US3444816A - Electromagnetic liquid pump - Google Patents

Description

FEPEBSZ May 20, 1969 H. J. KING ELECTROMAGNETIC LIQUID PUMP Sheet of2 Filed Sept.

Harry J. King,

INVENTOR.

Allen A. Dicke, Jr.,

AGENT.

y 1969 H. J. KING 3,444,816

ELECTROMAGNET IC LIQUID PUMP Filed Sept. 5, 1967 Sheet 2 of 2 3,444,816 ELECTROMAGNETIC LIQUID PUMP Harry J. King, Canoga Park, Califl, assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Sept. 5, 1967, Ser. No. 665,382 Int. Cl. F04b 19/00; H02k 45/00 US. Cl. 103-1 Claims ABSTRACT OF THE DISCLOSURE The electromagnetic pump produces a magnetic field in a first direction across a gap filled with electrically conductive liquid and has electrodes which cause electric current to flow through the liquid in the gap at right angles to the direction of the magnetic field to thus cause pressure and/or flow of the liquid in a direction normal to both the magnetic and electric fields. Through the use of a narrow gap in the direction of the magnetic field, a high magnetic field strength can be accomplished with magnets or magnetic coils of reasonable size. This pro-= duces a liquid space which is of small cross-sectional area. in the direction perpendicular to current flow to thus produce a relatively high electrical resistance in the liquid to produce a pump which employs a relatively low electric current to produce a high fluid head.

The invention described herein was made in the performance of work under a" NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 ('72 Stat. 435; 42 U.S.C. 2457).

Background The principle of electromagnetic pumping has been known for many years and was recognized as a possible means for pumping an electrically conductive liquid as soon as the directional relationships between magnetic field, electric field and direction of resultant force was recognized. The principle has been applied where large flow rates and relatively low heads have been required. The fairly short electrical path in such pumps produces large currents, in the typical structure, with the resultant large 1 R loss in the pump. With large flow, the generated heat is carried downstream with the liquid being pumped. With increasing head and resultant lower flow, heat reiection from the pump by means of the outfiowing pumped liquid becomes reduced. In some cases the resistive heating of the liquid being pumped, especially in the case where the liquid is mercury, causes liquid vaporization. Of course, this causes pumping failure.

Summary In summary, this invention is directed to an electromagnetic pump which is of such characteristics that relatively small magnetic field sources are required to pro duce an adequately strong field for proper pumping, and relative low currents are required so that proper pumping is accomplished with a minimum of heating. Furthermore, the pump structure is especially designed to reject heat through the pump body by using a thin electric insulation layer on the inside of a primarily metallic pump body. All of this is accomplished by positioning the iron pole pieces which direct the magnetic field close to each other to provide a small gap throguh which the liquid is pumped. Furthermore, the electrodes which provide the electric field are of extended area so that electrode to liquid resistance at the interface between them is mini-= mized. Furthermore, these electrodes are positioned to minimize the flow of pumped liquid outside of the mag States Patent Q netic field to thus prevent reverse leakage of the liquid within the pump.

Accordingly, it is an object of this invention to provide an electromagnetic liquid pump which is capable of pumping conductive liquid at a relative high pressure and very low flow rate. It is another object of this invention to provide an electromagnetic pump for conductive liquid wherein the liquid gap in the magnetic field is narrow in the direction of the magnetic field to thus provide both a strong localized magnetic field and a reduced cross section for electric current flow and thus raise the electric resistance through the pumped liquid to in turn reduce the electric current flow. It is another object of this invention to provide an electromagnetic pump for conductive liquid wherein the electrodes are positioned to reduce backflow of liquid along the electrode faces and are of extended area to reduce the electrical resistance be tween the liquid and the electrodes. It is a further object to provide an electromagnetic mercury pump in which the heat loss from the body of the pump is sufficient to prevent the mercury from rising to vaporizing temperature, even at zero flow.

Description of the drawings FIGURE 1 is an isometric view of the electromagnetic pump of this invention.

FIG. 2 is an enlarged view thereof with parts broken away.

FIG. 3 is a reduced section taken generally along the line 3-3 of FIG. 1.

FIG. 4 is a reduced section taken generally along the line 4--4 of FIG. 1.

