Submitted by YEETAWAYLOL t3_11bo63g in explainlikeimfive
It doesn’t seem like you are starving the fire of air by slapping it, so why does it extinguish?
Comments
thebarberbenj t1_j9yw49p wrote
Your hands coming together rapidly displaces air, pushing it in a focused direction towards the flame. If you watch on high speed cameras, the flame is extinguished before the clap. The wick has no air to combust the fuel anymore.
XxCotHGxX t1_j9ywbf7 wrote
It's the same as blowing out a candle. You are separating the burning gases from the fuel faster than it can burn more. At the point that there are no more burning gases touching the fuel, the flame is out.
YEETAWAYLOL OP t1_j9ywled wrote
Hang on. My understanding was that blowing out a candle suffocated it (your breath was all CO2). Is that understanding incorrect?
PixieBaronicsi t1_j9yxbz4 wrote
No, the air you breathe out is only about 5% carbon dioxide. It still contains about 15% oxygen, compared to about 20% oxygen in regular air
XxCotHGxX t1_j9yxdsd wrote
Yes that understanding is incorrect. Your breath is not all CO2 and contains enough oxygen for combustion.
camkatastrophe t1_j9yxhii wrote
The CO2 doesn’t help, but it’s not the reason it goes out. A candle can be extinguished by a fan or wind blowing regular air with normal oxygen richness just the same.
YEETAWAYLOL OP t1_j9yxoya wrote
Yeah, I guess I was kinda stupid there. You also blow on fires when they are first starting, so I should have realized that it doesn’t necessarily put it out.
TheHam06 t1_j9yxthl wrote
Think of the concept of blowing gently on a small fire to make it grow. They steady stream of fresh o2 from your breath gives it more oxygen than the air around the fire.
its-a-throw-away_ t1_j9z0h9f wrote
Wicked flame sources such as candles depend on convection to operate. Once lit, gasses in the candle's flame rise and cooler oxygenated air rushes in from the sides and below to replace it. As this new air approaches the flame it rapidly heats up, reacts with the fuel in the wick, ignites and rises, continuing the cycle. This is why the flame's colour transitions from blue (initial ignition) through orange and finally yellow (where the last of the evaporated fuel is consumed). This is also why a candle flame extends up from the wick.
Rapid air movement from blowing or clapping drastically increases the amount of air flowing past the wick, which elongates the flame and lowers the concentration of heat around the wick. Less heat near the wick reduces the rate at which its fuel vapourizes, which makes less of it available to react with the air.
The air itself absorbs heat. Slow moving air absorbs more heat per unit volume, so it more readily reaches the fuel's ignition temperature and sustains the reaction. Faster moving air absorbs less heat per unit volume, making ignition more difficult.
This is a long-winded way of explaining how blowing or clapping your hands cools the area around the wick to the point that ignition ceases.
A slight increase in airflow velocity beyond what simple convection produces actually improves ignition by making more oxygen available at the point of ignition. This is why blowing on a fire causes the embers to glow brighter and increase in temperature. But there's a tipping point beyond which the heat drawn away from the seat of the flame overcomes the more efficient ignition due to extra oxygen from the additional airflow.
[deleted] t1_j9yue7n wrote
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Porcelet_Sauvage t1_j9ywyrz wrote
The flame in your example need 3 things: fuel, oxygen and heat.
The fuel comes from the candle wax or lighter fluid or whatever, the oxygen comes from the air and the heat initially comes from the flint in a lighter or the friction of striking a match etc.
When you blow, or move air rapidly in some manner, on a flame you move the heat off the fuel for long enough for the reaction to stop.