Using Stealth Propulsion for Ocean Travel (MHD Thruster Build)

Magnetohydrodynamic thrust uses no moving parts in order to accelerate water. It has been known for half a century, but it may be possible that we're only now beginning to explore it for use in Marine travel. I built a modular MHD drive with great results, and documented the journey. The greatest strength of MHD thrust, may be its silence.

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#future #innovation

[PlasmaChannel]

Let me know your thoughts down below - I'll be revising this to increase output. For the time being, 3D files can be found on my Patreon site!

[dack]

Look into halbach array magnet configurations. You can double the field strength inside your thruster by arranging the magnets so that the field is contained entirely within the thruster and the external field is cancelled out.

[feynmandirac]

The force on water is =B*I*L where B is the magnetic flux density, I is the current in the water( between the electrodes), L is the spacing between the electrodes(i.e length of the conducting path), Also current (I=V/R) is voltage(V) by resistance and here the resistance(R) is clearly proportional to the electrode spacing L making R=k*L where k is a proportionality constant. Long story short the force B*I*L becomes B*(V/(k*L))*L that is B*V/k i.e it is independent of the electrode spacing and linear wrt B and V.
This should be fine for intuition, but the resistance is also non linear which only complicates things
I must also add this, there are two currents now here, one going between the electrodes (I) and the other being the thrust flow itself(i) if you use the same rule for this new current(i) a new force arises opposing the main current (I, between the electrodes), this new force is B*i*c where B again is the magnetic field, i is the flow of water causing thrust and c now is the overall length of the electrode. The direction of this force is ixB that is the cross product of the velocity of charge flow and B(I know it's cXB but that's hard to imagine) and it is opposite to the main current I between the electrodes. This is the back emf in this system where the faster your thrust flow the lesser the current between the electrodes which inturn reduces the thrust force.
To put all this mathematically, the thrust force which we saw as F=B*V/k should be replaced by F=B*(V-a*f)/k where 'a' is back emf constant, f is the thrust flow rate showing that flow rate will counter itself

[TheBackyardChemist]

I think the electrode spacing test is misleading you here. You are measuring flow velocity, but that is not your actual goal, thrust is. Thust means mass flow, which is proportional to cross section and velocity. If your velocity stays constant, but your cross section increases, it means more thrust. If you are testing with a constant voltage source, more distant electrodes will mean lower current thus lower power. You also likely have a larger flow cross section with more electrode spacing, so combine that with lower power, that means wider spacing should actually be an effective way to improve your thrust/watt.

[AaronHarper]

Good work, particularly the parametric testing. The reason the electrode spacing didn't matter was that you did not account for the return path of the magnetic field. The result is a counter magnetic field on the outer fringes closest to the plates creating turbulence and drag. You can see this at timestamp 4:28 on the upper plate on the right. It is even present during the 3cm test at timestamp 4:42. Wider spacing needs a wider magnetic field, at least as wide as the plates are. The second thing is that if you use a magnetic core, such as steel, laminated iron, or ferrite, to complete the return path, your magnetic field in the chamber will be higher still, leading to higher chamber medium velocity. PM me if you need more details. :)

[mikedrever]

It would be interesting to see how an electromagnet could be used to vary the thrust.

[ghosttheoremproductions]

A laminar flow straightener behind the flow with something to increase the Reynold's number would likely increase efficiency. Break the boundary layer at the electrodes and then columnate the fluid again to get an even thrust across the nozzle. While water is rather sticky it is also viscous enough to react nicely to boundary layer separators especially since it's practically incompressible so there's little spring effect.

[ElectroBOOM]

NICE! May closer spacing doesn't increase current draw because of some factors like bubbles on the metal surface could limit the draw. Good engine though, beside the side effect of electrocuting planktons!

