PowerLabs Unwise Liquid Nitrogen Experiments!

Having calculated (from density vs. temperature data) that on going from its boiling point of -196C to room temperature (25C) Liquid Nitrogen expands 645 times, it becomes easy to see why this liquid is used universally as a pressurant in very high pressure systems (for pumping crude oil from deep wells in the ground, for example). LN2 has always been a fascinating topic of study for me, since it was my main research topic for two years (1996 – ’98) and the results of my studies on it as an alternative fuel earned me numerous science awards in International science fairs. Having a regular Liquid Nitrogen supplier that delivers the liquid on my doorstep the same day I order it for a mere $4,5 per refill (2litres), I am very often found experimenting with it. From mater7ials science to superconductivity, Liquid Nitrogen plays a vital role in many of POWERLABS experiments. This page is about the pressurant aspect of Liquid Nitrogen, and how it can be used experimentally in rather entertaining ways. But first, the usual applicable warnings:
Liquid Nitrogen can cause severe frost burns! Sealed Containers filled with Liquid Nitrogen may rupture with great destructive force! Liquid Nitrogen may cause suffocation by displacing oxygen-laden air.

 This is yet another variant of the classic “cork in a bottle” experiment, in which a bottle is sealed and some form of gas generation is placed inside it. The gas pressure builds up and eventually the cork pops off. I learned about this experiment on my own, through experimentation with a chemistry set when I was 7. The original experiment used sodium bicarbonate and vinegar (Acetic Acid) to produce CO2 propellant pressure, but since CO2 dissolves back in the liquid that generates it, maximum resultant pressures are rather low (few tens of PSI). With Liquid Nitrogen it becomes possible to reach a ceiling of over 30000PSI (theoretical), which means that the potential for propulsion is spectacular. In a moment of deep inspiration it occurred to me that a Baseball Bat would have sufficiently thick walls to withstand very high pressures (since the walls cannot dent when striking a ball), if only this pressure could be harvested somehow. The solution came together with the idea, since 2 weeks before my friend Gabriel brought me an aluminium baseball bat which he was getting rid off, and I had the idea of removing the rubber covering in the end to modify it. Inside the bat there was a large amount of low density foam which I had to freeze with LN2 in order to powder and remove. I remember having the idea than of putting the rubber covering back on while it was full of LN2, but the cover had to be destroyed in order for access to be gained to the insides.
Enter Chemlabs: Some of my larger Erlenmeyer flasks have necks which just happen to be about the same diameter as the hole in the bat. Having noticed this, Gabriel and I started filling the bat with LN2 and corking it, to fire the cork off. His girlfriend got the experiment on video, and it can be seen here (.mpg, 1,60mB).

The process is very simple: First, a small amount of Liquid Nitrogen is poured inside the hollow aluminum bat. Than the cork is placed on top of it and hit hard so that it makes a tight seal. Depending on how cold the bat is, how much Liquid Nitrogen was used, and how tight the cork was placed, it can take anywhere from a few seconds to several seconds for it to pop off. In the beginning we were hitting the cork down by hand, which made it shoot out with considerable force. However, after that became boring, we started to hammer it down as far as it went, and in the end we were hammering a tape-reinforced cork with as much as 100mL of liquid nitrogen inside the bat (only a part of the liquid is used to make pressure; the rest comes out during the shot in a smoke trail). The report became as loud as a small caliber handgun, and recoil was quite noticeable! Our best shots imparted onto the cork the same destructive force as a hammer blow, which made this device quite a thrill to play with… Here is a video of one of the most powerful shots, in which the cork completely obliterates a CD case. (.mpg 158kB). Below are two frames from the videos where I can be seen firing the bat while wearing a black leather trench coat and sunglasses. Gabriel is the one in white. Clicking on the pictures will download the 2,34mb .mpg version of the video that shows the bat being loaded, corked, and fired.

PRESSURE BOMBS:

 Well, not really a “bomb” in the sense that it is meant to cause damage, but still, after my incident during a Liquid Nitrogen Demonstration to my class in which I corked a LN2 filled bottle expecting the cork to pop off and the bottle exploded, I couldn’t help wondering just how much force a strong bottle wouldn’t have on bursting if it was filled with a Liquid Nitrogen charge. The bottle below is a 2 litre cola bottle. It has a bursting point of around 300PSI, though some bottles can go higher. Since Liquid Nitrogen expands 880times its original volume, and the bottle bursts at 22ATM, we would need in theory ((880atm available/22atm required)x2litres)= 80mL of Liquid Nitrogen in order to burst the bottle. That calculation assumes the bottle gets up to 25C, but since that kind of heating would take too long I decided to add 100mL and have it burst while frozen. In order to take this video the bottle was filled with the correct amount of Liquid Nitrogen and the bottom was allowed to cool until the liquid was vaporizing at an acceptably low ratio. The bottle was than squeezed, capped, and thrown. An explosion took place 2 minutes later, and can be seen on video by clicking the frames below. This experiment is outlined here for information purposes only, because the concussion from such an explosion is very high and can thus be very dangerous.

 More to come!