Pressure to Blow Out a Candle

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Pressure to Blow Out a Candle

When wildfires occur, wind is a major threat to make them even more dangerous. However, a single breath can blow out a candle. One of the differences is the fuel.

Unlike the forest fire that continues to burn and consume everything in its path, the candle’s gas flame is highly unstable. After fire initially melts the wax, wax is continuously pumped into the wick and turned into combustible gas. Blowing into the flame blows away the gas that is burning. When flame disappears, there is not enough heat left to turn more wax into gas, so the candle goes out.

Blowing Out the Candles (Birthday) | MakingArtFun.com

To blow out the candle, puckering the lips creates a venturi so the airflow is much greater than exhaling or inhaling.  According to Bernoulli’s Principle, as the speed of air increases, the pressure decreases. Blowing against one side of the candle’s flame, creates an area of low pressure. Normal maximal expiratory pressure (MEP) values could be as high as 120 to 150 cm H2O, so the pressure to blow out the candle could be 3 to 5 times this value. However, the impact of air directed at a flame with a small area is sufficient to snuff it out.

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