Liquid nitrogen doesn't last.

[Storm W]

I purchased a 15 Liter LN dewar off of Ebay. On the details it said that it should hold for over 5 months. I have filled it twice now and both times it has lasted maybe 6 weeks and treated last than 10 blades. Is there something that I am doing wrong?

 

[Larrin]

Mine is 10 liters and lasted about 2.5 months. I don't do anything special other than keeping the cap on.

 

[jdm61]

Whats wrong? You keep opening the darn thing! Sounds like you have done that at least 40 times now?

 

[Willie71]

I have a 20l that lasts 5 months. Smaller ones don’t last as long. As the level goes down, the evaporation gets faster.

 

[Jrmysell]

And that time is for once it's filled, you don't ever open it again. The more you open it and the more blades you do the more will evaporate off. Sticking a room temp blade in -300F ish temp LN will boil quite a bit off.

 

[Mo2]

https://www.quora.com/How-long-can-...-portable-liquid-nitrogen-container-75-liters

Some good info.

Do you have it in a hot shop? I used ln2 a few times for overclocking cpus in a pc computer some years back. Went through it fast so never needed to save it.

 

[Nathan the Machinist]

I purchased a 15 Liter LN dewar off of Ebay. On the details it said that it should hold for over 5 months. I have filled it twice now and both times it has lasted maybe 6 weeks and treated last than 10 blades. Is there something that I am doing wrong?

Ten blades shouldn't put much dent in that. Assuming it's closed and not in a windy environment it should probably be holding better than that.

 

[Beanman13]

Which brand did you buy? I’m looking for one as well.

 

[Collin Johnson]

If where you live has a large fluctuation of pressure it would cause the ln to evaporate faster

 

[JTknives]

Oh a topic I can really sink my teeth into. I have posted about LN dewars in the past quite a bit. I am quite passionate about them and feel you get what you pay for. But I allways seam to be met with some resistance when I bring up that part.

First up 10 Knives like Stacy said is nothing for a 15L dewar. Also if you do the math 15L over 5 months is 15L/150D=.1L/D evaporation rate. That is not impractical if it’s true. But that kind of evaporation rate is what you see in higher end dewars. Just remember a manufacture can put what ever numbers thy want on the spec sheet. With all this being said I can tell you if your mouth is larger then 2.1” you will never get the .1L/D rate.

My dewar is 20L and it lasts for a really long time. Just to give you an idea what to expect with a good high quality dewar my last fill did 112 blades. I got it used as I could not afford the 2-3k price tag new. But I still paid like $800 I think for it. It’s opening is 2-1/8” and has an evaporation rate of .09L/D.

Now with your dewar there is somthing wrong. There could be a few reasions for your results. A: you bought a cheep one and thy greatly exaggerated thy evaporate. B: You bought a used one and it lost its vacuum and is no longer insulated. C: Has a really large mouth or missing the green foam plug.

We need more info to beable to help you. Just alittle tip, stay away from white brand dewars. Last one I had would not hold nitrogen for hardly any time.

 

[Stacy E. Apelt - Bladesmith]

It was nathan, not me who commented about 10 blades, but Iagree.

JT's reason B is my guess. A dewer with no vacuum is nothing but a metal bottle. It will loose the LN fast. They loose vacuum for a variety of reasons, but damage and age are the most common. When I see a $1000 dewar for sale at $100 I suspect it isn't keeping its insulation anymore.

 

[Storm W]

JTknives this is what I ordered. I bought the 15l one. Its supposed hold 16l. I have had it filled twice and while I don't know exactly how long it lasted it was a lot shorter than expected. If I recall the opening is 1.9 on paper but I think it's a bit less than that.

https://www.ebay.com/itm/3L-6L-10L-...-Container-Tank-Cryogenic-Dewar-/132752479077

 

[Mo2]

JTknives this is what I ordered. I bought the 15l one. Its supposed hold 16l. I have had it filled twice and while I don't know exactly how long it lasted it was a lot shorter than expected. If I recall the opening is 1.9 on paper but I think it's a bit less than that.

https://www.ebay.com/itm/3L-6L-10L-...-Container-Tank-Cryogenic-Dewar-/132752479077

That seller has terrible feedback. Looks like you may have bought something it's not probably.

 

[Storm W]

I'm not sure if it was that exact seller. At the time there were a few selling the same thing. Someone had a 10l and liked it so I grabbed a larger one. If there isn't anything I can do I guess I'll live with it. Its just a pain when you head out to heat treat and turn on the oven then give the can a shake I find it its empty.

 

[JTknives]

I browsed his discription and found one troubling item.

You should not be expected to vent pressure from it spilling or leaking into the vacuum area. Also that blue insulation covering is troubling as that should not be needed if it’s proper dewar with a vacuum barrier. If you pull the rubber cover off the bung you should see a steel plug that might have a threaded hole in the center. It should also be covered in petroleum jelly. I will take a picture of mine when I get home. I’m guessing your dewar is not vacuum insulated and you can tell by feeling the outside of the dewar. If it’s cold then it’s not insulated properly.

 

[JTknives]

Here is a few pictures of my bung.

 

[BluntCut MetalWorks]

I filled my BioCane 20L and YDS 30L dewars on 3/28 - after few hundreds dip & soak - both ~1/3 remain. Infrared ambient surface reading: 19.7c plywood, 19.3c biocane, 19.3c yds.