I read all of that and I'm still wide awake
One thing that interested me - The melt pool should be just less than the glass diameter. Doesn't this mean that you expect there to always be some tunnelling? I'd have thought the melt pool should be fractionally wider the the glass diameter. I'm sure you have a damn good explanation as to why it should be less though.
/edit - The book as a free pdf is available here along with what look like recreations of those lectures. I've not had a chance to look at them yet.
As the candle burns down the intensity of heat, or heat build up in the glass itself generally increases (a 'furnace effect), - though obviously dependant on the time of individual burns, so it is likely that as the candle burns down into the depth of the glass, the melt pool diameter will increase a little, as will the heat and flame size, hence melt pool. (Glass sides are also generally not parallel, being often wider at the top than at the bottom.)
Obviously there is a relationship between glass depth and heat, if the glass is too deep and narrow, then the flame may be starved of oxygen and the melt pool diameter may actually reduce, and sooting increase due to incomplete combustion, but a typical whiskey tumbler is a good size for making a filled candle.
When I made candles, the metal sustainer at the bottom of the wick was designed to cover the bottom 5 to 10mm of the wick itself, so that the candle would self extinguish while there was wax remaining in the bottom to prevent the candle running dry and the flame directly contacting the base glass, which could easily result in fracture due to thermal shock and differential heating, plus damage to the surface on which the candle was placed.
It is also amazing how room temperature can effect tunnelling. Testing was always done at a standard temperature, I think 20 to 22c from memory. On a cold winter day in a cold room, a candle that is fine on a summers day may tunnel, simply because the outer wax is cold and the flame / heat produced is insufficient to melt these outer layers.
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