[Stoves] Energy loss into stove walls

[Paul S. Anderson]

Dear Crispin and Penn and all,

Thank you to both of you for your assistance.  Crispin has stimulated 
discussion
about ceramic vs metal stoves.  I hope that Tom Reed will state his pro-metal
arguements.

About Crispin's message and my specific stove question, I was aware of several
of your key points, but it was instructive to read and think about them again,
plus the additional concepts.  I was assuming that the heat lost through the
sides of the ceramic gasifier was about the same as from a metal one.  Big
assumptions, but I am just after some preliminary findings.  Also, I did not
mention before:  The 6 insulative bricks were held together inside a very
thin-walled metal can (the kind in which you get 3-flavors of popcorn in the
USA at Christmas time.)

Crispin wrote:
> I welcome an open investigation and debate of this question.  That is what
> science is about.  We don't have to come to a firm conclusion, or even
> agree, but we can't over-simply the stove and then invest large amounts of
> money in multiplying the products based on an inaccurate theoretical
> representation of a partially understood truth.
>
>> How much heat energy (and wood equivalent) is needed to raise 5 kg of
>> material 700 deg C?
>
> Well, it is about 200 gm of wood (assuming no losses), but you forgot to
> divide by two at one point.

Thanks for the approx number.  I did not forget to divide by two.  The inside
temperature is well over 1000 deg C and the outside temp was much more than 30
C, so that is why I used the 700 deg C number.

I note and agree with your use of 0.84 because of what Wikipedia says is the
specific heat capacity of many construction materials (cement, soil, sand) as
being in the 0.8 to 0.9 with the units expressed as  J * 1/g * 1/K    or    J
g-1 K-1  or as Penn wrote:  J/(kg*K) .   That gives the heat at about 3000 J,
which is 200 gms of wood because we get about 15 MJ per kg of wood.

Nordica has not yet sent me the data sheet for my test of this stove, but from
the Report on Stove Camp recently posted by Tom Miles, the stove used 
231 gm of
wood per liter, time 5 liters = 1155 gms.  That was above the 850 gm benchmark
for 5 liters.  Subtracting 200 g would put it at 955 gms.  And there were
several other factors.

A.  I used about 50% of the fuel as Illinois woodchips that have a higher
moisture content (MC) estimated to be about 15 to 20 % compared to the kiln
dried wood (MC = 5 %) that Apro uses in the official testing.  An increase of
10% of MC for half of my fuel means 75 gm of water (meaning less fuel value)
and that the additional water must be raised from 30 C to 100 C and boiled off
from the fuel (consuming energy that could not heat the pot).

B.  Plus issues of the pot being too high from the fire and

C.  having a pot-skirt that was with a large gap, promoting a rather 
rapid fire
during the simmer stage.

Remember that this was done at Stove Camp and the stove configuration was only
finalize while at camp.  I had only tested other aspects (primary air inlet,
etc.) of the ceramic AVUD gasifier (or continuous feed TLUD) with 2 lightings
prior to arrival at Stove Camp.

I only had one chance to run a test of this stove under the emissions 
hood, so I
was not able to get all the variables fully controlled nor maximized with
repeated testing.  I was glad that I got the one test run of this stove and
that the CO and PM were wonderfully low!!! ( CO  =  1.2 g per liter,   and
PM = 63 g per liter.)   But fuel usage was high, and I am trying to understand
it and correct the situation.  I hope to drop the CO and PM even lower when I
am using only half the amount of fuel.

In conclusion, the updraft gasifier (continuous feed TLUD that becomes an
updraft AVUD gasifier for continuous feeding) is extremely hot, and I believe
that ceramic protection is important.  However, Crispin has help me realize
that a relatively thin but dense ceramic liner inside a sturdy steel cylinder
might be just fine, especially if it can be easily patched if cracks cause
parts to fall off.  That could be more appropriate than getting heavily
involved with the rather fragile insulative ceramics and the need to fire them
beforehand.

[NOTE:  If you are going to shift to a discussion of ceramics (and not 
continue
about the energy loss into stove wall and/or my stove test), please change the
Subject of your reply message.  Personally, I am annoyed when we have weeks of
discussion with one Subject line that has long been forgotten.  
Maintaining the
"threads" can be important, but so is having a Subject that reflects 
the content
of the message/thread.]

I love this Stoves Listserv!!!!!!!!!  Thanks for being so helpful.

Paul

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