How to transport 1-2 liters of nitrogen easily (must last 8 hrs)
August 15, 2006 4:54 PM   Subscribe

What's the best/cheapest/easiest way to transport 1-2 liters of liquid nitrogen from San Francisco to Burning Man?

I've made liquid nitrogen ice cream once before and my friend just brought it to me in a thermos. But he thinks it will evaporate en route if I try taking a thermos of it from SF to BRC. The thermos can't be sealed airtight (or so I'm told.) Is he wrong about how long it will last? Is there nothing I can do other than keep it packed in ice? It will probably take an hour for me to pick it up and then another 5 1/2 hrs to get there, so assuming I make it a couple of hours after we arrive, it would have to last about 8 hours altogether.
posted by jcruelty to Sports, Hobbies, & Recreation (15 answers total) 1 user marked this as a favorite
You don't want to transport liquid nitrogen in an airtight container. Pressure in the container will build up as the nitrogen evaporates.

The thermos might work; especially if it's big (1-2 L is pretty big). You could get a nice 3 L lab-grade dewar flask, but they're pretty expensive. Why not try a dry run with your thermos first? Just see how long it lasts sitting around.

Ice won't make much of a difference.
posted by mr_roboto at 5:01 PM on August 15, 2006

Put the thermos inside a styrene cooler (dry ice would probably help a little bit - and it's so cheap you might as well), and I would expect there to still be a good 50% left in the flask after those 8 hours, but this is based on storing a small flask in a freezer. The slopping around caused by the vehicle's motion is probably going to aid evaporation somewhat.

Is there a similar trick you could use any left-over dry ice for?
posted by -harlequin- at 5:22 PM on August 15, 2006

The neatest thing to do with dry ice is to carbonate rootbeer, but it takes a while. You can buy concentrated rootbeer flavor, mix it with sugar and water to dissolve, and then plop a big chunk of dry ice into it. In a couple of hours it'll be carbonated, and in the mean time it makes a nice fog overflowing the open-topped crock you've put it in.

My mom used to do this for Halloween parties, but I think it could be done anywhere for anything.
posted by Steven C. Den Beste at 5:26 PM on August 15, 2006

If you can get a thermos bottle which has a pour-top spout on top, you could leave that part open to vent the nitrogen as it boils away.

But the others here are right: if you put it in any kind of sealed container, including a thermos bottle with the top screwed on, you'll get a loud noise and a big mess long before you reach your destination.
posted by Steven C. Den Beste at 5:29 PM on August 15, 2006

(In case it's not already widely known, the standard low-tech storage method as far as I'm aware is to use a thermos flask, and plug the mouth of the thermos with a large wad of cotton wool - it's very insulating, but porous enough to not allow pressure to build up)
posted by -harlequin- at 5:36 PM on August 15, 2006

Ice wouldn't do much of anything, particularly through the walls of a dewar or thermos. [Even dry ice is way warmer than LN2.] With a large enough dewar, you could probably have enough LN2 left for some ice-cream making after 8 hours. Do realize that if you want to end up with 1-2 liters, you'll probably want to start out with more. LN2 is constantly evaporating [which is what causes the pressure to build up. It's the same way that dry ice bombs work. Several liters of LN2 could be pretty damn dangerous, that way...] You can put something light like a plastic cup over the mouth of the dewar or thermos - that'll be light enough to prevent the pressure from building up, but it'll provide a bit of a barrier between the dewar and the outside world. You'll probably also want to have the dewar cushioned well [and not full to the brim], since LN2 spilling at every bump would a waste.

If you're near a university, you might want to nose around and see if you can find any used dewars. It's definitely worth your while to see how long the LN2 lasts while sitting around your house in its dewar or thermos. [If it can't survive a night in a temperate indoor environment, odds are you're out of luck, since the conditions on the road will probably be worse.]
posted by ubersturm at 5:51 PM on August 15, 2006

Don't use cotton in the mouth of the dewar. Enough ice could collect in the fibers to form a solid plug. It could be very dangerous.
posted by joegester at 6:19 PM on August 15, 2006

You can always bring multiple thermoses/dewars so that you will have enough left at the end of your trip. The problem is that you really can die of asphyxiation in a car full of evaporating LN2.
posted by SteveTheRed at 7:30 PM on August 15, 2006

The best way would be to acquire a lab grade dewar, and over a week, it would only be half gone. It may be able for you to rent one. If you fashion a plug for a homemade dewar, don't use cotton, or foam that can absorb water, or really anything that can freeze. Dense, nonabsorptive foam for plugs, or loose styrofoam tops. Leave your windows down, so you're not this guy. The cheapest way is just a bunch of styrofoam coolers. They do crack in the cold, but are still useful if you're careful. Were it me, I'd borrow an unused dewar from the lab I work in, probably a 10L one, and just strap it so it can't fall over. Oh, and wear boots or don't wear shoes at all if you think you might spill it on your feet, since it soaks into socks and burns your skin through the prolonged contact.
posted by apathy0o0 at 10:20 PM on August 15, 2006

If your goal is to have ice cream on the playa, try taking a cooler full of dry ice packed with ice cream and other frozen goodies. It's far easier to manage than liquid nitrogen. My dry ice cooler lasted about half the week last year. If you want frozen goodies all week, you can take two dry ice coolers and only open the second one during the second half of the week.
posted by rhiannon at 11:58 PM on August 15, 2006

How long the LN2 stays liquid in a dewar depends largely on how efficient the dewar is. "Thermos" bottles vary widely in efficiency; my feeling is that the mirrored-glass ones are generally better, but some stainless ones have seemed pretty good. Most of the stainless ones I've had have degraded with age; they lose the vacuum.

I have transported LN2 in a pour-through Thermos with a loosened stopper, but it made me very nervous. If enough of an ice plug had formed in the pour-through passage, I might have had an Unfortunate Event. I think the cotton wool idea is good, actually - unless the cotton forms an ice plug and freezes solid to the mouth of the bottle, any overpressure would just pop the cotton out. I doubt that the cotton would adhere that well to the bottle.
posted by Kirth Gerson at 7:57 AM on August 16, 2006

To arrive with 1-2 liters, you'll need a thermos that's unusually large. The ones I've seen in shops never exceeded 1 liter. If you can, use one large bottle instead of several small ones. It's more efficient, since the exposed area per liter decreases with increasing volume. If you have a source for liquid nitrogen, it's quite possible that you can get a small dewar at the same place.

With a good enough thermos/dewar (such that radiation through the vacuum shield dominates the heating), surrounding the bottle with dry ice makes a big difference. Whether commercial thermoses are actually this good, I don't know, but neglecting other heat sources the dry ice would slow your boiloff by a factor of five.

Again, make sure that the car is well ventilated. The volume of the volume is about 1000 times that of the evaporated liquid.
posted by springload at 4:02 PM on August 16, 2006

You can get Thermoses that hold 5 gallons. Look for the barrel shaped ones that have a screw on top and a spigot on the bottom. Just get one of those and fill it up. Screw on the top loosely and you'll handle pressure build-ups.
posted by Mr. Gunn at 5:18 PM on August 16, 2006

Thanks for the advice all!
posted by jcruelty at 1:25 AM on August 17, 2006

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