We have found some things out recently on these LN2
traps that we do not particularly like, so tell me about your application
and I will try and be as candid as I can about drawbacks of LN2. The big
thing is length of time they last. Our people tested them for time and the
stated numbers are based on pressures of 10-6 Torr. Now at these pressures
there is not a whole lot of gas flow so therefore there is not a lot of heat
transfer between the cold trap (LN2) and the gas being pumped and the LN2
lasts. The traps last a long time at these pressures and are not exactly
"real world" applications. At higher pressures they do not "last" anywhere
close to the stated time frames. Ours or anyone else's. We are working on
some newer models, but are just at the end of the test phase for our new LN2
traps that do not even incorporate this new idea. It was determined during
testing of these traps.
Now the thing is many users are using these to stop say
water, some aliphatic alcohol or other low boiling chemical out of the pump
or to reduce it in their sample. In this example the pressure stays, for
talking sake with water, at like roughly 10 Torr until all the water is
turned into a gas and pumped by the pump. The pressure will stay at
this elevated “high pressure” and as a result, the trap, sees this elevated
gas flow and the liquid nitrogen is consumed at much higher rates.
Understand the application before getting a trap and ending up with a false
sense of security. We can help. Ask us.
It would be another 2 months if our hypothesis is
correct and we indeed have a higher pressure, longer term LN2 based trap.
With current traps in my opinion, in higher pressure application there is
also a need for an LN2 keep full pumping station that typically adds another
healthy kick to the price of the traps in order to maintain LN2 levels in
the trap and maintain affectivity of the trapping function. In this
scenario, the trap has a larger LN2 storage container placed nearby. A
special LN2 transfer pump is incorporated into the system design to keep the
trap maintained from the storage container so that trapping and the
evacuation process can proceed without constant monitoring by the end user.
It is also bad to have the trap lose temperature during evacuation as all
the condensable vapors trapped so far then re-evolve and end up in the pump
anyhow. I will be writing this all up soon and posting it soon as we get
all our ducks in a row for our 2nd "new" design and have a better mousetrap
which I think we will have in the relatively near future.
Dry Ice Traps typically may be better solutions for
high pressure applications but have some drawbacks namely availability of
supply that may impact user choice.