Well, I musta' been psychic! I just got my issue of Vacuum and Coating Technology magazine today at work. The Jan 2001 issue features an article on page 58 entitled "Water and Water vapor! Wow all you ever wanted to know and more.
One of the neat things is a vapor pressure list. I always knew water vapor is locked down in LN2 traps but it seems that its vapor pressure at those temps is on the order of 10e-22 torr. That is less than nothing. It makes interstellar space look like the inside of an airplane tire.
Cold traps are nice, but you have to fart with the un-handy and long term expense of the cryogenics. It really hurts when you spend $25.00 to get a 10L dewar topped off and realize while you are at work or eating supper, walkin' th' dog, at the movies, or whatever....that it is just boiling away back to the atmosphere from whence it came. It is like having a hole in your pocket with money continuously falling out on the sidewalk. I know this pain first hand. My 10L Linde dewar will keep usable amounts of LN2 for about 4 weeks. I recently demo'd the Meissner effect 4 times and used maybe 1 quart of LN2 in those experiments, I also used a few more ounces in small tests elsewhere around the lab. About 8.5 liters boiled off back into the atmosphere.
The magazine article notes that diff pumps will pump water vapor real fast and that turbos are sluggish. This is one reason I am considering not using my turbo pump in favor of an air cooled diff pump purchased at one of my Telsathons with pentavac fluid in my new system.
As an engineer, I am inundated with freebie "tech" magazine subscriptions, most of which I rarely read religiously. This rag is pretty good though.
Richard Hull
Created on Thursday, January 25, 2001 11:31 AM EDT by Richard Hull