US2756027A

US2756027A - Liquid-cooled gaseous-discharge tube

Info

Publication number: US2756027A
Application number: US371361A
Authority: US
Inventors: John H Hutchings
Original assignee: National Electronics Inc
Current assignee: National Electronics Inc
Priority date: 1953-07-30
Filing date: 1953-07-30
Publication date: 1956-07-24
Anticipated expiration: 1973-07-24

Description

July 24, 1956 J. H. HuTcHlNGs 2,756,027

LIQUID-COOLED GASEOUS-DISCHARGE TUBE Filed July 30, 1953 IN VEN'TOR.'

MW MMM ATTORNEYS.

United States Patent O LIQUID-COOLED GASEOUS-DISCHARGE TUBE John H. I Iutchings, Geneva, Ill., assigner to National Electronics, Inc., Geneva, Ill., a corporation of Illinois Application July 30, 1953, Serial N o. 371,361

1 Claim. (Cl. 257-2) The invention relates to liquid-cooled gaseous-discharge tubes;` it is particularly directed t a gaseous-discharge tube having design characteristics which permit it to be made primarily from inexpensive materials and at the same time to possess excellent performance characteristics.

The present invention is applicable to an extensive class of gaseous-discharge tubes, including particularly mercury-vapor tubes used as rectiers, circuit interrupters, and other applications wherein currents of large magnitude are involved. In all such applications, tube cooling is an important design consideration. In many instances, the quantity of heat to be dissipated by a given tube in normal operation is so great in proportion to its size as virtually to compel the use of liquid cooling. The liquid employed as coolant is in nearly all cases water, which makes an admirable liquid for the purpose, because of its negligible cost and high specific heat.

This situation has led to extensive prior-art development effort in the field of Water-cooled discharge tubes. Various types of successful water-cooled tubes have been developed in the past, and it is accordingly understood that the present invention does not purport broadly to cover that field. The present invention relates, on the contrary,

2,756,027 Patented July 24, 1956 ICC perhaps, than a thermostatic element responsive tothe temperature of the cooling water. In most cases no temperature control was even attempted. Protection was merely against water failure, a suitable shut-down means being provided to turn off the power if water ow dropped below a predetermined level. Obviously such an arrangement, requiring full water flow regardless of the load on the tube, is extremely wasteful of water and hence uneconomical. Another' important object of the present invention is to provide a water-cooled gaseous-discharge tube wherein means are provided for virtually instantaneous measurement of tube temperature, permitting much more precise control of tube temperature than was possible with prior-art tubes and, in consequence, permitting co-ntrol of the rate of water flow.

In the accompanying drawing, I have described a typical embodiment of my invention, consisting of a socalled ignitron tube, which is a mercury-vapor tube useful as a rectifier and also as a high-current switch.

In the drawing, Figure l is a perspective View in elev vation of a tube made in accordance with the present into a particular design of liquid-cooled discharge tube f whose performance is superior to that of earlier types and which has the advantage that it can be made with less expensive materials than required in prior-art types.

In the detailed specification of the invention which follows, I shall make frequent reference to water as a cooling medium, but it will be understood that water is being thus employed only as an illustrative material, and that the structure described can, if desired, be used with other cooling liquids.

Prior-art water-cooled gaseous-discharge tubes have in general been made with a metallic housing, glass being used only for the necessary seals permitting maintenance Within the tube of a low gas pressure while providing a means for making external connections to the internal electrodes of the tube, such as the anode and the ignitor. The use of such metallic jackets in conjunction with Water cooling, however, has in the prior-art tubes required that the housings be made of expensive metal, usually columbiumstabilized stainless steel. Use of cheaper iron or ordinary steel in prior-art designs has led to diiculty with rusting and loss of vacuum due to hydrogen leakage through the metal wall. It is a principal object of the present invention to provide a water-cooled gaseous-discharge tube which can be constructed of ordinary sheet iron or mild steel without vany deleterious effects on tube life or operation.

