How is the velocity of fluid through a magnethydrodynamic drive calculated?

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Offline stu

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Guys ,how can you calculate the flow rate of a saline solution thru a magnethydrodynamic drive.

If the input is blocked is negative pressure achieved

does any one have a solution calculator for working out the details
« Last Edit: 12/09/2012 19:12:46 by chris »


Offline evan_au

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Calculating the force on the fluid is given here:

To turn this into a velocity, you need to take into account the friction/viscosity of the fluid, and the shape of the thruster and nozzles.

Looking at photos of the Yamato prototype, it makes some sense that the nozzles would be tapered, so the velocity of the fluid at the inlet would be the same as the velocity of the boat, but the velocity at the output nozzle would be much higher (ie variable velocity along its length). 

If you blocked the inlet, I expect that you would have less pressure at the inlet end than at the nozzle end - but it would take a very high voltage & current, and a very strong magnetic field to produce cavitation ("negative pressure") at the inlet. On the other hand, cavitation is a common problem on motor-driven propellers, causing erosion of the propeller blades.