What Is an Electromagnetic Pump?

An electromagnetic pump is a pump in which an energized fluid in a magnetic field flows in a certain direction under the action of electromagnetic force. A device that utilizes the interaction of a magnetic field and a current in a conductive fluid to cause a fluid to undergo a pressure gradient due to electromagnetic forces, thereby promoting fluid movement. In practice, it is mostly used for pumping liquid metal, so it is also called liquid metal electromagnetic pump.

Chinese name: Electromagnetic pump
Also known as: Liquid metal electromagnetic pump

Features: Simple structure, good sealing and reliable operation
flow: 13000m3 / hour

Introduction of electromagnetic pump

The electromagnetic pump has no mechanical moving parts, has a simple structure, good sealing performance, reliable operation, and does not require a shaft seal. Therefore, it is used to transport some toxic heavy metals such as mercury and lead in the chemical and printing industries, and is used in nuclear power plants Liquid metals (sodium or potassium, sodium-potassium alloys) as heat transfer media are also used to transport molten non-ferrous metals in foundry production. The flow rate can reach 13,000 meters per hour, the pressure can reach 1.7 MPa, and the temperature can reach 1200 ° C.

The electromagnetic pump can be divided into AC pump and DC pump according to the power source form.

According to the current feeding method in liquid metal, it can be divided into conductive (conductive) electromagnetic pumps and inductive electromagnetic pumps. Conductive electromagnetic pumps use either direct current (Figure 1) or alternating current (Figure 2). It has a tube made of non-magnetic refractory metal (see picture). The tube is surrounded by magnets, and the magnetic lines of force are perpendicular to the tube. When a current perpendicular to the tube and the magnetic field lines is passed, according to the left-hand rule, a mechanical force is generated to send the conductive fluid out of the tube. The conductivity type is generally a small pump for low pressure and small flow. In a conductive electromagnetic pump, current is directly transmitted to the liquid metal from an external power source through electrodes on both sides of the pump trench. In induction pumps, multiphase AC power is used inductively. The current is induced by an alternating magnetic field. The latest inductive electromagnetic pump is a linear induction pump, which is equipped with a flat, linear stator winding. The induction force is axial, and the size is large. High-flow pumps are of this type.

Figure 1 Schematic diagram of DC pump

Figure 2 Schematic diagram of single-phase AC pump

Figure 3 Schematic diagram of inductive surface pump

Figure 4 Schematic diagram of induction screw pump

Figure 5 Schematic diagram of induction cylindrical pump

According to different structures, it can be divided into plane, screw pump and cylindrical pump. In induction pumps, the current of liquid metal is induced by an alternating magnetic field (single-phase or three-phase). FIG. 3 is a schematic diagram of an inductive planar pump, and FIG. 6 is a schematic diagram thereof. The working principle of the three-phase induction electromagnetic pump is similar to that of ordinary induction motors. The three-phase windings (where the current is shown in Figure 6 curve 1) in a flat or cylindrical iron core generate a traveling wave magnetic field (Figure 6 curve 2 is the magnetic induction intensity curve of the traveling wave magnetic field) or a rotating magnetic field. This magnetic field induces a current in the liquid metal (Figure 3 curve 3). The induced current interacts with the magnetic field to generate a magnetic field force, which creates a pressure difference at the inlet and outlet of the pump that moves the liquid metal. For a DC electromagnetic pump, the above pressure difference p can be written as:

Where is the conductivity of the liquid metal being conveyed; Q is the volume flow rate: a is the half height of the channel; b is the half width of the channel; L is the effective length of the channel; B is the magnetic induction strength. For inductive electromagnetic pumps, the pressure difference can be written as:

Where B _m is the magnitude of the magnetic induction intensity; v _a is the velocity of the traveling wave magnetic field; v _a = 2tf , t is the pole pole pitch, f is the power frequency; u is the velocity; S = is called slip.

The above formula for differential pressure is derived from the simplest model. If the effects of other practical factors are taken into account (usually making the differential pressure smaller), a corresponding correction factor must be introduced. These practical factors are mainly the armature reaction of the DC pump (the uneven distribution of the synthetic magnetic field caused by the magnetic field induced by the current flowing through the liquid metal), the current diffusion (the uneven distribution of the current caused by the current shunting on both sides of the magnetic field), the magnetic pole Air gap magnetic leakage at the edges, etc .; for induction pumps, it is mainly the lateral end effect (caused by the partial or full formation of the electric current induced in the liquid metal in a channel of limited width) and the longitudinal end effect (caused by the finite length of the iron core) Caused by an open magnetic circuit) and so on.

A device that utilizes the interaction of a magnetic field and a current in a conductive fluid to cause a fluid to undergo a pressure gradient due to electromagnetic forces, thereby promoting fluid movement. In practice, it is mostly used for pumping liquid metal, so it is also called liquid metal electromagnetic pump. Electromagnetic pumps can be divided into AC pumps and DC pumps according to the form of power supply; they can be divided into conductive electromagnetic pumps and inductive electromagnetic pumps according to the current feeding method in liquid metal; according to different structures, they can be divided into planar pumps and cylindrical pumps. In a conductive pump, the current is directly transmitted to the liquid metal by an external power source through the electrodes on both sides of the pump trench; in an induction pump, the current is induced by an alternating magnetic field. The electromagnetic pump has no rotating parts, simple structure, good sealing and reliable operation. Therefore, it is used to transport some toxic heavy metals such as mercury and lead in the chemical industry and printing industry; it is used to transport particularly active chemical properties in the atomic power industry. Metals, such as sodium, potassium, sodium-potassium alloys; can be used as a quantitative pump for active metals such as aluminum and magnesium in foundry companies, but now it is mainly used by large enterprises such as military industries. The disadvantage of electromagnetic pump is its low efficiency.

