Electric heating – Metal heating – Of cylinders
Patent
1988-07-27
1990-03-20
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1041, 219 1055R, 219 1055B, 219 1077, 99DIG14, 99358, 426244, 426524, H05B 654, H05B 680
Patent
active
049103717
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and to a device for heating by dielectric hysteresis a product containing at least a proportion of ice.
It is nowadays quite common to heat and/or to thaw products containing at least a proportion of ice by the dielectric ultrahigh frequency heating process using a magnetron generating microwaves having a frequency of about two thousand five hundred megahertz. The practice shows however, that the effects of this dielectric ultrahigh frequency heating process are not homogeneous throughout the volume of the product and that thawing and heating of the product also occurs by conduction inside the same. Further, this known process is less effective for heating and for thawing a frozen product than for heating the thawed product, and this lack of homogeneity in the heating results in some parts of the product being hot, while others are still frozen.
The object of the present invention is in particular to remedy the deficiencies of known dielectric heating processes, and to propose a heating process by dielectric hysteresis for a product containing at least a proportion of ice, which enables to heat said frozen product and/or at least to form molecules of liquid water in said product with a controlled distribution throughout its volume or throughout a portion thereof. Further, when liquid water appears, the process causes practically no heating of the liquid water obtained, nor of the thawed portions of the product. Further, the process according to the invention allows, through the choice of its duration and/or of the voltage applied, and whatever may be the volume of the treated product, to bring the product to a determined temperature below 0.degree. C. or to form a determined proportion of liquid water in the volume of the product.
To achieve these results, the dielectric heating process according to the present invention is such, that it consists in subjecting the product to an electric field created between two electrodes to which is applied an alternating voltage having a frequency in the range from one kilohertz to six megahertz.
According to the present invention, the frequency of the alternating voltage applied to said electrodes can advantageously be in the range from seven kilohertz to six megahertz, or in the range from twenty kilohertz to six megahertz, or in the range from seven kilohertz to one megahertz, or even in the range from twenty kilohertz to one megahertz.
The process in accordance with the present invention can advantageously comprise a step after the formation of molecules of liquid water in said product, where a second heating means in applied to the same, which second heating means can be dielectric heating with a magnetron generating ultrahigh frequencies or microwaves, the frequency of which would be, for example, above five hundred megahertz.
The process according to the present invention can advantageously consist in placing the product between two electrodes having their surfaces facing each other. In this case, the effect achieved by the process will be practically homogeneous throughout the volume comprised between these surfaces. It can also consist in placing a rodlike electrode into the product and an electrode with surfaces to face the product. In the latter case, the effect of the process will be restricted to the vicinity of the rodlike electrode.
Since the dielectric heating process according to the present invention allows the heating and/or the formation of molecules of liquid water in a frozen product to produced in a controlled manner, it can obviously be used for heating and/or thawing foodstuffs, but it can also be used for heating and/or thawing, for example partly, any frozen product such as for example snow for the purpose of studying specific phenomena.
The present invention will be better understood from a consideration of non limiting examples of dielectric heating devices carrying into effect the dielectric heating process according to the present invention, which are illustrated by the drawing, where:
FIG. 1 show
REFERENCES:
patent: 2761940 (1956-09-01), Mann
patent: 2821611 (1958-01-01), Mann et al.
patent: 4296299 (1981-10-01), Stottmann et al.
patent: 4612199 (1986-09-01), Miyahara
patent: 4739140 (1988-04-01), Reznik
patent: 4812609 (1989-03-01), Butot
Brun Eric
Panel Jean-Michel
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