Dewar Advice Needed

jhiggins

jhiggins

Joined
Jul 11, 2003
Messages
3,258
I'm looking into getting mysefl a dewar to hold some liquid nitrogen. Could any of you fine folks that have one tell me what is a good size to look for? How do you use it? Do you just submerge a blade into the dewar? How long does it last? I have some familiarity with a liquid oxygen and liquid nitrogen from my years in the USAF. I know that these gases in liquid form are actually at their boiling point, constantly evaporating into the atmosphere. Does the dewar actually prevent this, or does it simply just slow it down?

Any advice woudl be most appreciated. Looking on ebay at the dewars there is confusing at best.
 
I bought a 20L Dewar new in the box from "scientific salvage" at my old company, Jeff. It is designed for semen storage, so comes with 2 little dip cups that I'll use to lower the blades into the LN. It cost me $300, and was $745 new. It has a leak rate of 95mL/day. So, a liter every ten days. Really not so bad considering how fast LN boils off in an open-top benchtop lab Dewar.

Caffrey built an insulated box for his Dewar, gets a several month life out of a fill. LN is about a buck a liter locally, so that won't be too bad.

The pro companies that do cryo have fancy computer progs that ramp the gas-phase stuff into the chamber, then ramp it back up slowly to room temp. I think for home use, we'll have to stuff it in vermiculite or between two rather thick pieces of polystyrene foam after removing from the LN.

Personally, for the slow pace I make knives, I would have liked to find a 3-5L tall Dewar and just run it over the mile to the welding shop and get it filled more frequently. The key is not to get too large a storage vessel or it'll take too much fill to get a deep enough layer of liquid to submerge the blade vertically.
 
Jeff, Gary Riner (of Fibermascus) has three for sale at the moment, which are currently in my possession. Give him a call (www.fibermascus.com) and see what he wants for them....he told me, but I can't remember...I took them down to Batson's to try to sell for him, but I think it was probably the wrong crowd... Anyway, I'd look into his first before bidding on ebay, probably a better deal...

:)

-Darren
 
fitzo said:
I bought a 20L Dewar new in the box from "scientific salvage" at my old company, Jeff. It is designed for semen storage, so comes with 2 little dip cups that I'll use to lower the blades into the LN.
Click to expand...

With my luck, the one I bought would be full of goo. :eek:


rlinger said:
I'm getting ripped off. It cost me 70 buck to fill my 20L dewar.
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Its different everywhere, Roger. Some places buy from other places and resell it. I did some research and found some sources that were willing to sell to a small-timer like me, but its all the way across the state. Not very economical unless I do a bunch of stainless-series blades at once. One company would also love to lease me a dewar, with delivery to my door. I'll investigate further and let you guys know about this later as maybe being a viable option.
 
I think LN prices are like proane. Depends on the volume sold by the supplier. The Airgas place here in town is an area hub, and my old employer uses a bundle of LN so it's a bit cheaper. Propane, however, is high priced here: $65-70 for a 100 pound tank fill.

BTW, that is the dewar I have, and the people I bought it from. They are 3rd-party selling them on ebay for Abbott Labs salvage. Abbott had something like 300 of 'em, bought for a now-defunct project that they never got used on. They live about 9 miles from me. Good people to deal with.
 
I get mine from Airgas too. They are the only show in town and all around town. In fact, I am lucky I have any source near enough by. I do like my dewar. It seems to last up to about 5 1/2 months to a low of about 4 months, depending on amounts of steel being frozen.

RL
 
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