why does a candle need a wick to burn (Scientific answer please)?

Answer 1

I wish people would only answer questions they understand!!!
You want a scientific explanation - here goes;

Wax melts to form a high 'flash point' liquid. It can only be ignited if heated to above its 'fire point'. Applying a flame to a pool of the liquid, will result in eddy currents being set up in the pool, the hot upper layer of the liquid migrates from the impinging flame, cool, sinks and then rises to the flame again - its a standard eddy current effect.

This means that you would have to heat the entire mass of liquid to its fire point before ignition to occur - look at deisel - pour some into a saucer and drop a lighted match in - it will be extinguished - the deisel has to be thoroughly heated first for ignition to occur.

However, a high fire point liquid can be ignited very easily if it is absorbed onto a wick - which, by definition, is a porous medium of low thermal conductivity. Application of a flame to a fuel soaked wick causes a rapid local increase in temperature , not only because the layer of liquid (fuel) is too thin for convective (eddy) dissipation of heat to occur, but also because the wick is an effective thermal insulator (low kpc) Ignition, can therefore be acheived, at a point and will be followed by flame spread over the remaining surface of the wick exposed.

Capillary action causes fresh fuel to be drawn up into the wick.

A fresh supply of fresh fuel (molten wax) is ensured by the radiant heat from the flame front to the wax melting it - as the enthalpy of combustion of the wax is far higher than the energy needed to melt the wax, the capillary fuel fed flame is ensured to continue.

If you want a mathamatical representation of this effect please email me but it is very very complicated.

Simon

Answer 2

Because the candle is made of wax (high-molecular weight solid hydrocarbon). Lighting the candle causes the cellulose (polysaccharide) wick to burn. (It is best that the string be impregnated with wax. But they not always are. Pity.) The heat from the burning wick melts the wax and pyrolyzes some of the hydrocarbon into lower-molecular weight gases. These gases burn in oxygen, just above the wick. (This is called a flame. It is yellow) The wick draws molten wax up into itself by capillary action. Once the liquid wax is up in the the flame, you know the rest.

Answer 3

Melted candle wax is combustible without a wick, but not at the temperatures near to its melting point, as in the case of a candle.
If candle wax is heated fiercly to the point where it begins to smoke, it can be made to ignite by a naked flame.
If heated enough, it will spontaneously ignite, as will, for example, cooking oil. This phenomenon is responsible for many domestic kitchen fires.
The reason for the high temperature combustibility, in the absence of a wick, is because the wax has reached a temperature at which it is volatolising (evaporating) from the surface at a rate which will support combustion.
This is the clue.
In any liquid fire, it is the VAPOUR of the liquid which is "burning", NOT the liquid.
The provision of a wick, with its large surface area and small volume, allows a local elevation of temperature sufficient to combust the wax.
The molten wax is constantly replaced by capillary action, so the flame is maintained.

Answer 4

When the wick is ignited, a continuous process of Heating of the wax in the wick, (addition of Sensible Heat), then of melting the wax, (addition of Latent Heat of Fusion) followed by vaporisation of the wax, (Latent Heat of Vaporisation).
Therefore, a continuous combustion reaction is set up from the wick when ignited. The process is maintained by the same sequence of events carried out on the wax of the candle body receiving the necessary heat from the burning wick which continuously feeds the wick.

Answer 5

Because wax isn't flammable. The wax is there to slow down, control, and support the candle. Without the wax the candle is just a wick, which is really more like a fuse now. The candle can't be all wax because wax isn't flammable and even if it was the whole candle would go up in flames and that wouldn't be good.

Answer 6

because if you hold a flame to the candle wax it dont burn it just melts the wax so u need the wick to hold the flame in the candle to keep the flame burning and in place.