Electric heating – Capacitive dielectric heating – Specific heating application
Patent
1997-05-21
1998-11-10
Leung, Philip H.
Electric heating
Capacitive dielectric heating
Specific heating application
219779, 219780, 219775, 426244, 99451, 99358, H05B 654
Patent
active
058347461
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and apparatus for the heating of products.
It is known in several different connections to heat products by means of microwaves. The different techniques are used for different purposes, ranging as widely as from the drying of wood to the heat treatment of meat products and dairy products. Probably the best-known technique is in connection with microwave ovens, which have become a consumer commodity.
However, the hitherto-known techniques suffer serious disadvantages, and these are amplified and particularly pronounced in connection with large-scale operations.
From DK patent application no. 4718/86 it is known to continuously lead meat products through feeding elements, for example a tube, on which electrodes are mounted on diametrically-opposite sides. Before the meat products are fed to the active zone, the air contents are removed using a vacuum pump.
From DK patent application no. 1014/91 it is known to lead the products through a feeding element on which annular electrodes are mounted in two places around the tube.
Both of the above-mentioned methods are encumbered with certain disadvantages which become particularly pronounced during large-scale operations. The depth of penetration and herewith the tube diameter for the systems are thus limited. Moreover, a problem arises in connection with the non-uniformity of the electric field. This gives problems in connection with the heating, boiling or drying of products or materials which require a uniform heating. This is similarly problematic in connection with the heating of products having temperature-dependent conductivity, since the depth of penetration is herewith strongly reduced. Moreover, it also gives rise to problems in relation to the dimensioning of the HF generator, the reason being that the efficiency of the generator is reduced in connection with the heating of products to higher temperatures, for example in connection with boiling or the like.
OBJECT OF THE INVENTION
The object of the invention is thus partly to achieve a uniform and herewith a controllable heating or boiling of a wholly or partly fragmented medium, and partly to achieve a greater depth of penetration in the product.
This object is obtained by a method of the type disclosed in the preamble, which method according to the invention is characteristic in that at least one product electrode connected to the HF generator is placed in the centre of or in the vicinity of the centre of the cross-section of the tube in such a manner that the product substantially surrounds the product electrode or product electrodes.
ADVANTAGES OF THE INVENTION
By placing the product in the feeding element in which there is provided at least one product electrode, so that the product substantially surrounds the product electrode, said product electrode being placed in the centre of or in the vicinity of the centre of the cross-section of the feeding element, it is achieved that the applied field is short-circuited in the inside of the product, which means that the depth of penetration becomes optimal and can be adjusted in accordance with where the product electrode is placed. The product electrode thus serves as an antenna. According to the method, it is possible to achieve a hitherto-unknown depth of penetration for the field. This provides a special advantage in connection with products having dielectric characteristics which are temperature dependent, in that the heat from inside will spread outwards, whereby the product will be heated from inside. This must be seen in relation to hitherto-known heating methods, where the field is applied from the outside, and where the heating is concentrated around the surface of the product and hereby results in a kind of negative feedback, in that the product on the surface, as a function of the heating, is a better electrical conductor, the result being that the current will hereby flow in the surface of the product.
In addition by letting at least two of the electrodes be annular or cylin
REFERENCES:
patent: 2783350 (1957-02-01), Pircon
patent: 3214562 (1965-10-01), Sargeant
patent: 3309488 (1967-03-01), Francis
patent: 3327086 (1967-06-01), Cable
patent: 4221950 (1980-09-01), Lamberts et al.
patent: 4406070 (1983-09-01), Preston
patent: 4546226 (1985-10-01), Trembley et al.
Kjellerup Boerge
Pedersen Bo Kjeld
Pedersen Henning
APV Pasilac A/S
Leung Philip H.
Tulip International A/S
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