How much Liquid Nitrogen do I need?

S

Scaniaman

Joined
Jun 15, 2012
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I recently got a 20 L dewar, 80 mm neck with 0.13 L daily evaporation rate.
The plan is to pick up a bit of LN2 friday mornig, and heat treat on saturday evening. I am just doing 7 blades. A few kitchen and a few small hunters and edcs. After the heat treat I am just leaving the rest of the LN2 to evaporate. I'll do the same the next time I heat treat, maybe in a few months time. I just want enough LN2 to last one HT, not too much excess/waste.

How much should I expect to need to keep things cool enough? I can see a little will boil off when the blades are inserted. I am thinking of putting the blades in the freezer first..

I can afford a few liters extra, just interested to hear your ideas/experiences.

4-5 liters? That would give me about 7-8 cm of LN2 in the dewar.
 
Curious is it expensive where you live? I have a 34L dewar, I have ran low where only about 3 inches of the knife is actually submerged and was told that this was ok. I usually just fill mine up about 4-5 a year.
 
Yep, he's mentioned before how expensive LN is for him to purchase, I don't remember how much, but was expensive. Refresh our memory please on the cost.

I would think 3 liters should be more than enough to HT all you wish. I'd be interested in hearing from other folks. With only a couple of liters in my 10 liter dewar the vapor area is still cold - a -300°F or so if I remember correctly.

Get 5 liters to be sure and make ice cream with the LN left over.
 
Ken H> said:
and make ice cream with the LN left over.
Click to expand...

This is probably the best advice to date here :thumbsup:

As for my cost, a litre LN2 is a little more than 12 USD currently I think. A litre here and there won't break the bank like I said. But really curious to hear from you guys on this subject.
 
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