled by a dielectric, for example air. 10 Apparatus according to any of claims 8-12, characterized in that external fitting capacitors (24, 25) are inserted between the terminals of the generator (1) and electrodes (20, 22). Apparatus according to any one of the preceding claims 8-13, characterized in that an extended electrical extension extends from the connecting points (27, 28) to the electrodes (2, 3; 20, 22). conductive structure (29, 30) over the primary pipe portion and encircling a smaller portion of its length. Apparatus according to any one of the preceding 8- 14, characterized in that the capacitive reactance 25 is a tubular capacitor which encircles the entire pipe part. Apparatus according to any one of the preceding claims 8-15, characterized in that a preheating mechanism is arranged before the inlet end, i.e. outside the pivot circuit, in the opposite direction of the direction of the media supply. Apparatus according to any one of the preceding claims 8-15, characterized in that the external electrical components are mounted on the primary guide tube (4) so that the tube can be replaced with the finished parts.