EP2604090A1

EP2604090A1 - Method for uniformly heating products by means of a high-frequency electromagnetic alternating field

Info

Publication number: EP2604090A1
Application number: EP11758377.3A
Authority: EP
Inventors: Thomas Pfeiffer; Peter Eisner
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2010-08-11
Filing date: 2011-08-09
Publication date: 2013-06-19
Also published as: WO2012019756A1; BR112013003132A2; US20130168386A1

Abstract

The invention relates to a method and device for uniformly heating products, the products (8, 15) being heated by a high-frequency electromagnetic alternating field. The method and the device are characterized in that the high-frequency electromagnetic alternating field for heating the products (8, 15) is produced by means of a semiconductor generator (4). By using a semiconductor generator (4), temperature fluctuations in the event of fluctuating load due to the transport of the products (8, 15) through the heating volume (7, 17) are reduced, so that a more uniform temperature of the products (8, 15) can be achieved in the heating process.

Description

Process for the even heating of products by a high-frequency electromagnetic

alternating field

Technical application

The invention relates to a method and a device for the uniform heating of products, in particular of food, pharmaceutical and / or

Cosmetic products in which the products are heated by a high frequency alternating electromagnetic field.

Heating methods are used i.a. necessary for

To sterilize food or pharmaceutical products and thus to keep them. Examples are the pasteurization or sterilization of food.

State of the art

Methods are known for heating liquid products by means of heat exchangers. For example, Milk is heated during pasteurization in plate or tube heat exchangers, kept at pasteurization temperature for a defined time and then cooled again. This process has been established for liquid foods and has long been proven.

Cans or glasses with vegetables, fruits, ready meals, stews or similar contents are usually heated in hot water and hot air or in autoclaves and thus preserved. At the Sterilizing packaged products in autoclaves is initiated under pressure steam or hot water at temperatures above 120 ° C. The steam transfers the energy to the outside of the cans. From there, a warming of the can interior takes place almost exclusively via heat conduction, so that the products have reached the desired final temperature in the middle of the preserve only after 30 to 60 minutes. The same applies to the heating of liquids with chunky proportions, such as pieces of meat in sauces or of fruits in

Fruit preparations or jams. These suspensions must be kept at temperature for a very long time until the desired temperature is reached in the core of the solid pieces by thermal conduction.

In both cases, the long heating can cause a significant deterioration of the taste, the vitamin content as well as the consistency and color of the fruit

Products occur. Preserved canned foods therefore often have inferior quality of consumption and marked changes in the diet

Comparison to the fresh starting product e.g. to the fresh fruits.

Products that need to be heated for pasteurization, sterilization or other reasons include:

• Packaged food, pharmaceutical products and

Cosmetics as liquid, solid or

Suspension in packaging such as jars, cans, Trays, foil bags, tubes, sausage skins, intestines, and others;

• Low and high viscous or pasty liquids and pastes, sauces, creams, foams and other multiphase systems, which also lumpy

Contain shares such as pieces of meat, fruit pieces and others and due to the heterogeneous composition and / or solid and / or

Gas contents in conventional plate heat exchangers or tube heat exchangers can not or only very inhomogeneously heated;

• substances which lead to deposits, incrustations, and the like on the superheated heat exchanger surfaces; such as

Substances which are very temperature sensitive, e.g. Pharmaceutical products, infusion solutions,

liquid medicinal food or other substances that need to be heated particularly evenly and gently.

In the present patent application, the substances and mixtures mentioned are used as products

designated . A solution to reduce the heating time and thus to improve the quality of the

preserved products represents the fast,

penetrating heating with electromagnetic

In addition to microwave heating, whose low penetration depth of 5 to 20 mm is not sufficient for uniform heating of the products mentioned above, the use of a high-frequency alternating field (HF Heating). Conventional HF heaters consist of two parallel electrodes to which a

alternating electric field with a frequency of, for example 27.12 MHz and a voltage of 2 to 10 kV is applied. These fields are able to penetrate deep into electrically conductive wet solids and suspensions and to heat them. Ideally, fabrics can be heated completely evenly. In order to heat packaged products, the packages may be transported by means of a suitable transport device through the space between the electrodes where the products are exposed to the high frequency electrical conductors for a sufficient period of time. To heat liquid or flowable products in a continuous process, they can be pumped through a tube made of an electrically insulating material, the so with electrodes

is equipped so that the products are exposed to the electrical high-frequency field during the passage.

