Chill to dry deuterium gas?

For posts specifically relating to fusor design, construction, and operation.
Post Reply
Tony Lai
Posts: 15
Joined: Mon Aug 10, 2020 8:05 pm
Real name: Tony Lai

Chill to dry deuterium gas?

Post by Tony Lai »

Hi there.
While constructing my fusor I happened to stumble across the problem of deuterium drying.
Now most of the members are utilising some sort of a drying tube after electrolysis stage, however in my memory all those silica gel and dririte (use as optical stuff desiccant) contains a bunch of fine dusts. Wouldn't that just contaminate everything and risk destroying the precious turbo pumps?
It actually inspired me when viewing one of the posts of constructing a cold trap, isn't it a good idea to chill the moist gas for drying? I recall that D2O has a melting point at around 4 degree celsius and typcal semiconductor cooling devices go down to around -7 to -10. Is it a good idea to just hook up the gas line through a ice cold spiral so that all those left over D2O can be seperated?
Please let me know if it is just purely nonsense, I appreciate for any help.
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: Chill to dry deuterium gas?

Post by John Futter »

Tony
The clue is the vapour pressure of water /D2O you have to really cool it to make inroads to lowewr the vapour load ie -180 degrees Celsius ie liquid nitrogen temperatures

either a Thin palladium baffle or chemical drying---with the last option being in your realm
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Chill to dry deuterium gas?

Post by Richard Hull »

John's right....It is the devil's on work to keep water out of vacuum systems, especially scientific vacuums. Liquid nitrogen is th' cats PJs for those who would warrant no water in there systems. You just have to keep the entire condenser LN2 cool for as long as you use the system. Expensive? Depends on what you call expensive. It is more of a hassle than costly for the "sometime" or occasional operators. Dririte is probably fine for the average fusioneer who is "in it to win it".

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
User avatar
Mark Rowley
Posts: 909
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: Chill to dry deuterium gas?

Post by Mark Rowley »

If you’re using a Horizon type PEM cell there is absolutely no immediate reason for drying the gas. Unlike classic electrolysis the PEM cell provides a comparatively dry product. I have used a cold trap to try and improve the already decent product with marginal results. Yes, a cold trap does improve the quality a bit, but nothing even close to warrant a mandate.

If you’re using classic electrolysis, yes, you’ll have a sloppy wet London Fog of deuterium that’ll absolutely require drying.

Use the search function, it’s golden! I have posted quite a bit about this over the past 6-12 months...inc the cold trap.

Mark Rowley
User avatar
Rich Feldman
Posts: 1470
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

Re: Chill to dry deuterium gas?

Post by Rich Feldman »

Mark, thanks for the reminder.
I think you said the practical effect of water in PEM-electrolyzed deuterium is minor, as indicated by neutron counts in your fusor.

For anyone wanting to be quantitative about wetness of a gas stream, dew point temperature is an obvious and practical metric.
Cold traps using various consumable refrigerants (ice, dry ice, LN2) establish an upper bound on the dew point of the dried gas.
If you know the flow and dew point of the wet gas, you can determine how much moisture the cold trap needs to hold without clogging.

Has anyone seen evidence that PEM gas has dew point higher than 0 °C ?
That would mean partial pressure of D2O exceeds 4.6 torr, and moisture would condense on surfaces at that temperature.
Salt and ice baths (or mini refrigerators) can get water vapor pressure lower than 1 torr (concentration in gas < 1 part in 760 by volume).
Dry ice gets it below 1 micron.
All models are wrong; some models are useful. -- George Box
User avatar
Dennis P Brown
Posts: 3160
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Chill to dry deuterium gas?

Post by Dennis P Brown »

As a water vapor trap dry ice works very well (in alcohol) and most major cities have a local supplier. It is also likely to be shipped. But frankly, this would really only be best for very high vacuum work - like 10^-5 torr and below.

The dust issue for most desiccant's is a trivial matter to deal with - really. One just uses a fiber filter - a plug of standard aquarium fiber fill would also work. Of course, just a trace of such dust wouldn't exactly cause issues for most vacuum turbo systems - there is such in air (dust) that also enters your vacuum system. So a simple filter should work fine.
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”