US2224750A - Vapor electric device - Google Patents

Description

ATTORNEY Dec. 10, 1940. .1. SLEPIAN ET AL VAPOR ELECTRIC DEVICE Filed Sept. 15, 1-939 H I a 6 5 4 3 2 1 wi k Q WITNE SES: 6

Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE 2,224,750 VAPOR ELECTRIC DEVICE Application September 15, 1939, Serial No. 295,099

Claims.

Our invention relates to a vapor electric device, and in particular to means for controlling the vapor pressure in vapor electric devices such as mercury arc converters.

In the operation of vapor electric converters, considerable diiificulty has been experienced be cause of the occurrence of arc-back and other related faults in the converters. Ithas long been suspected that these occurrences are in some manner tied up with the vapor pressure within the converters.

Recent investigation has disclosed that the condensing surfaces in such converters have only a small fraction of the theoretical condensing ability. In fact, the best heretofore known condensing surface, a freshly cleaned, sand-blasted surface, is found experimentally to condense only approximately 8 per cent of the theoretical condensing capacity of such surface; and under actual operation conditions the condensing capacity may be reduced to a fraction of 1 percent of the supposed condensing capacity; and in some instances the condensing capacity may, at least momentarily, be zero. The reason for this loss of condensing capacity is not definitely known, but is believed to be tied up in some manner with the surface condition of the condensing surface. Possibly, a molecular layer of some form of impurity, or even an electric condition at or adjacent to the surface, may be the cause of this so-called poisoning of the condensing surface.

We have found that nickel condensing surfaces are not subject of this poisoning eiTect, and

-' maintain their condensing capacity at substantially that of a new clean sand-blasted surface throughout the working life of the converter. Experimental results have indicated that, after a period of several days of identical operating conditions, a nickel condensing surface will condense approximately six times the amount of mercury vapor that will be condensed by a steel surface of the same life-history when subjected to the same conditions of temperature and pressure.

We are aware that it has heretofore been proposed, as in the Swiss Patent 148,613 of July 31, 1931, to utilize solid nickel or nickel-coated cooling-coils and cooling-bodies in mercury vapor devices in order to eliminate the corrosiveeffect of the cooling fluid. However, this use has in no way indicated that a nickel co ndensing surface on the mercury-side, rather than the water-side, of a cooling-wall would improve the condensing capacity of the-converter. According to our present invention, we have found that the use of a nickel condensing surface for condensing a major portion of the cathode vapor results in a condensing capacity heretofore unsuspected in vapor electric devices. Thus, it has hitherto been entirely unknown that a coating of nickel, placed over condensing surfaces of any other material, will increase the condensing efficiency of that surface many times. Thus, it is possible to use cooling-coils or cooling-walls of the cheaper metal, iron or steel, and by coating these coils or walls with nickel on the side exposed to the mercury vapor, to greatly increase the condensing elficiency of these surfaces.

It is, accordingly, an object of our invention to provide a vapor-electric device with a nickel condensing surface.

A further object of our invention is to provide a vapor-electric device in which the condensing efliciency is maintained throughout the life of the converter. 7

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

Figure 1 is a sectional elevation of a converter according to our invention, and

Fig. 2 is a diagrammatical illustration of the condensing ratio of nickel surfaces to steel surfaces. v

In the illustrated embodiment of our invention, the converter comprises a container or tank I which is composed, in the main, of a suitable metal less expensive, and more easily fabricated, than nickel; and preferably we make our tank I of a ferrous metal such as steel or iron. The

container I is provided, in its bottom, with a pool-type cathode 2, preferably mercury, by which term we mean to include any cathodematerial which is predominantly mercury. The converter is also provided with one or more suitable cooperating anodes 3, preferably of graphite construction, suitably spaced from the cathode 2. The illustrated tube or converter has a single anode 3 which is encased in a suitable shield, herein illustrated as a perforated graphite cup 4 mounted in insulating relation to a portion, such as the top 5, of the container I. Disposed between the active cathode area and the end of the anode shield, we have provided a suitable end-shield 6 such as is shown in copending application of William E. Pakala, Serial No. 222,799, filed August 3, 1938 and assigned to the Westinghouse Electric & Manufacturing Company. A suitable excitation device such as a make-alive electrode I is disposed in cooperative relation to the cathode 2.

In order to provide a condensing surface for the vapor evolved from the cathode 2, suitable cooling means such as cooling coils 8 are arranged in intimate contact with the side walls of the container I so that the side walls are suitably cooled for condensing the cathode vapor. In order to prevent poisoning of th condensing surface, a layer 9 of nickel is applied, by electroplating or other means, to the inside of the lateral walls of the tank I which constitute the principal condensing surface in the illustrated embodiment of our invention.

Experimental tests using nickel and steel surfaces under identical operating conditions gave a ratio-characteristic such as that shown in Fig. 2, in which the ordinates represent the ratios between the amount of vapor condensed from nickel and the amount condensed from iron after a given time expressed in days. It is found that, at the end of the first day, both the nickel and the iron have condensed substantially the same quantity of mercury, giving a ratio of l to 1. However, at the end of the first day, the radio in favor of nickel began to increase, so that, after from 10 to days, the ratio had risen to a ratio of 6 to 1 in favor of nickel, and was maintained substantially constant at that ratio for a test period of over a month. Further tests have indicated that this ratio apparently remains substantially constant throughout the usual life of the converter.

While we have showna specific embodiment of our invention, in connection with the inside or condensing surfaces of the enclosing tank of a mercury arc converter, it will be apparent that our inventiomin its broader aspects, is applicable to other mercury-condensing surfaces, either in a converter (including its attachments and appurtenances, which are subjected to mercuryvapor) or in any other device containing mercuryvapor which is to be condensed. We desire it to be understood, therefore, that various changes 1. and modifications can be made without departing from the true spirit of our invention or the scope of the appended claims.

We claim as our invention! 1. A vapor-electric device comprising an evacuated container composed in the main, of a metal other than nickel, at least one pair of cooperating main electrodes one of which is a mercury cathode, means for cooling the side walls of the container to provide a condensing surface for the mercury vapor evolved from said cathode, and a coating of nickel applied to said condensing surface on the side exposed to the mercury vapor to increase the condensing efiiciency thereof.

2. A mercury arc device comprising a ferrous metal container, a plurality of cooperating main electrodes in said container, one of which is a mercury cathode for providing operating vapor for said device, means for cooling the side walls of said container for providing a condensing surface for the mercury vapor and a coating of nickel on the side of said condensing surface exposed to the mercury vapor.

3. A vapor-electric device comprising an evacuated container, a plurality of cooperating electrodes in said container, one of which is a mercury cathode, and a cooling, heat-exchanging wall which is composed in the main, of a metal other than nickel, and which is coated with nickel on the side exposed to the mercury vapor.

4. A mercury-vapor device comprising a container composed, in the main, of iron, said device comprising a mercury pool therein and means for operating the device so that some of the mercury is vaporized, means for cooling a portion of the walls of said container, and a coating of nickel applied to the surface of a cooled wall of said container, which is exposed to mercury vapor.

5. A mercury-vapor device comprising a container, a mercury pool therein, means for operating the device so that some of the mercury is vaporized, and a cooling, heat-exchanging wall which is composed, in the main, of a ferrous metal and a nickel coating on the side of the Wall exposed to the mercury vapor.

JOSEPH SLEPIAN. WILSON M. BRUBAKER.

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