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Re: [Phys-l] Crackling of a fire

We occasionally suffer from cold snaps (outside ~ 0 C; this is the coast of California, remember?). Last time this happened I used recently cut wood which exploded. I then placed wood soon to be used in front of the fire place to dry. The explosions were noticeable less. [Anecdotal and should be treated as such.] I also noticed difference between pine and harder woods. IIRC, tho a hard wood, eucalyptus, especially bad.


p.s. The cover over our wood storage was winded off, so the water soaking may have been a contributer.

On 2009, Jan 22, , at 11:52, Steve Highland wrote:

I think it would be fun to dehydrate some firewood (what would be the best
way?) as much as possible and then build a fire with that to see if it
crackles less.

Experiments with fire are always fun...

Steve in Duluth

A student has posed this question to me, and I'm not sure I have a good
answer, so I am seeking help...

The Question:
Why, when you put a log on the fire does it 'pop, crack and crackle'?

My proposed answer:
I think the answer lies in the sap content, even i dry wood. As the wood
gets hotter, the sap trapped within the fibers heats and then boils
bursting forth, breaking the fibers giving the 'crack' sound. Sap trapped
at the surface would expand and then burst giving the 'pop' sound.

Refinements, clarifications, and debunking are welcome!
Peter Schoch

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