Magnetohydrodynamics in a model boat
A model boat demonstrates magnetohydrodynamics. In one of its forms it gives electrical propulsion with no moving parts by applying an electric current to a fluid in a magnetic field generating thrust. This applies to any conductive fluid including water (preferably salt), liquid metal or plasma. Here I am demonstrating the principle with water.
“Continue reading” for further explanations and using powers up to 1 kW. 8 photos and links..
Essentially two electrodes in water have a current passed between them in a magnetic field. Water is forced out the back creating thrust. It is not really a commercial proposition but was featured in “The Hunt for Red October” as the Soviet stealth sub.
In my model there are two 1 inch NIB magnets about an inch apart. At right angles to this are two electrodes which pass about 1.6 A 9.6 VDC in salt water. i.e. about 15 watts. Power is by a model car NiCd pack. The whole decidedly unseaworthy construction is made of Balsa and is about 8 inches long.
Performance is underwhelming and I would guess at 1cm/sec boat speed.
Using off board power of 1 kW (100 V 10 A) there is a lot more action and production of hydrogen and ?oxygen or chlorine bubbles streaming from the stern, but I don’t have a big enough tub of salt water to test it for speed. On the right is the ignition of the hydrogen bubbles with the bright yellow flame from the sodium in the seawater bubbles. Normally a hydrogen flame is almost colourless. After a short while the electrodes wear away and the water fills with debris, presumably insoluble salts of the metal electrodes.
The 2005 model was a significant milestone in maritime history.
Features: 2.5 times the power (16 alkaline AA cells giving 24V – previously 9.6V NiCd pack). Typically 50W output from salt water swimming pool (20V 2.5A) through to near saturated salt solution (12V 4.5A.
Vertical twin magnets to avoid compass rotation effects. One magnet is now within the hull hence reduced friction.
Heavy aluminium electrodes more completely contained in the magnetic field.
It’s red hence should go three times as fast.
Small print. It’s still incredibly slow.
Handles like a brick.
It’s still no use to anyone.
Full sea trials yet to be conducted
A Japanese magnetohydrodynamics boat , the “Yamoto” was built as proof of principle. This was made by Mitsubishi in the 1990’s and weighing 185 tons. I went 15 km/h in top gear. Thank goodness it was streamlined. It uses a superconducting 4 Tesla magnet. The round cross section of the motor looks remarkably like mine but about 10 times the diameter (260mm). Electrodes are Titanium with anode coating of DSA (?) and the cathode plated with Platinum. The length of electrodes is 3.4 m.
Note that these aren’t all around the place so I guess magnetohydrodynamics haven’t put propellers aren’t out of business yet.
Related pages
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External links
Magnetohydrodynamics – Wikipedia
Photo Date: 2004, 2005