Magnetohydrodynamics
(MHD)

Magnetohydrodynamics involves magnetic fields (magneto) and fluids (hydro) that conduct electricity and interact (dynamics).¹ MHD technology is based on a fundamental law of electromagnetism: When a magnetic field and an electric current intersect in a liquid, their repulsive intersection propels the liquid in a direction perpendicular to both the field and the current.²

Magnetohydrodynamics Simple Equations

A computer actuated relay clicks in the small control room at Israel’s Ben Gurion University of the Negev. Nearby, a two story high power generator starts up.… But there’s a strange silence. There’s no whine from high speed turbine blades, no hum from copper generator coils whirring in a magnetic field, no hiss of pressurized, superhot steam. That’s because Etgar 3, the world’s first liquid metal magnetohydrodynamic (MHD) plant, has no moving mechanical parts. Instead, a stream of relatively low temperature metal is forced through a magnetic field. Electricity is then tapped directly from electrodes contacting this metal — up to 30 percent more efficiently than with turbine based generators, say proponents.³

Electropaedia writes: "Magnetohydrodynamic power generation provides a way of generating electricity directly from a fast moving stream of ionised gases without the need for any moving mechanical parts - no turbines and no rotary generators. Several MHD projects were initiated in the 1960s but overcoming the technical challenges of making a practical system proved very expensive. Interest consequently waned in favour of nuclear power which since that time has seemed a more attractive option." ⁴

In place of a propeller or paddle wheel, [the Yamato 1] uses jets of water produced by a magnetohydrodynamic (MHD) propulsion system.… Inside each thruster, the seawater flows into six identical tubes, arranged in a circle like a cluster of rocket engines. The ten inch diameter tubes are individually wrapped in saddle shaped superconducting magnetic coils made of niobium titanium alloy filaments packed into wires with copper cores and shells. Liquid helium cools the coils to –452.13°F, just a few degrees above absolute zero, keeping them in a superconducting state in which they have almost no resistance to electricity. Electricity flowing through the coils generates powerful magnetic fields within the thruster tubes. When an electric current is passed between a pair of electrodes inside each tube, seawater is forcefully ejected from the tubes, jetting the [craft] forward.⁵

	Yamato II
The boat, 30m/100ft long, was designed to travel at 8 knots. – Brock Hampton, Dictionary of Science (London: Brockhampton, 1994), p. 356.

Sources

¹ “Magnetohydrodynamics (MHD),” Dictionary of Scientific Literacy, Richard P. Brennan (New York: John Wiley & Sons, Inc., 1992), p. 195.

² Dennis Normile and Robert Langreth, “Superconductivity goes to sea,” Popular Science, Nov 1992.

³ John Free, “Now: liquid-metal MHD; magnetohydrodynamic power,” Popular Science, July 1985.

⁴ Electropaedia, "Battery and Energy Technologies: Magnetohydrodynamic (MHD) Power Generation," at http://www.mpoweruk.com/mhd_generator.htm (retrieved: 1 June 2014).

⁵ Normile and Langreth, “Superconductivity.”

	The Magneto Hydrodynamic Explosive Munition (MAHEM) program offers the potential for higher efficiency, greater control, and the ability to generate and accurately time multiple jets and fragments from a single charge.
	A little frog (alive !) and a water ball levitate inside a Ø32mm vertical bore of a Bitter solenoid in a magnetic field of about 16 Tesla at the Nijmegen High Field Magnet Laboratory.
	The 1,500-pound Dodge Tomahawk can reach 60 miles an hour in about 2.5 seconds, and has a theoretical top speed of 300 mph.
	Solotrek XFV Exo-skeletor Flying Vehicle

See also

MAHEM (Magneto Hydrodynamic Explosive Munition): "Science fiction inspires DARPA weapon," 22 April 2008, at http://www.newscientist.com/blog/technology/2008/04/science-fiction-inspires-darpa-weapon.html (Retrieved: 25 April 2008).