What method should i use in order to remove moisture from air of a container completely? Should i flush it with N2 or argon (its air-tight) or is there a device that i could use to remove moisture from the container? The container is prone to condensation due to extremely low temperatures. I need that water out :D

  • $\begingroup$ Use the crystal packets that new electronic equipment is packed with that absorb moisture... or rice or salt... Mind you if it is gas tight then how do you open it to get the crystals out? A larger container ... $\endgroup$ – Solar Mike Sep 7 '17 at 11:46
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    $\begingroup$ It doesn't matter with what gass mixture you flush it with as long as it's been dehumidified first. $\endgroup$ – ratchet freak Sep 7 '17 at 12:02
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    $\begingroup$ You might get better answers if you edit your question to say: 1) how cold, 2) how dry is required, 3) how big the container is, 4) if the container has or could easily have gas fittings, 5) whether this is a one-off or whether the container will be opened periodically for maintenance, 6) whether water could leak in e.g. along cables, 7)how many you are doing (and thus whether you're minimising capital or ongoing costs), 8) any equipment you already have such as vacuum pumps. $\endgroup$ – Jack B Sep 7 '17 at 12:18

The de-facto standard way of getting all the water out of a cyrostat before cooling it is to pump it out with a vacuum pump, then back-fill with dry gas from a cylinder. Nitrogen is cheap and easy, helium is preferred if the cryostat will be cooled below -190C (but I guess "extremely low temperatures" probably isn't that low). Depending on the achievable pressure with the vacuum pump and how strict the requirement is, you might pump and flush more than once.

If the requirement is not as strict, it may be enough to blow out the air with dry gas without pumping down to a vacuum first.

If you want to get rid of a small amount of water after purging, or take up moisture seeping in through a leak, you can use silica desiccant. It's dirt cheap, but has limited capacity. When it's full, it can be dried out in an oven and used again. It's the same stuff that you get in little "do not eat" bags with clothes and goods, but you can buy it in big containers too.

  • $\begingroup$ Well, i was thinking about just flushing it with nitrogen. Its electronics motherboard and some components that are very sensitive and unprotected. Its imperative that no dielectric grease is used. They will be cooled down to -30 max. Should i just flush it or remove air then flush it? $\endgroup$ – Sci00213 Sep 7 '17 at 13:39
  • $\begingroup$ This really depends on exactly how sensitive those components are, which might be quite hard to find out. I would flush with nitrogen and then add silica desiccant, and it'll very probably work. For complete confidence I would pump out the air. You might also consider potting the delicate components. $\endgroup$ – Jack B Sep 7 '17 at 13:57
  • $\begingroup$ do you know if places that offer nitrogen filling for tanks also have vacuum pumps? $\endgroup$ – Sci00213 Sep 7 '17 at 16:43
  • $\begingroup$ Not sure. We have all that kind of thing in-house. I would guess no though. $\endgroup$ – Jack B Sep 7 '17 at 20:17
  • $\begingroup$ @Sci00213 You can pick up a reasonable rotary vane vacuum pump on eBay for 100-150 USD, but they typically won't have them at places like Airgas or a welding supply store (which is where I get inert gases). $\endgroup$ – phyllis diller Sep 7 '17 at 21:40

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