Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Microwave energy
Patent
1992-11-16
1995-03-28
Bennett, Henry A.
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Microwave energy
219700, 219695, B23K 1510
Patent
active
054005248
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an installation for continuously drying, dehydrating or microwave baking of granular or powdered products.
French patent 2 606 577 describes a device enabling rapid heating with low thermal gradient of a liquid absorbing microwaves. Said device comprises an applicator coupled with the wave guide of a generator comprising an emitting tube, such as a magnetron and its supply.
In said patent, an advantageous embodiment provides for the applicator to have a parallelipiped internal cavity of which each of the three dimensions is between 20 and 30 cm for a guided radiation frequency equal to 2450 MHz and that the applicator cooperates with two coupling slots or two coupling antennas spaced apart at approximately 17 cm. An embodiment of this type enables a microwave field to be obtained in hybrid mode inside said internal cavity of the applicator in which the product to be heated is located. Thus, heating of the product throughout this space is remarkably homogeneous and the increase from one temperature level to another takes place very quickly.
The disadvantage of said known device is that treatment of the product is intermittent and requires operations to insert said conditioned product in the applicator and extract it after heating. This results in considerable timewasting and relatively high cost. It cannot in point of fact be applied to bulk products.
European patent application no. 0 141 657 discloses an embodiment in which the product treatment is continuous. Said known embodiment consists in using an Archimedes screw passing through an applicator coupled with a microwave generator. The Archimedes screw is solid and fills the conveyor sheath in section.
The disadvantage of such an embodiment is that the energy efficiency is low and is not therefore profitable.
The aim of the present invention is to heat continuously, preferably but non restrictively, with this known applicator, powdered or granular products, such as cereals, flour, metal oxide powders, etc., so as to subject them to special treatment: drying, dehydrating, cooking or other.
To achieve this aim and in compliance with the invention, the installation comprises, in conjunction with at least one applicator connected to a generator by means of a coupling device, a dielectric duct which passes through said applicator and contains a rotating metal screw for transporting the product to be treated, said metal screw comprising at least one helically wound wire extending at a distance from the axis of the duct and close to the internal surface thereof.
Thus, the product to be treated which is microwave-permeable, flows continuously through the applicator and is heated under the effect of microwaves. What it surprising is that the screw, which for reasons of resistance to mechanical stresses under temperature, is metal, does not interfere with the heating operation by microwaves and does not uncouple the applicator from the wave guide.
According to one particular embodiment, the generator of the or each applicator is controlled in such a way as to excite in said applicator a TM type hybrid whose electric field has a component parallel to the axis of the duct.
The coupling device is a single window connecting the or each applicator to the respective wave guide of the generator.
Each applicator has an parallelipiped shape internal volume whose length on each side is 20 to 30 cm for a radiation frequency equal to 2450 MHz, the dimensions of the window being adjusted to minimize the reflection coefficient towards the generator and in particular so as to be equal to 65.times.46 mm.
The internal diameter of the dielectric duct is 40 to 150 mm, arranging clearance of 2.5 to 15 mm with the screw whose thread, when it is round, has a diameter of 5 to 15 mm.
Advantageously, several applicators centered on the duct are arranged side by side and separated by perforated partitions, trapping the microwaves in their cavities without possible transfer from one to the other, but letting hot air pass through them which prevents condensat
REFERENCES:
patent: 4714812 (1987-12-01), Haagensen
Crosnier Leconte Dominique
Deramond Frank
Germain Alain
Bennett Henry A.
Microondes Energie Systemes S.A.
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