Liquid Nitrogen

Discussion in 'General Discussion' started by B540glenn, Oct 5, 2006.

  1. B540glenn

    B540glenn Should Be Working Founding Member

    I plan to do a liquid nitrogen (LN2) demonstration for a small group of elementary school children at the end of this month. The demonstration will include (but not limited to) the whistling tea kettle, the spinning ping pong ball, the frozen banana and ice cream. I am currently looking into getting the LN2. I have not done this before and have a couple questions for those who have.

    1) Is food/medical grade LN2 required? I would not want impurities being eaten in the ice cream.

    2) How much do I need?

    3) Other than handling it with care (similar to boiling water that will burn) are there any special precautions I need to take. The demonstration will be outside so I'm not worried about filling the room with pure N2 nor spilling it on the carpet.

    4) Do you have any other demos I cold do?

    Thanks for any suggestions,
  2. Panhead

    Panhead On the Loose Founding Member

    Put a small amount in a swimming pool dude and watch the FOG appear!
    Other than that I dont know.
  3. ghrit

    ghrit Bad company Administrator Founding Member

    1) No. The N2 will disipate, and since is completely gas, there will be no residue.
    2) One small Dewar will be way more than enough. Keep the lid on as much of the time as possible.
    3) Handle with very care.
    4) Break some water soaked handkerchiefs
    Drive a nail with the banana
    Demonstrate simultaneous freezing and boiling by putting a couple ounces in a beaker, watch for frost while the liquid bubbles. (Not strictly accurate, but a pretty good simulation.)
    Blow up a balloon with air, cool it with off gas, then shatter it.
    If you are very, very, quick, you can stick a kid's finger in the liquid and yank it back out without harm. The little bit of moisture on the finger will protect it.
    Shatter a rubber glove.
    Take two ten penny nails, put one in the liquid, bend the other and have a try at the other.


  4. B540glenn

    B540glenn Should Be Working Founding Member

    I asked the vendor what the differences were between the food/medical and industrial grades. She stated that for food/medical the container is tracked to verify that it held nothing else but LN2. The industrial grade containers take no such measures. I'm not worried that there will be left over N2, I'm worried that there will be some other unknown inpurity picked up from the dewar then eaten by the kids.

    Speaking of swimming pools...

    Here's a video of LN2 put into a pool at this year's Penguicon (Linux conference). Though, I was not there to witness it, one of my cow-orkers was. He said it was very entertaining.

    YouTube- Liquid Nitrogen Into A Swimming Pool
  5. ghrit

    ghrit Bad company Administrator Founding Member

    Point taken about tracking for contamination. That said, it wasn't always that way, and thus far, I've not seen a low pressure (atmospheric) Dewar that wasn't easily checked when MT for particulate or surface contamination (open topped back in the good old days, may no longer be so.) Pressurized Dewars are closed much the same as high pressure gas cylinders (tho' nowhere near as high) and are closed. These pressurized units are most often what the medical community uses, frequently seen along the side of the facility. You won't need that much, I don't think, for your purposes. (May also not be available these days, either. Have had no recent experience.)
    It is going to be fun, I betcha, watching the kid's faces --
  6. E.L.

    E.L. Moderator of Lead Moderator Emeritus Founding Member

    Now you are in my area. My pop owned a Cryogenics company and I was raised in the business. A small dewer will be more than enough and the vacuum between the inner and outer shell should keep it liquid for a good while. One cool (no pun intended) trick is to try freezing some ants and watch to see if you can see them thaw out and come back. Another is to pour a little in a plastic and I repeat PLASTIC Coke bottle, then close twist the lid closed, but not tight. After the pressure builds from the head gas that thaws from the liquid it will blow the top of the Coke bottle and make it shoot way up in the air. Do not stick a kid's finger in there. I have been burned several times when liquid nitrogen and liquid oxygen splatter caught me.

    Don't worry about inpurities, liquid N2 (code 1977) is far less inpure than say CO2 which is used in your soft drinks. It is a very clean gas, and there is no food/medical grade no matter what they tell you. I should know, as I picked it up straight from the plant more times than I can count. The only difference is that some is colder than others, yes it does make a difference because when it is colder you can load more in your cryogenic tanker. Not to mention that in my current job I have seen a lot of nitrogen tunnels that are used to quick freeze food.

    Make sure you have thick gloves, usually welding type gloves are what is used, also make sure that the area is outside or really well ventilated as the N2 will actually displace the oxygen in an area with little or no ventiation and it will cause you to suffocate. My dad used to make us home made ice cream with it all the time. He even set up a booth one year at the Chilifest in New Braunsfels and sold it. It was outstanding. Good luck.
  7. monkeyman

    monkeyman Monkey+++ Moderator Emeritus Founding Member

    Takeing a small (hollow) rubber ball and bounceing it a few times then freezing it and dropping it on the floor to shatter, same as a balloon is cool. Shattering a frozen rose is also kind of neat. Something else that might show the temperature in a way more of the kids, especialy early grade schoolers, might understand better would be something as simple as some water in a plastic cup dipped in for a few seconds to turn to ice. I dont remember just how fast it dose freeze it but I know it would be quick enouph to show the kids its a LOT colder than outside in the winter or their freezer at home and that it IS cold and not just that it is some kind of 'chemical thing' that makes the stuff change but actualy the temp.
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