BioEnergy Lists: Improved Biomass Cooking Stoves

From ventfory at IAFRICA.COM Wed Sep 8 06:09:46 1993
From: ventfory at IAFRICA.COM (Kobus)
Date: Tue Aug 10 18:30:36 2004
Subject: Reflective insulation
Message-ID: <WED.8.SEP.1993.120946.0200.VENTFORY@IAFRICA.COM>

Richard S,

You said:
> Did you read this from guru Tom Reed
> What if you coated the sleeve with a reflective material, or, you added a
> liner inside the sleeve, (we talked about a 1/4" wire mesh to protect the your
> sleeve or a plain insulative clay liner: what about making this out of a
> reflective material one which could be removed and cleaned periodically. ..

My reason for using refractory ceramics (riser sleeves) from the start as opposed to using steel or clays was due to the insulative and reflective nature of these ceramics. As Tom R says "Insulation can work in two ways - by slowing the conduction of heat or by stopping radiation of heat by reflecting the heat back to the source". Risers do both very well and being almost snow white in colour (does not get dirty at all) it reflects and radiates infra-red light/heat exceptionally well.

Adding a wire mesh to "protect" the riser from wear and tear sounds good, but would have to be made of titanium or something? The alternative is to use cheap wire mesh, which is replaced from month to month. Richard, also bear in mind that the fuel briquettes are not in contact with the side of the riser in the briquette gasifying stove, so I do not envisage any damage caused by scrapes in any case. As far as long term wear of risers or clays go, I would think risers would eventually wear out (lightly carcinogenic in other words) just like metal combustion chambers wear through. I am not sure on the life expectancy of say a 5mm thick steel cylindrical combustion chamber (Crispin, perhaps you could come in here), but a riser sleeve with a wall thickness of 20mm, used every day, should last 2 years burning charcoal or 4 years burning biomass. Perhaps someone else could give their thoughts on the wear rate of clays (used in a JIKO for instance). Mine are only educated guesses and going on what the manufacturers claim, and I am using a special silicon hardener to increase its durability.

I would consider switching to non-refractory specific clays if someone manages to make white clay combustion chambers and it has good insulative properties.

Regards

Kobus

----- Original Message -----
From: Richard Stanley <rstanley@legacyfound.org>
To: Kobus Venter / HBGS <ventfory@iafrica.com>
Sent: 04 September 2003 15:47
Subject: [Fwd: [STOVES] Reflective insulation]

> Kobus,
> Did you read this from guru Tom Breed
> What if you coated the sleeve with a reflective material, or, you added a
> liner inside the sleeve, (we talked about a 1/4" wire mesh to protect the your
> sleeve or a plain insulative clay liner: what about making this ot of a
> reflective material one which could be removed and cleaned periodically. ..
> Cannot ignore the power of four...
> Thoughts for the moment anyway ,
> anon,
> Richard
>
> tombreed wrote:
>
> > Dear Dean and all:
> >
> > Insulation can work in two ways - by slowing the conduction of heat or by
> > stopping radiation of heat by reflecting the heat back to the source. The
> > second method is best where it can be employed. The radiation heat loss
> > increases as T^4 power, while conduction is only T^1 power, so reflective
> > insulation is particularly important in furnace design.
> > ~~~~~~~~~~~
> > The simplest example of both is the thermos bottle. There is a vacuum
> > between the inner and outer glass to prevent CONDUCTION of heat through the
> > gas. There is a layer of silver on the inside of the glass to prevent
> > RADIATION.
> > ~~~~~~~~~~~~~
> > While at MIT I developed a TRANSPARENT furnace that uses a layer of gold on
> > a Pyrex sleeve to reflect the heat back into the furnace. The gold is only
> > 200 atoms thick so costs < $1 and the gold is transparent in the visible
> > region of the spectrum, but >99% reflective in the IR. See for instance
> >
> > http://www.thermcraftinc.com/transtemp-furnaces.html
> >
> > Our company, Transept sold these furnaces for 25 years and I received ~
> > $50,000 in royalties over that period. (MIT gave its inventors 5% of
> > royalties, industry gives nothing.) Now the company has been sold to others
> > and Bill King, President, is retired.
> >
> > ~~~~~~~~~~
> > There are many ways to stop radiation heat loss.
> >
> > I was head of the crystal growth department at MIT (Lincoln Labs) and
> > developed many high temperature furnaces. One of the highest used similar
> > principles.
> >
> > A tungsten heating element can achieve temperatures > 2500 C (4500 F), but
> > must be well insulated. We wrapped a 6 cm diameter by 10 cm high tungsten
> > element in a coil of ~10 layers of embossed tantalum foil. The embossing
> > kept contact between successive layers to a minimum.
> > ~~~~~~~
> > So I would urge all of you to consider wrinkled foil as an insulation where
> > you can \keep it clean and where temperatures don't exceed the MP of
> > aluminum (~600 C).
> >
> > Onward!
> >
> > TOM REED BEF STOVEWORKS
> >
> > Silver is the best IR reflector, Gold is one of the best, but aluminum foil
> > also have a very high reflectance.
> > Yours truly,
> >
> > Dr. Thomas Reed
> > tombreed@comcast.com
> > www.woodgas.com
> > ----- Original Message -----
> > From: "Dean Still" <dstill@epud.net>
> > To: "ethos" <ethos@vrac.iastate.edu>
> > Sent: Tuesday, August 26, 2003 1:39 PM
> > Subject: [ethos] insulation
> >
> > > Dear ETHOS:
> > >
> > > Lanny Hensen shares a great recipe for use in places where aluminum foil
> > > won't burn up...less than 700F, I think...
> > >
> > > I plan to add more plies of insulation to the inner
> > > sleeve which will be aluminum foil with sawdust and sugar water (all
> > common
> > > materials) wrapped in about 6 plies to build up about 1/2". The sawdust
> > and
> > > sugar burn to make a crusty spacer to keep the aluminum foil from touching
> > > itself. The aluminum foil is a good air barrier to block conduction,
> > > convection. I tried
> > > it on a camp stove, seems to work. This insulating method cheap, simple
> > and
> > > uses common materials if it proves to work.
> > >
> > > Peter Scott writes from Uganda:
> > >
> > > Just a couple of words. So I found my dream accomplice. This guy named
> > > George Sizoomu. He has been building stoves for years and he has already
> > > perfected an insulated brick in Uganda . 1 part rock dust , 1 part normal
> > > clay, 1 part kaolin and 1 part fine sawdust by weight. Works out to 4
> > parts
> > > sawdust , 1 part other by volume. incredibly light!We fired a couple of 6
> > > brick stoves using his mix and ours.
> > >
> > > Details to follow...By the way, I count 12 folks from ETHOS going to the
> > > conference in Boulder!
> > >
> > > All Best,
> > >
> > > Dean
> > >
> > >
>