[Stoves] Energy loss into stove walls

[Dean Still]

Info from the amazing Dale Andreatta from:

See http://www.bioenergylists.org/stovesdoc/Andreatta/Heatloss.htm

Heat loss from stoves: Thermal properties of insulative bricks Overall heat
losses, Dale Andreatta, FTI Consulting, April 30, 2003

"The heat lost from the gases goes to 2 places.  A portion of the heat goes
into the stove body and is retained in the body.  Another portion goes into
the stove body but then passes through and into the environment.  For the
lightweight materials, the amounts of heat going into the 2 places are
generally about equal.  For the heavier materials (baldosa) a larger
proportion is retained in the stove body. 

 

It turns out that the thickness of the stove wall is relatively unimportant
in determining the total heat loss.  As the stove wall gets thicker a
greater amount of heat is retained in the stove body, but a lesser amount
passes through the stove wall.  As the wall thickness decreases below about
2 cm, the loss increases rapidly, but increasing the thickness much beyond 3
cm has little effect.  Very thick walls actually loose more heat since so
much heat goes into the body.  The optimum thickness is generally around 5
cm, but there is usually a broad band in which heat loss is near minimum.
The 3 cm used in these calculations is a compromise.  The detailed heat
transfer calculations described in Appendix 2 could be used to find an
optimum thickness, but for most materials this is about 5 cm, and the heat
loss isn't much less than at 3 cm. 

 

I believe that, as a rule of thumb, a heat loss of 1 MJ is about as low as
we need to go.  This would correspond to about 56 grams of dry wood.  This
is only a small percentage of the heat being released, perhaps around 5%.
Lowering the heat loss further would not give substantially better
cookstoves.  We can see in the above chart that several materials currently
available get heat loss close to about 1 MJ.  Hence, future work might be
directed at increasing their longevity if necessary rather than improving
their thermal properties much further."

Best,

Dean 



-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Sunday, August 05, 2007 9:08 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Energy loss into stove walls

See http://www.bioenergylists.org/stovesdoc/Andreatta/Heatloss.htm

Heat loss from stoves: Thermal properties of insulative bricks Overall heat
losses, Dale Andreatta, FTI Consulting, April 30, 2003


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