US2397785A - Electromagnetic pump - Google Patents

Description

DiUll Agn-il 2, 1946. E. FRIEDLANDER ELECTROKAGNETIC PUK? Filed nay 27, 1943 FIG. l.

INVENTOR QTTOR NEY EICH FRIEDLANQER Hlllll Patented Apr. 2, 1946 ELECTROMAGNETIC PUMP Erich Friedlander, North Wembley, England, ossignor to The General Electric Company Limlted, London, England Application May 27, 1943, Serial No. 488,701 In Great Britain June 10, 1942 (Cl. 10S- 1) 4Claims.

This invention relates to electromagnetic pumps for conducting liquids (for example mer ciu'y) of the type wherein the liquid is caused to tlow along a duct by passing through it an electric current having a component perpendicular to the direction of ilow and exposing it at the same time to a magnetic eld having a component perpendicular both to the current and to the Said direction.

Hitherto in such pumps the current has been usually direct and the magnetic eld constant. It has been realised that alternating current might be used if the magnetic eld were also alternating and the phases of current and eld were suitably related. The use of A. C. would have the advantage that it is easy to generate the large currents at low voltage which are required for the most efficient working oi the pump; but if single-phase A. C. is used, there is the disadvantage for many purposes that the pressure applid to the liquid is intermittent and the ow consequently pulsating; moreover the optimum phase-relation between held and current Icannot be obtained Without much waste of power or expensive phase-shifting devices.

An object of this invention is to provide a method and means for overcoming this objection.

This invention depends on the realisation that objection can be overcome by using 3phase (or more generally n-phase) current and subjecting the liquid successively and similarly to all nphases: then, at least if the phase relations of current and eld necessary for efficient working are fullled, the resultant of the varying pressures due to the individual phases is a constant pressure.

In carrying this invention into practice, therefore, in an electromagnetic pump of the type specified the said conducting liquid flows along a channel successively past at least three places at each of which it passes between a pair of electrodes adapted to cause current to pass through the liquid transversely to the direction of ow and between pole pieces of an electromagnet adaptevzl to produce lines of magnetic intensity transverse to both the said current and the said direction, and means are provided for supplying each pair of electrodes similarly with currents respectively from different phases of an n-phase supply and the exciting coils of the electromagnets similarly with currents vrespectively from different phases of the said supply. Although different phases must feed the electrodes and the electrcmagnet at dierent places it is not necessary, though it will often be convenient, that the wenn# electrodes and the electromagnet at the same place are fed by the same phase. Again the possibility is not excluded that each phase supplies the electrodes or the electromagnet at m places, so long as m is the same for each phase, m being greater than 1, so that there are in all nm said places.

Maximum efliciency is attained when at each place the current and the magnetic field attain their maxima simultaneously. This result can usually be achieved with suillcient accuracy by feeding the exciting coil of each electromagnet from the supply and deriving the current for the electrodes at the same place from a secondary winding of a few turns wound on the core of that electromagnet. It can then usually be arranged, by means of star and/or delta. connections or their known equivalents, that the phase diiference between the electrode current and the field in the associated electromagnet is not more than 15. But, if desirable, the phase dinerence may be reduced to zero by the use of asymmetric zg zag windings or any of the other known devices.

One embodiment of the invention will now be described by way of example with reference to the accompanying diagrammatic drawing, where- 1n:

Figure l shows the general arrangement in section.

Figure 2 is a section on the line 2--2 in Figure 1, showing the way in which the electrodes are introduced into the duct and,

Figure 3 shows the electrical connections.

I is an E-shaped magnetic core. 2, 3, 4 are exciting coils wound on the three limbs of the core; for the purpose of the invention the three limbs are to be regarded as three electromagnets at di'erent places along the duct. 5, 6, l are secondary windings, each of three turns, also wound on the limbs. 8 is a tube forming the duct through which the mercury flows; it lies in gaps between the ends of the limbs of the E and a common opposing pole piece 9. The tube 8 is flattened, the longer dimension of its cross section (shown in Figure 2) being, say, 5 mm. and the shorter (shown in Figure 1) say, 1 mm. The wall is made of a nickel-chromium alloy, having about the same electrical resistivity as mercury. The electrodes l0, l0', ll, ll', l2, l2' are strips of nickel brazed into slots cut in the wall, these slots lying in a plane perpendicular to that of Figure 1. One set of electrodes IB', Il', l2' is in terconnected by a star-point conductor I3; the other set l0, ll, I2 is connected to the windings 5, 6, 1 which are in delta-connection; the primary windings 2, 3, 4 are in star-connection. In alternative embodiments both sets of windings may have to be connected in star or delta according to the phase shift required; the optimum phase shift depends on resistance and stray reactances in the secondary circuit.

