US2137836A - Discharge device - Google Patents

Description

Nov. 22, 1938. T. A. ELDER DISCHARGE DEVICE Filed Sept. 16, 1937 r v e w E m OE/MO t. mum s h vv/ b a a 1 Eh [I 11 n i v. a 3" Patented Nov. 22, 1938 DISCHARGE DEVICE Thomas A. Elder, Scotia, N. Y., usignor to General Electric Company, a corporation of New York Application September 16, 1937, Serial No. 184,177

4 Claims. (Cl. 25027.5)

pool and for that reason are referred to in this application as "pool type cathodes. It should be understood, however, that the term "pool type, as used herein and in the appended claims, is not limited to liquid metals such as mercury but is intended to include solid substances which are capable of analogous use. Particular examples of such solid substances include cadmium and tin.

In connection with a pool type discharge de- -vice (that is, a device employing a pool type cathode) the vapor generated from the cathode material plays an important part in the operation of the device. In order to prevent arc-back or other undesirable interelectrode discharges, it is necessary to provide some means for limiting the pressure of such vapor to a desired value. In discharge devices adapted to handle substan- 5 tial power it is customary to accomplish this result either by providing a large condensation space somewhere in the discharge envelope or by liquid cooling a large portion of the surface area of the envelope. The former solution tends w to produce a cumbersome and unwieldy structure while the latter involves the disadvantage of requiring the presence of a cooling liquid and of some means for circulating such liquid.

It is one object of the present invention to 5 provide a high capacity discharge device of the type in question which is of compact and sturdy construction and in which air may he used as the cooling medium. One feature of the invention which contributes to the attainment of this ob- 40 ject comprises enclosing the cathode material in a metal container having its lateral walls in good heat-exchanging relation with an effective heat-dissipating means and providing an anchoring element effective to confine the oath- 45 ode spot to a region of the cathode surface which is closely adjacent to such walls. In this way the heat generated at the cathode spot is readily communicated to the heat-dissipating means.

In certain of its aspects my invention is pri- 50 marily applicable to a multi-anode device in which a cathode spot is maintained continuously throughout the operation of the device. In this connection it is my object to provide means for successfully combining an enclosing envelope 65 consisting mainly of metal with a pool type cathode which is in direct electrical contact with the main body of the envelope. More specifically. i this regard. my invention provides means for confining the cathode spot to the cathode surface in spite of the fact that such surface is electrically continuous with the walls of the discharge device. A feature of the invention which is important in this connection comprises the use of a cathode-spot-anchoring member so arranged as to prevent the cathode spot from 10 wandering to the walls of the discharge envelope and becoming fastened thereto.

The features of novelty which I desire to protect herein will be pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 represents a sectional view of a discharge device suitably emgo bodying the invention; Fig. 2 is a full section 7 taken on line 2-2 of Fig. 1; and Fig. 3 is an ir-' regular section taken on line 3-3 of Fig. 1.

In the particular embodiment of the invention shown in Fig. l I have illustrated an enclosing g5 envelope constituted principally of an'elongated metal tube ill, for example, of seamless steel. This tube, which is represented as of cylindrical outline but which may obviously assume other configurations, is closed at its upper end by a transverse metal header ll adapted to support.

a plurality of anodes l2, suitably of graphite. Another header of a character to be more fully described hereinafter closes the lower end of the envelope and serves as a container for a pool type cathode.

Each of the anodes i2 is insulated from the main body of the envelope by an insulating ring it which also comprises an element of a pillar seal through which a lead-in conductor 18 may be brought into the interior of the envelope. In order to prevent excessive cross currents between anodes during the operation of the device they are separated by means of metallic baflies 20 interposed between them. The shielding thus efiected is still further increased by the use of a transverse header 2| abutting against thelower ends of the bailies 20 and having openings 22 substantially aligned with the various anodes. Accumulation of condensed cathode material on the upper surface of the header 2| is avoided by causing the header to slope inwardly toward the center of the envelope and by providing a cenv tral opening 23 as an outlet for such material.

Angle irons 24 may be used to secure the. bailles 20 to one another and to the header ii.

The cathode of the discharge device may comprise a quantity of mercury or of some material capableof analogous use located at the lower portion of the discharge envelope. This material may, if desired, fill the entire bottom of the envelope, thus being laterally confined by the walls of the metal cylinder il. However, for reasons to be more fully explained in the following, I prefer to confine the active portion of the cathode to a cup-like metal container 25 forming the central portion of the bottom header of the envelope.

For the sake of clarity, the cathode material is not shown in the drawing but its normal level during operation is indicated by the dotted line 28. This level may be established, for example, by means of an overflow device comprising a small eyelet 21 projecting a predetermined distance above the floor of the discharge device and communicating with the exterior of the envelope through an aligned tube 28 (which is sealed off before the device is placed in use). During fabrication an indeterminate amount of cathode material may be introduced into the envelope through the tube It and then as much material allowed to fiow out as the position of the opening of the eyelet 21 will permit. In this way a desired quantity of cathode material, determinable in accordance with the length of the eyelet 21, may be deposited in the envelope. Because the upper end of the eyelet 21 may be slightly exposed during the operation of the device, it is desirable to cover it with a protective coating II, for example, of a glass which is relatively immune to the action of the cathode spot.

