The Physics Behind Fanning The Flames ?

[Erwin Schrodinger]

The Physics Behind "Fanning The Flames"?

So no one in class knew the answer and, of course, I don't know the answer (that's why I come to the geniuses on this board) . The question was:

Explain why blowing on a fire may make it burn better.


I'm pretty sure it has something to do with increasing the reaction rate of the fire so that oxygen combines with carbon and hydrogen at a greater rate. But why does blowing on a fire cause this to happen? This is where I'm stuck. Any help would be appreciated.

 

[Astronuc]

I usually associate it with getting the air (oxidant) to the fuel (wood, coal, etc). The air displaces the combustion products like CO and CO₂ which interfere with the combustion process.

Edit: Some matters Erwin Schrödinger and I discussed by PM.

Blowing the ash away would help, but getting the air to the fuel is what increases combustion. CO forms when insufficient oxygen is present, and CO₂, carbon dioxide is the more stable compound forms when oxygen is abundant. CO, carbon monoxide and CO₂ are gases. The ash is the non-combustable residue including oxides and carbonates of metals like potassium, magnesium, calcium, etc (http://en.wikipedia.org/wiki/Ash_(analytical_chemistry) , http://en.wikipedia.org/wiki/Fire) .


In wood, the heat breaks down the wood fiber or cellulose (http://en.wikipedia.org/wiki/Cellulose) by pyrolytic decomposition, and in some cases, the wood may contain flammable compounds like pine pitch or resins (http://en.wikipedia.org/wiki/Resin) , some of which contain terpenes (http://en.wikipedia.org/wiki/Terpene) . The are complex hydrocarbons and can burn directly or are broken down. Air combines with hydrocarbons (C, H) and forms CO, CO₂, and H₂O.

See also - http://www.iit.edu/~smile/ch96m3.html
http://www.iit.edu/~smart/pawebar/lesson3.html