Not all alternative energy sources on planet Earth have so far been studied and successfully applied. Nevertheless, humanity is actively developing in this direction and is finding ever new options. One of them was the production of energy from an electrolyte that is in a magnetic field.
The incorporated effect and origin of the name
The first works in this field are ascribed to Faraday, who worked in laboratory conditions as early as 1832. He investigated the so-called magnetohydrodynamic effect, or rather, he looked for electromagnetic driving force and tried to successfully apply it. The current of the Thames River was used as an energy source. Along with the effect name, the installation - magnetohydrodynamic generator - got its name.
In this MHD device, there is a direct conversion of one type of energy into another, namely mechanical into electrical energy. Features of such a process and a description of the principle of its action are generally described in detail in magnetic hydrodynamics. In honor of this discipline, the generator itself was named.
Effect action description
First of all, you should understand what happens during the operation of the device. This is the only way to realize the principle of operation of a magnetohydrodynamic generator in action. The effect is based on the appearance of an electric field and, of course, an electric current in the electrolyte. The latter is represented by various media, for example, liquid metal, plasma (gas) or water. From this we can conclude that the principle of action is based on electromagnetic induction, using a magnetic field to generate electricity.
It turns out that the conductor must intersect with the field lines of force. This, in turn, is a prerequisite for the flow of ions with charges opposite to the relatively moving particles to begin to arise inside the device. It is also important to note the behavior of the lines of force. The magnetic field constructed from them moves inside the conductor itself in the opposite direction from the one where the ion charges are.
Definition and history of the MHD generator
The installation is a device for converting thermal energy into electrical energy. It fully applies the above effect. At the same time, magnetohydrodynamic generators were once considered a rather innovative and breakthrough idea, the construction of the first samples of which occupied the minds of leading scientists of the twentieth century. Soon, funding for such projects has run its course for reasons that are not completely understood. The first experimental installations had already been erected, but their use was put an end to.
The very first designs of magnetodynamic generators were described back in 1907–910, however, they could not be created due to a number of conflicting physical and architectural features. An example is the fact that materials have not yet been created that could function normally at operating temperatures of 2500-3000 degrees Celsius in a gas environment. The Russian model was supposed to appear in a specially built MGDES in the city of Novomichurinsk, which is located in the Ryazan region in the immediate vicinity of the state district power station. The project was curtailed in the early 1990s.
How the device works
The design and principle of operation of magnetohydrodynamic generators for the most part repeat those of ordinary machine options. It is based on the effect of electromagnetic induction, which means that a current arises in the conductor. This is due to the fact that the latter crosses the lines of force of the magnetic field inside the device. However, there is one difference between machine and MHD generators. It lies in the fact that for the magnetohydrodynamic options, the working fluid itself is used directly as a conductor.
The action is also based on charged particles, which are affected by the Lorentz force. The movement of the working fluid occurs across the magnetic field. Due to this, flows of charge carriers with exactly opposite directions arise. At the formation stage, MHD generators used mainly electrically conductive liquids or electrolytes. They were the very working fluid. Modern variations have switched to plasma. The charge carrier for new machines has become positive ions and free electrons.
The design of MHD generators
The first unit of the device is called the channel through which the working fluid moves. Currently, magnetohydrodynamic generators use mostly plasma as the main medium. The next node is a system of magnets that are responsible for creating a magnetic field and electrodes to divert the energy that will be received during the working process. In this case, the sources may be different. The system can use both electromagnets and permanent magnets.
Then the gas conducts an electric current and heats up to the temperature of thermal ionization, which is approximately 10 thousand Kelvin. After this indicator must certainly be reduced. The temperature bar drops to 2.2-2.7 thousand Kelvin due to the fact that special additives with alkali metals are added to the working environment. Otherwise, the plasma is not sufficiently effective, because the magnitude of its electrical conductivity becomes much smaller than that of the same water.
Typical device cycle
Other nodes that make up the design of the magnetohydrodynamic generator are best listed along with a description of the functional processes in the sequence in which they occur.
- The combustion chamber receives the fuel loaded into it. Oxidizing agents and various additives are also added.
- Fuel begins to burn, which allows gas to form as a combustion product.
- Next, the generator nozzle is activated. Gases pass through it, after which they expand, and their speed increases to the speed of sound.
- The action reaches the camera, which passes a magnetic field through itself. On its walls are special electrodes. This is where gases come at this stage of the cycle.
- Then the working fluid deviates from its primary trajectory under the influence of charged particles. The new direction is exactly where the electrodes are.
- The final stage. An electric current is generated between the electrodes. This cycle ends.
Main classifications
There are many versions of the finished device, however, the principle of operation will be virtually the same in any of them. For example, it is possible to start a magnetohydrodynamic generator based on solid fuel such as fossil fuels. Also, alkali metal vapors and their two-phase mixtures with liquid metals are used as an energy source. According to the duration of their work, MHD generators are divided into long and short-term ones, and the latter are divided into pulse and explosive ones. Among the sources of heat are nuclear reactors, heat exchangers, and jet engines.
In addition, there is also a classification according to the type of duty cycle. Here, the division occurs into only two main types. Open-cycle generators have a working fluid mixed with additives. The combustion products go through the working chamber, where in the process they are cleaned of impurities and released into the atmosphere. In a closed cycle, the working fluid enters the heat exchanger and only after that enters the generator chamber. Next, the combustion products await the compressor, which completes the cycle. After that, the working fluid returns to the first stage in the heat exchanger.
Key Features
If the question of what the magnetohydrodynamic generator produces can be considered fully covered, then the main technical parameters of such devices should be presented. The first of these in importance is probably power. It is proportional to the conductivity of the working fluid, as well as the squares of the magnetic field strength and its speed. If the working fluid is a plasma with a temperature of about 2-3 thousand Kelvin, then the conductivity is proportional to it by 11-13 degrees and inversely proportional to the square root of pressure.
Data on the flow velocity and magnetic field induction should also be provided. The first of these characteristics varies quite widely, ranging from subsonic speeds to hypersonic speeds up to 1900 meters per second. As for the induction of the magnetic field, it depends on the design of the magnets. If they are made of steel, then the upper bar will be set at around 2 T. For a system that consists of superconducting magnets, this value grows to 6-8 T.
The use of MHD generators
The widespread use of such devices today is not necessary to observe. Nevertheless, theoretically, it is possible to build power plants with magnetohydrodynamic generators. There are three valid variations in total:
- Thermonuclear power plants. They use a neutron-free cycle with an MHD generator. It is customary to use plasma at high temperatures as fuel.
- Thermal power plants. An open type of cycle is used, and the installations themselves by their design features are quite simple. It is this option that still has prospects for development.
- Nuclear power plants. The working fluid in this case is an inert gas. It is heated in a nuclear reactor in a closed cycle. Also has prospects for development. However, the possibility of application depends on the appearance of nuclear reactors with a working fluid temperature above 2 thousand Kelvin.
Device perspective
The relevance of magnetohydrodynamic generators depends on a number of factors and still unsolved problems. As an example, we can cite the ability of such devices to generate only direct current, which means that for their maintenance it is necessary to design sufficiently powerful and, moreover, economical inverters.
Another visible problem is the lack of the necessary materials that could work out for a sufficiently long time under conditions of heating the fuel to extreme temperatures. The same applies to the electrodes used in such generators.
Other applications
In addition to functioning at the base of power plants, these devices are able to work in special power plants, which would be very useful for nuclear power. The use of a magnetohydrodynamic generator is also allowed in hypersonic aircraft systems, but so far no progress has been made in this area.