If oscillating electromagnetic field, as per dictated by laws of Maxwell, Joule, Navier-Stokes (and Lorentz) holds, then for an unidirectional circulation of molten metal by electric field can easily raise the bath liquid level rise in center. but in a high frequency AC induction furnace, time period of AC currents is just a few milliseconds. so, unidirectional angular velocity maintenance is impossible. then how the bath level is so? Again, are the metals' atoms' ionic cores and 1/2/3 outer electrons of atomic shells are detached during melting, and follow their own course in a melt under electromagnetic field? because. there would be no electromagnetic force on an unionized atom.
Hi Sumit Bhowmick ,
please have a look at this video:
https://www.youtube.com/watch?v=Pl7KyVIJ1iE
The molten metal is still an electrical conductor, and, as in the aluminum ring, the phase of the eddy current is always such that the current (and the conductor) is repelled by the source of the magnetic field. In your case, I guess, the source is located at the bottom of the furnace or at least below the mean height of the metal.
The easiest explanation for the fact that the surface of the liquid is higher at the center than at the periphery seems to be that the magnetic field (and hence its variation) is strongest in the center. But there might be more to it.
Did you observe a flow of the metal, perhaps centrifugal at the top surface?
I think you may have the magnetic field strength the wrong way round Joerg Fricke . If the field is stronger at the edges (which I expect it is), then will the metal will try to move away from the edges into the centre, where the field is lower, resulting in a hump in the middle?
Also, looking at it another way I think that if there is a coil around the bath the induced currents in the bath will be in the opposite direction to the currents in the coil, and the force on the liquid metal, from the RH rule for field direction, and LH rule for force, will be towards the centre.
Malcolm White , you are certainly right. Visualizing the rigid aluminum ring, I forgot about the centrifugal forces which sum up to zero in the ring, of course, but not in the fluid.
Taking these forces into account, now I think the result would even be the same (qualitatively) for a coil around the bath or a (flat spiral) coil under the bath. The second case could be tested perhaps with a highly concentrated NaCl solution in a fireproof glass pot on an inductive hot plate for kitchen use. (If one succeeds in feigning the presence of a metal pot to the plate controller.)
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