Watch the video below, then stick around for some science:
This biblical looking backyard creation is taking advantage of a few things involving some really interesting science.
First, and most obviously, the fans are increasing the amount of oxygen that can be consumed by the fire. This sustains the fire and allows it to grow to a terrifying size.
Second, the correct positioning of the fans is crucial here. I have drawn (very roughly) a diagram of the wind vectors below:
As you can (hopefully) see, if you position the fans just right (what the man in the video was trying to do) you are left with a number of wind vectors that create a circle, defined by tangents. And because all of the fans are oriented to create counter-clockwise tangents (in the diagram and in the video), the “Tornado of Death Zone” created gets a counter-clockwise spin. This spin gets imparted to the fire, giving it the hellish look.
Lastly, as you know from grade school, hot air rises. The flames of the burning fire naturally rise upwards, adding height to the tornado and adding more spin to it. The upwards motion of the rising air combined with the sideways spin from the fans creates that classic Vortex of Doom appearance.
So, you could, with a few fans and some lighter fluid, build your own fire tornado. But I wouldn’t recommend it.
Cross posted at the There Are Four Lights blog