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[DPRG] Re: thermal shock

Subject: [DPRG] Re: thermal shock
From: Sluggy! slugmusk at linuxlegend.com
Date: Sat Oct 13 00:47:05 CDT 2001

David M. wrote:

> I don't imagine that thermal shock should be much of a concern;
> practically all superconductors are used when cooled to a few degrees
> above absolute zero, and with basically no resistance, there most be
> alot of current gong thru it... 

Pretty much by definition, a superconductor does not heat up with all 
those marauding amperes coursing through it.

The thermal shock problem comes from the uneven heating at the 
microscopic level. The dry ice would cool the entire chip well below 
it's rated operating temperature, though probably not anywhere near the 
temperature of dry ice. Operation of the chip will heat it, intensely in 
the case of the 200A motor controller, in a very localized manner. The 
hot spots expand while the cold spots don't. The phyical stress of this 
uneven expansion is what does the damage to the glass-like silicon.

> I would assume the electronics would work better the colder
> they got; as heat increases resistance. 

Like just about everything else in life, compromise is in order. The 
movement of electrons is facilitated by cooling the conductors. It can 
affect operation enough to change the operation of the circuit and not 
all components will react the same.

I think that the dry ice approach could help dissipate a lot of heat 
with a smaller heatsink, but I don't think it should be applied until 
the system is in operation.

Sluggy!


-- 

  ... because I'm a huge Beach Boys fan. I'll
  never forget the first time I saw them in
  person, back in 1964, at a fantastic concert
  in New York... Wait, no, it was Philadelphia,
  and it might have been 1967. And come to think
  of it, it wasn't the Beach Boys; it was the
  Bee Gees. Or maybe the Turtles. It was
  definitely a plural name. Although, now that
  I think of it, I'm not 100 percent sure I
  was there.
 
                               Dave Barry


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