The aim of HF heating is a rapid and uniform and thus gentle heating of temperature-sensitive substances that are not or only poorly accessible to conventional heating in heat exchangers. RF heating is widely chosen to deliver products throughout

Heat cross-section evenly, e.g. with the aim of pasteurization, sterilization or the

Preparation. It turns out, however, that in HF heaters when operating with the products mentioned some significant temperature inhomogeneities occur. The products are heated inhomogeneously, which has the advantage of pervasive heating and can lead to significant product damage.

Thus, e.g. in packaged foods, especially on the edges of the packaging, on the

Outside and in very thin areas of the products pronounced overtemperatures occur. Overheating and damage to the products can occur at these locations. Similar effects are also observed in the heating of flowable products in tubular HF water heaters. The tube can be used for heating highly viscous, pasty liquids, suspensions or chunky goods (such as sausages) promoted. It also can

Damage caused by severe overheating. In some places in the pipe are only inadequate

Temperatures reached, despite high temperatures elsewhere. Thus, in individual cases along the flow direction temperature inhomogeneities

determine. This is especially pronounced with pulsating flows whose inhomogeneous flow characteristic is often caused by pulsation in the delivery unit (for example in the pump). Despite the attempts to equalize the electric field and the energy density between the electrodes by adjusting the electrode geometry, it is not possible to completely avoid overheating and temperature inhomogeneities with the known methods according to the prior art. This is true in

Especially for packaged products that are heated in the HF field and for high-viscosity fluids and suspensions in HF heater tubes. The heating of products in an HF heater leads to a fluctuating load of the high-frequency generator. This occurs both in the case of Erhitzer- tubes through the already explained pulsating

Flow or other effects as well as in cases in which lumpy products, such as packaged food, are transported by the specified by the RF heater heating volume. The heating volume is to be understood as meaning the spatial area between the electrodes of the HF heater, in which the products are heated by the coupled-in HF radiation. At different times, a different number of food packaging in the

Heating volume may be present. This results u. a. when a package enters the Erhitzerstrecke or the heating volume or from the

Heating volume expires. A higher number of

Packaging leads to a higher electrical load for the generator. Further load fluctuations occur when the electrical properties of the

Change products, for example as a result of serial variations of the products. To avoid this problem can be an active

Regulation are used, which via actuators the power flow into the load, d. H. in the present

Example in the food packaging, keep to a predetermined value. The regulation needs

however, a certain amount of time for the metrological

Detecting the power flow and acting on the actuators until finally a control response can occur. For the supply of HF heaters are

Generators with an impedance matching element used. The impedance adapter for electrical adaptation of the generator to the load (heater volume with the products contained) is also used to control the power flow. But this adapter, also referred to as Matchbox or matching network, with electromechanically adjustable

Capacities and inductors equipped.

The disadvantages of the known methods and

Devices for heating products by a high-frequency alternating electromagnetic field can therefore be summarized as follows:

• uneven heating of the packaged products along the transport through the RF field;

• uneven heating of the product stream

along an RF heater tube by pulsation during conveyance through the RF field.

The object of the present invention is to provide a method and a device with which the above disadvantages of the heating of

Products in RF fields can be avoided or at least reduced.

Presentation of the invention

The task is with the method and the

Device according to claim 1, 7 and 11 solved.

Advantageous embodiments of the method and the device are the subject of the dependent patent claims or can be the following

Description and the exemplary embodiment.

