BF2S Forums What Does A Candle Flame Look Like In Zero Gravity?

Snipe=UKLF= wrote:

Stumbled across this pic today and it got me thinking...

Why does the flame look like this?

http://microgravity.grc.nasa.gov/combus … ity_lg.jpg


..no doubt some people will settle with "because its in zero gravity" but if you have any views on why it is entirely blue or that shape etc etc plz share.

You might have noticed.

Sun?

Exactly.

Bertster7 wrote:

I'd imagine it's to do with the blue part of the flame being the hottest part of it. Without gravity the flame would be centered around a smaller point, the heat wouldn't rise because there wouldn't be an up. The same amount of calorific energy would be produced from the flame, in a smaller area, so it would be hotter and therefore blue.

Yeah thats pretty much what i first thought..

But then i started thinking, if theres no up then obviously heat can't rise so would the heat remain in the flame and just get hotter and hotter eventually turning white or something?

Bernadictus wrote:

You might have noticed.

Sun?

Exactly.

eh?

Last edited by Snipe=UKLF= (2006-10-11 03:43:39)

Bubbalo wrote:

No, because the candle is still exo-thermic.  Just the same as if you give a rocket a baseplate, it still works in space.

Exothermic just means heat is produced in the reaction, right?.. and if the heat was leaving in a certain direction would that not be reflected in the shape of the flame?

Does energy abide by the rules of gravity? Perhaps under normal circumstances, there is a higher concentration of air molecules on the base of the flame, thus dissipating the energy faster. In microgravity, the air molecules are evenly spaced thus creating a more uniform shape. I don't know, I'm only guessing. Can anyone answer my question please? (Look at the first line)

Snipe=UKLF= wrote:

Exothermic just means heat is produced in the reaction, right?.. and if the heat was leaving in a certain direction would that not be reflected in the shape of the flame?

Exo-thermic means to give off heat, endo-thermic means to suck in heat.  The more there is, the more it will disperse.  We get heat from the sun all the way down here, yet you can't experience the heat my oven gives (or I give?  Humans are exothermic aren't they?) off.

if it's in zero grav it's most likely in a very oxygen rich environment as well, making it burn all purty blue like that, also a flames teardrop shape has something to do with the hot gases becoming lighter and rising as they are produced, in zero grav this doesn't matter so they expand in all directions at once, like the sun as bernie said

DoctorFruitloop wrote:

Snipe=UKLF= wrote:

Bertster7 wrote:

I'd imagine it's to do with the blue part of the flame being the hottest part of it. Without gravity the flame would be centered around a smaller point, the heat wouldn't rise because there wouldn't be an up. The same amount of calorific energy would be produced from the flame, in a smaller area, so it would be hotter and therefore blue.

Yeah thats pretty much what i first thought..

But then i started thinking, if theres no up then obviously heat can't rise so would the heat remain in the flame and just get hotter and hotter eventually turning white or something?

2nd law of thermodynamics should still apply even if there is little gravity. The flow of heat is still gonna be from hot to cold so the flame will spread out.

I know, but it won't be up, it'll just be spherical so all of the outside of the flame will be an equal distance from the centre of the flame. I think it's because if you make the flame elongated the tip is much further from the heat source. In this example the flame is all very close to the heat source so it's hotter and blue.

Does gravity effect air?  interesting.

IRONCHEF wrote:

Does gravity effect air?  interesting.

Of course gravity affects air. Air has mass, even if it isn't much.

Snipe=UKLF= wrote:

Bertster7 wrote:

I'd imagine it's to do with the blue part of the flame being the hottest part of it. Without gravity the flame would be centered around a smaller point, the heat wouldn't rise because there wouldn't be an up. The same amount of calorific energy would be produced from the flame, in a smaller area, so it would be hotter and therefore blue.

Yeah thats pretty much what i first thought..

But then i started thinking, if theres no up then obviously heat can't rise so would the heat remain in the flame and just get hotter and hotter eventually turning white or something?

Bernadictus wrote:

You might have noticed.

Sun?

Exactly.

eh?

