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I was looking at the graphs for the density of air at different temperatures (link below) and I was wondering if air would not react with itself at high temperatures? I read that oxygen and nitrogen react at 1600 degrees Celsius, but even below that average temperature (because of the Maxwell Boltzmann distribution) I’m guessing the reaction takes place? Also would it just catch fire with contact with anything in the environment like carbon / almost anything? I’m wondering about the hypothetical use in hot air balloons with very high temperatures and low volumes.

https://www.engineeringtoolbox.com/air-density-specific-weight-d_600.html

Anters Bear
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  • Radiation loses increase proportionally to the fourth power of the temperature (Boltzmann law), so your baloons would be extremely inefficient – Francis L. Dec 21 '19 at 07:35
  • Are you aware 1000 Deg C hot surface thermally radiates about 150 kW/m2 ? Even if surface itself was 500 Deg C, it would be 20 kW/m2. If we consider the mass 500 kg, and lift about 1 kg/m3, it would have radius 4.9 m and surface 305 m2. That is 6.1 MW for 500 deg C surface. It would need impossibly huge power source and the useful load would be baked in a huge grill. – Poutnik Dec 21 '19 at 09:18
  • For just 200 Deg C surface, it would be cca 2.8 kW/m2 and 866 kW.(orvsone 10-15% less after subtracting background radiation) Still very mighty power. Some light aircraft would be more energy efficient. – Poutnik Dec 21 '19 at 09:24

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At $\pu{1000^oC}$, oxygen and nitrogen will not react substantially or probably even noticeably if at all. Besides that, whatever organic material you are using for a hot air balloon will most definitely ignite immediately. The average temperature that most organic materials char and eventually ignite is $\pu{270^oC}$. At almost double the kinetic energy at $\pu{1000^oC}$, most things will almost instantaneously ignite. Note that in air, temperature diffuses rather quickly so even if the fire or whatever you are using to get to $\pu{1000^oC}$ will probably be significantly colder when it reaches anything flammable. In fact, most fuel used in normal hot air balloons burn at over $\pu{1000^oC}$, but it diffuses very quickly that the average temperature of the air in the balloon is around $\pu{110^oC}$

airhuff
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Erik Low
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  • Perhaps to make clearer use of terminology it is better to say "Note that hot air diffuses rather quickly so even...."? – Buck Thorn Dec 21 '19 at 11:39