Magnetohydrodynamics: possibly the most intimidating name for a relatively simple concept ever!
If you’ve ever seen The Hunt for Red October and the quest for the “silent submarine”, you may have heard of MHD. Basically, MHD involves taking the cross product of a magnetic field with an electric field to produce the resultant vector, the so called “Lorentz force.” This force can then be used to propel an ionized solution with no turbines or any moving parts.
The Lorentz force is sometimes used to define the strength of magnetic and electric fields. That’s because F, the Lorentz force, equals q(E + (v X B)) , where E is the electric field and B is the magnetic field (both vector quantities).
So where does the cool project come in? Well, I was researching MHD on Wikipedia and saw that someone has built a full sized boat powered by a magnetohydrodynamic drive. I saw an image of one of the thrusters, and minus the multi-million dollar electrodes, I decided building one at home shouldn’t be too complicated.
The first thing I decided to do was create a tube with a relatively uniform magnetic field inside. To accomplish this and create a reasonably powerful field, I bought two 4″ x 1″ x .25″ neodymium magnets from kjmagnetics.com . These things are scary powerful. To hold them in place without having to secure them with adhesive, I decided to use a framework of laser cut acrylic spacers to keep the magnets in place. I’m not home at the moment, so I’ll try to remember to post the files.
That left me with something like what you see below (though I haven’t installed the second magnet in this picture).
The magnets are oriented such that the magnetic field inside, at least on a small scale, looks just about linear. This means that when I add my electrodes in a perpendicular direction, we should get interaction that models the Lorentz force quite nicely.
So now that this part is completed, I have to begin work on the electrodes. This is surprisingly tricky, as driving electrodes not made from precious metals in salt water (the ionized solution I’ll be using) with DC tends to cause electrolysis and the corrosion of the leads.
To be continued very shortly…