In order to initiate a discharge in the device during its initial starting period, there is provided in permanent contact with the cathode material a make-alive electrode 3i having a separate lead-in conductor 32 which is insulated from the cathode material. The electrode ll may suitably comprise a short tapered rod of semiconducting material having a resistivity between about land ohms per centimeter cube. A particular example of such a material comprises silicon carbide coated superficially with iron nitrate as described and claimed in a copending application of J. M. Cage, Serial No. 132,760, filed March 13, 1937, and assigned to the same assignee as the present application. For the most satisfactory operation, it is desirable that this electrode project a substantial distance, on the order of one-half inch, into the cathode material. For this reason a cathode pool of substantial depth, as indicated, must be provided. However, by confining the cathode material to the cup-like container 25, which has substantially a smaller diameter than the main envelope cylinder II, the amount of such material required can be kept within reasonable limits.

In order to assure stable and satisfactory operation of the discharge device, means must be provided for limiting the vapor pressure of the cathode material. This vapor pressure is primariiy a function of temperature, and for this reason the problem is largely one of disposing of or limiting the heat developed in the cathode Pool.

Much of this heat is generated at the cathode spot and must ordinarily be eliminated by conduction through the cathode material. Since cathode materials such as mercury are of low thermal conductivity, this mode of heat elimination is inherently inefilcient and unsatisfactory. For this reason it is extremely dimcult, for example, to eliminate heat with suflicient rapidity by conduction to cooling means associated with the bottom of the cathode pool. In accordance with my present invention, however, effective cooling is accomplished by confining the cathode spot to a portion of the cathode surface which is closely adjacent to an eil'ective heat dissipating means.

Referring again to the particular structure illustrated in the drawing, this is accomplished by the use of means adapted to confine the oathode spot to a region close to the lateral walls of the container and by providing heat dissipating means in good heat-exchanging relation with such walls. This arrangement assures the existence of only a short heat path through the cathode material.

The heat-dissipating means may take various forms and is, in the present case, exemplified as a heat radiator comprising a plurality of metal vanes 35 unitary with a circular member 36 which is secured in good heat-exchanging relation with the outside wall of the container 25. The radiator structure may suitably be composed of a highly conductive material, for ex-g, ample, copper, and may be maintained in good; thermal contact with the container 25 by an interposed filling I. of solder. Such solder may be applied, for example, with the discharge device in an inverted position; a gasket 39 of asbestos or the like being provided to prevent escape of liquid solder during the soldering process. A heavy copper plate 4| secured to the bottom surface of the container 25 serves to maintain a good heat path from such surface to the radiator structure. The heat-dissipating capacity of the radiator (and of the device as a whole) may be increased in use by subjecting w it to a forced draft of air, such air being preferably provided in an axial direction, for example, upwardly along the length of the device. The efiiciency of this mode of cooling may be increased by surrounding the device with a conforming enclosure adapted to confine the air stream and to increase its velocity.

The cathode spot may be confined to a region closely adjacent to the cooled wall of the container 26 by the use of cathode-spot-anchoring means of known character. In connection with the particular envelope structure under consideration, one may use, for example, a ring 43 of cathode-spot-anchoring material, such ring being in continuous contact with the cathode material throughout its entire circumferential extent and projecting substantially above the oathode surface. Numerous materials may be employed for this use but I prefer to utilize a refractory metal, such as molybdenum, which has been thoroughly cleaned as by the use of an acidbath and hydrogen firing.

In connection with the use of such an anchor, I have noted that the cathode spot appears as a fine line following the intersection between the anchoring member and the cathode material, the length of the-line depending on the amount of current being drawn. In order that the anchoring member may be effective to anchor the cathode spot during the passage of discharge currents of substantial magnitude, there may be provided in connection with the ring ll auxiliary members I! of anchoring material. These members are shown in the drawing as inwardly pro- Jecting radial portions secured to the interior.

circumference of the ring 43, and afford additional surfaces along which the cathode spot or line may extend.

From a thermal standpoint, the ideal arrangement of the ring 43 would be to have it in direct and continuous contact with the interior surface of the container 25. From a manufacturing standpoint, however, it is difllcult to obtain such continuous contact without the occurrence of small gaps or voids between the two parts. These gaps may be so fine as effectively to exclude the cathode material, in which case they constitute an effective insulation against heat transfer. I, therefore, prefer to arrange the ring 43 so that its outer periphery. is sufllciently spaced from the interior wall surface of the container to permit a thin layer of cathode material to exist between them. In the event that mercury is to be used as the cathode material, a space of about 100 mils is satisfactory for this purpose. With a spacing substantially less than this value,-the surface tension of the mercury is sufficient to prevent its filling the .intervening space. A further useful aspect of the provision of a narrow space between the anchoring member and the container wall lies in the effectiveness of such a space in preventing the cathode spot from transferring itself to the wall of the container, even in cases where there is a tendency for the spot to become dislodged from the anchoring means. This effectiveness is a result of the known tendency of a constricted space to inhibit the flow of arc current therethrough, and in the present situation to prevent the cathode spot from traveling into the constricted region on its way to the envelope wall.

