The "cooking area" in stoves

["Paul S. Anderson" <psanders@ilstu.edu>]

Stovers,

Just a thought:

We seem to sometimes overlook that there are really at least 3 (THREE) 
fundamental parts of the "stoves" stuff.

1.  Fuels (many varieties)

2.  The "fire box" or combustion chamber(s)  (where the heat is generated)

3.  The cooking area or the "working area"  (where the heat is utilized, 
mainly for domestic cooking, but also to heat rooms or for commercial 
ovens, etc.)

This third one seems to be most neglected.

Therefore, I am re-printing below a message from Dean Still, dated 14 
November 01.  After he discusses efficiency of fires, he discusses the what 
occurs in the "cooking area."  And we did not carry that discussion forward.

Are we focused on fuels and combustion, or SHOULD WE HAVE MORE DISCUSSION 
ABOUT WHAT HAPPENS AFTER THE HEAT IS GENERATED??

I for one am moving in that direction.

Paul
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Dear Paul and Stovers:

I'd like to comment on the issue of fuel efficiency as touched on below:

 >Do others agree that 30% and 40% are sufficiently accurate to be a target
 >against which we can measure some successes and failures?
 >
 >Prediction:  We will significantly improve upon the percentages by using
 >gasifier stoves, and those gasifiers will be sufficiently in-expensive to
 >allow for some (not all) stoves to be pot-specific in size.

How would the combustion pattern have a big effect on fuel efficiency? If a
really horrible open fire results in 80% of the fuel combusting and a
wonderful stove achieves 100% combustion efficiency there is no huge gain in
total heat transfer efficiency since pots are very bad heat exchangers. For
example, 80% combustion efficiency times 40% heat transfer efficiency is
32%. 100% times 40% is 40%.

Tended open fires are closer to something like 95% combustion efficiency.
When our stoves get close to 100% it's no big improvement.

Pots don't have enough surface area to effectively capture heat. So in our
experiments, like those done by A.D. Karve, we are doing great to get 30% of
the 8,600 BTU's released from a pound of dry wood into the water in a pot.
Big pots do better than small pots. Full pots are better than half empty
pots. Multiple pot stoves raise efficiency up to 40%. In the lab it's
possible to get close to 50% but that's using a skirt that covers the top of
the pot forcing hot flue gases to pass over that surface as well. Not
practical. Fans help to raise percentages, maybe because hot flue gases hit
the pot faster. But fans are not practical where we work.

All cooking stoves can be responsive to different sized pots by manually
sizing the fire to the pot size but much more importantly, the skirt around
the pots can be opened and closed, fitted, to create the optimum gap next to
the particular pot. A adjustable sheet metal skirt that surrounds the pot
forcing hot flue gases to scrape against the pot sides results in the big
fuel savings we are desiring. Paying attention to the pot rather than the
fire results in greater gains in fuel efficiency.

A sheet metal cylinder around the pot isn't as sexy as combustion trickery
but it works wonders. As does it's bigger brother: the HAYBOX, which
improves heat transfer to the pot so well that food can be cooked using 1/4
the fuel. There's your miraculous breakthrough, Paul...a box full of
insulation that does all the simmering using only retained heat in the
enclosed pot.

Best,

Dean
 >

Paul S. Anderson, Ph.D.,  Fulbright Prof. to Mozambique 8/99 - 7/00
Dept of Geography - Geology (Box 4400), Illinois State University
Normal, IL  61790-4400   Voice:  309-438-7360;  FAX:  309-438-5310
E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders


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