[Stoves] Designs/Swosthee Stove

[lannych]

I notice that the Swosthee Stove/burner has insulation in direct contact 
with the inner metal pars. This is what caused the failure and the short 
life. Move the insulation to the outer wall and maintain an air gap (even a 
dead air gap will work) around the inner metal parts and they will last a 
lot longer. I learned this from the  fire marshal while building kitchen 
grease exhaust ducts, which can not fail under intense heat if there is a 
fire. See NFPA96 fire codes. I have also experienced this with tin can 
burners. The will only last about 3 or 4 burns with direct contact 
insulation, but with an air gap there seems to be little ware after a dozen.

> Regarding the Swosthee stove about which you have specific questions -
> About a thousand were built during 1990 - 1884 and field tested. The key
> problem has been the life of the stove. Because the inner metal walls
> experience temperatures of 750 to 1000 C, the hardware lasts only a few
> months.

A draft body for a pan or pot module sitting on this burner should provide 
enough draft to make it work without a fan.

And perhaps a curved piece of metal to lean against the slots would control 
the intake air.

Also the complicated cone/funnel shape  fab parts seem unnecessary.

Lanny Henson



----- Original Message ----- 
From: "Mukunda" <hsm at cgpl.iisc.ernet.in>
To: <stoves at listserv.repp.org>
Sent: Monday, August 07, 2006 10:43 AM
Subject: Re: [Stoves] Designs


> Regarding the Swosthee stove about which you have specific questions -
> About a thousand were built during 1990 - 1884 and field tested. The key
> problem has been the life of the stove. Because the inner metal walls
> experience temperatures of 750 to 1000 C, the hardware lasts only a few
> months. One of the key things that we uncovered in this period was that we
> cannot get higher effioiencies unless the air-to-fuel ratio is close to
> stoichiometric value. It was also clear that any of the stoves that
> utilized free convection process for delivering the air won;t be able to
> maintain the correct air-to-fuel ratio for the duration of the operation
> of the stove. This is the reason that further development in this
> direction was not pursued, We examined the possibility of using a fan to
> deliver the air, some thing that we did in laboratory experiments to
> determine the role of air-to-fuel ratio. Unfprtunately, during 1990 to
> 1994, there was no cheap harware for delivering the air at a fixed flow
> rate. And even after we saw the fixed fuel stove with Dr. thomas Reed in
> 1996 or so, we could not identify for a long time a reasonable source of
> fans. It is only in the last three years that computer fans that are
> really cheap have arrived in the market. This as given life to the reverse
> downdraft stoves all over the place. We have done some serious scientific
> study over the last four years and uncovered features of the stove that
> will give high efficiencies. We have been able to get up to 55 % thermal
> efficiency through various optimization strategies. We are still exploring
> how to get up to values in excess of 60 % particularly because the
> kerosene and gas stoves promise 70 to 75 % efficiency. This has ben our
> aim over the last twentyfour years.
>
> The meeting at Kunming was very interesting. I met with three stove people
> from US working on stoves for long time. What became clear to me at the
> end of the workshop is that very few have clue to the science and
> technology. They are genuine enthusiasts and other people. As soon as they
> see something working, they want to ruch and adopt. For instance, at a
> factory in Kunming, every body saw a beautiful concept on steam injection
> to obtain clean combustion. Almost the next day some wanted to introduce
> it into their designs without (a) really understanding how things work
> or(b)care or sensitivity to intellectual property protection aspects. This
> is a tragedy that stove enthusiasts have to face.
>
> I was told in addition, that a stove performance test protocol was being
> developed at Berkeley with the support of many people. After some
> conversation I learnt that serious sceintists are not involved in this
> activity. A set of data that were presented that showed the amount of fuel
> required to heat 5 L to boil and associated emissions, in my view is very
> faulty as the power level is not a subject of consideration. Th epower
> level makes a seroius differnce to every thing. I also explained in a
> strong way that neither candle nr a furnace can be used for deriving
> cooking heat and I do not know if it went across.
>
> In summary I have concerns on less-than-scientifically correct input going
> into the stove design aspects. I have just expressed it to you here.
>
> We will continue our efforts to produce a high efficiency clean burning
> continuous feed biomass stove in coming times.
>
> I will be happy to interact with you or others on any scientific aspects.
> The paper that you enquired is available on a web site for downloading. i
> shall intimate you the address on Monday/Tuesday.
>
> I am sorry for the long mail and Thanks for the inspiration to express my
> thoughts. - H S` Mukunda