|
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Fire in microgravity
I have been thinking about the way the fire behaves in microgravity. I
have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: In absence of gravity, the flames create a sort of sphere around the core of the fire (of course, this sphere will be limitated by the object in fire; depending on its shape, we will have an almost entire ball for a match, or just a semi-sphere in the case of a fire on a flat surface). Well, if the core of the fire is surrounded by flames (incandescent gases), how can the core be feed by fresh oxygen to keep the fire burning? Maybe this creates a sort of pulsating effect on the spherical flame, contracting it when the oxygen is running out, and allowing thus the flux of more oxygen into the core, which feeds again the flames to its previous size? If someone knows where can I find more information on this matter, I would be very grateful. Best regards, Javier Casado Space stuff in spanish in: http://es.geocities.com/fjcasadop |
#2
|
|||
|
|||
JotaCe wrote: I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: [...] If someone knows where can I find more information on this matter, I would be very grateful. Best regards, Well, SpaceHab/SpaceLab/ISS experiments on flames are relatively recent, but there should be something published by now (Rusty?). In addition to the NASA servers, you might check sites with abstracts of journal submissions. You might also look up some mission status reports to find Principal Investigator names, and do a search for their papers. The largest flame experiment was done on Mir, but the documentation was a bit sketchy. Check Jim Oberg's book for a summary ;-} /dps |
#3
|
|||
|
|||
On 18 May 2005, JotaCe wrote: I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: In absence of gravity, the flames create a sort of sphere around the core of the fire [...] [snip] Actually, no. The traditional incandescent flame mostly doesn't happen in zero g fires. The problem with zero g combustion is that the heat creates no convection... as a result both the combustion products (heat, ash, co2, water vapor, etc) all stay more or less right where they were produced. Now most of this is actually a good thing since it retards further combustion... But because the heat stays put too, and will continue to build so long as the immediate supply of either the oxidizer or fuel are not exhausted, that heat can grow to *VERY* intense levels. It's usually the oxidizer that is the limit. And that's ordinary air. So the moment an astronaut or cabin fan (or something else) causes airflow, the fire spreads... First by allowing more oxygen to get to the hot fuel and secondly by transporting *extremely hot* exhaust gasses away... which can transfer their heat and trigger other combustion. There will only be a visible "flame" for as long as there's fuel and oxygen actively mixing... but the hazardous heat bubble can persist for a very long time since air is a poor conductor of heat without convection to assist it. So the danger is this: A fire starts and quickly chokes itself, but in the process triggers an alarm... The astronaut comes to investigate, and as he approaches to have a look causes eddy currents in the air which feed the fire... and worse yet, could stumble into a pocket of superheated combustion products that aren't visible but are more than hot enough to set *him* on fire... It's *not* pretty. And to the extent that materials *do* get hot enough to glow... that's heat radiation. It spreads the heat around. Perhaps enough so to trigger other fires nearby. If you still the air (or remove it), generally zero g fires go out on their own... very slowly, as the heat dissipates below the ignition threshold. (All bets are off though if the environment contains mixtures of hypergolics... just mix and watch your fire re-ignite!) Gene P. Slidell LA -- Alcore Nilth - The Mad Alchemist of Gevbeck |
#4
|
|||
|
|||
I don't really know, but I bet some sort of diffusion keeps the oxygen
coming in. The hot gas surrounding the match or whatever would be less dense, so oxygen atoms would slip in between the other gasses' atoms. |
#5
|
|||
|
|||
"JotaCe" wrote in
oups.com: I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: If someone knows where can I find more information on this matter, I would be very grateful. Best regards, No problem: http://exploration.grc.nasa.gov/combustion/ (Just how hard did you look, anyway...?) -- JRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. |
#6
|
|||
|
|||
"Maybe this creates a sort of pulsating effect on thespherical flame,
contracting it when the oxygen is running out, and allowing thus the flux of more oxygen into the core, which feeds againthe flames to its previous size?" In perfectly still air I would expect the core of the fire to gradually lose heat by radiation and go out. This will take much longer than heat loss by convection, which can't happen without gravity. If there is any movement of air I would expect combustion to continue to the extent that oxygen can reach the core of the fire. I wonder if you could make a fire retardent bag for use in microgravity. You would enclose the fire in the bag and seal it. Oxygen in the bag would be used up quickly and the mess inside would slowly cool. Of course, if a fire starts on the ISS, it is unlikely to cooperate to this extent. Michael Smith ...who wishes he new how to quote in google groups |
