Liquid Nitrogen (LN2) has some great demonstration properties! LN2 is super cold -321F and has an expansion ratio of 1:694. For every liter of LN2 you will get 694 liters nitrogen gas.

Concepts:

Expansion ratio, inert gas, dewars, oxygewn deficiency, pressure, boiling points, atmosphere constituents.

Safety:

Safety glasses MUST be worn at all times by demonstrator and the audience.

Cryogenic gloves.

Open area with good ventilation.

Students to stand back ~50 feet.

Equipment:

• LN2 Dewar with LN2 ~10/20L (Air Gas Linde or local gas supply)

• Large metal pot.

• Propane burner or large coffee maker for hot water.

• Leather gloves.

• Large container for LN2.

• Apron & face shield.

Preparation:

• Heat water to about ~160F.

• Find a location where you can be elevated about 8' above the container on the floor.

• Stage hot water and LN2.

Demonstration Instructions

1. Pour a lot of the LN2 into the container on the floor, ~6L.

2. Get in position above the liquid, hold the hot water and aim for the center of the container on the floor.

3. Have the student's give you a countdown from 3-2-1!

4. Dump the hot water with a little force and get ready for a fast expansion of LN21

5. Start at 2:21min https://www.youtube.com/watch?v=9Nkt2Z3Mo2o

Observations:

As soon as thot water 150F hits the LN2 -350F, the students will see a large white cloud and loud thump. This is a 500F differential in temperature!

Learning Outcomes:

• Helps to demonstrate the expansion ratio of cryogenics.

• What you are seeing in the air is the condensation of water/water vapor. The LN2 is cold that it will condense water vapor in the air and you will see a cloud. You can see the same condensation when you open the Dewar.

• You can talk about atmosphere constituents, Nitrogen ~80%, Oxygen ~20% other small amounts of inert gases.

• Atmospheric Dewar's, not under pressure, always venting.

• LN2 motor carriers venting is called in as a leak many times. Always good to get a LN2 motor carrier to come to the class to demonstrate the "Dog House" (Pump house). Valving can be difficult to understand but all are tagged and have a legend on the door.

• You can also put out a 4-gas near the demo or use it to show the oxygen deficiency. Also touch on the rule of 5K. Remember you are displacing 1 oxygen AND 4 nitrogen. For every 0.1% oxygen drop you can have 5,000 ppm of contaminate in air.

Chemical Disposal:

None. LN2 will evaporate back to the atmosphere

Additional Information:

LN2 is super cold make sure you wear gloves to prevent skin burn.

1. Get some long balloons and blow it up with a pump, you cant blow these up with your lungs! You can survey the students and ask them "What will happen when I put this balloon in the LN2." Most will say it will pop but the balloon will cause the LN2 to boil a bit as the balloon is "HOT" compared to the LN2. The "Air" in the balloon will start to condense, molecules come closer together as the get cold. In general COLD slows reactions and condenses gases/vapors and HOT increases the reactions or vapor pressure. You can touch on the condensation of oxygen (LOX) at -297F. Remember LN2 will condense LOX. When you pull out the balloon you can actually see a liquid in the balloon. using a light colored balloon will allow you to see the liquid better. As soon as you pull it out the liquid will start to boil and expand the balloon

2. Freeze some stuff! Here are some items you can freeze to show how cold LN2 is and how it can cause skin damage.

   • Flowers are the classic demo. Dip the flowers in LN2 for about 10-15 seconds and grab them with a gloved hand and they will shatter like glass and then go soft again.

   • Use a small plastic ball and tongs to put in LN2 and you will see that the air in the ball condenses and creates a vacuum on the ball denting it. Using leather gloves take the ball and throw it at a hard surface and it will implode (Not explode) making a pop sound.

   • Get a large rubber band and make a small v-trough out of foil. Pour some LN2 into the foil v-trough. Use two Chop Sticks and stretch out the rubber band and put into the trough. Hold there for about 10-15 seconds and you can take out and hold it vertically as its frozen but will soon go back to being a normal rubber band.

   • You can freeze hot dogs to simulate tissue and break it in half.

   • Graham Crackers! This is a fun demo but do not try this unless you are taught how to do it correctly. You can freeze your tongue! Soak graham crackers in LN2 for about 15 seconds. Pull them out with tongs and drain ALL the LN2 off the cracker. Having built up some saliva in your mouth you can then put the frozen cracker in you mouth and roll it around. Don't leave it in one spot! When you exhale and you can see your breath as the moisture condenses and creates a cloud effect!

There is another demonstration that is very awesome but can be dangerous. See Steve Spanglers video here https://www.youtube.com/watch?v=p_9jEX1EFC0 The LN2 expans quickly in a 2L bottle and will over pressure it fast! Much faster than dry ice. This can be donsidered an explosive device so check your local regulations.