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What shape is a flame, on a match or candle, in zero gravity?

What shape is a flame in zero gravity?
Kate Exton from Suffolk (Age 25-34)

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One Response

  1. Candle and match (after the head has consumed its charge of oxidising agent) flames rely on convection currents of air to continuously bring fresh oxygen to the wick, to maintain the chemical reaction that is combustion. The hot air produced is less dense than the air coming in to the base of the flame, so it rises away from the wick producing the streamlined shape of the flame.
    In a zero gravity environment, density differences do not produce the force to create convection currents. The only way that fresh oxygen can get to the wick, and the carbon dioxide can escape, is by diffusion. The carbon dioxide from the reaction produces an ever-growing sphere around the wick, which the oxygen has to diffuse through. The rate of reaction diminishes, and the heat to maintain the reaction becomes insufficient to keep the reaction going. The flame goes out.
    (As an analogy, imagine a crowd of people trying to shake hands with a celebrity. If they form a queue and walk up, shake hands, and walk on they can shake hands at a high rate. This is similar to convection.
    If they all crowd around the celebrity, those who have shaken hands cannot get out through the crush of people pushing forward for their turns. As a result, the time taken for each handshake is much greater. This is similar to diffusion.)

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