Q: “What is the difference between the vacuum pulled on the liquid cylinder annular space and the vacuum pulled on a high pressure gas cylinder at filling?”
A: The difference is the level of vacuum needed to meet your intended purpose. The vacuum needed to insulate cryogenic liquids and inhibit energy transfer to keep them in a liquid state is a lot harder to achieve than the vacuum needed to remove impurities and contaminant gases for refilling a gas cylinder. Vacuum for cryogenics or cylinder filling is usually expressed as inches or microns of atmosphere. The smaller the value is the better the vacuum. Since microns are a lot smaller than inches (1 micron = 0.00003937 inches) it is easy to see that a 5 micron vacuum is much better than a 5 inch vacuum.
As mentioned in Part 1, vacuums for super-insulated cryogenic vessels are typically pulled down well below 10 microns. This is only 1/100 of a millimeter of atmosphere. Conversely, Ric Boyd of Cryovations (good people) notes that the vacuum level needed to pull impurities for a gas cylinder refill is typically only about 27 inches although there are specialty gas fills that require 50-100 micron vacuum levels.
A: The difference is the level of vacuum needed to meet your intended purpose. The vacuum needed to insulate cryogenic liquids and inhibit energy transfer to keep them in a liquid state is a lot harder to achieve than the vacuum needed to remove impurities and contaminant gases for refilling a gas cylinder. Vacuum for cryogenics or cylinder filling is usually expressed as inches or microns of atmosphere. The smaller the value is the better the vacuum. Since microns are a lot smaller than inches (1 micron = 0.00003937 inches) it is easy to see that a 5 micron vacuum is much better than a 5 inch vacuum.
As mentioned in Part 1, vacuums for super-insulated cryogenic vessels are typically pulled down well below 10 microns. This is only 1/100 of a millimeter of atmosphere. Conversely, Ric Boyd of Cryovations (good people) notes that the vacuum level needed to pull impurities for a gas cylinder refill is typically only about 27 inches although there are specialty gas fills that require 50-100 micron vacuum levels.
Posts
