US2593869A - Air purification device - Google Patents

Description

April 22, 1952 H. F. FRUTH 2,593,869

AIR PURIFICATION DEVICE Filed July 15, 1948 [n z/emor Hal Frederick Hui Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE Hal Frederick Fruth, Skokie, 111.

Application July 15, 1948, Serial No. 38,882

3 Claims. (Cl. 183-7) The present invention relates to air purifiers and more particularly to means for ionizing airborne particles preparatory to precipitating them on charged collector plates.

It is an object of the present invention to provide improved means for charging suspended dust and the like by the action of an electrode containing a material capable of emitting charged particles into the air stream. It is a more detailed object to provide an improved electrode construction to facilitate the emission and acceleration of ions enabling precipitation of pollen and other microscopic dispersions as well as large particles of dust and the like. Still another object is to provide an ionizer which is simple and inexpensive and sufliciently durable to withstand rough usage in domestic and industrial air conditioning applications.

Other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 is a schematic view showing an air duct and collector plates and illustrating the manner in which ionizing electrodes are associated therewith.

Fig. 2 is a fragmentary view showing on an enlarged scale the detailed structure of an electrode, fabricated in accordance with the invention.

Fig. 3 shows a transverse section of the electrode of Fig. 2 together with an adjacent electrode of opposite polarity.

While the invention is susceptible of various modifications and alternative constructions and uses, I have shown in the drawings and will herein describe in detail one embodiment of the invention. It is to be understood, however, that I do not intend to limit the invention by such disclosure, but aim to cover all modifications and alternative constructions and uses falling within the spirit and scope of the invention as expressed in the appended claims.

Referring now to the drawings, Fig. 1 is a diagrammatic view showing an air duct ID, a set of oppositely charged collector plates I I, and ionizing electrodes indicated generally at l2. Conventionally, alternate ones of such electrodes are connected in sets [4, 15 to a source of high po tential so that the resulting brush or corona discharge causes suspended particles in the immediate vicinity of the electrodes to become ionized and therefore attracted to the charged collector plates. In this instance a positive charge is applied to the electrodes l5 and a negative charge is applied to the electrodes M. Tests have shown that the degree of ionization attainable in this manner using moderate voltages is small and that a very elaborate arrangement of precipitator plates is necessary in order to insure that a high percentage of the suspended foreign matter is removed from the air before it is again discharged into the air-conditioned chamber.

In accordance with the present invention, the degree of ionization is greatly increased by an improved physical construction of the ionizing or negatively charged electrodes I4 and by including therein certain ionizing substances capable of emitting charged particles, primarily electrons.

As shown, each electrode l4 comprises a stringlike body 28 having frayed strands 29 of conducting Wire or the like projecting from the surface of the body in closely spaced relation to each other. The electrode body 28 is formed from thermally non-conducting material and in this instance constitutes a frayed strand of woven or spun yarn composed of glass or textile fibers. A layer of conducting material is deposited on the surfaces of the electrode body and the projecting strands 29. This surface layer may, for example, consist of an electrically deposited or chemically reduced layer of aluminum, magnesium, or zinc.

If desired, however, and without departing from th invention one or more of the following metals may be employed in the formation of this coating layer: beryllium, calcium, zinc, strontium, cadmium, and barium, all from group II of the periodic classification. Caesium from group III and thorium from group IV may also be successfully used. The metals need not be in their metallic state since the characteristic low work function may also be obtained using the metals in the form of compounds such as the oxide formed in situ.

When potential is applied between a negative electrode I4 and an adjacent positive electrode or rod [5, an electrostatic field is set up. The positive rod I5 is preferably smoothly rounded and consequently most of the potential drop occurs in the vicinity of the sharp points of the frayed strands 29. Due to the resulting high gradient, electrons are freed from the points of the strands and are rapidly accelerated in the direction of the adjacent electrode l5. Because of the large number and speed of the electrons, efficient ionization is produced causing eifective precipitation of particles over a wide range of sizes. By using an emitting electrode of the above type it is possible to employ voltages much 3 lower than conventionally required without sacrificing precipitation efficiency. Thus the production of ozone may be kept within reasonable bounds and the disagreeable physiological effects associated therewith completely eliminated.

