Magnetohydrodynamics: The physics of the motion of electrically conducting fl uids in the presence of magnetic or electric fi elds.
Magnetohydrodynamics (MHD) offers the potential of substantially increasing the effi ciency of fossil fuels for producing electricity, thereby reducing carbon dioxide emission.
The interaction between moving, electrically conducting fl uids and magnetic or electric fi elds can be complicated. For example, MHD forces operate in the molten interior of the Earth and generate the magnetic fi eld surrounding our planet. MHD is also involved in the cauldron of the sun and in the magnetic confi nement of plasma used to produce nuclear fusion as well as in auroras and solar fl ares.
MHD power plants can be more effi cient than normal plants because they use higher temperatures for power production. In MHD power generation, the fuel is burned, usually using preheated air for combustion, and the resulting high combustion temperatures produce a plasma exhaust that is sent through a magnetic fi eld. In physics, a plasma is an ionized gas that contains a mixture of free electrons and charged ions. In normal power plants, steam turbines spin copper coils in a magnetic fi eld to generate electric current. In MHD power plants, it is a hightemperature, electrically conducting plasma that acts as a conductor moving through a magnetic fi eld, not copper coils. One major diffi culty in making MHD power plants practical arises from the need to extract the electric current that the magnetic fi eld induces in the plasma.
Typical power plants operate normally with steam temperatures less than 1000 ยฐ F (538 ยฐ C) and have effi ciencies usually less than 40%. MHD power plants operate at temperatures much higher than this, and could reach effi ciencies of 60% or more. Getting the electric power from the plasma into normal wire electrical conductors is one major problem confronting MHD power plant designs. Another is their need for very strong magnetic fi elds that extend through a large volume. Let ' s follow the path from fuel to power in an MHD system and see how all this works.
The fuel for MHD power plants can be any combustible material. This fuel is burned in a combustion chamber, where preheated air is used to increase the