It happens almost every day that someone accidentally cracks open a vacuum evacuation valve on a cryogenic bulk tank or springs a leak in a vacuum probe tube and WHOOSH! The vessel just lost all or a lot of its vacuum.
Referring back to one of the #1 Laws of Science—“Nature Abhors a Vacuum.” Given any opportunity at all, a vacuum space will find molecules and pull them in to recover atmospheric molecule levels. And, we’ve discussed this before.
Untouched, though, is the element of just what kind of molecules get sucked in when a vacuum goes south. The millennium answer: It Depends. What it depends on is the kind of molecules that are available to suck in. In humid environments, a lot of those molecules are going to be moisture (H2O). The problem with moisture is that it is a bear to get out of a vacuum insulated vessel’s annular space once it gets in. This is particularly true if the vessel has perlite instead of super-insulation in the annulus.
Q: Once molecules get into an annular space, how do you restore the vacuum?
A: The only way to restore really strong vacuum in the annulus of a cryogenic vessel is with a really good vacuum pump.
Q: And what is the central dilemma?
A: The stronger the vacuum the less energy there is in the vacuum space. Since energy equals heat that means that the moisture in the annular space will freeze out making it almost impossible to withdraw all the molecules.
We’ll discuss this, the effects and cures some more next post………
Referring back to one of the #1 Laws of Science—“Nature Abhors a Vacuum.” Given any opportunity at all, a vacuum space will find molecules and pull them in to recover atmospheric molecule levels. And, we’ve discussed this before.
Untouched, though, is the element of just what kind of molecules get sucked in when a vacuum goes south. The millennium answer: It Depends. What it depends on is the kind of molecules that are available to suck in. In humid environments, a lot of those molecules are going to be moisture (H2O). The problem with moisture is that it is a bear to get out of a vacuum insulated vessel’s annular space once it gets in. This is particularly true if the vessel has perlite instead of super-insulation in the annulus.
Q: Once molecules get into an annular space, how do you restore the vacuum?
A: The only way to restore really strong vacuum in the annulus of a cryogenic vessel is with a really good vacuum pump.
Q: And what is the central dilemma?
A: The stronger the vacuum the less energy there is in the vacuum space. Since energy equals heat that means that the moisture in the annular space will freeze out making it almost impossible to withdraw all the molecules.
We’ll discuss this, the effects and cures some more next post………
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