When you blow on a candle, the air produced creates a draft that extinguishes the flame by dispersing the flammable mixture formed by the melted wax and the oxygen in the air, thus interrupting the combustion process.
When a candle burns, it is not just the wick that fuels the flame, but primarily the melted wax. This wax rises through capillarity in the wick and then transforms into vapor as it approaches the flame. It is this wax vapor that reacts with the oxygen in the air, producing combustion and releasing heat, light, and various hot gases. As long as there is fuel (that famous melted wax), enough oxygen around, and a high temperature to sustain the reaction, the candle remains lit.
A candle burns thanks to the dioxygen present in the air around the flame. When you blow on it, you disturb this balance by quickly projecting air towards it. This wouldn't be a problem in itself, since the air also contains oxygen, but the breath creates a kind of chaotic turbulence that momentarily pushes the available oxygen away from the flame. As a result, the combustion no longer receives enough fresh oxygen to sustain itself, and poof, it goes out almost immediately. The stronger the breath, the more massive the interruption of oxygen, making immediate relighting impossible.
When you blow on the flame of a candle, you send it air at room temperature, relatively cool compared to the very hot gases from combustion. This breath induces a sudden cooling of the area where the wax vapors burn, quickly dropping the temperature. However, for a flame to continue burning, it must maintain a certain high temperature. If this temperature drops too quickly, the wax can no longer evaporate properly, and the combustion chemical reaction abruptly halts. The flame then immediately goes out due to this sudden decrease in its necessary minimum temperature.
When you blow on a candle, you violently disperse the hot gases surrounding the flame. These gases act as a thermal insulator that maintains an ideal temperature for sustaining combustion. Without them, the temperature quickly drops below the point necessary for the flame to sustain itself. As a result, you instantly break this delicate balance, depriving the air of the essential heat: the flame detaches, flickers, and eventually goes out.
The speed of the breath is really important: the faster the expelled air, the more quickly it removes heat around the flame. This causes a drastic cooling and stops combustion abruptly. Orientation also plays a big role: blowing softly and horizontally on the flame makes it flicker; blowing hard and directly above cuts off the supply of oxygen and instantly pushes away the hot gases necessary for combustion. Essentially, the combination of speed and direction determines how quickly a candle surrenders to your breath.
The melted wax at the base of a wick is drawn up by capillarity. Without this remarkable phenomenon, the flame would not be able to persist by consuming the liquid wax produced by melting.
Blowing out a candle does not only work by removing oxygen; it also significantly reduces the temperature around the wick. Without a sufficiently high temperature, the wax stops vaporizing, and combustion ceases immediately.
If a candle is placed in a microgravity environment, such as aboard a space station, the flame becomes spherical due to the lack of upward convection. This particular phenomenon allows researchers to study combustion in a completely different way.
Lighting a candle in a closed room can slightly decrease the atmospheric humidity level. Indeed, the combustion of a candle generates carbon dioxide and hot water vapor, which tends to rise and condense elsewhere in the space.
Yes, this can be explained by the fact that a candle produces wax vapor when it goes out. By placing a flame close to the smoke trail, the flammable vapor ignites again, allowing the flame to travel back to the wick.
This happens when the wick is too long or the wax is of poor quality. Incomplete combustion then produces more unburned carbon particles, resulting in visible smoke when the flame is extinguished.
The wick allows the liquid wax to rise by capillary action toward the hot zone, where it vaporizes and burns. Thus, the wick sustains the combustion process over time.
This is primarily due to variations in oxygen supply or the chemical composition of the wax. Less oxygen produces a more orange and flickering flame, while better oxygenation results in a more stable, bluish, and hotter flame.
The heat produced by the flame creates an upward current of less dense warm air. This air naturally rises, causing a flame that is oriented upward due to the phenomenon of convection.
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