16-11-2012, 02:12 PM
Magnetohydrodynamics
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MAGNETOHYDRODYNAMIC (MUD) POWER
GENERATION
When an electrical conductor is moved so as to cut lines of magnetic
induction, the charged particles in the conductor experience a force in a
direction mutually perpendicular to the B field and to the velocity of the
conductor. The negative charges tend to move in one direction, and the
positive charges in the opposite direction. This induced electric field, or
motional emf, provides the basis for converting mechanical energy into
electrical energy. At the present time nearly all electrical power generators
~tilize a solid conductor which is caused to rotate between the poles of a
magnet. In the case of hydroelectric generators, the energy required to
maintain the rotation is supplied by the gravitational motion of river water.
Turbogenerators, on the other hand, generally operate using a high-speed
flow of steam or other gas. The heat source required to produce the.
high-speed gas flow may be supplied by the combustion of a fossil fuel or by
a nuclear reactor (either fission or possibly fusion).
It was recognized by Faraday as early as 1831 that one could employ a
fluid conductor as the working substance in a power generator. To test this
concept Faraday immersed electrodes into the Thames river at either end of
the Waterloo Bridge in London and connected the electrodes at mid span on
the bridge through a galvanometer. Faraday reasoned that the electrically
conducting river water moving through the earth's magnetic field should
produce a transverse emf. Small irregular deflections of the galvanometer
were in fact observed. The production of electrical power through the use of a
conducting fluid moving through a magnetic field is referred to as magnetohydrodynamic,
or MHO, power generation. One of the earliest serious
attempts to construct an experimental MHO generator was undertaken at the
Westinghouse laboratories in the .period 1938-1944, under the guidance of
Karlovitz (see Karlovitz and Halasz, 1964). This generator (which was of the
annular Hall type-see Fig. 20) utilized the products of combustion of
natural gas, as a working fluid, and electron beam ionization. The experiments
did not produce the expected power levels because of the low
electrical conductivity of the -gas and the lack of existing knowledge of
plasma properties at that time.