In the proposed method, the products are exposed to an RF field generated in an RF power generator implemented in semiconductor technology. An RF field is to be understood as meaning an electromagnetic field in the frequency range between approximately 10 kHz and approximately 300 MHz, in which the products are heated by dielectric heating. Preferably, the frequencies 13.56 MHz, 27.12 MHz or 40.68 MHz used for industrial

Applications are released. In general, however, other frequencies are suitable for HF heating.

The inventors have found that at

Use of HF power generators that work with semiconductor technology (so-called semiconductor generators) surprisingly lower temperature fluctuations from product to product or packaging to packaging occur than in the previously used tube generators. This also applies correspondingly to flows in a heater tube. Also, a semiconductor generator is over

Impedanzanpassungsnetzwerk connected to the load, that is connected to the lying between the electrodes heating volume with the products therein or the medium therein. The impedance matching network is preferably equipped with electromechanically adjustable capacitances and inductances. Preferably, the products in the proposed method are continuously through the

Heating volume transported. In an advantageous embodiment of the method for packaged products, this transport takes place in a liquid medium, preferably a liquid channel, which runs through the HF heater. The electrodes of the HF heater are preferably arranged on both sides of the liquid channel. As a liquid, for example, water can be used. The fluctuating load caused by the entry and exit of the individual products from the

Heating volume and produced by any change in the product composition or number of products in the heating volume, surprisingly significantly lower on the temperatures of

Products than when using a tube generator. Thus, with the proposed method and the associated device, a more uniform heating of the products in a series is achieved with the lowest possible thermal load and at the same time ensuring complete pasteurization or sterilization. A typical temperature rise of the products as they pass through the heating volume is from 25 ° C to 90 ° C during pasteurization and from 25 ° C to 125 ° C during sterilization.

In a further embodiment of the proposed method and the associated device is not the matching network to achieve a constant temperature of the products regulated, but the semiconductor generator itself. By an electronic control or regulation of the semiconductor generator can be an up or down rules of Power flow to the electrodes or a change in the electrode voltage can be performed, each resulting in a correspondingly rapid thermal response in the heating volume.

Both the direct electronic control of the semiconductor generator and the regulation of the matching network result in additional

Options for equalizing the temperature distribution in the heating volume or in the products. Due to the fast thermal response in the products, temperature inhomogeneities can be further reduced with appropriate control circuits. In the case of heating liquid products in a tubular RF heater, temperature inhomogeneities in the product along the direction of flow may occur due to, for example, regular or irregular pulsation of the flow.

For power control, in this situation, e.g. a continuous measurement of

Flow rate. With exact knowledge of this size, the mean residence time of the product in the electric field can be determined and the product of field power and the mean

Residence time an average energy consumption of the product and thus the temperature increase can be calculated.

If the flow rate changes, e.g. due to pulsation effects, compensation can be made by adjusting the field strength. The manipulated variable used to control the field strength

Is available in the case of the HF heater the Electrode voltage or the power flow from the HF generator to the HF heater or the electrodes.

Alternatively, as already mentioned, the adjustment of the power flow and the electrode voltage can also take place via the matchbox, i. the electrical

Capacitance and inductance matching network, which measures the electrical impedance of the HF heater, for example an RF heater tube, with the load to be heated therein, i. the products promoted therein, to which the electric impedance of the generator adapts.

By such a scheme, the

Product temperature in the flow direction are evened out. Other parameters are conceivable, such as the temperature or the electrical conductivity of the products, which are used as a measure of the

Control of the power flow can be used.

The heating process of the products and thus also the uniformity of the product temperature at the outlet of the HF heater is subject to the flow rate of a number of other factors that are often subject to considerable fluctuations and disturbances in the real production process. Important sizes are:

+ the product inlet temperature

+ the heat capacity of the product

+ the electrical conductivity of the product

Variations in these influencing variables can also be achieved with the method according to the invention when using a

Semiconductor generator can be effectively countered. The skilled person is able, with knowledge of the influence great to make an efficient and sufficiently fast control loop.

