MAGNETOHYDRODYNAMIC POWER GENERATOR

(MHD) any of a class of devices that generate electric current by means of the interaction of an electrically conducting fluid and a magnetic field. Various countriesincluding Japan, China, Poland, Russia, and the United Stateshave undertaken active developmental programs in magnetohydrodynamic technology, since MHD power plants offer the potential for large-scale electrical power generation at reasonable cost with comparatively little detrimental impact on the environment. Generators of the MHD type are also attractive for the production of large electrical power pulses, and their first practical application has been for this kind of service (see below). any of a class of devices that generate electric current by means of the interaction of an electrically conducting fluid and a magnetic field. Unlike conventional electric generators, MHD devices are able to achieve direct energy conversion. In a regular power plant the energy stored in a fossil fuel yields heat with which to produce steam. The steam in turn actuates a turbine to drive an electric power generator. MHD devices, in contrast, change the thermal and kinetic energy of the conducting fluid, which generally consists of ionized combustion gases from fossil fuels (chiefly coal), directly into electricity. Such an ionized gas, or plasma, passes through a duct with two opposite conducting walls (electrodes) and two opposite insulating walls. A powerful magnetic field is created at right angles to the duct. As the plasma flows through the duct and the magnetic field at a given speed, it produces an electrical voltage across the electrodes. Although the basic principles of magnetohydrodynamics were established during the 19th century, the first significant experimental MHD generator was not constructed in the United States until 1938. The device, moreover, failed to operate properly owing largely to an inadequate understanding of the factors involved. By the late 1950s advances in both knowledge and technology made it possible to produce 10 kilowatts of electric power with an MHD generator. In 1973 U.S. and Soviet researchers undertook a joint project to develop a high-magnetic-field MHD generator at a test facility near Moscow. This device, equipped with a 40-ton superconducting magnet, successfully operated for 10 hours in December 1977. A later program, undertaken by the Soviet Union, involved the use of an MHD generator in conjunction with a conventional turbogenerator system for commercial power production. Various other countries, including France, Great Britain, and Japan, have been engaged in MHD research-and-development programs. Coal-fueled MHD power plants promise greater efficiency than conventional facilities. Whereas the latter are able to convert only about 35 to 40 percent of a fuel's energy potential into electricity, installations equipped with MHD generators have the potential of achieving roughly 60 to 65 percent. One additional advantage of MHD generator facilities is that they produce less air pollution than do conventional power plants. Additional reading Stanley W. Angrist, Direct Energy Conversion, 4th ed. (1987), provides a historical introduction and overview. Richard J. Rosa, Magnetohydrodynamic Energy Conversion (1968, reprinted 1987); George W. Sutton and Arthur Sherman, Engineering Magnetohydrodynamics (1965); and V.A. Kirillin and A.E. Scheindlin (eds.), MHD Energy Conversion: Physiotechnical Problems (1986; originally published in Russian, 1983), are general texts on principles and applications. Journal articles include three from Magnetohydrodynamics: An International Journal, vol. 2, no. 1 (1989): L.H.Th. Rietjens, MHD for Large-Scale Electrical Power Generation in the 21st Century, pp. 1725; E.P. Velikhov et al., Pulsed MHD Facilities: Geophysical Applications, pp. 2733; and A.E. Scheindlin and W.D. Jackson, Ninth International Conference on Magnetohydrodynamic Electrical Power Generation: Status Report Summary, pp. 1116. Open-cycle MHD is treated in J.B. Heywood and G.J. Womack (eds.), Open-Cycle MHD Power Generation (1969); and M. Petrick and B. Ya. Shumyatsky, Open-Cycle Magnetohydrodynamic Electrical Power Generation (1978), a joint U.S.U.S.S.R. publication. Two conference proceedings are important sources of current information: papers from meetings of the Symposium on the Engineering Aspects of Magnetohydrodynamics, an American conference; and from the series of meetings of the International Conference on MHD Electrical Power Generation. William D. Jackson