Another serious problem with prior-art Water-cooled tubes was temperature control. On the one hand, it is always imperative that the power be removed from the tube the instant its temperature exceeds a safe value, but, on the other hand, shut-downs because of transient over-heating are expensive and are to be avoided except when tube safety requires them. Prior-art tubes, generally speaking, had no temperature-control means other,

vention. Fig. 2 is a vertical sectional view of the tube of Fig. 1, the section being chosen to bring out the details of its internal construction. Fig. 3 is a sectional view in the horizontal plane, taken along the line 3 3 of Fig. 2.

The ignitron tube shown in the drawing has a cylindrical metal housing 10 and a coaxially disposed outer jacket 11. Housing l0 may be made of welded or seamless steel tubing, and jacket 11 may be made of sheet iron, suitably formed. Jacket 11 may if desired be suitably plated to protect its outer surface and to give it a dressy, finished appearance. Near the top and bottom of the cylindrical housing 10 metal end plates 11a and 12 are inserted and welded thereto. To insure the existence of a gas-tight seal between the end plates and the housing, the end plates are provided with annular anges 11b and 12a, which are preferably seam-welded to casing member 10 around the entire periphery of the end plates. the respective ends of housing 10 and jacket 11, thus closing off the annular space between the housing 10 and the jacket 11.

A spirally disposed coil of tubing 15 is Wrapped aro-und and brazed to the housing 10, the coil being made of copper or other suitable rust-resistant and heat-conducting metal and terminating at the respective ends of the tube in inlet terminal 16 and outlet terminal 17. The coil thus formed by tubing 15 is a cooling coil through which water or other cooling liquid will be circulated during tube operation. l

The coil formed by tubing 15 will normally, be wound with greater density near thesbot'tom portion of housing 10, since it is in that zone that the mercury condenses, and maintenance of relatively cool walls in that region is therefore of paramount importance. Brazed to the outer surface of tubing 15, and covering suiiicient area to embrace one or more turns of the cooling coil, is a disc or plate 18 preferably made of copper. Overlying disc 18 jacket 11 contains an aperture 19, providing access from outside the tube to the outer surface of disc 18. Disc 1S is not brazed to jacket 11, and may preferably be insulated from jacket 11 by a very thin layer of the hightemperature sealing compound to be described. The shape of element 18, it will be understood, is a matter of choice; rather than being formed as a disc, it may be rectangular or any other desired shape. While I have shown the upper surface of disc or plate 18 recessed slightly below the outer surface of jacket 11, the plate may, if desired, be made of suliicient thickness to be ush with, or to extend outwardly beyond, the surface of jacket 11.

Similarly, annular caps 13 and 14 are iitted over' The entire 'space-between housing 10 and jacket 11, apart from the` space Yoccupied by the tubing and the disc 18, is filled with artificial rubber or other high-temperature sealing compound 20. This material is placed in `the annular Space `between `housing 110 tand ,ijacket 11 whenfn a;plasticy condition, and isintroducedin any suitable manner to insure that it lls thetentirespace available to'it. This materiabprovides completeinsulation of the tubing l15 and the housing `10 against contact `with air. It Awillbe understood-thatannular caps :13 and 14 thus function asmechanical closuresonly, the sealing function being :entrusted to compound 20.

The components `of the `tube'inside `the housing 19may beconventional. `In the` device illustrated in the drawing, Ihave -shown the lowenportion of the tube interioreccupiedbyia `pooliof liquid mercurytl, ywhich may fill thetube to a depth of-perhaps one-`fourth inch. Suitably weldeduinto apertures in bottom plate 11a, are an evacuation tube 26a and `a glass seal-member 22 for supporting theiignitor lelectrode .and providing a means for making externalncontact thereto. Passing through ,glass yseal 22 is afrelativelyrigid conductor 23 extending into the space abovethernercurypool 21. The upper end of conductor 23 carries a'transversel metallic support member 24 which is `crimped at its free end around a .carbon electrode 25. Theflowerend of electrode 2S, which is `generallypenclshaped, isgprovided with a tip -26 made ofiboron `carbide or `other lmaterial of intermediate conductivity. .Tip 26 extendsdownward into mercury pool 21. A lead 27 may be provided if desired to insure good electrical contact between support `member 24 and `electrode 25.