The coated projecting strands 29 of the electrodes I4 are poor thermal conductors. Thus, by proper spacing of the electrodes i4, 15, the flow of current may be adjusted so as to cause heating to take place at the tips of the projecting strands. The latter is apparently due to positive ion bombardment as well as electron flow. This has been found to greatly increase the facility with which the electrons are emitted and increases the total number of electrons available even at moderate ionizing voltages. While a number of diiferent alloys may be employed having the desired emissive properties as mentioned above, it is preferable to select one having at the same time a high resistance to continued oxidation and not subject to appreciable loss as a result of cathode sputtering. Alloys having the wear characteristics of magnesium-aluminum alloy are preferred because of the thin self-protecting oxide coating formed on the surface. Although the invention has been described as particularly suited for use with direct current, it will be understood that alternating current is also suitable, each electrode being fabricated similarly to the electrodes I4 and serving asv a cathode for half the time.

To further increase the electron emission of the electrodes M, a conductive coating is used containing radioactive material. The latter may consist of a dispersion of radium, polonium, uranium, or the like, but preferably less expensive materials are used which have been made artificially radioactive by bombardment. Examples of such materials are the following radioisotopes and compounds containing them: strontium 90, carbon 14, chlorine 36, technitium 99. These have sufficient emission of electrons (beta radiation) to give increased ionization and have a half-life of at least twenty-five years. Due to the substantial absence of gamma radiation there isno danger that harmful radioactivity'will be imparted to the air.

In the foregoing discussion the efficiency of the present electrode construction and arrangement has been discussed particularly as regards the charging of larger air-borne particles preparatory to their collection by the collector plates. Studies have shown that the arrangement disclosed herein possesses practical advantages not to be found in prior art ionizing devices. I have found, for example, that the arrangement is particularly effective for removing particles. of extremely small size, for example, such as pollen grains, bacteria and filtrable viruses. As a result, the precipitator including the present ionizer is extremely valuable to hay fever sufferers and for germicidal purposes-in hospitals, laboratories and the like.

What is claimed is: i

1. A precipitating device for ionizing air-borne particles including, in combination, two ionizing electrodes disposed in spaced relation to each other, one of said electrodes comprising an elongated body formed from interlaced fine strands of yarn having high electrical and heat insulating properties, said body being of sufficient strength to be self-supporting between its ends, the surface of said body being frayed so as to present a large number of closely spaced outwardly extending projections of said fine strands of yarn, and a fine coating of electron emissive metallic material on the surface, of said body and on said projecting strands of yarn, the strand projections thus coated having substantial length but being of small transverse cross section, said coated strands having both good heat insulating properties and good electrical conducting properties, the ends of said projections presenting minute electron emitting points which become heated to high-temperatures when said device is in operation.

2. A precipitating device for ionizing air-borne particles comprising, in combination, two ionizing electrodes disposed in spaced relation to each other, one of said electrodes comprising an elongated body of heat insulating material, a pluralityof fine strands of material including at least one component of substance having good electron-emitting qualities, said strands having closely spaced relation to each other and projecting outwardly in random directions from the surface of said insulating body to present a. large number of minute electron emitting points disposed on the ends of relatively long but thin supporting members having very small transverse cross sections.

3. A device as set forth in claim 2 in which said electron-emissive substance of said strands constitutes radioactive material.

HAL FREDERICK FRUTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 617,618 Thwaite Jan. 10, 1899 945,917 Cottrell Jan. 11, 1910 1,067,974 Cottrell July 22, 1913 1,357,201 Nesbit Oct. 26, 1920 1,399,422 Chubb Dec. 6, 1921 1,409,901 Anderson Mar. 21, 1922 2,231,330 Gove Feb. 11, 1941 FOREIGN PATENTS Number Country Date 338,796 Great Britain Nov. 27, 1930 816,463 France May 3, 1937 425,273 Germany Feb. 16, 1926 442,644 Germany Apr. 2, 1927 507,914 Germany Sept. 22, 1930

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