ELECTROMAGNETIC PUMP:

Electromagnetic pump operates on the principle that a force is exerted on a current-carryingconductor in a magnetic field. The high electrical conductivity of the liquid metals pumped(liquid metals are used as the heat-transfer media in some nuclear reactors andmagnetohydrodynamic systems) allows a pumping force to be developed within the metals whenthey are confined in a duct or channel and subjected to a magnetic field and to an electric current.These pumps are designed principally for use in liquid-metal-cooled reactor plants where liquidlithium, sodium, potassium, or sodium-potassium alloys are pumped. Other metallic andnonmetallic liquids of sufficiently high electrical conductivity, such as mercury or moltenaluminum, lead, and bismuth, may also be pumped in nonnuclear applications. The absence ofmoving parts within the pumped liquid eliminates the need for seals and bearings that are foundin conventional mechanical pumps, thus minimizing leaks, maintenance, and repairs, andimproving reliability. In liquid-metal-cooled nuclear reactor plants, electromagnetic pumps witha capacity of up to several thousand gallons per minute have operated without maintenance fordecades.

CLASSIFICATION OF ELECTROMAGNETIC PUMP:

The major classifications of electromagnetic pumps, either conduction or induction, is basedon the method employed to cause the electric current to flow in the pumped liquid.

1) Conduction Typea. Direct-current conduction pump.b. Alternating-current conduction pump.

2) Induction Typea. Linear induction pump.b. Helical induction pump.

Topic: Electromagnetic Pump

Stator Punching

ThermalInsulation

Fluid (LiquidMetal) Duct

(1) Conduction-type electromagnetic pump: In conduction pump, current is directlyconducted into the fluid through electrodes that are normally attached to the outer wall of the ductcontaining the liquid metal. There are two basic variants of this pump- Direct Current (DC) andAlternating Current (AC)

(a) Direct-current conduction pumps: In this simplest form of electromagnetic pump theliquid-containing pump duct has two heavy electrodes to provide a path for direct current to beconducted at a right angle to the direction of pumping force in the duct. A magnetic fieldgenerated by either a permanent magnet or electromagnet is impressed across the duct at thelocation of the electrodes in a direction at right angles to both the current flow and the pumpingdirection. This orthogonal arrangement of current, magnetic field, and pump duct produces aforce in the liquid which is dependent on the magnitude of the current, magnetic field, and thelength of the current path in the liquid. It is also possible to arrange the duct so that the currentflowing in the liquid also produces the required magnetic field (that is, the self-induced pump).The physical arrangement of the conduction pump allows only a single passage of currentbetween electrodes, resulting in a relatively short length of current path in the liquid. Tocompensate, the current must be very high (thousands of amperes), thus requiring special dcpower supplies such as homopolar generators. However, the very low voltage allows specialelectrical insulation to be used, which is suitable for high-temperature (1500°F or 800°C)operation.

(b) Alternating-current conduction pump: This pump uses a pump duct, magnetic field,and electrode arrangement similar to the dc conduction pump, except that the magnetic field isproduced by an ac (single-phase) electromagnet and the current is produced by the transformeraction of the same or separate single-phase electromagnet with a secondary (step-down)winding of usually one turn. The heavy secondary winding connects to the electrodes. With thesinusoidal magnetic field and duct current in phase with each other, a pumping force will bedeveloped. This design can be operated directly from normal single-phase ac power equipmentsince it has an integral transformer to develop the necessary high current. It too can have ahigh-temperature application.

(2) Induction Pump: Induction pumps differ from conduction pumps in that the current inthe conducting fluid is induced by a traveling magnetic field. These pumps use a stationarypolyphase ac winding to produce a traveling magnetic field that induces a current in the liquid.The reaction between the induced current and the traveling magnetic field causes the liquid tofollow the traveling magnetic field. The force generated in the liquid is confined in the duct,producing linear flow.