US2761940A - Immersion high frequency heating apparatus and method - Google Patents

Description

Sept. 4, 1956 JKW. MANN ET AL 2,761,940

IMMERSION HIGH FREQUENCY HEATING APPARATUS AND METHOD Filed April 2, 1951 R. F. COIL. E}

INVEWTORS .1 Jul |us W.r\/1ANN GEORGEIF- RUSSELL.

mitw cw ram ATTORNEYS United States Patent INIMERSION HIGH FREQUENCY HEATING APPARATUS AND METHOD Julius W. Mann and George F. Russell, Tacoma, Wash. Application April 2, 1951, Serial No. 218,798 4 Claims. (Cl. 219--10.41)

An object of our invention is to provide an immersion high frequency heating method which is a continuationin-part of the application filed by us on November 24, 1947, Serial No. 787,726 now bandoned, and entitled, Immersion High Frequency Heating and Method. In the application just mentioned, we set forth that in the heating of certain dielectrics by a high frequency electric field of force, much damage to material is caused by arcing where a high electrostatic strain exists and/ or where the material being heated is of non-uniform thickness, density, size, etc., or is composed partly of particles such as carbon which are particularly sensitive and attractive to the fields effect. The dielectrics to be heated are placed between two electrodes which are alternately charged positively and then negatively by a source of high frequency energy such as a vacuum tube electronic generator. The frequencies employed vary from one million to two hundred million cycles per second, the usual range being under thirty million cycles when large masses of material are heated.

The invention is directed to the heating of foods, such as peanuts; the blanching of vegetables, such as carrots; or the heat treating of apples, turnips, etc. When peanuts are placed between two electrodes across which a high frequency electric field of force is maintained, there is is an extreme tendency for arcing to take place between the electrodes and the dielectric, with the consequent burning of the product. In like manner, when vegetables are blanched with or without an air gap between the vegetables and the electrodes, arcing will generally take place with the resulting ruination of the material. Arcing is therefore a deterrent to rapid blanching. Foods having a higher sugar content, such as prunes, raisins and fruits, are particularly subject to heavy arcing tendencies. Rubbers which are heavily carbon compounded, have a great tendency to are when placed between the electrodes. We have set forth by way of example only a few of the many possible illustrations which could be given.

The principal object of our invention is to heat treat solid dielectric material in the high frequency electric field while they are immersed in a liquid or flowable dielectric and are suspended in the dielectric as they pass between electrodes so that the arc would have to pass through the liquid or flowable dielectric before it could reach the materials. There are various ways of accomplishing this. One is to immerse the dielectric in a liquid dielectric such as oil or water or in a fiowable dielectric which upon being subjected to heating by the high frequency field of force, does not materially change viscosity of flow characteristics, and place the electrodes out of the liquid or b flowable dielectric, but in positions to dispose the dielectric therebetween.

A second way is to immerse the dielectric in the liquid dielectric or fiowable dielectric and surround the liquid dielectric with a second liquid dielectric in which the elecice trodes are imersed, care being taken that the dielectric will lie within the high frequency electric field of force. Difi'erent liquids have different specific heats and specific inductive capacities. It has been found desirable to vary the type of liquid dielectric used as the agent which surrounds the solid dielectric to be heated in order to secure varying heating results from the high frequency electric field of force in the heated solid dielectric. Varying the relationship between the specific heats and/ or the specific inductive capacity of the liquid dielectric and the solid dielectric which it surrounds, creates a condition whereby a greater or lesser proportion of high frequency heat effect may be concentrated in the solid being heated. The liquid dielectric between the electrodes of the high frequency generator will be heated in proportion to its specific heat and dielectric loss factor by the high frequency field of force which is employed primarily to heat the solid immersed within it. This is desirable in many cases since the interior of the solid dielectric material will be heated by the effect of the high frequency field of force to a greater degree than will its surface. Reference is made to our copending applications on a method of heating the interior of plastic preforms, Ser. No. 192,416, filed October 27, 1950, now Patent No. 2,642,627; and a process of controlling and placing of radio frequency heat in a dielectric, Ser. No. 750,836, filed May 27, 1947, now Patent No. 2,599,850.

It is possible to raise the temperature of the liquid dielectric by external means in addition to that caused by the heating effects of the high frequency electric field of force. This is highly desirable in many cases as for example, the purpose of balancing the natural non-uniform higher internal heat distribution resulting from the sole use of high frequency heating, by the application of external heat to the solid dielectric from its surfaces inwardly due to the elevated temperature of the surrounding liquid dielectric.

Other objects and advantages will appear in the following specification, and the novel features of the device will be particularly pointed out in the appended claims.

