@fluxcapacitor

10 months ago

Great video! A few suggestions. As there is no more moving parts in an MHD drive, you don't necessarily have to put the engine inside like a conventional motor. Instead, you can put the engine outside ;) i.e. deploy the MHD interaction everywhere around the external fuselage, making it an "external flow MHD accelerator" with the benefit of acting on the wavefront and the drag along the whole wetted area. Another trick: when you glue the same poles of two 1T magnets together, face-to-face, you nearly double the magnetic flux density and get almost a 2T magnetic field strength right on their junction plane. In addition, in order to avoid electrode corrosion due to electrolysis, it is best to use graphite electrodes, even if steel is better than cooper indeed. Speaking of electrolysis, you are limited by the conductivity of salt water: you could use an acidic bath instead and boost the induced flow velocity even further (except if your aim is to eventually test a boat or submersible down the road).

What limits the efficiency of such a small drive is the relative weakness of the magnetic field, and the limited amount of current density that the fluid can bear before electrolysis becomes dominant up to the deleterious situation of thermal blockage, a phenomenon that could be compared to a conventional motor burning due to heat accumulated by the Joule effect (same mechanism). Therefore, you should use a power supply that controls direct current not voltage, to better tune the whole thing, and even calculate precisely the current density J your fluid can accept depending on its electrical conductivity and the surface of your electrodes. Indeed the Lorentz force acting on a fluid is a body force, a force per unit volume, in newtons per cubic meter (in SI units). That's also why the electromagnetic force J×B can be very powerful as it can act on a large volume of fluid. But this is another longer story and I was speaking of the efficiency. Compared to a traditional propeller, the magnetic field B of an MHD drive is akin to the pitch angle of the blades, while the current density J is the rotation speed. With such a low power magnetic field and electric current set too high wrt the fluid (its electrical conductivity), it's like someone who would use a propeller with blades having an infinitesimal pitch angle. He would have to rotate the propeller at an insane amount of RPMs to barely move. The main thing we're doing in this case is not propulsion, but heating the ambient fluid! That's why MHD drives appear so "inefficient". But they are not: they simply don't have the appropriate input values, as our technology is not yet advanced enough (hint: room-temperature superconducting multitesla electromagnets and powerful yet light and compact electrical power generators onboard).

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