Dewar Selection

[Jonathans]

I found this dewar available. It is 5 liter, and has a 6" wide mouth id.
Will this type of dewar hold LN for a month?

 

[slamosam]

I don't think so. It's a LN2 flask not a dewar.

 

[12345678910]

No

That's more like a portable carry something from one lab to another


The large ones have larger capacity, more insulation and small opening = less evaporation surface area

We need large holes, but that's a trade off vs evaporation.


For holding LN for a month, the dewar be so large, it looks like it's too large / heavy for one person to move.

 

[jdm61]

I think that the 10 liter ones will hold LN for a month. The 34-35 liter ones will hold it for longer from the specs that I have seen. The wide mouthed ones obviously won't last as long. From what I saw, most of the "regular" 50mm/2 inch mouth dewars will work for anything other than say kitchen knives or big bowies. In my case, I would want them for long kitchen knives so I would have to get a big mouth dewar that is tall inside. Make sure that you check the true INSIDE height. It can be significantly shorter IIRC, but go by the actual demeans of the chamber, not the dimensions of the "bull spooge carrier" rack. LOL. That internal dimensions issue knocked out most dewars smaller than say 10 liters if you are doing kitchen knives even with a big mouth.

 

[Jonathans]

Thanks. I didn't realize that the flask wasn't meant for storage. Too bad. I was pretty excited about the width of the mouth.
The 2" mouths won't work for a lot of my projects. Bigger ones seem to be pretty spendy. I have a cooler type now that works for a dry ice/alcohol mix but I am hoping to step up to LN

 

[jdm61]

The need for LN depends on the steel that you are using. And yes, the big ones are pretty spendy and the ones that you see on Ebay that are "cheap" sometimes look pretty ratty, like to the point of needing a whole new cap assembly and such.
Now this is second hand info here, so take it for what it is worth, but I have been told that the dewar does not have to be even close to being full for it to work for our purposes. I have had one guy tell me that not only is immersing the blade in the liquid nitrogen unecessary, but it may be undesirable. I was told that if your dewar is in proper working order, the "air" space above the surface of the liquid gets WAY more than cold enough for our purposes.

Thanks. I didn't realize that the flask wasn't meant for storage. Too bad. I was pretty excited about the width of the mouth.
The 2" mouths won't work for a lot of my projects. Bigger ones seem to be pretty spendy. I have a cooler type now that works for a dry ice/alcohol mix but I am hoping to step up to LN

 

[Jonathans]

Thanks for the advise guys. I ended up picking up a 35L dewar that is in good shape and complete. Mouth opening is 4.7 inches and overall height is 25", so I should be fine. Company specs say it has static holding of 130 days, but I doubt I'll ever see that! I'd be very happy with 3 months.

 

[jdm61]

From what the industrial gas guys near my shop told me, once you get the dewar, the LN is not really expensive.

Thanks for the advise guys. I ended up picking up a 35L dewar that is in good shape and complete. Mouth opening is 4.7 inches and overall height is 25", so I should be fine. Company specs say it has static holding of 130 days, but I doubt I'll ever see that! I'd be very happy with 3 months.

 

[Bob Ohlemann]

Once you get past the obstacle of finding and buying a dewar, getting it filled and transporting becomes the next PIA. It is a 40 minute trip (one way) to the nearest gas supplier that will fill my dewar. I had to make a special rack to hold the dewar in the back of my truck so it would stay upright and stationary on the trip. Mine only has a 30 day capability which is a undisturbed storage capability. Knifemaker use is more like 10 days.

Bob

 

[butcher_block]

i get alittle over 45 days and 2 big HTs out of my big mouth "3.75") 20l the 10l i had before was great till i really got into making the wider kitchen stuff. for most of the guys here making stuff less then 2 icnh tall that 10l is great has good hold time and does not cost too much to fill (left overs can be ised to make ice cream also )

 

[Alpha Knife Supply]

Once you get past the obstacle of finding and buying a dewar, getting it filled and transporting becomes the next PIA. It is a 40 minute trip (one way) to the nearest gas supplier that will fill my dewar. I had to make a special rack to hold the dewar in the back of my truck so it would stay upright and stationary on the trip. Mine only has a 30 day capability which is a undisturbed storage capability. Knifemaker use is more like 10 days.

One solution is get a bigger dewar. You've already solved the problem of transporting the dewar. The number of miles you must drive is the same. Increasing capacity would reduce the number of trips made.

Chuck

 

[Andy Lewis]

Bob, I don't know where you have been going, but suggest you call up Wayne Ratliff at the Airgas Branch in Gainesville (940.612.0245). They are less than 20 miles from Sanger proper and will get you hooked up.

We maintain a half dozen dewars and have had stellar LN2 service and good pricing from the Airgas folks in Longview for many years.

Also as Chuck said, look into selling your tank and upgrading to a larger capacity model as even our ancient tank from the '60s holds better than 30 days in real-world use. I picked up an older, all stainless, 35L dewar with a 3" bung for $150 a few months ago for a a buddy of mine. New tanks are a poor value for knifemakers in my opinion. The user deals are out there if you're patient and persistent.

 

[Jonathans]

One of the dewars I was watching on the auction site has been relisted at a great price. No lid though, but they can be made or purchased separately.
Search for: Taylor Wharton UNION CARBIDE 35 VHC TANK for Cryogenic Storage with wheels