Of course, the regulation can also be applied to cases in which lumpy products, for example packaged foods, are transported through the heating volume.

The proposed device for carrying out the method comprises a heating volume with electrodes arranged on both sides, at least one high-frequency generator, which is connected to the electrodes via a matching network, and a transport device for transporting the products through the

Heating volume. The high frequency generator is formed in the proposed device as a semiconductor generator. The heating volume can be formed in one embodiment by a liquid channel or a portion of a liquid channel through which the products with the transport device

be transported. The transport device can by a conveyor belt or similar

Device for guiding the products through the

Heating volume to be realized.

The heating volume can in another

Design also by a section of a

Heater tube may be formed, are promoted by the liquid or flowable products. The transport device can hereby be realized, for example, by a pump or another conveying element. In the case of using a heater tube, a reduction in the temperature inhomogeneities in the tube cross-section can also be achieved by an alternative embodiment of the device, in which the electrodes are shaped such that they are between their along the

A longitudinal axis of the tube extending edges

have smaller mutual electrode spacing than between their centers. This alternative embodiment can be realized both with a tube generator and with a semiconductor generator, wherein in combination with a semiconductor generator, however, a further improved temperature uniformity is achieved.

In advantageous embodiments, the devices described above also include a control of the matching network to adapt to changing loads and / or an electronic control of the output power of the semiconductor generator, each with the corresponding sensors for receiving the for the

Control required measured variables.

The proposed method and the associated apparatus will be explained in more detail below with reference to an embodiment in conjunction with the drawings. Hereby show:

Figure 1 shows an example of a device for

uniform heating of products according to the present invention;

Figure 2 is a transverse and longitudinal section through a

exemplary fluid channel with electrodes through which solid products or Packaging can be transported to heat evenly; and

3 shows a cross section through an exemplary

Pipe / electrode assembly of an HF heater, wherein the electrodes have a surface contour for improving the field strength distribution in the pipe cross-section.

In the following exemplary embodiment, the control capability of the combination of the HF generator in semiconductor technology and the associated matchbox is added thereto

used to set up an HF heater control, detects the fluctuations in the influencing variables already at the input of the HF heater tube and already starts to control them via a disturbance variable switch, before it has noticeably affected the product discharge temperature control variable.

FIG. 1 shows a highly schematic illustration of this

Example of an embodiment of the proposed

Device with a HF heater tube 1 for flowable products, which are conveyed through the tube with the two electrodes 2. The electrodes 2 are connected via a matchbox 3 with a semiconductor generator 4, through which the high frequency is generated, which is coupled into the limited by the two electrodes 2 heating volume 7. The product 8 is pumped through the heater tube 1 by means of a pump and heats up as it passes through the heating volume 7. For controlling heating, several are used in this example

Measured variables recorded. Thus, in this example, the device comprises one or more sensors 9 for

Acquisition of product flow, one or more sensors 10 for detecting the inlet temperature, one or more sensors 11 for detecting the electrical conductivity of the product, one or more sensors 12 for detecting the electrode voltage and one or more sensors 13 for detecting the outlet temperature. The measured values of the product flow, the

Inlet temperature, the electrical conductivity and the outlet temperature of the temperature control 6 are supplied, which is connected to the RF power control 5, which in turn the performance of

Semiconductor generator 4 controls accordingly.

Figure 2 shows an embodiment of the

Heater volume as a liquid-filled channel through which pieces or packages are transported.

Part of a) shows the cross section and

Teilabbildung b) a longitudinal section through the channel. The channel is equipped with two opposite electrodes 2 and a liquid 14, such as water, filled. With the help of a transport device 16, packages or pieces 15 through the

Heater volume 17 transported. The number of packages present in the heater volume at the same time can fluctuate and thus the load on the generator.

