How Do MHD Generators Work?
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What an MHD Generator Is
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MHD stands for magnetohydrodynamic, so an MHD generator is a magnetohydrodynamic generator. In simple terms, this means this type of generator creates electrical power by using an electrically conducting fluid with a magnetic field. In effect, it changes thermal or kinetic energy into electricity.
How Electrical Conductivity Is Achieved
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While there are several ways to achieve electrical conductivity with an MHD generator, three will be discussed here. The conducting fluids that are usually considered are all gases that are made from alkali metal vapors, noble gases and combustion. When combustion gases are chosen as the conducting fluid, then potassium carbonate is added to the flow in tiny amounts. It is thermally ionized and makes up the electron density necessary for conductivity. Cesium is used in the case of monatomic gases, and the electron temperature is raised above the gas, which makes electrical conductivity possible at a lower temperature than would be the case with thermal ionization. Finally, in the case of liquid metal, electrical conductivity happens when the liquid metal is injected directly into the vapor or gas stream. This makes a continuous liquid phase possible.
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The First MHD Generators and How They Worked
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Michael Faraday created the first MHD generator in 1831. It was a homopolar generator that used a copper disk that rotated between the two poles of a horseshoe magnet. It created a lot of current, but only a tiny amount of DC voltage.
The first MHD generator to actually be used industrially was the Dynamo. This type of MHD generator is a little different from the one created by Michael Faraday. In this case, the generator is made up of a stationary structure that has a magnetic field that is constant, and which contains rotating wingdings that turn inside the magnetic field. On a large dynamo such as would be used in industry, the constant magnetic field is created by electromagnets called field coils.
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