MHD Generators

[d3x0r]

Just a thought; I started searching for homopolar generator in a helmholtz coil (homogenous magnetic field), and ended up finding out about MHD dynamo/generators.  They are driven from heat sources in most research, and they don't use the heat so can be stacked in-line with existing heating water plants... they restrict the flow somewhat, but the overall heat is maintained...  they use a gas run through a fixed magnetic field and differentiate a +/- potential. Low voltage, high current usually. [/font][/size]


I don't see the design I would think of... a disk with a bunch of insulated plates to pass the hot gasses through, like many narrow grooves, which could be put in a fixed magnetic field. Well no mechanical part moves, the fluid/gas/(plasma even) does move through it.


Maybe something like a bifilar pancake coil style thing, with two channels between, with a CW flow and a CCW flow between those, so in the same field the opposite sides get +/- potential... have to be bare wires though not insulted sorta...


This one is powered from the exhaust of a rocket engine
http://www.youtube.com/watch?v=s7c3zz0rWZM

[d3x0r]

It works!  Well; it's a result more than 0, but somewhere less than I was hoping.


0.130V !


I used two straps of 1" wide aluminum tape separated by 3/16" tubing on top and bottom.  I strapped the whole thing together to fit within a 6" OD, 4"ID neodymium magnet that I have, and used silicone glue on top and bottom to seal it.  I rigged a fitting of a couple sheets of thin plastic... one sheet along the inside of the tube, and reglued, one sheet on the outside of the band, and decreasing in thickness along... I'll make a video tomorrow during the light I think.... but anyway


Hooked up some semi salty water with a gravity feed (a funnel and a length of hose above and below the device, and a volt meter on the two outer straps (left a gap between the supply fittings to attach for power).


But I guess this is good, if I did end up with a good voltage, I would have to draw it off externally or I would electrolosize the water medium....


The idea would probably work better with mercury as a fluid, anyone know where I can get 1L of Hg?

[TinselKoala]

Nice work!
You are right about low voltage/high current, I think, so your 130 mV is actually quite respectable; I presume that's into a highimpedance voltmeter. It would be interesting to see how the voltage drops as the load impedance decreases. This will give you an idea of the actual power output available.

Forget about mercury, try to find some GalInStan instead. It's non-toxic and has very low vapor pressure, can even be used in a vacuum chamber.

[d3x0r]

Right See interesting things;  I'd have to redo this particular one, galistan aggressively corrodes aluminum by disolving it

[TinselKoala]

Yah, that's true enough, I forgot about that. But mercury does too, just not as fast or insidiously. And it's toxic.

You could try running the whole apparatus at elevated temperatures and use molten solder or something like that. I am not kidding, some of the best homopolar research work (Valone, Trombley, Tewari, etc) used liquid metal, molten solder "brushes", so why not use it as the working fluid in a MHD device?

I also think a plasma would work, but the current density might be low in any apparatus I might be able to build.