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Dear Crispin,
Thanks very much for the info on wood! I really appreciate
your finding this so quickly and it does help move things ahead at Colorado
State. You are a gentleman and a scholar.
Peter Scott, Aprovecho consultant, and I have been working on
sunken two pot stoves for about a month now getting him ready to go to South
Africa to teach. I posted a photo of one of the first prototypes a while back.
In this type of stove two pots are sunk down to the level of the handles and a
seal is made there in a sheet metal top so that all smoke remains in the stove
and exits from a chimney. The benefits are that fuel efficiency rises
dramatically as much more pot surface area is exposed to direct heat. Also the
destructive heat, above say 900F. or so, is hitting the pots not a griddle so
after a bit of design help even sheet metal should last a while. The second pot
can boil at about the same time as the first if the heat contacts both pots
simultaneously. Or if desired, heat can be directed, in our case in a Rocket
combustion chamber, to the first pot which then boils faster leaving enough heat
to simmer sauces in the second pot. Provision can be made as well to lift the
pots to set levels exposing less of the pot to heat which is a secondary heat
control besides feeding less wood into the fire. Depending on pot size this type
of stove scores between 40 to 50% efficiency, using sheet metal (or tincanium),
vermiculite, wood ash, insulation, and forcing heat to pass the pots in
1/2" gaps. Peter created a oven that lies under the range from a five
gallon square tin can. Heat is shunted around three sides of the can in a sheet
metal one inch high duct, surrounded by insulation on all sides. A sliding door
of sheet metal shuts the passage between the two pots forcing heat to follow the
contour of the oven before exiting.
The negative side of such a stove is that the cold pots quench
the fire creating soot and more smoke, as pointed out by Kirk Smith and Grant
Ballard-Tremeer. I found that it was necessary to add much more air than usual
to reduce smoke. Also using a higher than usual Rocket combustion chamber helps,
say 14" instead of 10". This reduces over all efficiency but since
heat transfer is so good it seemed like a good compromise to get cleaner
burning. To avoid condensing harmful particles on enlarged pot surfaces it seems
necessary to pay more attention to cleaning up combustion
primarily.
I'll take a few photos of how the stove was constructed and
post them here.
Best and thanks to Crispin once again,
Dean
Dear Dean
I did find the following analyses done by
Gottlieb:
C
H
N
O
Ash Calories
B.t.u.
Oak
50.16 6.02
0.09
43.36 0.37 4620 8316
Ash
49.18 6.27
0.07
43.91 0.57
4711
8480
Elm
48.99
6.20 0.06
44.25
0.50 4728
8510
Beech 49.06
6.11 0.09
44.17
0.57 4774
8591
Birch
48.88 6.06
0.10
44.67 0.29
4771
8586
Fir
50.36 5.92
0.05
43.39 0.28
5035
9063
Pine
50.31 6.20
0.04
43.08 0.37
5085
9153
Regards
Crispin
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