Method of and apparatus for alternating current to direct current conversion utilizing a liquid metal circulation loop

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Oct. 22, 1968 MASAO HOR 3,407,316

Method of and apparatus for alternating current to direct

Current conversion utilizing a liquid

Metal circulation loop

Inventor

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United States Patent 1.

Method of and apparatus for alternat

Ing current to direct current conver

Sion utilizing a liquid metal circula 5

Ton loop

Masao Hori, Naka-gun, Japan, assignor to Nihon Genshiryoku Kenkyu-sho, Tokyo, Japan

Claims priority, application Japan, Apr. 2, 1964,

Abstract of the disclosure

This apparatus for converting alternating current to 5 direct current includes a closed loop circulation system with liquid metal therein and means to circulate the liquid metal through the system. A magnetohydrodynamic generator surrounds at least a portion of the piping circu lation system. Cooling means are present to control the 20 temperature of the liquid in the system and other means , are provided to control the average flow velocity of the liquid metal through the system.

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This invention relates to alternating current to direct current conversion, and particularly to methods of and apparatus for converting an alternating-current power to a direct-current power by utilization of a liquid metal circulation loop. 30 The present invention has for its object to obtain a direct-current power of low voltage and high current value from an alternating-current power supply.

Another object of the present invention is to obtain a low-voltage high DC current power from an alternating 35 current power supply in a manner so that the voltage and current values of the DC power output may readily be controlled.

As used herein, the term “low voltage” refers to a volt age of not higher than 10 volts and the term “high current” 40 to a current of not lower than 1,000 amperes. Such low voltage high DC currents are usable in various applica tions involving a high power consumption at low voltage, for example, in the direct heating of metals and the ener gization of superconductive magnets. The low-voltage 45 high DC current powers are also utilizable in practicing - the "method of electromagnetically separating a dispersed phase from a mixed-phase fluid' which is disclosed in the copending application Ser. No. 385,979 filed on July 29,

Previously, various systems have been in use to obtain a direct-current power of low voltage and high current value from an alternating-current power supply. In one system, a combination of a transformer and a rectifier unit is used and in another a rotary direct-current generator is 55 driven by an alternating-current power supply. In any of previous systems, however, various technical difficulties have been involved. For example, the extraordinarily high current value necessitates use of heavy conductors render ing the entire apparatus excessively bulky. Particularly, 60 where a rotary generator is employed, a technical difficulty is involved in taking the current from the armature since use of ordinary brushes is not allowed with high currents, such as the present invention concerns.

Overcoming the above difficulties, the present invention 65 provides a novel method of obtaining a direct-current power of low voltage and high current value from an alternating-current power supply with efficiency. Also, according to the present invention, an apparatus for alternating current to direct current conversion is pro 70 vided which comprises a liquid metal circulation loop in cluding a circulating pump driven from an alternating current power supply source, a magnetohydrodynamic generator comprised of a permanent magnet or a direct current electro-magnet and electrodes, and a cooling unit for controlling the temperature of the liquid metal. The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which: -

FIG. 1 is a schematic illustration of the apparatus for AC to DC conversion according to the present invention; FIG. 2 is a modification of the apparatus of FIG. 1 including a flow control valve;

FIG. 3 is another modification of the apparatus of FIG. 1 including a bypass line; and

FIG. 4 is an explanatory illustration of one form of magnetohydrodynamic generator usable in the present in vention.

Referring to the drawing and first to FIG. 1, the princi ples of the present invention will be explained. Liquid metal is circulated through a loop form of conduit 4 in the direction of the arrow a by a pump 1 driven by an alter nating-current power supply. Reference numeral 2 indi cates a magnetohydrodynamic generator comprised of a direct-current (electromagnet or a permanent magnet) and electrodes and in which generator the mechanical work done on the liquid metal by the pump 1 is converted into a direct-current power. A cooler unit 3 is provided to control the temperature of the liquid metal in the circulation loop. .

The liquid metal circulating pump is preferably of the centrifugal or other mechanical type because of its efficiency or alternatively may be an AC electromagnetic pump. Usable forms of liquid metal pump of the mechan ical type include the following:

(1) Canned rotor membrane seal centrifugal pump; (2) Magnetic drive membrane seal centrifugal pump; (3) Frozen seal centrifugal pump;

(4) Totally enclosed centrifugal sump gas seal pump; (5) Shaft seal centrifugal sump gas seal pump; and (6) Reciprocating gas seal pump.