Description The electromagnetic pump of this invention is generally indicated at 10. Top pole piece 12 and bottom pole piece 14 extend for the length of the pump. Magnets 16 and 18 are positioned between the pole pieces. The pole pieces are clamped onto the magnets by means of screws 20. As is best shown in FIG. 2, where parts are broken away, the magnets 16 and 18 are cylindrical in form. They are magnetized in the direction parallel to the cylindrical axis and are positioned so that the same poles are directed in the same direction. As is shown in FIG. 3, the north poles are positioned in the upward direction. Permanent magnets are illustrated, but it is clear that eIectr magnets can be used instead. In the preferred embodiment a high magnetic field force is desired, thus magnets of the greatest magnetic field strength are used. The usual aluminum-nickel-cobalt magnet alloys are considered the most desirable in this service. Pole pieces 12 and 14 are clamped directly against the magnet poles so that a minimum gap exists.

Poles 22 and 24 are respectively formed upon pole pieces 12 and 14. Poles 22 and 24 extend toward each other and define a narrow passage 26 therebetween. Poles 22 and 24 have their passage defining faces coated with a uniform and thin layer of electrically insulating material. Furthermore, this material should have relatively high thermal conductivity. Any material which meets the functional requirement is suitable for the application. However, in view of the need for uniformity of the film for reasons of uniformity of the height of passage 26, and good bonding in accordance with good thermal conductivity, a number of synthetic polymer composition materials are most suitable. The preferred material is polytetrafluoroethylene, and another preferred material is hexafiuoropropylene, or a copolymer of the two. These can be fused directly to the faces of the poles 22 and 24 to define a passage 26 of accurate size. The electrically insulative material is indicated at 28 and 30 on the two pole pieces.

Electrodes 32 and 34 respectively close the ends of the passage defined by the pole pieces. Insulative material 28 and 30 extends past the electrodes so as to electrically isolate them from the top and bottom pole pieces. Electrodes 32 and 34 have solid backs 36 and 38 which lie between the pole pieces to provide fluid tight integrity to passage 26. Each are provided with fins 40 which provide extended contact area between the electrodes and the liquid in passage 26. The fins are formed so that they extend parallel to the height dimension h so that all of the interfin spaces are in liquid communication with the passage 26. Additionally, this orientation of the fins effectively closes off any flow in the plane of passage 26 in the electrode spaces and confines the flow to the passage 26. Electrodes 32 and 34 respectively have electric connectors 42 and 44 which extend exteriorly of the main body of pump 10 for electrical connection. These connectors are suitably insulated from the pole pieces to prevent electrical short circuits.

The remaining sides of passage 26 are covered by side plates 46 and 48. These side plates are conveniently of synthetic polymer composition material because electrically insulative character is required. As is best seen in FIG. 4, side plates 46 and 48 extend past the backs 36 and 38 of the electrodes to provide a complete closure of the liquid space, including the passage 26. Openings 50 and 52 respectively provide entrance and exit for the material being pumped through passage 26. The openings 50 and 52 are shown as tapped connections at the exter nal surfaces and these relatively large connection openings are connected respectively orifices 54 and 56 to passage 26. The relatively short dimension of orifices 54 and 56 in the direction of electric current flow prevents any substantial electric current flow through the liquid outside of the main magnetic field directly between poles 22 and 24.

The electromagnetic pump 10 is restricted to the pumping of electrically conductive liquids. Furthermore, it is particularly suited for the pumping of liquid mercury at very low rates and at heads which are high when compared to other electromagnetic pumps. In a particular pump having external physical dimensions of about 1" x 1" x 2%", the passage dimension between the in-= sulation on the pole pieces can conveniently be .005. Furthermore, suitable permanent magnets can be capable of providing a magnetic field in the order of 10 kilogauss, when the dimension of the poles in the direction of electric current flow is .500" and in the direction of liquid flow is .300".

When mercury is the pumped fluid the electrical re sistance between the electrodes is about 0.015 ohms. With the application of voltage to the electrodes, electric current flows therebetween in accordance with the resistance. As the current is increased from O to 15 amperes, the pumped head of mercury at outlet opening 52 increases from to about 35 inches of mercury with no flow. This is the maximum static head capability, and with pumped liquid flow this head is decreased by the pressure drop in the system due to such flow.