Whether the anchoring member is in direct contact with the container wall or is slightly spaced therefrom, as shown, it is clear that only a short heat path through the cathode mate- 'rial exists between the region of the cathode spot and the heat dissipating means. For this reason, eflicient and rapid heat transfer is assured and a satisfactorily low cathode temperature may be maintained by the use of a heat radiator of practical dimensions.

There is naturally some tendency for heat generated in the discharge space above the oathode and particularly in the vicinity of the anodes l2 to be communicated to the cathode material through the metal walls of the envelope. This effect is minimized in the construction shown by the fact that a relatively long heat path is provided between the anode space and the cathode container 25. One portion of the path comprises an annular transversely extending wall portion 41 associated with the lower header and which serves to connect the container 25 with the cylinder l0. This wall portion is preferably composed of substantially thinner metal than the main body of the envelope and thus acts as an effective throttle for heat tending to flow toward the cathode pool. It is also possible and in some cases preferable to obtain this throttling effect by forming the annular wall portion 41 of a metal such as chrome-iron (stainless steel) which has a lower heat conductivity than the main body of the envelope.

In addition to the foregoing, the portion of the envelope lying between the header 2| and the annular wall portion 41 is made of somewhat greater length than would be otherwise necessary in order still further to decrease the heat flow from the portions of the envelope wall adjacent to the anodes. This interposed envelope portion also serves to provide a relatively cool receiving surface for cathode material which may be splashed from the cathode'pool by agitation thereof caused by the cathode spot. In this way the amount of vapor generated from the splashed cathodematerial may bemaintained at a low value.

By consideration of the drawing it will be seen that my invention provides a discharge device which is of compact construction and convenient shape. By virtue of the fact that the cathode container is of less diameter than the main envelope cylinder, the radiator structure associated therewith does not need to project materially beyond the main confines of the envelope. For this reason, the envelope, as viewed externally, comprises a cylindrical structure which is of substantially the same diameter throughout its entire length. This is a factor of considerable value in mounting the device and in assembling it with other apparatus.

While I have exemplified my invention by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. 1, therefore, aim in the appended claims to cover all such modiflcations as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to obtain by Letters Patent of the United States is:

1. A discharge device comprising an enclosing envelope consisting predominantly of metal, anode structure within the envelope, means electrically continuous with the main body of the envelope providing a metallic receptacle for cathode material, a mercury pool of relatively extensive surface area contained in the receptacle and in electrical contact with the lateral walls thereof, a metallic cathode-spot-anchoring means effective to prevent a cathode spot from leaving the mercury pool surface while retaining it at all times at a portion of such surface which is closely adjacent to the lateral wall of the receptacle, and a varied heat radiating structure in direct heat-exchanging relation with the outer lateral wall surface of the receptacle, whereby a short heat transfer path of low thermal resistance is maintained from the cathode spot to the said radiating structure.

2. An air-cooled discharge device including the combination of an elongated metal cylinder comprising the main body of a discharge envelope, a first transverse metal header closing the upper end of said cylinder, a plurality of anodes insulatingly supported from said header, a second transverse metal header closing the lower end of said cylinder, said second header including a central cup-like portion of smaller diameter than the cylinder and an annular portion electrically and mechanically connecting the cup-like portion to the main body of the envelope, a quantity of cathode material in said cup-like portion, a cathode-spot-anchoiing body projecting above the surface of the cathode material and formed to retain the cathode spot at all times in a region closely adjacent to the inner lateral wall surface of the cup-like portion, and a heat radiator comprising varied surfaces in good heat-exchanging relation with the outer lateral wall surface of the cup-like portion.

3. An air-cooled discharge device including the combination of an elongated metal cylinder forming a discharge envelope, a transverse metal header fitted into and closing one end of the cylinder, an anode structure insulatingly supported from said header, a second transverse metal header fitted into and closing the other end of the cylinder, said second header including a central cup-like metal portion or smaller diameter than the cylinder and an annular transversely extending metal portion electrically and mechanically connecting the cup-like portion to the main body or the envelope, a quantity of cathode material in said cup-like portion and in electrical contact with the lateral walls thereof, means including a metallic cathode-spot-anchoring member for confining the cathode spot to the surface of the cathode material and a heat radiator comprising vaned surfaces in good heat- A a,1s7,sss

exchanging relation with the outer wall 0! the cup-like portion, said heat radiator being of substantially the same transverse extension as the discharge envelope, whereby the device as a whole comprises a structure of approximately uniform diameter throughout its entire length.

4. A discharge device according to claim 1 wherein the cathode-spot-anchoring means comprises a molybdenum ring having its circumference slightly spaced from the lateral wall of the cathode retaining means to permit a thin layer of mercury to exist therebetween, and thereby to assure good heat transier from the cathode spot to the heat-radiator.

THOMAS A. ELDER.

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