Usable types of AC electromagnetic pump for liquid metal use are as follows:

(1) AC Faraday type;

(2) Helical induction type; and (3) Linear induction type.

The cooler unit used may be of any convenient type. The magnetohydrodynamic generator may be of any known type for direct current generation. Kinds of metal usable as circulating liquid include Na (sodium), NaK (sodium potassium alloy), K (potassium) and Hg (mercury). The entire loop of conduit for circulation of liquid metal is preferably formed of a material, such as type 304 stainless steel.

Fluctuations of the load upon the entire loop can be compensated for by varying the amount of work done on the circulaing liquid metal thereby to regulate the direct current power output, either by varying the r.p.m. of the pump or by providing a flow control valve in the circula tion loop or a bypass line thereto. For example, in case the load is increased, the r.p.m. of the pump is increased or the flow control valve in the loop of circulation or a valve in the bypass line is controlled so as to increase the rate of flow of liquid metal through the circulation loop there by to obtain an increased DC power output. The circula tion loop including a flow control valve is illustrated in FIG. 2 and the loop having a bypass line in FIG. 3. The output voltage of the magnetohydrodynamic gen erator can be varied by changing the distance between the electrodes, or the magnetic flux density of the electro magnet, or also the velocity of flow of the liquid metal.

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For example, increase in voltage of the generator output... . is obtainable with increase in the electrode distance, the magnetic flux density of the electromagnet, and/or the velocity of the liquid metal flow.

An embodiment of the present invention will next be 5 described which employs NaK as working fluid and pro duces a direct current output of 13,500 amperes. As shown in FIG. 4, the embodiment includes a mag netohydrodynamic generator comprised of a direct-current electromagnet and a rectangular duct P. Assuming that the O direct-current magnet produces magnetic lines of force extending in the direction of the arrow b and the fluid, NaK, is caused to flow in the direction of the arrow a, direct-current electromotive force is produced in a direc tion at right angles to the magnetic lines of force as well 5 as to the liquid metal flow, i.e. between the electrodes 4 and 5. The direct current produced flows from the posi tive electrode 4 through load 8 to the negative electrode 5 in the direction of the arrow c. The walls 6 and 7 of the duct P are made of an appropriate electrical insulator to 20 minimize the loss of the power output. The fluid, NaK, is circulated by a suitable centrifugal pump (not shown), ther.p.m. of which is variable to adjust the magnitude of the converted power output. Also, an appropriate cooler (also not shown) is provided in the fluid circuit to prevent 25 temperature rise of the fluid, NaK.

The particulars of the AC to DC converter are listed below.

(1) Conversion capacity: 30 AC input (pump input)-49.8 kW.

(In case of the lead resistance including resistances of conductors and other components is 9X100, the internal resistance of the generator is 10 S2.) 35 Conversion efficiency-36.5% (2) Working fluid:

Composition-Na 22%, K 78% (melting point (3) Magnetohydrodynamic generator:

Magnet-Electromagnet, 10,000 gauss

Electrodes-50 mm. (height)x100 mm. (length)

Duct section-Rectangular, 50 mm. (height) X 150

Average flow velocity-10 m./sec.

Type-Two-stage turbine, frozen seal centrifugal pump

Flow rate-75 l/sec.

Pumping efficiency-60%

Shaft horsepower-64.3 PS (5) Cooler:

Type-Air-cooled finned-tube type

Capacity-27,000 kcal./hr. at 50° C. NaK tempera;

Having described the principles of the present invention and one preferred embodiment thereof, it will be apparent that according to the present invention a high DC current can be obtained relatively easily by employing a liquid metal circulation loop for magnetohydrodynamic power generation.

What is claimed is

1. In an apparatus for converting alternating current to direct current, the combination of:

a closed loop piping circulation system, a liquid metal in the system, means to circulate the liquid metal through the system, alternating current power supply means for the circulat Ing means, cooling means for controlling the temperature of said liquid metal through the system, means to control the average flow velocity of said liquid metal through the system, a magnetohydrodynamic generator surrounding at least a portion of the piping circulation system which in cludes means to direct a magnetic field substantially perpendic ular to the flow path of the liquid metal, and elec trode means adjacent the piping system to pick up DC current generated by the movement of the liquid metal through the magnetic field, a by-pass line connected to the circulation system across the circulating means, and a control valve connected in the by-pass line to control the average flow velocity of the liquid metal in the portion of the circulation system including the mag netohydrodynamic generator.

References Cited

United states patents

MILTON O. HIRSHFIELD, Primary Examiner.

D. X. SLINEY, Assistant Examiner.