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Dear Tom
Given that 1 litre is a convenient water volume, and given
that the test should be available universally, I would propose that the standard
"pot" be the standard 1.36 litre "juice can" which measures about 7" (176 mm) by
4-2/8" (106 mm) outside dimensions. My assumption is that this is indeed a
universally available can size.
A 1 litre measure would be at a height of 127.2 mm from the
inside bottom.The can I have in front of me now just happens to rolled rings in
it. The second ring from the top is almost exactly 127.2" from the inside
bottom. This would serve as a very simple "fill level indicator." This can size
also has about 50 mm of ullage or "head space" to prevent
boil-over.
Note that this is a test system, and does not necessarily have
to use a "real world cooking container."
A very interesting point was raised by Ron: Who has the
"World's fastest stove?" If there was sufficient interest, my Company, Energy Engineering Ltd, would post a $100 First
prize to the Contest entrant having the "Worlds Fastest Stove," using a
maximum of 500 gms solid biomass fuel
charge
Contest Rules could tentatively include:
1: The stove system must be at room temperature before start
of the timing.
2: The time clock starts when the fuel is
lit.
3: Any "common solid biomass fuel" may be used.
4: A "common solid biomass fuel" is defined as any naturally
occurring solid non-fossil biomass material that is economically
available to at least 1 million people throught the
World.
5: The stove system must be entirely self powered. Internal
powering, such as would result from a thermopile and motor, or a Sterling
engine system to provide forced draft or suction effects, is permissable,
providing that their source of energy is the permitted fuel charge.
6: The container employed shall be a standard commercially
available "juice can" with the top cut off with a standard can opener.The can
shall not be modified to increase its surface area.The Judges can, at their
slole discression, supply the Entrant with a "standard" can if they feel the
entrant's can has been modified in any way.
7: The can shall have a snug fitting cover with a 10 mm hole
in the top center, and a 2 mm hole to act as an air vent, 25mm away from the
center of the cover..
8: Water content in the container shall be 1.0 kG of potable
water, measured at 20.0 degrees C. Water temperatures more than 20.0 C shall be
lowered to 20.0 starting tempreature with ice cubes..
9: A copper penny shall be placed over the 10 mm hole in the
cover prior to the start of the test.
10 Timing will stop when the penny is seen to more as a result
of steam created.
11: The winner shall be the entry whose penny moves as a
result of steam generation in the shortest time.
Judging the stoves will be a bit more difficult, in that this
is a potentially a "World Class Event." If there is sufficient
interest, then Contest and Judging Details can be worked out.
I would tentatively propose that the Final Tests and Award of
the Prize would take place no later than 1 Nov 2002
Perhaps the Stoves List, or some other suitable
Organization could sanction the event, to give it stature?
Possibly we could discuss the Contest Concept on the Stoves
List, to see if there is interest, and if so, to see if a practical way can be
found to run the contest.
Kindest regards,
Kevin Chisholm
----- Original Message -----
Sent: Saturday, January 05, 2002 8:51
PM
Subject: Re: LETS ADOPT A UNIVERSAL
POT
Dear Dean
and All:
I like the idea of a universal stove test with a prescribed
pot size. However, I was puzzled during my visit that you boiled 5 lb of
water when so many other people (and therefore we do it) seem to use 1 liter.
I vote for 1 liter because
The test is faster
It is
enough to do most cooking since the steam condenses on the food (when there is
a lid)
It is easier to divide by 1,000 cm3 than 5 lb or 2.72 liters.
Ron asked this morning whether 3 minutes to boil 1 liter was a record.
Possibly. We most always boil in less than 7 minutes, sometimes 5
minutes on the various forced draft stoves. FOr water at 20 C boiling at 100
C, 5 minutes to boiling implies a heat transfer rate of (1 liter X 4.18
kJ/liter-degreeX80degrees/300 sec) 1.11 kJ/s = 1.11 kW, a respectable heat
transfer. (The small element on an electric stove consumes 1.5 kW, the
large 2.5 kW).
I hope you are taking a census on the answers,
having asked a good question.
Yours truly,
TOM REED
BEF
STOVEWORKS
In a message dated 1/5/02 12:25:15 PM Mountain Standard
Time, dstill@epud.net writes:
Dear Lanny,
Glad to hear that you want to continue the
Rocket Wok project. I'll try from
my end to use the stove as much as
possible, get the students to use it and
give it a real try out. And
I'll get you all the feedback. Also inform the
List.
I looked at
your improved pot skirt and my two cents worth would be that
using a
insulated Rocket combustion chamber under the pot gives us a lot of
draft so I wouldn't think that diminished draft would be a problem. Mark
Bryden who advises me about stoves, has the idea that increasing the
force
with which hot flue gases contact the pot helps to punch through a
still air
boundry layer so I wonder about the value of increasing dwell
time, slowing
hot gases, as a big determinant of heat transfer. I don't
know and the
perfect test might be to compare results from a straight
skirt and your
spiral. I do know that the right sized gap has a
tremendous effect on heat
transfer and that this gap is very small.
Larry uses as a rule of thumb
keeping the same cross sectional area all
through the stove so bigger pots
use smaller gaps.
Of course,
the pot shape is a huge factor. A pot that touches more water
inside is
better, therefore a large diameter pot with a little water in it
boils
quickly. In our tests, big pots generally score higher than small
pots.
Could I then take this opportunity to forward a suggestion which Ron
and I
tossed about on a train heading from Rugby to London? Let's form
one center
of sanity in the bigger stove world here on the CREST list
and all agree on
a pot size/amount of water that we all use in our
tests! Then we can compare
results of tests. Until we do so, this factor
will confound comparisons.
At Aprovecho we now use a nine inch in
diameter steel pot that is five
inches high. We use five pounds of water
in it. But I'm perfectly happy to
switch to liters!!
If we
establish the UNIVERSAL POT SIZE FOR TESTING/AMOUNT OF WATER we will
have done something that the befuddled stove world has not accomplished
in
decades! Let's do it and maybe we'll force the rest of the stove
world to
follow...
Best,
Dean
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