A strong wind can blow out a candle because it disrupts the flame by dispersing the heat and moving the air needed for its combustion, leading to its extinguishment.
A flame needs oxygen to burn properly, but be careful, too much air at once and it's all over! A strong wind brings a lot of fresh air around the candle, but paradoxically, it's not always great for it. Why? Because it blows so fast that it constantly pushes away or disperses the hot gases and combustible vapors around the wick. Normally, these heated gases stay close to the flame, promoting continuous and steady combustion. But when a too-strong wind arrives, these gases are abruptly replaced by a flow of cold air, strongly disrupting this delicate balance and preventing the flame from maintaining its combustion. The result: it goes out, lacking a stable supply of oxygen and fuel.
The temperature of a flame is related to the heat accumulated around it. A strong wind constantly moves this heat away, much like when you blow on an overly hot spoon: the moving air quickly carries away the produced heat. As a result, the flame struggles to maintain its ideal temperature to burn the fuel efficiently. However, for a candle to work well, the temperature must be high enough to vaporize the wax. A powerful wind disperses this heat, prevents the wax from vaporizing properly, and the flame eventually goes out because its thermal equilibrium is broken. This excessive cooling disrupts the normal functioning of a candle, as to burn efficiently, the flame must reach and maintain a certain critical temperature.
When the wind becomes strong, it no longer circulates quietly around the flame. Instead, it creates unpredictable whirlwinds and chaotic movements known as turbulence. These turbulence constantly shifts the flame, changes its angle, and destabilizes its balance. As a result, the flame loses its usual long and stable shape, becoming short, irregular, and flickering. This instability maintained by the turbulence is enough to disrupt the combustion zone for an extended period. The result: the candle struggles to take in oxygen properly, and the combustion process is too disrupted to sustain itself correctly. A stronger gust of wind, and poof, the flame disappears!
A strong wind creates direct pressure on the candle, pushing the melted wax out of the flame. This wax is normally essential as it rises through capillarity via the wick to nourish the flame. But with the wind pushing it, the wax flows down the candle instead of participating in the combustion. As a result, the flame gradually loses its fuel supply, becomes unstable, and eventually goes out. Another effect: by blowing on the wick, the wind can even cool it abruptly, temporarily blocking its ability to effectively draw up the wax. Without a good supply of melted wax, sustainable combustion is impossible.
When you blow too hard on the candles of a birthday cake, you often notice that some remain lit while others go out immediately. Why? Because the breath creates a turbulence that disperses the heat around the wick and disrupts the oxygen supply. The same happens when you try to light a candle outside on a windy day: it's difficult to achieve a stable flame because the wind cools the liquid wax so quickly that it can no longer properly fuel the wick. The same scenario occurs with tealights placed on the terrace during windy evenings: the flame flickers constantly, the melted wax spreads unevenly, the wick ends up deprived of fuel, and eventually goes out. In contrast, when the flame is protected in a lantern or placed behind glass, it stays lit effortlessly despite the wind, because the protection effectively blocks the strong drafts and maintains a consistent heat around the candle.
The slender and elongated shape of the candles helps to reduce air turbulence around the flame, thus helping to prevent accidental extinguishing by slight drafts.
There are specially designed candles, called windproof candles, whose wax and wick are protected by a wall or a specific design that prevents them from being extinguished prematurely outdoors.
The intensity of a gust of wind needed to extinguish a standard candle is generally estimated to be around 8 to 10 km/h, depending on the size of the flame and the type of wick used.
In the field of wilderness survival, the ability to maintain a flame (for example, with a windscreen) is essential: even the slightest breeze could jeopardize the key resource that fire represents for warmth, cooking, and safety.
Yes, a thicker candle or one protected by a container (like a glass lantern) will generally be more resistant to the effects of the wind, as the container limits airflow around the flame and protects it from the direct influence of drafts.
To prevent the wind from blowing out your candle outdoors, opt for protected candles, such as enclosed lanterns or high-walled candle holders. A sheltered location or the use of special wind-resistant candles can also be helpful.
By gently blowing on the flame, you introduce a moderate amount of fresh oxygen, briefly stimulating the combustion. A strong wind, on the other hand, quickly moves away the warm air and the heat necessary to sustain combustion, thereby cooling the flame and causing it to extinguish.
Not necessarily, even though a hot candle generates a more stable flame at first. A strong wind quickly dissipates the heat necessary for combustion and disrupts the gas-air balance essential for maintaining the flame, regardless of its initial temperature.
Even in the absence of perceptible wind, slight air movements or subtle temperature differences around the flame can cause variations in pressure, leading to oscillations or flickering of the flame.
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