3 ms·

Hmm, does the cap screw on tight like a normal thermos? Maybe it's designed to always have a loose cap for venting. The dewars I was talking about above hold

Hmm, does the cap screw on tight like a normal thermos? Maybe it's designed to always have a loose cap for venting. The dewars I was talking about above hold several hundred liters, are about 5-8 feet tall, and primarily for liquid helium (where evaporation is way more of a factor. The pressure relief valves were built in to the storage dewar's we would get from LN2 and LHe suppliers, but I don't think the cryostats in our lab had them built in, you needed to add them separately by connecting onto the dewar's main flange. The one my colleague exploded didn't have the extra valve hardware attached, and he just capped it and walked away.

tptacek 12y ago
The "cap" is a long styrofoam tube with a plastic top that comes on and off with no resistance (if you upended the dewar, that cap would slide right out).
mechanical_fish 12y ago
The non-pressurized LN dewars I've seen had a "plug" that was just a cylinder of foam that slid into the neck of the dewar, with a light plastic cap on top. It was lightweight enough to bob upward at the slightest pressure, releasing gas. It probably had a design with channels such that the lip never sealed completely anyway. They could easily preserve LN for days. Dewars are impressive.
- tptacek 12y ago
  Static hold time: 100 days. Evaporation rate: 0.20 liters/ per day. 2.25" Necktube inside diameter. 15" Outside diameter. 25.50" Overall height. Empty weight: 23 lbs. Full weight: 60 lbs. :)
  - mechanical_fish 12y ago
    Wow, I forgot just how many days that was, I see. Though I now remember that one of my labs had a storage dewar full of precious biological samples that was a bigger version of this design, and we only refilled it a couple times a month. $500, eh? Hmmmmmmmmmmmmm.
    - tptacek 12y ago
      I felt bad about the purchase before we actually used it, but now I'm feeling like it made at least as much sense as the circulator did as a purchase. Malort ice cream!

tptacek 12y ago

The "cap" is a long styrofoam tube with a plastic top that comes on and off with no resistance (if you upended the dewar, that cap would slide right out).

mechanical_fish 12y ago

The non-pressurized LN dewars I've seen had a "plug" that was just a cylinder of foam that slid into the neck of the dewar, with a light plastic cap on top. It was lightweight enough to bob upward at the slightest pressure, releasing gas. It probably had a design with channels such that the lip never sealed completely anyway. They could easily preserve LN for days. Dewars are impressive.

tptacek 12y ago
Static hold time: 100 days. Evaporation rate: 0.20 liters/ per day. 2.25" Necktube inside diameter. 15" Outside diameter. 25.50" Overall height. Empty weight: 23 lbs. Full weight: 60 lbs. :)
- mechanical_fish 12y ago
  Wow, I forgot just how many days that was, I see. Though I now remember that one of my labs had a storage dewar full of precious biological samples that was a bigger version of this design, and we only refilled it a couple times a month. $500, eh? Hmmmmmmmmmmmmm.
  - tptacek 12y ago
    I felt bad about the purchase before we actually used it, but now I'm feeling like it made at least as much sense as the circulator did as a purchase. Malort ice cream!