In the operation of the pump, alternating current is introduced to each of the three windings 5, 6, 1 in such phase relationship that peak magnetic flux is attained successively in one after the other of the limbs of the E-shaped magnetic core I. At the end of each of these limbs, the induced magnetic field will flow through the mercury in the conduit 8 in a direction at right angles to that at which the mercury passes. At the same time, current is induced in the coils 5, 6, 1 and is fed to the electrodes I0, Il, I2 and I0', Il and I2'. The current and magnetic field attain their maxima substantially simultaneously. It will be noticed that the electrodes are so placed that the current flowing therebetween also ows through the mercury at right angles to the direction in which the mercury passes through the conduit 8. However, the electrodes are arranged to pass the current at right angles to the lines of magnetic intensity. As noted above, first the current and magnetic leld reach their maxima in the limb associated with the coil then the current and magnetic eld reach their maxima in the limb rassociated with coil 6. Next, the current and magnetic iield reach their maxima in the limb associated with the coil 1. Now the cycle repeats. As the current and magnetic intensity reach their maxima at any one of the points in the conduit above one of the limbs of the core,

the current and eld being at right angles to each other and the conduit, a unidirectional force is exerted upon the liquid in the conduit, causing it to move in the desired direction. Thus, a series of pulsating pressures is engendered within the conduit at the several points thereof adjacent the ends of the limbs of the core. These pressures are all out of phase, but their total eiect is to provide a substantially constant pressure.

I claim:

1. An electromagnetic pump of the type specined for applying a substantially constant impelling pressure to a liquid, said pump including a duct for conveying the liquid to be pumped successively past at least three places at each of which it flows both between a different pair of electrodes capable of passing current through the liquid in a direction transverse to the direction of liquid now, and at each of which places the liquid also ows between a different pair of pole pieces of an electromagnet capable of producing lines of magnetic intensity in a direction transverse to both said current direction and said direction of liquid flow, and means for supplying said pairs of electrodes similarly with alternating currents respectively from diierent phases of a polyphase supply and for supplying the exciting coils of said electromagnets similarly ,with alternating currents respectively from different phases of said supply so that out-of-phase intermittent impelling pressures are applied tothe liquid at each of the three places which merge to provide a resultant substantially constant impelling pressure.

2. An electromagnetic pump of the type specined for applying a substantially constant impelling pressure to a liquid, said pump including a. duct for conveying the liquid to be pumped successively past at least three places at each of which lt flows both between a dilerent pair of electrodes capable of passing current through the liquid in a direction transverse to the direction of liquid flow, and at each of which places the liquid also ows between a different pair of pole pieces of an electromagnet capable of producing lines of magnetic intensity in a direction transverse to both said current direction and said direction of liquid now, means for supplying the exciting coils of said electromagnets similarly with alternating currents respectively from different phases of a polyphase supply, and secondary windings on said electromagnets serving to supply said pairs of electrodes respectively with alternating currents so that out-of-phase intermittent impelling pressures are applied to the liquid at each of the three places which merge to provide a. resultant substantially constant impelling pressure.

3. An electromagnetic pump of the type specified for applying a substantially constant impelling pressure to a liquid, said pump including a duct for conveying the liquid to be pumped successively past three places at each of which it flows both between a diierent pair of electrodes capable of passing current through the liquid in a direction transverse to the direction of liquid flow, and at each of which places the liquid also iiows between a different pair of pole pieces of an electromagnet capable of producing lines of magnetic intensity in a direction transverse to both said current direction and said direction of liquid ow, means for supplying the exciting coils of said electromagnets similarly with alternating currents respectively from different phases of a three-phase supply, secondary windings on said electromagnets in delta-connection, and a starpoint conductor connecting together three of said electrodes selected one from each pair, and said secondary windingsfbeing so connected to the remainder of said electrodes that, in operation, at each of said places the electrode current and the eld in the associated electromagnet are at least approximately in phase so that out-of-phase intermittent impelling pressures are applied to the liquid at each of the three places which merge to provide a resultant substantially constant impelling pressure.

4. An electromagnetic pump of the type specied for applying a substantially constant impelling pressure to a liquid, said pump including an electromagnetic core having three limbs disposed in parallel between a pair of common yokes, each of said limbs having a gap, a duct for conveying the liquid to be pumped through each of said gaps in succession transversely to the directions of the magnetic fields therein a pair of electrodes associated with said duct at each of said gaps for passing current through the liquid transversely to the directions of both the magnetic eld and the liquid ow in the gap, exciting windings on said limbs, means for supplying from a three-phase source alternating currents to' the windings on said three limbs respectively from dierent phases, and secondary windings on said limbs connected for supplying to said pairs of electrodes alternating currents at least approximately in phase with the magnetic fields in the respective gaps so that out-of-phase intermittent impelling pressures are applied to the liquid in the duct at each of said gaps which merge to provide a resultant substantially constant impelling pressure.

ERICH FRIEDLANDER.

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