Any serious research laboratory requires a good supply of Liquid Nitrogen. From superconductivity experiments to preservation of organic matter, through Nitrogen gas production and pressurization purposes, this is by far the most widely used and most convenient Cryogen* of them all. Hence, for its alternative fuel and liquid oxygen experiments, POWERLABS acquired (for $400!) a brand new 1500mL Dewar Flask: A Cryocan TA-1.5 from HCI Cryogenics. The flask is at the top of their low capacity line, made from aluminum and steel, with an ultra high vacuum seal in between the walls and a low density foam stopper, and has a static holding time of 10 days. Having completed its alternative fuel research, POWERLABS started to investigate some “Alternative” uses for this most interesting product. Although most of it was not recorded, some pictures were taken for your entertainment purposes. Enjoy!
*Cryogens are liquefied gases having a boiling point lower than -150 degrees centigrade.
1: Leidenfrost Effect: Hovering experiments.
As soon as Liquid Nitrogen comes into contact with any surface it starts to boil and vaporize rapidly. This brings about an interesting effect called “Leidenfrost Effect”. The Leidenfrost effect occurs when a liquid comes into contact with a surface that is at a temperature much greater than its boiling point, and it causes the liquid to vaporize at such a rate that it forms a layer of insulating vapor between it and the surface. This means that a cryogenic liquid (or any light porous material soaked with it) will lift itself up from the floor and start to hover. It also allows me to dip my hand in a beaker full of Liquid Nitrogen and pull it out quickly and unharmed, as see on the picture.
Since for liquid nitrogen ANY surface will be at a temperature significantly above its boiling point, the mere act of spilling some on a smooth surface floor will cause it to move about with virtually zero friction. As it does so it moves and changes shape like an amoeba, and smokes slightly. A more interesting effect comes when it is poured on the floor: A large puddle shoots across the surface and travels very rapidly until it hits something and becomes spread apart. You can also cause it to hover on your hand, or even on water (though it doesn’t last long).
Here is a short (909KB) .mpg video showing a beaker being filled with LN2 from the flask and than poured on a 6 X 12cm piece of tissue paper (the kind you use to blow your nose) which, soaked with the cryogen, glides effortlessly over a plastic surface when pushed around. This is an interesting demonstration of the Leidenfrost effect.
2: Supersaturated vapors: Making Smoke.
When Liquid Nitrogen comes into contact with a surface that does not allow Leidenfrost to occur (such as a rough or irregular surface), it vaporizes *VERY*, VERY rapidly. Spilling it on the carpet causes a ring of smoke to appear and travel outwards (real neat simulation of a blast wave) rapidly. The reason why liquid nitrogen (or any really cold object really) smokes is because air under normal conditions always contains a small amount of water vapor dissolved in it. The actual amount of H2O dissolved depends on the temperature the air is at: Hotter air can hold more steam than colder air. When the air is cooled to -196C, all of the steam dissolved in it condenses out as water droplets, and they scatter light, making the white smoke that is so characteristic of cryogenic experiments. Interestingly enough a very similar process gives rise to the formation of clouds.
Mixing LN2 with water (or some other volatile liquid) causes even more smoke to appear, as the air surrounding that liquid has more vapor to start off with. With about 250millilitres of Liquid Nitrogen a small room can be filled with non toxic smoke.
Notice how the smoke on this second picture looks much denser than the previous one. This is because the water in which the Liquid Nitrogen was dropped had some ammonia solution in it. Being more volatile than water, the ammonia makes for a denser smoke. Using other volatile liquids, such as ethanol, even denser smokes can be created (it does pose a bit of a safety hazard though, so pure LN2 and water are always preferred.
Erm… What can I say… I guess I got a bit overexcited here 😉 The Mad scientist face is pretty characteristic of when I am doing something either silly or dangerous… This one was just silly:)
The picture was taken at the 1998 European Union Contest for Young Scientists. I was representing the European School League with my cryogenic propulsion research, and as such had access to 1.5litres of liquid nitrogen every day. In the end of each session I would get together with a large crowd of like-minded contestants and we would use up the remaining LN2 in some stupid or dangerous manner (read below). In this photo I was trying to fill the stand with smoke for a photo.
Here is a (3.18MB) .mpg video of liquid nitrogen being poured into a Erlenmeyer flask and than the super cooled water vapor being used to freeze a CD.
A 5 liter water bottle was filled halfway with water and some 100 milliliters of Liquid Nitrogen were put into it. The cap was than screwed on tightly and the bottle was left standing up. The bottle inflated into a circular shape, made some snapping sounds, and, when it seemed as though it would explode, ejected its cap at extremely high speed with a sound that seemed like artillery fire from a distance.
The same trick was repeated, but with the bottle upside down this time. It than made a loud “WOOOSH” sound and proceeded to travel over 100 meters upwards, propelled by the high speed ejection of the water and gas inside it. It landed unharmed.
A third and final experiment was tried, with Teflon thread sealant on the mouth of the bottle (with the intent of making it hold more pressure). I am sure most of the readers will be familiar with the classic “Dry Ice bombs”, so I will simply say that this is analogous to those, with the exception that Liquid Nitrogen vaporizes at -196C, as opposed to the -80C of dry ice, and that it releases 960Joules per kilogram, more than twice as much as CO2. This time the bottle inflated more than ever before, and than exploded with a such a loud sound that it could be heard echoing miles away. It produced a huge cloud of steam. The experiments were than ended and all participants and crowd left before someone came to check what that sound was.
These experiments served as inspiration for the JETCAR.
5: The useless: Freezing the toilets:)
Have you ever wondered what would happen if you were to put Liquid Nitrogen in the urinal? What about the sink? Maybe the toilet…? Well, you need worry no more! POWERLABS presents you free of charge the pictures of such things… The purpose… Ummm… I had to get rid of the LN2 before my flight back from Porto (LN2 is not allowed in planes) and we were out of ideas…
Here you can see a smoking urinal… The sink looked about the same… The toilet was the coolest one, but I lent the picture to a friend and he lost it 🙁 Well, here goes a description of what happened:
I poured half a liter of liquid Nitrogen into a normal toilet, and watched as a HUGE dense cloud of smoke shot up and clouded everything on sight. Not satisfied with the display, I attempted to flush the toilet, at which point a blast of smoke and water shot up all the way to the ceiling and quickly filled everything on sight. I had to leave the toilet because visibility had dropped to zero… Minutes later when I returned I found that the water in the toilet had been frozen solid, and it would be almost a day before it all thawed out!
WARNING: Liquid Nitrogen should only be handled by those experienced with cryogens. Painful burns, asphyxiation, and explosions can result from the mishandling of it. Large amounts should never be stored or handled in small, unventilated rooms, and the liquid should never be allowed to contact skin. Sealed containers holding Liquid Nitrogen can rupture with explosive force and cause great injury.
For even more interesting Liquid Nitrogen and Cryogenic demonstrations, please check the Cryogenic Experiments Page!