Eli5: Why when you blow a little “wind” on a candle it will blow out? But very strong winds are known to increase the size of wildfires and make them spread more easily?

Question

You would think the more wind the faster the fire gets extinguished, I have a feeling the size of the fire matters but i just wonder why and where the line is drawn between a candle and a wildfire in extinguishing it when blowing wind on it goes from a very effective to a super ineffective technique.

In: 0

Answer 1

ELI5. Think of it as two competing opposing “forces”. Moving more air through the flames, means the flame has to work harder to heat the additional air in order for the flames to stay alive. So this wind, removes heat from the flames. The opposing thing is that the additional air also brings along more oxygen which allows the flames to burn faster and stronger (as long as there is sufficient fuel).

So a small flame benefits a bit less from the wind bringing oxygen and the air takes away enough heat that the flame dies.

A larger flame with a lot of fuel, say a forest fire, benefits a lot more from additional oxygen and the flame is so large that it can heat the additional air from the wind. So the flames burn even stronger and the wind cannot put it out.

Both factors are at work, it just depends on the situation which factor outweighs the other.