#7
|
|||
|
|||
"JotaCe" wrote in message oups.com... I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: In absence of gravity, the flames create a sort of sphere around the core of the fire (of course, this sphere will be limitated by the object in fire; depending on its shape, we will have an almost entire ball for a match, or just a semi-sphere in the case of a fire on a flat surface). Well, if the core of the fire is surrounded by flames (incandescent gases), how can the core be feed by fresh oxygen to keep the fire burning? Maybe this creates a sort of pulsating effect on the spherical flame, contracting it when the oxygen is running out, and allowing thus the flux of more oxygen into the core, which feeds again the flames to its previous size? I'm sure NASA has some sort of article on this as they've done several experiments on-board the shuttle with fire. Ibeleive the pulsing effect is exactly what happened with a "candle" they were testing. Of course then there is the Mir fire, where the "candle" WAS the oxygen source and as such had no trouble burning. If someone knows where can I find more information on this matter, I would be very grateful. Best regards, Javier Casado Space stuff in spanish in: http://es.geocities.com/fjcasadop |
#8
|
|||
|
|||
"JotaCe" wrote in message oups.com... I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: In absence of gravity, the flames create a sort of sphere around the core of the fire (of course, this sphere will be limitated by the object in fire; depending on its shape, we will have an almost entire ball for a match, or just a semi-sphere in the case of a fire on a flat surface). Well, if the core of the fire is surrounded by flames (incandescent gases), how can the core be feed by fresh oxygen to keep the fire burning? Maybe this creates a sort of pulsating effect on the spherical flame, contracting it when the oxygen is running out, and allowing thus the flux of more oxygen into the core, which feeds again the flames to its previous size? If someone knows where can I find more information on this matter, I would be very grateful. Best regards, Javier Casado Space stuff in spanish in: http://es.geocities.com/fjcasadop If heat cannot rise and draw in cool oxygenated air from the bottom it seems to me that the fire would tend to smother itself. |
#9
|
|||
|
|||
The flame itself is much smaller, and oxygen can easily permeat the flame
zone. The rate of permeation is what limits the size of the flame. The lack of convection allows the reduced combuston rate to sustain the temperatures necessary to maintain the reaction. The flame itself can burn much hotter as a result of the lack of convection, since the primary loss of heat is limited to radiation. "JotaCe" wrote in message oups.com... I have been thinking about the way the fire behaves in microgravity. I have found little information on this in the internet, so I am mostly just wondering, and these thoughts are what I want to share with you for discussion: In absence of gravity, the flames create a sort of sphere around the core of the fire (of course, this sphere will be limitated by the object in fire; depending on its shape, we will have an almost entire ball for a match, or just a semi-sphere in the case of a fire on a flat surface). Well, if the core of the fire is surrounded by flames (incandescent gases), how can the core be feed by fresh oxygen to keep the fire burning? Maybe this creates a sort of pulsating effect on the spherical flame, contracting it when the oxygen is running out, and allowing thus the flux of more oxygen into the core, which feeds again the flames to its previous size? If someone knows where can I find more information on this matter, I would be very grateful. Best regards, Javier Casado Space stuff in spanish in: http://es.geocities.com/fjcasadop |
#10
|
|||
|
|||
"Greg D. Moore \(Strider\)" wrote:
Of course then there is the Mir fire, where the "candle" WAS the oxygen source and as such had no trouble burning. It wasn't really a 'candle' (per se), but a source of pressurized oxidiser and fuel. (I.E. the published descriptions sound to me like the O2 candle was acting as a (small) SRM.) D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
News Story: Mysterious Ball of Fire Fell From Sky In India | neo | Astronomy Misc | 1 | January 12th 05 04:32 PM |
Pyro Relays vs. Isolation Valves | LaDonna Wyss | History | 43 | July 9th 04 10:37 AM |
UFO Activities from Biblical Times (Long Text) | Kazmer Ujvarosy | UK Astronomy | 3 | December 25th 03 11:41 PM |
UFO Activities from Biblical Times (LONG TEXT) | Kazmer Ujvarosy | SETI | 2 | December 25th 03 08:33 PM |
UFO Activities from Biblical Times | Kazmer Ujvarosy | Astronomy Misc | 0 | December 25th 03 06:21 AM |