Thestructure just describedis commonly known in the art as an ignitor, the particular discharge tube described in the present specification being of the type commonly called .ignitron.

The 4upper portion of `the tube is provided `with an anode 28,;preferably made ofv graphite, which is insulatedly-supported on top plate'12 by means of an annular glass seal 29. Ailexible lead 31 extends outward and `upward from seal =29'to.provide aconvenient external connection to anode28.

Extension 32 ,provides asimilar external contact element .for making `electrical connection to the .mercury pool 21, `which functions electrically ascathode.

Operation In the operation of my invention, cooling water may be pumped through tubing 15,at a rate determined by the` load ontheitube and the initial temperature of-the water. In anycase, the heatgenerated in the tube operation may in that mannerbe carried awaypromptly, the tube temperature beingheld at a safe value at all times. A .thermostat may be mounted in .contact with plate 18, which, `by reasoniof `being brazed to tubing 15, provides a reliable measure of the housing temperature at all times. (Since the tubing 15 is highly heat-conductive and is`itself jbrazedto housing 10, the.temperature.of plate '18 `at all times closely approximates the actual temperature of housing 10.) The ,external circuit controlled by the thermostat may be connected in conventional fashion to control the ow of water to maintain the tube at optimum operating temperature, and, of course, may be arranged to turn off the power in the event the temperature, for any reason, exceeds a safe value.

In operation, no air ever reaches either tube 15 or the surface of housing 10 adjacent tube .15, due to the protective action of the filler material `20. As a result, no condensation of moistureever-takes place onthesurface of housing `10, and `no problem of hydrogen leakage through the walls of housing 10 exists even when housing 10 is made of inexpensive sheet iron.

It s accordinglypossible by means of the structure herein disclosed, to provide a long-lived, Water-cooled discharge tube, at a manufacturing cost substantially below that required for prior-art Water-cooled tubes, which has .great advantagesoverprior-art tubes, particularly in respect to economical use of cooling water.

It will be understood that numerous changes andmodifcations in the disclosed structure may be'made bypersons` skilled in the art without departing from the spirit of my invention. Itis accordingly my desire that the foregoing description be regarded `asillustrative only, and that the Vscope of my inventionybe determined primarily withreference to the appended claim.

lclaim:

-iFor-use with a sourceof cooling liquid and .thermostaticallycontrolled means for regulatingthe ow :thereof,.a gaseous-discharge device adaptedl to be cooled by circulation of liquidycomprisinga metal'housing, an elongated `metal, liquid-tight tube `spirally surrounding said housing and bonded thereto along a substantial portion of its length, said tube having inlet and outlet ends adapted for connection to said source, an outer jacket surrounding said housing and said tube, providing `therebetween an enclosed space, means 4withinsaid `enclosed space etfectively sealing off fromaccess to air the outer surfacesfof saidhousing and of `theportion .of said tube in intimate contact with said housing, said sealing means being .operative to provide at least partial thermal insulation for said housing andsaid tube, `and means adapted for cooperation with said thermostatic `means comprising a metal plate bonded to said tube on the surface thereofopposite said housing, said plate being substantially heat-insulated from said jacket, the portion of saidjacket adjacent said plate beingiat least `partially relieved to permit contact between said plate and saidrthermostatic means.

References Cited in the le of this patent UNITED STATES EPA-TENTS 2,121,579 Bahls June 2l, `1938 '2,275,852 Herskirld Mar. 10, 1942 2,313,379 Wood Mar. `9, y1943 2,595,150 Lemeshka Apr.'29, 1952