Electric heating apparatus

Application filed November 19, 1930. Serial No. 490,741.

My invention relates to electric heating apparatus, more particularly to electric heaters of the type in which the heat is generated in the heated body itself, and has lor its object 5 simple, reliable and effective electric heating apparatus utilizing currents of high frequencies.

My invention has particular application to heating apparatus wherein the material or io body to be heated is placed between spaced electrodes electrically connected to a source of high frequency supply, whereby the body is heated by an electrostatic field. In the application of this type of heater it has been io found that the portion of the body adjacent the source of high frequency supply is heated with greater rapidity than the remaining more remotely situated portion. In accordance with my invention I provide in one form 20 thereof a series of pairs or heating electrodes with separate source of high frequency supply which are arranged on opposite sides of the pairs of plates, together with means for passing the body to be heated in succession 25 between the pairs of plates thereby it is heated uniformly.

My invention is especially useful in the heating of food products, such as milk and meat, for sterilization, cooking or other pur80 poses. It has wide application, however, to neating processes wherein a uniform rate of heating is desirable. This method of heating is to be distinguished from the usual method of heating in which heat is applied to the ex⁸⁸ terior of the body and must be transmitted by conduction into the interior portions. Such methods require a longer heating period and furthermore, the outer portions of the body are subjected to the maximum tempera⁴⁰ ture for a greater length of time than the interior portions, which is of especial disadvantage where the heating period is quite critical and must be closely controlled.

For a more complete understanding of my ⁴³ invention reference should be had to the accompanying drawing in which Fig. 1 is a view showing in simplified partially diagrammatic form apparatus for applying high frequency current to the heating plates in accordance ⁸⁰ with my invention, while Fig. 2 is a diagrammatic representation of heating apparatus embodying my invention.

Referring to the drawing, in Fig. 11 have shown a typical heating system comprising spaced electrodes, shown as plates 10 and 11 ⁸⁸between which the material to be heated is placed, and a source of high frequency supply, shown as a three element electron discharge device or tube 12. The plates 10 and 11 are mounted on suitable electrically insu- ⁸⁰lating supports (not shown). The material to be heated is placed between the plates in spaced or electrically insulated relation with them, for example in a suitable container 18 made of an electrically insulating material, ⁸⁸such as glass.

It will be understood that the electron discharge device 12 operates in a manner similar to a high frequency short wave tube oscillator, such as used in radio transmission, and pro- 70 duces current of similar high frequencies, on the order of twenty to fifty million cycles per second. In the particular system shown the plates 10_and 11 are connected respectively to the grid 14 and the anode or plate 15 of ⁷⁸the discharge device, suitable inductances 16 and 16α being included in the respective connections so as to form a resonant high frequency oscillation circuit. At these very high frequencies the inductance in the conductors ⁸⁰themselves may be sufficient to produce this desired resonant condition in which case no auxiliarv inductance would be provided.

The filamentary cathode 17 of the discharge device is heated from a suitable source ^wof alternating current which is connected to the cathode through a suitable transformer 18. Radio frequency coils 19 and 20 are included in the sides respectively of the cath- _Mode circuit. A tap 21 on the secondary of the transformer 18 leads through a grid leak resistance 22 and capacity 23 connected in parallel with each other, and through a choke coil 24 to the grid 14. A suitable source of 95 electrical supply, for example a direct current source of 500 volts or more, is connected to the tap 21 and the plate 15, a radio frequency choke coil 25 being included in the connection with the plate. The positive side 100 pairs of plates and consequently the material irt each container is subjected alternately on opposite sides to the higher rate of heating and as a result the material is heated uniformly throughout. It will be understood ⁷⁰that the number of pairs of heating plates may be varied as desired to give the desired temperature and rate of heating.

While I have ghown a particular embodiment of my invention, it will be understood, ⁷⁸of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope ⁸⁰of my invention.