Our invention is illustrated in the accompanying drawings forming a part of this application, in which:

Figure l is a diagrammatic showing of heating a dielectric by immersing it in a liquid or flowable dielectric and placing the electrodes outside of the liquid, but in a position to cause the high frequency electric field of force to pass through the dielectric;

Figure 2 is a schematic view of a portion of Figure l and illustrates the series condenser effect created between the oppositely charged electrodes;

Figure 3 is a diagrammatic view in which the dielectric is immersed in one liquid or flowable dielectric and the electrodes are immersed in a second liquid or non-flowable dielectric that surrounds the first liquid dielectric; and

Figure 4 is a schematic view of a portion of Figure 3, and illustrates the series condenser effect created between the oppositely charged electrodes.

While we have shown only the preferred forms of our invention, it should be understood that various changes or modifications may be made within the scope of the appended claims without departing from the spirit and scope of the invention.

In carrying out our process, we illustrate in Figure 1 the placing of electrodes A1 and A2 on the outside of a container B, in which a liquid or flowable dielectric C is disposed. The dielectric D to be heat treated is immersed in the liquid C. The electrodes A1 and A2 may be spaced from the container B as shown, or they may contact it. The placing of the electrodes A1 and A2 outside of the container B is followed where it is not advisable to immerse the electrodes in the liquid dielectric C that contains the dielectric D which is to be heat treated. In the treatment of certain chemical liquids where direct immersion of the electrodes into the chemical is not desirable, the method illustrated in Figure 1 may be followed and the solid dielectric D eliminated, the liquid C becoming the dielectric to be heat treated.

Figure 2 illustrates electrically what takes place between the electrodes Al and A2 when they are connected to a radio frequency coil E, shown in Figure 1. When the coil E is connected to the high frequency electric current of a radio frequency output generator, not shown, the polarity of the two electrodes A1 and A2 are always different from each other and are changed simultaneously. We have indicated the electrode A1. as positive and the electrode A2, negative for an instant of time. The radio frequency lines of force travelling between the two electrodes will create a series condenser etfect therebetween as indicated by the small condensers placed between the various parts in Figure 2.

There is a condenser effect between the electrode A1 and the wall 1 of the container B, this condenser effect being indicated by a condenser 2. There is also a condenser etfect between the wall 1 and a solid dielectric D in the liquid C, and this is shown by the condenser 3. Another condenser 4 is shown between the two solid dielectric particles D and D1 in Figure 2, and another condenser 5 is indicated between the second dielectric D1 and the right hand wall 6 of the container, while still another condenser 7 is located between the wall 6 and the electrode A2. The series condenser effect thus produced between the electrodes A1 and A2 reduces the tendency for any arcing to occur between these electrodes and the adjacent walls 1 and 6, respectively, of the container.

It is obvious that the container B could be a tube through which the solid dielectric D and the fluid dielectric C, would pass. The high frequency electric field of force existing between the electrodes would be sufficient to heat the solid dielectrics as they passed between the electrodes and were carried by the fluid dielectric. The fiuid dielectric would prevent any arcing between the solid dielectrics and the electrodes.

In the blanching of vegetables with water as the liquid dielectric agent surrounding the solid dielectric being heated, it may be desirable to circulate the water and add constantly to its supply to prevent the water temperature from reaching the boiling point. In blanching fruit and vegetables, it has been found that water at a temperature between 180 and 190 F. will not injure the product. This is true even though the instantaneous blanching of the fruit or vegetable, caused by it being passed through the radio frequency field, may raise the temperature of the product above the 190 F., which is the temperature level of the surrounding liquid.

If it is necessary to place the electrodes A1 and A2 in a second liquid dielectric in order to prevent arcing between the electrodes and the container B shown in Figures 1, the method illustrated in Figure 3 may be used. in this figure, the inner container F1 is placed within an outer container F2. The inner container may contain a chemical liquid G1 to be treated and the outer container F2 carry a liquid dielectric G2 in which electrodes H1 and H2 are immersed. In this arrangement, the liquid G1 becomes the dielectric to be heat treated by a high frequency electric field of force and the solid dielectric particles J, shown in Figure 3, would not be used.

A slight variation of this method would be to change the inner container F1 into a tube and to fiow the dielectric liquid to be heat treated through the tube either by gravity or under pressure. The tube could be considered a dielectric and the tube surrounded by the water G2 or other liquid dielectric having thesame or a different specific heat and/or dielectric constant from the primary liquid dielectric G1 being heated. The electrodes H1 and H2 or the inductance, not shown, are immersed in the outer liquid dielectric G2 at least to the extent of that portion of their area used for the high frequency primary heating. The dielectric tube will therefore carry the primary liquid dielectric G1 through the electric or magnetic field established between the electrodes H1 and H2 or within the inductance means, not shown.