Well, it wouldn't stay around the candle, it would get hotter around the candle, but not stay entirely there.

The flame passes on the energy to the air, and in normal gravity, this causes this to rise. In microgravity, I'd imaging that the heat can't move up, as such, but it would still pass on the energy in an area around it, so the energy would still change into other forms except heat, but it wouldn't stay in the same place.

The reason (I may be wrong, this is my mind working here, not fact) a flame is only a certain area is because of this:

When the hot area reaches a certain surface area to mass ratio, the energy isn't enough to keep it at a constant/rising tempereture, so all the air around it would take the energy out of the hot region and pass it on, but it would be at such a small temperatue compared to the source, the oxygen wouldn't ignite anymore, which is (I think) the outer area of the flame.

The blue part of a flame is the hottest, in normal gravity, the air moves due to gravity and the hotter air being "lighter" than the colder air, which causes it to rise and change temperature quickly, as the energy isn't sufficient to keep the region warm at that distance from the source (and the contact area of the surrounding cold air is so large that it takes all the energy out of it) in microgravity, the air doesn't move because of gravity, it moves by transfering the energy from one particle to another (It does this aswell in normal gravity, just at a slower pace). This allows the area of the flame to become very hot (Blue) and the heat doesn't dissapate as quickly, but is smaller, meaning the contact area of the colder air is alot larger, making the flame lose heat from it's outer edges very quickly, so it doesn't get colder slowly enough to change from a blue flame to an orange one...

That's what I think anyway.

I meant this to be a short post, but that's what bloody Physics in school does to you, makes you over think....


Damn....


PS: I probably repeated myself a *lot* in that, and it might not make any sense, but hey, I made it up as I went along, can't blame me for trying =p



PPS: My fingers are tired....


PPPS: (and edit) I didn't read much of the posts above, so I didn't know that the yellow flame was caused by impurities, so most of this is a wee bit off.... That sucks.... I was enjoying feeling smart....

Last edited by ilinear (2006-10-11 12:33:24)

A related question.....

What does an explosion look like in the vacuum of space?  Unprotected, just blown up, boom.  I know there can't be any fire, but what exactly would it look like?  Does anyone know?

And to think.... Star Wars has been wrong this whole time.

Spearhead wrote:

A related question.....

What does an explosion look like in the vacuum of space?  Unprotected, just blown up, boom.  I know there can't be any fire, but what exactly would it look like?  Does anyone know?

And to think.... Star Wars has been wrong this whole time.

There's a documentary called Nukes in Space which shows this sort of stuff. It's a sequel to Trinity and Beyond, another quite interesting documentary. They look quite pretty.

Got this off some website, not sure on accuracy, but it sounds believable.

In space, the first few milliseconds proceed as they would in air (say), but then the transfer of energy to the surrounding air never takes place. As a result the initial small, intensely hot fireball simply keeps expanding at very high speed, and the expanding gases and any fragments fly off in straight lines. The fireball cools by radiation at first, but as its density drops it becomes so transparent that radiation is suppressed. For a chemical high explosive, the expansion speed would be a few thousand feet per second. So for a moderate size explosive -- say 1 meter across -- the products will expand to 100 meters in probably less than 0.1 sec, meaning the density will have decreased by a factor of a million, and the visible explosion will effectively be over. Visually the effect would be of a very brief, brilliant flash in a region only a little bigger than the actual extent of the explosive material. Of course there would be no billowing swirling smoke, and any fragments would almost certainly be moving too fast to be visible. The effect would probably be something like that of a big flashbulb.

For a nuclear explosion, the fireball would radiate mainly in the x-ray and ultraviolet, which are not visible to the eye, although the visible part of the radiation would produce a blue-white flash. The expansion speed would be many hundreds or thousands of times faster than for a chemical explosion, so that the time scale would be less than a millisecond. All the material near the source would be vaporized, so there would be no fragments. If the explosion was truly in space, and not in a tenuous atmosphere, then viewed from a survivable distance the effect would probably be similar to, but even less spectacular than, a chemical explosion.