The use of semiconductor generators for

Generation of alternating RF fields can for further homogenization of the temperature distribution in the

Products can be combined with a number of other measures. So are an improvement of

Heating uniformity and a reduction of the required electrode voltage by effective Dielectric coupling of the electrodes to an HF heater tube possible.

An HF heater tube is a known type of high frequency heater. This is a tube made of a dielectric material, which is acted upon by a high-frequency field and through the liquid, pasty food or food, which consist of particle suspensions, flow and are heated when flowing through. For the function of such an arrangement, the good control of the electric field strength in the cross section of the heater tube and the effective coupling of the RF field in the tube of great importance. They require a dielectrically well-controlled connection between the electrodes and the tube, which itself consists of an insulator material (plastic, glass, ceramic, combinations). The electrodes are flat, made of metal

Structures, in the simplest case metal plates, the

are arranged on both sides of the heater tube and parallel to this. The electrodes are connected via suitable connecting lines with the matchbox for impedance matching and power regulation and these in turn connected to the high-frequency generator as a voltage and energy source. Through the over the generator

applied electrode voltage arises in the space between the electrodes a strong electrical high-frequency field, which also penetrates the heater tube and the food flowing therein.

When using HF heater tubes, it can be seen that larger air gaps (> 5% of the electrode gap) between electrodes and tube lead to a considerable part of the available Elek ^¬ troden voltage over the air gap is pending and

hence for the route through which to be heated

Product only a small proportion of the electrode voltage remains. To be in these circumstances in the

To achieve high electric field strengths and high heating rates, very high electrode voltages have to be used, which in turn require extensive electrode voltages

Take measures to prevent electrical flashover between the electrodes and between electrodes and parts of the equipment.

Reducing the air gap by bringing the electrodes to the tube wall on the other hand, due to mechanical tolerances leads to uneven air gaps (<1% of the electrode gap), which are difficult to control in pipe designs. Local variations of the air gap between 0 and 1% of the electrode span can lead to significant variations in the electric field strength in the tube interior, which in turn cause a local variation of the power input and unevenness of the heating. It turns out that both minimizing the

Distance electrodes tube wall to direct contact and thus minimizing the required

Electrode voltage for a desired field strength in the product as well as the good control of the field distribution in the tube are possible if completely filled with a moldable or flowable dielectric material, the gap between the electrodes and tube and thus an air gap is avoided. A prerequisite for the effective function of such a filling is that the filling material has a permittivity number significantly greater than air and the dielectric losses of the material are very low. Furthermore, the material must have sufficient thermal stability with respect to the temperatures prevailing at the heater tube. Particularly advantageously, this filling will at the same time create a firm connection between the electrons and the heater tube, for example by using a mass which is poured between the tube and the electrode and hardens there.

Possible embodiments proposed filling are:

• Deionized water as coupling medium between

Electrodes and pipe wall. The water is characterized by a high permittivity number and in the

Case of deionized water at the same time due to very low dielectric losses in the

High frequency range.

An elastic or hard-hardening potting compound, the space between electrodes and

Filling the pipe wall. An elastic potting compound is characterized by the fact that temperature gradients in the construction of pipe material, potting compound and electrode material no

create mechanical stresses due to different thermal expansion.

An elastic or solid hardening potting compound, which at the same time is a mechanically stable potting compound

Establishes a bond between the electrodes and the pipe wall and thus provides additional fastening eliminates the need for high-voltage electrodes.

Practical embodiment is an elastic potting compound of 2-component silicone rubber, which provides in addition to the electrical coupling for the mechanical connection between the electrode and pipe. In addition to the design of the filling between

Pipe wall and electrode surface are the design and in particular the profile of the electrodes for uniform heating of great importance. The simplest electrode arrangement for tubular

Food heaters are two flat plates placed on both sides of the tube and parallel to it. The electrical high-frequency field between the electrodes passes through the tube and the food flowing therein and leads to its heating. However, if the plate-shaped electrodes are mounted very close to the tube in order to minimize the electrode voltage required for rapid food warming, it turns out that the field distribution and the power input in the tube cross section become very inhomogeneous. This is especially true

unfavorable if the product flow in the tube at

high-viscosity products laminar and a

Mixing of the flow and thus a convective temperature compensation does not take place. Particularly high field strengths and heating rates are in the tube cross section on the shortest connecting line of a

Electrode surface over the center of the tube to the other Electrode surface (the axis of symmetry of the arrangement, which is perpendicular to the electrodes) reached.

