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Consensus on Calcing Fire
- Thread starter Agnaa
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Would this calculation be affected?
Agnaa
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- #43
That calc would be affected by the stuff discussed earlier in the thread, but it already includes a fine version just above it. Temperature change of 2977 degrees, density of 0.244 kg/m^3, and specific heat capacity of 919 j/kgk are all close enough to be fine.
speedster352
He/Him- 17,551
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In other words?
speedster352
He/Him- 17,551
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I mean does it reduces the calc by 10 to 15 percent?
- 11,099
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So heat capacity is the correct way to calculate fire creation, and heat conduction for tanking it?
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I'm not sure heat capacity is the best way to calculate deflagration explosions though since they do have an epicentre and spreads out like explosions.
Agnaa
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For that sorta thing, I have two main concerns:
Heat capacity of fire gives higher results than the ordinary explosion formula. Like, for the calc of yours, it gave results 20x higher. When ordinary calculations already create fireballs, do we really want to rate deflagration explosions as being massively higher just because they lack force? I may not be properly understanding the suggestion, but it concerns me.
I'm not quite sure what the alternative would be. Inverse square based on fire-temps at the edge? I wouldn't expect fires to actually spread in spheres like radiation, shockwaves, and energy blasts do.
Heat capacity of fire gives higher results than the ordinary explosion formula. Like, for the calc of yours, it gave results 20x higher. When ordinary calculations already create fireballs, do we really want to rate deflagration explosions as being massively higher just because they lack force? I may not be properly understanding the suggestion, but it concerns me.
I'm not quite sure what the alternative would be. Inverse square based on fire-temps at the edge? I wouldn't expect fires to actually spread in spheres like radiation, shockwaves, and energy blasts do.
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I think the reason heat capacity is inflated for explosion-esque fires is because the temperature is not uniform across the entire fireball.
Agnaa
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- #57
So would the idea be that there's some amount of heat inside the explosion, that gets dispersed as it expands?
Rather than the entire sphere being one temperature at once, the inside is very hot, then that drifts to the outer front being somewhat hot with the inside being even less hot, etc.?
Rather than the entire sphere being one temperature at once, the inside is very hot, then that drifts to the outer front being somewhat hot with the inside being even less hot, etc.?
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And as the hot air explodes outward, the hottest air goes outward too.
The heat capacity goes within a larger volume to dissipate.
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To my knowledge
Deflagrations and detonations are the same thing in essence, what sets them apart is the speed at which they occur .
Gunpowder inside a small container would detonate because the pressure would build up inside said container, making it so the material is consumed at supersonic speeds
On the other hand if you were to lay the same amount of gunpowder on the ground and ignite it, the material would consumed at subsonic speeds and be considered a deflagration instead.
The energy in the end is by all accounts the same because the amounts of gunpowder used didn’t change.
the difference is that the first example does generate a shockwave measurable in psi of force whereas the latter doesn’t.
Deflagrations and detonations are the same thing in essence, what sets them apart is the speed at which they occur .
Gunpowder inside a small container would detonate because the pressure would build up inside said container, making it so the material is consumed at supersonic speeds
On the other hand if you were to lay the same amount of gunpowder on the ground and ignite it, the material would consumed at subsonic speeds and be considered a deflagration instead.
The energy in the end is by all accounts the same because the amounts of gunpowder used didn’t change.
the difference is that the first example does generate a shockwave measurable in psi of force whereas the latter doesn’t.
- 821
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Real life explosions release energy in the form of heat and a shockwave, the reason the standard explosion formula needs to be cut in half is because the heat part of the explosion is assumed to be missing in fiction ( I think )
To have a somewhat accurate guess of how much of the energy is released in the form of heat, nukes are the answer with 50% of their energy being just heat that is being transferred by radiation.
Agnaa
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- #61
We only cut it in half if it's non-nuclear.
My guess behind that is that nuclear bombs release half of their energy in ionizing radiation that normal bombs of the same size (destructive explosion radius-wise) don't have. And that it isn't about the pure heat component.
That is just my informed guess, though.
My guess behind that is that nuclear bombs release half of their energy in ionizing radiation that normal bombs of the same size (destructive explosion radius-wise) don't have. And that it isn't about the pure heat component.
That is just my informed guess, though.
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That explains how we explain on the formula for the air blast non-nuclear detonation yield.
Also, even if it is nuclear, there is half as heat and half as KE of air.
I guess nothing new is accepted so far.
Feel free to further discuss. I may not be joining all the time though.
Arkenis
They/Them- 17,089
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Surtrs flame calc, could ya check this
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Awaken
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Bump
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Bump
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Bumo
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Bump
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Bump
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We were having a debate on density here?
Like, it of course depends, but generally I guess air density when at the temperature of the flame would be used to figure out mass and then do a regular heat change calc.
Unless you are burning a chemical, in which case you could use chemical energy as well.
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I think that was the situation? Because Bambu made mention of density of fire, but IDK.
So basically, as per your reason, we'd use the density of air at the specific temperature it is burning in? Like say, air is x density at y temperature or something like that? And then it's just normal specific heat capacity and latent heat of vaporization?
Hmmmmmm...
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Yeah... I mean, no vaporization. Air starts out as gas and all.
I'm fairly sure the whole oxygen method on there is wrong.
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Ah. Okay.