[novakma]

You can significantly increase the magnetic field strength by using a closed magnetic circuit instead of an open one. You can also use Halbach array

[MichaelStangeland]

This was super interesting, thanks for doing it. I had a scan through the comments and didn't find any of these points:
1) The electrode spacing doesn't change the deltaV, but it might increase the thrust because more volume is being pushed. It would be worth to measure the thrust (hang your device by a string and measure the string angle/displacement). Ultimately thrust force is what you were looking for, so that might be a better metric than DeltaV.
2) Does the current go down with increased electrode spacing? Coupled with point 1, more spacing could be even more efficient (or maybe you did test this and I missed it...)
3) When increasing the voltage, does the current increase linearly or instead have inflection point(s)? I would expect at certain voltages the chemical process (electrolysis) to change as you reach the threshold voltage for new electrolytic reactions. Although you might get less thrust from lower voltage, you might find it more efficient
4) How does the thrust change if there's already an input velocity. I suspect it doesn't (if you can rule out the drag of your vessel).

[laerau]

I like how your adds are seamlessly integrated into the video. It's very creative and much less obtrusive

[jackmarshall]

I think this is really cool. A nice upgrade would be a hexagonal configuration and you could run it like a bldc. It could make a water screw improving velocity further

[SpeederXL]

Fun idea!
As some other said, I think that smaller opening at the back might decrease the thrust rather than increase it. It does increase velocity of the water coming out but total thrust is dependent on the flow of water as well and the increased velocity most likely doesn't make up for the lost flow.
This gets even more a problem if used to power a boat - because the movement forward of the boat will cause the water to also enter the inlet at some speed relative to the unit and get accelerated to even higher speed - which increases the total flow thru the unit by a lot. This will cause that opening to act like a big choke - making the thrust decrease faster with the speed as well.
If the channels have the same cross section area thru the whole unit, the water will just enter with some speed and accelerate freely to even higher speed, and continue to produce thrust even when getting up to some speed.

[kevinmccarthy]

It's been a while, but the novel of the Hunt for Red October the RO used ducted turbines deep in the hull. It was called a "caterpillar" because it had many turbines spinning pushing the water. IIRC it did use magnets to move the turbines (instead of prop shafts and motors).

[TheCybrKnyf]

Excellent job at communicating a complex process and theory into something easily understood. Way to go!!!

[ancienttechnology]

Drag is going to be the limiting factor in this thruster. On top of the thruster drag there will be a vessel drag component as well. So the lengh making faster flow is great for a practical display, but optimizing the design would require that drag be the factor used to determine field strength and voltage inputs. For any given thruster size, it will have a maximum velocity in the water due to it's drag. Practically speaking this would mean that the nozzle used in this video would be a limiting factor of volume because the fluid cannot be compressed. Therefore the nozzle increases drag, and limits volume. I would imagine that a thr

[atrumluminarium]

One design consideration that you're not considering here is the drag of the thruster. It's fine for this test to have a bulky design since the surrounding water is fairly static, but on a boat once it gets going there comes a point where the bulk will definitely be a hindrance.

STRICTLY SPEAKING, a MHD could be built with very little drag by lining the boat's hull length-wise with alternating electrode-magnet strips in the pattern +, N, -, S, +, N, -, S, +, N, -, S, +, ... This would mean that the hull of the boat is almost "wrapped" with an EM field where the electric and magnetic field are intersecting almost perpendicularly at every point thus generating a skin layer of thrust along the entire hull. My hypothesis with this is that the thinner the strips (and hence the more +, N, -, S sets per unit length one has along the crossection) the more efficient the energy transfer will be because the field will be more localised around the boat. Also maybe putting some thought into how the wiring is run to the electrodes might help by orienting the magnetic field their current generates to form additively to the fields of the bar magnets rather than have them be wasted EM emissions.

[mpturp]

have you considered a column of ring magnets in the center of an aluminum tube? Forcing the current to run only through the magnetic fields could have an interesting effect.

[keithnoneya]

Try using Pulse Width Modulation (PWM) with a Pulse Repetition Frequency (PRF), it may save on the overall wattage. You may also try and use some low amp high voltage supply. This will allow the water once it's moving to help keep the water flowing even when the voltage is off. Kinda like once you get a tire rolling it doesn't take as much force to keep it going. You may also consider using Idler Plates, they are used in Hydro Gas Generators to keep the water charged while using less electricity. Hope that helps give you some more things to consider and test with. Best Wishes & Blessings. Keith Noneya

[christopherkent]

Electrolysis, top secret navy propulsion systems !!! And separating the molecular bond between hydrogen and oxygen that are also explosive ... Love the Channel