*BLOWING UP A GARBAGE CAN USING A SODA BOTTLE AND LIQUID
NITROGEN.***
Suggestion: In the spirit of improved communication, it
might be better to market this as /launching/ a garbage
can. AFAICT the objective is not to blow up the can.
Also AFAICT blowing up the soda bottle is incidental; it
is just part of the nitrogen-powered launch system.
This is better in terms of marketing, because blowing stuff
sounds destructive, whereas launching stuff is in another
category.
Also, if you /think/ about it as a launch, there are a lot
of things you can do to optimize the launch performance,
things that are rather different from maximizing the
explosion itself.
For starters, try slipping a 40 gallon can over a 30
gallon can. Fill the inner can with something not
very compressible, such as water. The inner can then
acts like a piston, greatly improving launch efficiency.
You'll either get a higher launch ... or the same launch
using less nitrogen.
Assuming the cans have sloping sides, the geometry
works better if the inner can is inverted, just
like the outer can. Put the lid on the inner can,
invert it, and cut a hole in the bottom. Then put
in a heavy-duty /bag/ of water, to keep the can from
getting crushed.
Also note that setting the bottle on top of the inner
can, high within the outer can, greatly reduces the
chance of high-energy shrapnel escaping.
Note that the internal pressure will try to convert
the outer can from a cylinder into a sphere. This
places high stress on the corner where the side meets
the bottom. See if you can relieve some of this stress
using wide heavy-duty fiber-reinforced tape packing
tape. Run tape up one side, over the top, and back
down the other side, along the lines of longitude.
Also, to reduce the side-splitting stress, wrap some
tape around the cylinder, along the lines of latitude.
In addition to helping distribute the forces and
preventing distortion of the shape, the tape improves
safety somewhat. If there is a split, the tape
increases the chance that the pieces will stay taped
together, so that the thing just sits there and leaks,
rather than blowing shrapnel all over the place.
Consider putting the observers at a distance *and*
behind a tall chain link fence. Anything small enough
to go through the holes in the fence will have lost
a lot of energy over the intervening distance due to
aerodynamic drag.
Even better is two layers: A chain link fence plus
a layer of transparent shatterproof plastic window
material.