Ok this may be long winded, and be warned... you will see Lego!
To start with, some background info...
Magnetohydrodynamic propulsion (A.K.A. MHD motor, MHD drive or Catterpiller Drive).
This system was 'used' in the film 'The Hunt for Red October'.
This started out with this thread on HV Community ( http://forum.4hv.org/index.php?board=4;action=display;threadid=1287 ).
After some research I found some info about the system.
And a nice image of a 'boat' with a MHD drive.
http://www.physics.brocku.ca/courses/1p22/images/f21019.jpg
The basics of how it all works.
http://www.sanu.ac.yu/English/Shipbuilding/Tema4.htm
For the MHD drive unit, the information here is very helpful although incomplete.
http://www.spots.ab.ca/~belfroy/magnetoWaterPropulsion.html
Armed with this info here's what I came up with...
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The 'motor' contains no moving parts.
The casing is made from acrylic sheet cut to size.
The electrodes are stainless steel, the stainless is very slightly attracted to a magnet. Experiments with the stainless in electrolysers reveals that the stainless is corrsion resistant, even when using sodium hydroxide solutions.
The enamelled copper wires are soldered to the stainless. To do this, I used flux paste, gas cooker flame and normal electrical solder.
The magnets are NdFeB 1/4"(h) x 1/4"(w) x 1"(l) (available from http://www.neo-magnet-emporium.co.uk )
The motor dimensions are approx 1"(h) x 1/2"(w) x 1 1/4"(l), the top magnet and casing fit nicely inside a hollowed out Lego 2 x 4 brick.
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Initial stationary testing using salted tap water and food colouring (as 'smoke') produces a good flow through the motor using a 8.4v 250mAh NiCad pack.
The salt water is at about the same proprtions as sea water, i.e. 35g table salt to 1 Liter water.
A breakdown of the salts found in seawater is here.
http://www.science.edu.sg/ssc/detailed.jsp?artid=2462&type=6&root=5&parent=5&cat=51
All good fun :)
The motor does move the boat... very slowly.
With this setup there are gas bubbles produced, suggesting that the components and power supply are disproportionate.
(i understand the MHD drive to be an inefficient propulsion system.)
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And now for the interesting stuff...
As with an electric motor, the device can be used to generate electricity.
High power generators and motors can be made using gas superheated to plasma...
http://www.plasma.inpe.br/LAP_Portal/LAP_Site/Text/Classical_Applications.htm
There's more info about plasma flow here.
http://www.fortunecity.com/greenfield/bp/16/electrolyticflows.htm
And a method for a MHD generator here.
http://users.erols.com/sclufer/mhd.htm
Before I mounted the motor in the Lego, I ran tap water through the chamber.
And got an open DC voltage reading (0.136v), and 0.001A short circuit on a cheap meter.
Considering the size of this unit (the plates have a total of 2.88 sq cm exposed to the water) I was very surprised at the output.
So now I'm thinking the MHD generator, whilst not particularly efficient has some nice features;
No moving parts, simple construction, debris and wildlife can pass through the generator.
And then I thought, what if the water passing through the generator was flowing from one chamber to another and back again (like an egg timer)?
What if the MHD generator could be used in a rotary fluidyne heat difference engine ( http://www.rotarystirlingengines.com/rotacola.htm )?
Would the water in the system have to be replenished over time?
Food4Thought:::
Could the MHD motor/generator principles explain why magnetic water treatments seem to work?
Do the materials with postive ions attract or get broken down by releasing electrons to the grounded metal water pipe?
Having fun 8))
paul
