[Stoves] Energy loss into stove walls

[Paul S. Anderson]

Stovers,

Some calculation assistance please.

At Stove Camp I used an insulative ceramic 6-brick chamber for my updraft
gasifier (AVUD style) (  http://www.hedon.info/docs/BP53-Anderson-14.pdf  )
with a single-pot application above it to burn the gases.  My fuel consumption
was surprisingly high, and I want to know how much energy (and the
corresponding amount to woody fuel) was absorbed into the walls.

Total weight of the gasifier (not the rest of the stove structure) is 7 kg.  I
will allow for 1 kg of excess weight of construction and another 1 kg for the
equivalent device made of steel, and therefor call it 5.0 kg of "extra body" to
be heated.  The material is 2 inches (5 cm) thick, and it does get rather hot on
the outside (but not measured).  Inside there is a 6 inch (15 cm) diameter
vertical cylindrical area for the hot gasification.  Height is 11 inches (28
cm).

This is not a TLUD with pyrolysis around 400 deg C in a small zone of pyrolysis.
 This is a true updraft unit with red-hot char in the base of this ceramic mass,
and very hot throughout the whole mass.  I will estimate that it was 900 deg C
or perhaps even higher, but that also is not known for sure.

Help please.  Can we simplify this?  What about saying that 5.0 kg of mass was
raised from ambient temperature (30 degrees C ) to an average temperature of
730 deg C.  (Net change of 700 degrees C.)   How much heat is needed for that? 
and what amount of wood would provide that amount of heat?

Basically, the issue is:  A water boiling test takes 25 minutes to boil and 45
minutes of simmer (total 70 minutes, but we could make it easier to just say
one hour of operation, as if boiling was done in 15 minutes).  During this time
the stove body radiates heat (wasted through the sidewalls) and also takes in
heat that is held in the sidewalls (also wasted as far as the water heating is
concerned).  An equivalent metal version weighs 1 kg and the ceramic version
weighs 6 kg (mine was 7 kg, but I allow 1 kg for excess and then another 1 kg
as the equivalent weight of the metal version, leaving the 5 kg mentioned at
the start.)

Can we please get some numbers to work on, and then we can discuss the merits
and demerits of metal vs. insulative ceramic.  How much heat energy (and wood
equivalent) is needed to raise 5 kg of material 700 deg C?

Thanks

Paul
-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson





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