In electromagnetic pumps, the driving forth is developed by the mutually perpendicular electric and magnetic field. In a rectangular channel, the pressure is directly proportional to the magnetic field strength and the current and inversely proportionate to the height of the channel in the direction of the magnetic field. Thus, in the pres= ent pump structure, pressure is developed at reasonable electric currents by keeping the passage height at a minimum. Furthermore, this small height h of the passage provides only a small air gap in the magnetic field to thus permit an efficient, lightweight magnet design. Furthermore, the pressure is maintained because the backfiow of mercury on the face of the electrodes is minimized by keeping the magnetic air gap very small and positioning the vanes on the electrodes so that they physically impede such ba k cw.

The pump is capable of continuously providing a head upon mercury without vaporizing the mercury. This is accomplished by several means. First of all, the large area of the electrodes in contact with the mercury reduces the interface resistance between the two and thus reduces the resultant electrical heating as current flows from the electrode. This heat source into the mercury is thus min imized. Furthermore, it is important that the electrodes are made from a metal that is wetted by mercury to assure low contact resistance. Suitable contact materials are copper, platinum or molybdenum. In the case of copper and molybdenum, it is preferable that the electrodes be cleaned, such as by acid, and then the mercury poured in to displace the acid to assure complete wetting of the clean electrode surface. With this complete wetting, the contact resistance between the pumped liquid and the electrode is virtually zero.

Additionally, the electrical insulation on the poles and the pole pieces confine the current flow to passage 26 except for the small amount that might pass outside the main magnetic field by curving through the orifices 54 and 46. This eliminates electric current flow outside of the region of the high magnetic field where it would not produce a substantial pumping force. The thin electrical insulation upon the main metallic pump provided by the pole pieces does not seriously impede the thermal con ductivity which is necessary to maintain temperatures in the mercury at a reasonable level. At the illustrative operating conditions given above, the resistive heating in a normal room temperature environment is not sutficient to cause any problems with mercury vaporization.

This invention having been described as preferred embodiment, it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

What is claimed is:

1. An electromagnetic pump for the pumping of conductive fluid, said electromagnetic pump comprising first and second pole pieces and first and second electrodes, the improvement comprising:

said pole pieces being spaced apart, a magnet positioned between said pole pieces to magnetize the said pole pieces, a first pole on said first pole piece and a second pole on said second pole piece, sai-d first and second poles extending toward each other and defining a passage therebetween, electrically insulative material secured to said poles;

sai-d first and second electrodes being positioned adjacent said poles and being sealed with respect to said pole pieces to close the ends of the passage defined by said poles; and

first and second side plates secured to said poles, an

inlet opening in said first side plate and an outlet opening in said second side plate to define a liquid flow direction through said passage defined by said poles.

2. The electromagnetic pump of claim 1 wherein the direction of liquid flow defined by said openings in said side plates is substantially parallel to the passage defining faces of said poles and is substantially at right angles to the direction between said electrodes.

3. The electromagnetic pump of claim 2 wherein said poles have ends and said electrodes lie against said ends of said poles. I

4. The electromagnetic pump of claim 3 wherein fins are formed on said electrodes, said fins lying against said poles to define the ends of said passage, said fins being positioned substantially normal to the flow direction through said passage.

5. The electromagnetic pump of claim 4 wherein said insulative material on said poles extends adjacent said electrodes to electrically isolate said electrodes from said poles and said pole pieces.

6. The electromagnetic pump of claim 5 wherein at least one permanent magnet is mounted directly against both of said pole pieces to produce a magnetic field across the poles,

7. The electromagnetic pump of claim 6 wherein there are two magnets positioned between said pole pieces, both of said magnets lying against said pole pieces, both of said magnets being permanent magnets.

8. The electromagnetic pump of claim 6 wherein said poles have substantially planar faces and said side plates have substantially planar faces to define the substantially rectangular flow passage, the'flow passage having a dimension normal to said pole faces of substantially 0005",

9., The electromagnetic pump of claim 6 wherein said openings in said side plates are orifices to prevent sub stantial electric current flow away from said passage 10. The electromagnetic pump of claim 1 wherein said side plates are made of electrically insulative non-mag netic material References Cited UNITED STATES PATENTS 2,865,291 12/1958 Watt 103-l 3,026,807 3/ 1962 Hutchinson et ale 1031 ROBERT M. WALKER, Primary Examiner,

U.S. Cl X.R, 31011

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