[DMCForum] Re: PCV Routes Manifold Vacuum Through The Crankcase

["bkp944" <bk_pollard@xxxxxxxxxxx>]

--- In DMCForum@xxxxxxxxxxxxxxx, "checksix3" <jetjock11@xxxx> wrote:
 
> Of course. There is only the lack of heat, same as lack of 
> pressure. 
> 
> You must also talk in terms of Kelvin. I gotta admit, there 
> is nothing like the clean vacuum a good cryopump makes. No wonder 
> too, they go all the way down to 10K...that's cold. It's amazing 
> helium can go that low as long as it's not ballon gas. No phase 
> change on the He side of the pump either..
> 
> Physics may be odd but it's the truth. If one is going to 
specialize 
> in any technical endeavor there is no better way to achieve a 
solid 
> understand of a discipline than studying it on that level.

Yes, we are particularly interested in the boiling point of liquid 
helium-4, 4.2K. We can lower the pressure on a bath of liquid helium 
and easily reach 2.2K. 

We manufacture superconducting magnets and the common method of 
operating them is in a bath of liquid helium. 

The cryopumping you mention can cause us problems with helium 
diffusion through the welds in the cryogenic vessel. This degrades 
degrades the vacuum and the vessel will no longer keep the helium in 
a liquid state. These "cold leaks" are difficult to avoid and it 
takes a very specialized welder to construct these vessels.

Dilution refrigerators using Helium-3 can get down to 100 milli-
Kelvin or less. This is in a very small sample space and the time at 
the lowest temperatures is somewhat short - measured in minutes.

-Brian
VIN# 4494

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