All you need to make a fire tornado is:
Put a little bit of the lighter fluid into the empty tea light. Not too much. Put in less that a millimetre. That way it'll safely burn itself out after a short time.
Put it all together like in the video and light it. Give the whole thing a little spin.
I experimented with different diameters of mesh tube and different containers for the lighter fluid. I discovered:
- A wider mesh is better. I'll explain why later
- A smaller container is better. This produces a much more dramatic change in high when the vortex kicks in.
Why does this happen?
A flame draws air in from around it. That's because it heats the air. Hot air is less dense and so it rises up. Air is drawn in from the sides to fill the space left behind.
In our case the air is drawn in through the mash of the bin. As it passes though it gets pulled around in a circle. It's now got some kinetic energy. When the air is pulled further into the middle, that energy is conserved. It's still going round in a circle but the circle is much smaller so it's orbital speed will increase to keep it's kinetic energy the same. This is the conservation of angular momentum.
So the reason a wider mesh is better is that for the same orbital speed a wider mesh will be travelling faster and imparting more kinetic energy.
I'm not sure why the flames get bigger. Any ideas?
You might also like these giant steel balls you can burn things with.