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Inspired by this youtube demonstration by ChemicalForce, I'm prompted to ask what is the coldest possible flame.

What the video seems to show is phosphorus vapour in an inert gas being blown into air. This seems to create a flame, but one so cool you can hold a finger in it and not be harmed.

So is this the coolest known flame or are there other known phenomena that are cooler?

NB I suspect that flame temperature depends not just on the stuff that is burning but also on the details of the flow and concentration, so please specify what they were if there are other candidates.

matt_black
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    If you include plasmas among flames, then there are plasmas which can rather freeze water rather than boil it. There is a nice video "Fire That Actually Freezes Things Instead of Burns Them" https://www.youtube.com/watch?v=cUpv2AqbZ1E – AChem Jul 30 '21 at 18:37
  • If the rising air convecting from a warm object counts as a "flame" (it certainly is shaped like one and flows like one), then a flame can be formed at any temperature warmer than ambient. – Oscar Lanzi Jul 30 '21 at 21:23
  • I missed the duplicate question despite a search. Perhaps because the dupe is tagged [thermodynamics] and nothing else. Also, while there is a good answer, the accepted and most upvoted answer is blatantly wrong. – matt_black Aug 02 '21 at 08:32
  • Also, and a possible reason this question is not a perfect dupe, the other question is theoretical in the way it is posed, this question is not about theory but about kown observed phenomena. None of the dupe's answers address the theory but would be better answers to this question. – matt_black Aug 02 '21 at 08:37

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