A Magnetohydrodynamic drive or MHD propulsor, is a method proposed for propelling seagoing vessels. An electric current is passed through seawater in the presence of an intense magnetic field. Functionally, the seawater is the moving, conductive part of an electric motor. Pushing the water out the back accelerates the vehicle.
MHD is attractive to engineers because it has no moving parts, which means that a good design might be silent, reliable, efficient and inexpensive. Also known as a caterpillar drive for submarines, this was popularised in the movie The Hunt for Red October as being a "silent drive," an undetectable stealth superweapon in submarine warfare. The current traveling through the water would create a great amount of gases.
In the 1990s, Mitsubishi built several prototypes of ships propelled by an MHD system. These ships were able to reach speeds of 15 km/h despite projections of higher ones;
Japan began sea trials of a prototype magnetic ship. Yamato 1 is propelled by two MHD (magnetohydrodynamic) thrusters that run without any moving parts. When completed, the MHD ship should be able to attain speeds of more than 100 knots (125 miles or 200 kilometers per hour), with little noise. This is several times the top speed of today’s ships, which are slowed down by turbulence created by the ship’s propellers. MHD works by applying a magnetic field to an electrically conducting fluid. The electrically conducting fluid used in the MHD thruster of the Yamoto 1 is seawater. [1]
The major problem with MHD is that with current technologies it is more expensive than a propeller driven by an engine. The extra expense is from the large generator that must be driven by an engine. Such a large generator is not required when an engine directly drives a propeller.
If fuel cells become common, MHD propulsors may have lower costs in some applications than electric motors driving propellers.
NASA and other organizations are also sponsoring exploratory development of the magnetohydrodynamic drive for interplanetary craft.[2],[3] In this context, it is usually called "plasma propulsion".[4]
Further application proposals indicate increasing the speed of rocket and other vector thrust engines in order to make them more efficient, however this has not been practical due to high weight of magnets.
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