Liquid Nitrogen Dewar question

[killthelights]

I just bought a used dewar but it's missing the plug that seals the hole at the top. Can I make something that will work(rubber, styrofoam, ect) or is it a specialized piece that I need to get from the manufacturer? Thanks!

 

[Stacy E. Apelt - Bladesmith]

Post a photo, but they are usually just a Styrofoam plug that has slits along the side to allow some gas to escape. You can buy them on ebay ansd elsewhere.

 

[HSC ///]

Previously I had a dewar with no cap as well

I used the leftover styrofoam I had glued together and made a conical plug wedge

 

[CallumRD1]

The one important consideration is to not seal the dewar completely, a very rough strofoam plug like shown above is absolutely sufficient and will avoid any unfortunate explosive events. The cold nitrogen gas is heaver than air so all you're really doing with the plug is keeping air currents from mixing warm atmospheric air with the cold nitrogen and providing some insulation against heat intrusion via conduction. The channels allowing newly formed gas to escape won't allow appreciable heat transfer into the dewar.

 

[fitzo]

While they certainly allow the gas to escape, the cutouts in the plug are meant to fit around the handles and space straw holders for semen storage.

 

[CallumRD1]

While they certainly allow the gas to escape, the cutouts in the plug are meant to fit around the handles and space straw holders for semen storage.

In dewars targeted at medal uses, yes you’re right. The ones we use in our physics research laboratories don’t have any internal features so the lids just have channels for gas to escape.

 

[fitzo]

let’s see if this will paste:

https://www.amazon.com/U-S-SOLID-Cryogenic-Container-Nitrogen-Canisters/dp/B00URDEJ3E

the straw holders aren’t an internal feature per se. depending on the size in our chem labs over the years, some came with the straw cups, some not. my 30L dewar for HT here at home came with one holder. small bull, i guess.

 

[killthelights]

While they certainly allow the gas to escape, the cutouts in the plug are meant to fit around the handles and space straw holders for semen storage.

No worries there as I won't be storing any of that!

 

[killthelights]

The one important consideration is to not seal the dewar completely, a very rough strofoam plug like shown above is absolutely sufficient and will avoid any unfortunate explosive events. The cold nitrogen gas is heaver than air so all you're really doing with the plug is keeping air currents from mixing warm atmospheric air with the cold nitrogen and providing some insulation against heat intrusion via conduction. The channels allowing newly formed gas to escape won't allow appreciable heat transfer into the dewar.

I can do rough. It's kinda my specialty. Thanks!

 

[killthelights]

Previously I had a dewar with no cap as well

I used the leftover styrofoam I had glued together and made a conical plug wedge

Exactly what I was thinking. Thanks!

 

[killthelights]

Post a photo, but they are usually just a Styrofoam plug that has slits along the side to allow some gas to escape. You can buy them on ebay ansd elsewhere.

Thanks Stacy! I'll check ebay if I can't find any leftover materials in the shop to make one