Figure 3 further illustrates solid dielectrics J suspended or placed in the liquid dielectric G1. In this case the dielectric I would be heat treated and the two liquids G1 and G2 would be used to prevent arcing between the electrodes H1 and H2 and the dielectrics J. The inner container F1 could be made a tube for the flowing of the liquid dielectric G1 and the dielectrics through the high frequency electric field of force in the manner explained in the preceding paragraph.

In Figure 4, we indicate the electrical effect produced by the radio frequency field lines of force passing between the electrodes H1 and H2. A series condenser effect is set up and the five condensers indicated as lying between the electrodes are numbered from 8 through 12, consecutively, starting from the left hand condenser. There is a condenser effect between the electrode H1 and the left hand wall 13 of the inner container F1, another condenser etfect between the same wall and the left hand solid dielectric I1, and a third condenser effect between the left and right hand dielectrics l1 and I2. A condenser effect indicated by the condenser 11, is established between the right hand dielectric J2 and the right hand wall 14 of the inner container F1, and there is another condenser effect, indicated at 12, between the wall 14 and the electrode H2. The series condenser effect established between the two electrodes H1 and H2 by the use of liquid dielectrics G1 and G2 will prevent arcing to the dielectrics I.

Where the statement is made that the liquid dielectric surrounds the solid dielectrics in the specification, the literal as well as the practical meaning of the word surround is meant. For example, should the solid dielectric be green peas and the liquid dielectric be water, the statement that the liquid surrounds the pea is meant even though the peas while in the liquid might contact each other. To all intents and purposes, the peas are surrounded by the liquid because a layer of water, no matter how thin, surrounds each pea.

In the various forms of the process illustrated, the liquid dielectric may have a specific heat lower or higher than the specific heat of the solid dielectrics immersed therein. Again, the specific heat of the liquid dielectrics may approximate the specific heat of the solid dielectrics. It is further possible to have the specific inductive capacity of the liquid dielectrics lower than that of the solid dielectrics or approximate the specific inductive capacity of the solid dielectrics.

The continuous or batch process is contemplated for either one of the two different forms .disclosed.

We claim:

1. The herein described method of internally heating a solid dielectric without arcing between the dielectric and the electrodes, which comprises surrounding the solid dielectric with a liquid dielectric, enclosing the liquid in a container, placing electrodes near the outer surface of the container and diametrically opposite each other, the electrodes being connected to a source of high frequency current and developing a high frequency field of force between the electrodes that will internally heat the solid dielectric.

2. The herein described method of internally heating solid dielectrics by high frequency current without arcing occurring between the solid dielectrics, which comprises: immersing the solid dielectrics in a liquid dielectric; and placing the two dielectrics between two electrodes that lie clear of the liquid and connecting the two electrodes to a high frequency source of current for creating a high frequency field between the two electrodes and through the liquid and solid dielectrics for internally heating the solid dielectrics.

3. The herein described method of internally heating solid dielectrics by high frequency current without arcing between the solid dielectrics which comprises: immersing the solid dielectrics in a liquid dielectric; and in creating a high frequency field of force exteriorly oi the liquid dielectric but which will extend through the liquid dielectric and the solid dielectrics for internally heating the solid dielectrics; the liquid dielectric preventing any arcing between the solid dielectric.

4. The herein described method of internally heating solid dielectrics by high frequency current without arcing occurring between the solid dielectrics, which comprises: immersing the solid dielectrics in a liquid dielectric; enclosing the liquid in a container; placing electrodes near the outer surface of the container and diametrically opposite each other, the electrodes being connected to a source of high frequency current and developing a high frequency field of force between the electrodes that will internally heat the solid dielectrics; and immersing the electrodes in a second liquid dielectric that surrounds the container.

References Cited in the file of this patent UNITED STATES PATENTS Gillespie Mar. 6, Grotenhuis Mar. 5, Russell et al. Dec. 28. Hickok Jan. 18, Bierwirth June 27, Gard Oct. 24, Bradley Oct. 24, Kinn Mar. 20, Taylor Mar. 27, Bewitt Apr. 10, Robertson Jan. 15, Rosenthal Feb. 26, Seifried Sept. 23, Newhouse June 30,

FOREIGN PATENTS Switzerland Nov. 1, Great Britain Mar. 24, Great Britain Oct. 18, Great Britain Apr. 26, France Nov. 5, France June 17,

France Jan. 29,

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