In this case, it was recognized that the distribution of the electric field strength in the pipe cross-section can be controlled by suitable deformation of the electrodes or of the electrode surfaces facing the pipe, and thus the power input into the product in the pipe cross-section

can be influenced.

In particular, a reduction of the electrode spacing at the edges of the electrodes makes it possible to even out the field strength distribution in the pipe cross section. FIG. 3 shows a cross section through a correspondingly designed one

Heater tube 1 with the tube wall 18. The electrodes 2 then have a surface contour which has the greatest distance (electrode spacing 20 in FIG. 3) on the direct connection axis 19 from electrode to electrode and the smallest distance at the electrode edges (electrode spacing 21 in FIG. 3). , The smallest possible electrode spacing must be chosen so that sufficient electrical insulation for the

highest expected electrode voltages remains.

Arrangements of tube and electrodes are particularly advantageous in which the electrode width is 50% to 200% of the tube outer diameter, the electrode gap 20 is 100% to 120% of the tube outer diameter and the electrode gap 21 is 10% to 90% of the tube outer diameter. The optimal distances must also depend on the geometric and dielectric ratios of the device,

in particular the dielectric properties of the product in the pipe, the pipe diameter, the

dielectric properties of the tube material, the tube wall thickness, the dielectric relationships in the space between the electrode surface and tube wall, z. Example, the presence of a dielectric filling material, the electrode width and the operating frequency of the HF heater are selected.

Figure 3 shows the embodiment of a tube electrode assembly that has been built and tested. This contour of the electrode surface has a width of 146% of the tube outer diameter, the

Electrode gap 20 is 100% and the electrode gap 21 is 37% of the tube outside diameter. For a product with a relative dielectric constant of 45, a loss factor of 120, a pipe material with a relative permittivity of 3.78, a pipe outside diameter of 48 mm, a pipe wall thickness of 4 mm, a dielectric filler with a relative dielectric constant of 2.7, and one

Working frequency of 27.12 MHz showed an almost ideal uniform field strength distribution and heating uniformity in the tube cross section.

By means of suitable geometrical arrangements, effects similar to those of a firing glass can also be achieved in optics, so that the maximum of the energy density can be placed almost in every volume element in the product, for example on the tube axis. The preparation of the electrode contours can be done by molding, by milling from a metal block or by bending a sheet. The efficient dielectric coupling of electrodes and tube is preferably carried out by a dielectric filling compound, as described above.

Another aspect that affects the uniformity of heating is the average power density, i. the amount of RF power supplied relative to that exposed in the RF field

Product volume that is introduced into the product in an HF heater for packaged products or in an HF tube. It turns out that at low

Power densities below 1 W / cm ^3, the heating of the

Product runs unnecessarily slow and correspondingly long heater tubes with higher heat losses, longer reaction time during control operations and higher demand for pump pressure are needed.

At very high power densities (greater than 50 W / cm ³ ), on the other hand, the danger of an uneven temperature distribution through hot spots, ie due to local overheating, increases, which can lead to damage to the product quality.

For this reason, uniform heating in an HF heater tube is advantageously achieved with a power density of between 1 W / cm ³ and 50 W / cm ³ in order to largely rule out temperature inhomogeneities while at the same time carrying out the heating so quickly that the product quality

is conserved and the heater tube can be short and compact dimensioned. Especially advantageous prove power densities in the range between 4 and 20 W / cm ³ ; this corresponds to heating rates of 1 K / s to 5 K / s in typical food products.

