[Stoves] Down with Fantasy-draft stoves

[Andrew Heggie]

On 27 March 2018 at 23:25, alex english <aenglish444 at gmail.com> wrote:
> Andrew,
> Setting aside the solid fuel variables, I conceive of the gasses self
> stratifying with what ever their temperature/density properties dictate.
> With wide fuel chambers and low velocities/momentum you might see that the
> coolest of the hot gasses, which are the second most dense gasses in the
> chamber, will spread out sideways as a cap over the fresh un-reacted air
> that is laying/rising under the MPF.  Again, I see the cool fresh air as
> being pulled down by gravity (even as gravity is forcing more into the
> chamber) as opposed to being pulled up even though it is in fact rising to
> replace its own transformation in to new less dense compounds with in the
> MPF.
>
> There are perhaps more than a few additional variables  associated with the
> chamber and burner configuration that I am not considering.
>
> Does this description answer your question, or make any sense to you?

Yes the description makes sense  but in the absence of being able to
probe a wide bed for temperature I don't know. I had conjectured that
the middle would remain hotter, as the outer lost heat to the walls
and on a wide bed the middle would start moving downward faster. Then
it might expand out sideways and the outer parts might act as normal
bottom lit updraught fires.

The trouble with me was impatience as I would need over a season to
dry my material to below 15% (the equilibrium moisture content in
winter here in UK}. So I dried my small scale experiments in the oven
but large scale experiments were with material tht was probably too
wet. I had a brief period with our prototype small scale dryer but
didn't make the best of it at the time and now don't have the
facility.

Also with the bigger material (I was after making lumpwood charcoal
rather than biochar in those days before we heard about terra preta)
there was danger of burning debris slipping down between the lumps. I
saw this with my early burns when I arranged the fuel sticks
vertically, if a burning particle fell to the bottom it kindled a
simple updraught fire which inevitably smoked badly.

Andrew