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Post by Easy on Feb 8, 2017 17:57:12 GMT
Does anyone have equations for the heating on coilgun projectiles?  Iron loses its magnetic properties above its Curie point of 1043K, meaning it will lose functionality long before it physically melts. A 1 gram projectile at 6km/s is 18,000 Joules of kinetic energy. Iron has a specific heat of 449 J/kg K. So solving for joules: Heat_Capacity = (Joules)/(Mass*Change_in_temperature) we get Joules = Heat_Capacity*Mass*Change_in_Temperature Assuming a 1g iron projectile heated from 0 Kelvin to 1043 we have: Joules = 449 * (1/1000) * 1043 = 468 J. So we have an upper limit for what heat our projectile will handle. Now resisitivity is low at 9.61nOhm*m, but how much energy is imparted onto the projectile as heat? |
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Post by Enderminion on Feb 8, 2017 18:57:43 GMT
the shot is traveling through vaccum with no contact with the coil so there is no friction heating. as for other sources of heating I don't know
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Post by bdcarrillo on Feb 8, 2017 19:42:12 GMT
the shot is traveling through vaccum with no contact with the coil so there is no friction heating. as for other sources of heating I don't know That's why he pointed out inductive heating, not friction. I suppose some of the materials might become molten blobs that would cool fairly quickly out of the barrel, or radiate some heat to the inside of the coil. We'd have to know more about the (essentially unknown) structure of the barrel to figure out how it would absorb heat. There are a few papers on the subject, but I can't seem to find a freely available one. |
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Post by vegemeister on Feb 10, 2017 18:12:20 GMT
You could make the projectile out of thin laminations or polymer-bonded powder like a transformer or motor core. Also, I think reluctance coilguns like the ones used in CoADE don't require subjecting the projectile to a rapidly changing magnetic field. You just have to move the magnetic field up the barrel a little in front of the projectile. So you could pre-magnetize the projectile with a winding at the breech end of the barrel. Then the projectile would get only a single pulse of heat as it left the barrel.
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Post by n2maniac on Feb 11, 2017 21:59:43 GMT
It is a similar situation to what the rotor of an AC induction motor sees. Those typically have the magnetic field move about 5% faster than the rotor for best efficiency. A coilgun is roughly this unrolled into a linear array, then powered up for good measure.
Usually a good assumption to assume no external cooling takes place, though with the 1g pancakes we make I not so sure.
This might be able to help someone start looking.
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Post by Easy on Feb 15, 2017 18:10:18 GMT
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Post by n2maniac on Feb 16, 2017 7:00:05 GMT
Another way to look at this: how strong of a magnetic field can you exert on the projectile? A superconducting projectile may have some relevance, given the high critical field of many superconducting materials.
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