LIST OF REFERENCE NUMBERS

1 HF heater tube

2 electrodes

3 matchbox

4 semiconductor generator

5 RF power control

6 temperature control

7 heating volume

8 product

9 Sensor for product flow

10 sensor for operating temperature

11 Sensor for electrical conductivity

12 Sensor for detecting the electrode voltage

13 Sensor for detecting the exit temperature

14 liquid

15 products / pieces

16 transport device

17 heating volumes

18 Pipe wall of the heater pipe

19 symmetry axis perpendicular to the electrodes

20 electrode gap

21 electrode distance

Claims

claims

Process for the uniform heating of

Products in which the products (8, 15) are heated by a high-frequency alternating electromagnetic field,

characterized,

that the high frequency electromagnetic

Alternating field for the heating of the products (8, 15) with a semiconductor generator (4) is generated.

Method according to claim 1,

characterized,

in that the products (8, 15) are transported continuously through a heating volume (7, 17) in which they are exposed to the high-frequency electromagnetic alternating field.

Method according to claim 1 or 2,

characterized,

the products (8, 15) are transported in a fluid channel through the high-frequency alternating electromagnetic field.

Method according to claim 1 or 2,

characterized,

in that the products (8, 15) flow in a tube (1) of electrically insulating material and are transported in the tube (1) by the alternating electric field. Method according to one of claims 1 to 4, characterized

the high-frequency electromagnetic alternating field is coupled via electrodes (2) into the heating volume (7, 17), which are arranged on both sides of the heating volume (7, 17).

Method according to one of claims 1 to 5, characterized

that the high - frequency electromagnetic alternating field is coupled into the heating volume (7, 17) via an electromechanically adjustable adaptation network (3) for impedance matching, which is connected to the heating volume (7, 17) via an active control (5, 6)

Depending on the instantaneous load is regulated.

Apparatus for uniform heating of

Products through a high-frequency

alternating electromagnetic field, the

a heating volume (7, 17) with electrodes (2) arranged on both sides,

at least one high-frequency generator,

the via a matching network (3) with the

Electrodes (2) is connected, and

a transport device (16) for transporting the products (8, 15) through the heating volume (7, 17),

wherein the high frequency generator is a semiconductor generator (4). Device according to claim 7,

characterized,

that the heating volume (7, 17) through a liquid channel or a portion of a

Liquid channel is formed.

Device according to claim 7,

characterized,

the heating volume (7, 17) is formed by a tube (1) or a section of a tube (1) of electrically insulating material.

Device according to one of claims 7 to 9, characterized

the adaptation network (3) is designed to be electromechanically adjustable for adaptation to a changed load and is connected to an active control (5, 6) which regulates the matching network (3) as a function of the instantaneous load.

Apparatus for uniform heating of

Products by a high-frequency alternating electromagnetic field, in particular after

Claim 7, the

a heating volume (7, 17) with electrodes (2) arranged on both sides,

at least one high-frequency generator,

the via a matching network (3) with the

Electrodes (2) is connected, and

- Wherein the heating volume (7, 17) by a Tube (1) or a portion of a tube (1) is formed of electrically insulating material, characterized

that the electrodes (2) are shaped so as to be between their along a longitudinal axis of the tube

(1) extending edges have a smaller ^gegen¬ side electrode spacing (21) than between their centers.

Device according to claim 11,

characterized ,

in that the electrodes (2) have an electrode width measured along the longitudinal axis of the tube (1), which is 50% to 200% of an outside diameter of the tube (1), and are shaped so that the distance between the electrodes (21) between their edges is 10% to 90% of an outer diameter of the tube (1) and the distance between the electrodes (20) between their centers amount to 100% to 120% of the outer diameter of the tube (1).

Device according to claim 11 or 12,

characterized,

in that the electrodes (2) are connected to the tube (1) via a moldable or flowable dielectric filling material such that no air gap occurs between the electrodes (2) and the tube (1).