What Is a Magnetic Fluid?

Also known as magnetic liquid, ferrofluid or magnetic fluid, it is a new type of functional material that has both the fluidity of liquids and the magnetic properties of solid magnetic materials. It is a stable colloidal liquid made of magnetic solid particles with a nanometer diameter (less than 10 nanometers), a base carrier liquid (also called a medium), and a surfactant. The fluid has no magnetic attraction when it is static, and it exhibits magnetism when an external magnetic field is applied. Because of this, it has a wide range of applications in practice and has a high academic value in theory. The magnetic fluid produced by nano metal and alloy powder has excellent performance and can be widely used in various fields of magnetic fluid sealing, shock absorption, medical equipment, sound adjustment, light display, magnetic fluid beneficiation and other fields.

Magnetic fluid

Also known as

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The preparation methods of magnetic fluid mainly include grinding method, degumming method, thermal decomposition method, and discharge method.

(1) Milling method. That is, the magnetic material is milled together with the active agent and the carrier liquid into extremely fine particles, and then the large particles are separated by centrifugation or magnetic separation to obtain the required magnetic fluid. This method is the most direct method, but it is difficult to obtain magnetic fluid particles with a diameter below 300 nm.

(2) Degumming method. It is the iron salt or ferrous salt that produces Fe3O4 or -Fe2O3 under the chemical action, then adds a dispersant and a carrier, and stirs it to make its magnetic particles adsorb. After heating, the colloid and solution are separated to obtain a magnetic fluid. This method can obtain small particles of magnetic fluid, and the cost is not high, but it is only used for the production of magnetic fluid of non-aqueous carrier.

(3) Thermal decomposition method. The magnetic material is dissolved in an organic solvent, and then the free metal is decomposed by heating, and then a dispersant is added to the solution to separate it, and the magnetic fluid is obtained by dissolving it in the carrier.

(4) Steaming method. It is a kind of high-purity magnetic material that is heated and evaporated under vacuum. The evaporated particles meet the underground liquid film composed of dispersant and carrier and then solidify. The current liquid film and magnetic particles move into the lower liquid, and they are mixed evenly. Magnetic fluid. The magnetic fluid particles obtained by this method are very fine, and most of the particles are generally 2-10nm.

(5) Discharge method. Its principle is similar to that of EDM. It is to place coarse particles of magnetic material between two electrodes in a container filled with working fluid (often the same as the carrier), and then add pulse voltage to perform EDM corrosion. The medium solidifies into fine particles, and the large particles are filtered off and then a dispersant is added to obtain a magnetic fluid. ^[1]

The range of plasma density is wide. For extremely thin plasmas, collisions between particles and

The theory of magnetohydrodynamics is difficult to be fully verified like the general theory of fluid mechanics. As in

Magnetohydrodynamics is mainly used in three areas: astrophysics, controlled thermonuclear reactions, and industry.

Stars and interstellar gases in the universe are both plasma and have magnetic fields. Therefore, magnetohydrodynamics was first developed and applied in astrophysics, solar physics, and geophysics. At present, research topics on the sun include: the nature and origin of the solar magnetic field, and the influence of the magnetic field on the corona, sunspots, and flares. In addition, there is the possibility that no force field exists in interstellar space, bow shocks generated by the interaction of the solar wind and the Earth's magnetic field, the eruption of nova and supernova, the origin of the Earth's magnetic field, and so on.

The application of magnetohydrodynamics in controlled nuclear reactions is likely to enable humans to obtain huge energy from deuterium in seawater. For deuterium and tritium mixtures, the temperature is required to reach 50 million to 100 million degrees, and there are higher requirements for particle density and confinement time. The use of a toroidal magnetic restraint device has shown good applicability and superiority in the study of controlled thermonuclear reactions.

In addition to being related to the development and utilization of nuclear fusion energy, magnetohydrodynamics is also closely related to the generation of magnetic fluids. The principle of magnetic fluid power generation is to replace the generator rotor with plasma, eliminating the need for rotating components. This can increase the efficiency of ordinary thermal power stations or nuclear power plants by 15-20%, or even higher, which can save energy and reduce pollution.

When the aircraft reenters the atmosphere, the shock waves and air friction on the aircraft cause the surface air of the aircraft to be heated and ionize into plasma. Therefore, the magnetic field can be used to control the heat transfer and resistance to the aircraft. But because the magnetic field device is too heavy, this kind of assumption has not been realized.

In addition, electromagnetic flowmeters, electromagnetic brakes, electromagnetic bearing theory, electromagnetic shock tubes, etc. are also achievements made by magnetic fluid mechanics in industrial applications.

Magnetic fluid

Magnetic fluid power generation is a new type of high-efficiency power generation method. It is defined as when a plasma with a magnetic fluid crosses a magnetic field, according to the law of electromagnetic induction, electricity is cut by magnetic lines of force; it is installed on the channel through which the magnetic fluid flows. When the electrode is connected to an external load, it can generate electricity.

In order to make the magnetic fluid have sufficient conductivity, it is necessary to add alkali metals such as potassium, cesium and inert gases (such as helium, argon, etc.) as working medium at high temperature and speed to use the principle of non-equilibrium ionization. To increase the degree of ionization. The former uses open-loop magnetic fluid power generation by directly passing the combustion gas through the magnetic field, and the latter uses closed-loop magnetic fluid power generation after heating the working fluid through a heat exchanger.

The efficiency of magnetic fluid power generation is only about 20%, but due to its high smoke exhaust temperature, the gas discharged from the magnetic fluid can be sent to a general boiler to continue burning into steam, driving the steam turbine to generate electricity, forming an efficient combined cycle power generation, and the overall thermal efficiency. It can reach 50% to 60%, which is the highest among the high-efficiency power generation technologies currently under development. Similarly, it can effectively desulfurize and effectively control the production of NOx. It is also a low-pollution coal gasification combined cycle power generation technology.

Magnetic fluid magnetic fluid seal

The magnetic fluid sealing device is composed of a non-magnetically permeable seat, a bearing, a magnetic pole, a permanent magnet, a magnetically permeable shaft, and a magnetic fluid. Under the action of a magnetic field, the magnetic fluid fills the annular space and establishes a series of "O-rings" So as to achieve the effect of sealing.