The disadvantage of electromagnetic pump is its low efficiency, which has not been widely used in the smelting and foundry industries.

The electromagnetic pump is similar to the ordinary solenoid valve. It uses alternating current as the working power. The current forms an alternating fixed magnetic field through the electromagnetic windings. It interacts with the movable pump body to drive the pump body to vibrate and promote the output of liquid.

The principle of electromagnetic pump

Principle of electromagnetic pump conductive electromagnetic pump

The principle of a conductive electromagnetic pump is: When a conductor in a magnetic field passes an electric current, the conductor will be subject to the thrust of the magnetic field. The three directions are perpendicular to each other, and the magnitude of the thrust is F = I × B × L.

The conductive electromagnetic pump does not have any rotating parts, which solves the problem of mechanical pump wear and forms a maintenance-free welding machine. However, during the process of conducting current to the liquid metal by the high-current electrode in contact with the liquid metal, due to the adhesion and shielding of the oxide slag on the electrode, the wave crests were unstable, and even the fluctuations were large. Almost 50 units have been deactivated.

Induction electromagnetic pump principle

It adopts the principle of using a single-phase C-type open electromagnet, which generates a phase difference between the inner and outer ring magnetic fields due to the magnetic path difference between the inner and outer rings, and then forms a forward magnetic field component, that is, a forward magnetic field component that points from a leading phase to a lagging phase. The liquid metal solder in the component of the advancing magnetic field cuts the magnetic lines of force, so it receives a forward induction force to achieve the purpose of pumping the liquid metal solder.

Because the phase difference is generated using the magnetic path difference to form the advancing magnetic field component, its advancing magnetic field component is very limited. Most of it is a pulsating magnetic field that does not produce advancing thrust. It is necessary to produce a wide wave peak (300mm 400mm peak width) and Extremely high peaks (40mm height) are very difficult.

Principle of electromagnetic pump three-phase asynchronous induction pump

This is another patented technology obtained by the wave soldering machine in China, which not only solves the problem of wave instability caused by the slag shielding of the conductive current electrode of the conductive electromagnetic pump of the conductive electromagnetic pump, without any rotating parts and current. The converter is maintenance-free, wear-free, and highly efficient, and can obtain high and powerful wave peaks and wide wave peaks.

The principle of the three-phase asynchronous induction electric pump is to use three-phase power sources with a phase difference of 120 ° from each other. They are distributed in space to form their respective magnetic fields. The combined magnetic field is a cutting magnetic field in a forward magnetic field, which induces a current and forms a forward electromagnetic force.

Working principle of three-phase induction electromagnetic pump

The working principle of the three-phase induction electromagnetic pump is similar to that of an asynchronous motor, and the structure mainly includes a stator core and a winding. After the winding is energized, a traveling wave magnetic field is generated to interact with the liquid metal in the pump groove to generate an induced current. The liquid metal in the pump groove becomes a current-carrying conductor. It interacts with the traveling wave magnetic field to generate electromagnetic force to drive the directional flow of the metal solution.

Advantages and disadvantages of electromagnetic pump

Because the phase difference inherent in the three-phase power source is directly used, the pulsating magnetic field component of the synthetic magnetic field is basically a synthetic magnetic field that generates a forward force, which is exactly the same as the electromagnetic gun principle, so it has high efficiency, which can reach more than 70%. In addition to all the advantages of inductive electromagnetic pumps, the wave soldering machine composed of phase asynchronous induction pumps, such as superposition of acoustic perturbation vibration waves, enhances welding ability and hole climbing ability, without any rotating parts, no wear, no maintenance, The structure is simple, etc. It also has powerful peak heights, which can obtain ultra-high peaks of 40mm and wide peaks of 300-400mm width. ^[1]

Use of electromagnetic pump

The electromagnetic pump has no rotating parts, has a compact structure, reliable operation, and good sealing performance. It is especially suitable for transporting some toxic heavy metals (such as mercury and lead) and chemically active metals (such as potassium, sodium, potassium-sodium alloy, etc.). Electromagnetic pumps are used in some nuclear power reactors, especially fast neutron reactors. In some chemical plants, electromagnetic pumps are used to transport mercury, which is conducive to safe production. In the smelting and foundry industry, the use of electromagnetic pumps and electromagnetic flow tanks can improve product quality, but due to low efficiency, applications are not widespread. In a fusion reactor, a large-flow electromagnetic pump under the action of a strong magnetic field is required.

Small flow electromagnetic pumps make a big difference. With the progress of research on controlled thermonuclear reactions, corresponding research work on electromagnetic pumps is also needed.

Bibliography of electromagnetic pump

Qiu Jin, Yan Luguang Translation: (Liquid Metal Electromagnetic Pump), Science Press, Beijing, 1964;

"Liquid Metal Electromagnetic Pump", edited by the electromagnetic pump group of the Institute of Mechanics, Chinese Academy of Sciences and Shanghai Institute of Electrical Appliances, Science Press, Beijing, 1979.