[Stoves] Stove Camp Newsletter 2013/heat transfer

Fri Aug 2 14:24:09 CDT 2013

Hi all - 

Not a geometry or materials heat transfer issue, but controlling excess air is hugely important , since we want the gas temperature as high as possible. This probably in Baldwin. 

Ron 

----- Original Message -----
From: rongretlarson at comcast.net 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, lannych at bellsouth.net, "Dean Still" <deankstill at gmail.com> 
Sent: Friday, August 2, 2013 1:19:59 PM 
Subject: Re: [Stoves] Stove Camp Newsletter 2013/heat transfer 

Lanny, cc Dean and list: 

Only because I heard Dean talk several times a day last week - let me expand. 

1. I think Dean recommends material by Baldwin for his material on skirts. Generally I was hearing a 1 mm gap, but I know Dean has used less. I heard numbers like 10-15% efficiency improvement, which is huge. He probably would say that your use of a cylindrical vat bottom could also benefit from a cylindrical skirt, whose gap width starts large and narrows to the 1 mm gap size. Dean (?) has designed a combined pot and skirt being sold at StoveTec. 

2. Use of a Kelly Kettle, or anything to move the flame from the outside of the pot to inside. 

3. The stove top should have a conical shape, not flat, so that the flow resistance is the same along the gas path. 

4. Dean talked some about reducing the thickness of the boundary layer, by putting in gaps or obstacles, where the gas has to speed up. Thereby the boundary layer gets thinner, allowing better heat transfer. This was the work of Dale Andreatta, also referenced last week. 

5. There was some mention that some TLUDs do better than some rockets by having better radiative heat transfer. 

6. Plancha designs can improve by insulating unused surfaces. 

7. Shiny surfaces radiate less than black. Might even find some selective radiation (paints?) materials - as in some solar heaters. 

8. I have a friend who puts his pot on a flat plate to keep the pot clean. The bottom of that (not the pot) could be designed to be a better heat absorber. It also could be designed to support the skirt and even a better match to the stove top 

9. Wider shorter pots are more efficient. 

10 You have talked of enclosing the top. 

I'll bet you can add some. 

Ron 

----- Original Message -----
From: "Dean Still" <deankstill at gmail.com> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Sent: Friday, August 2, 2013 11:22:08 AM 
Subject: Re: [Stoves] Stove Camp Newsletter 2013/heat transfer 

Hi Lanny, 

I start with Sam Baldwin's book. 

http://ebookbrowsee.com/baldwin-biomass-stoves-engineering-design-pdf-d280999584 

Best, 

Dean 

On Fri, Aug 2, 2013 at 7:25 AM, Lanny Henson < lannych at bellsouth.net > wrote: 

Dean, 
Thanks for the report which mentioned the importance of heat transfer but mentioned no specifics. 
Could you or Dr. Winiarski or Dr. Baldwin expand on this? 
How are you improving heat transfer? 
Lanny 

>Both Rockets and TLUDs were improved by paying greater attention to heat transfer. Even though getting excellent heat transfer is well described and doesn’t have to cost more it is amazing that getting more heat into the pot is so frequently ignored. As Dr. Winiarski and Dr. Baldwin point out, optimized heat transfer is a vitally import element in a good stove. 

<blockquote>

----- Original Message ----- 
From: Dean Still 
To: Discussion of biomass cooking stoves 
Sent: Friday, August 02, 2013 12:07 AM 
Subject: [Stoves] Stove Camp Newsletter 2013 

	ARC_Logo

Aprovecho Summer Newsletter 

August 1, 2013 

Summer Stove Camp comes to a close 

Sidwell_StoveCampSidwell_StoveCampSometimes Stove Camp goes so well and summer 2013 was one of those occasions. Many folks camped out and cooked delicious meals for everyone. Large projects, like a couple of bread ovens, were made and used. Manufacturers spent long, long hours testing and improving their products. Everyone worked hard and made huge progress throughout the week, especially the two prize winners. 

There were two challenges for the week. One was sent to us by Jordan Kowalke who is working for Total Land Care in Malawi. He is designing a TLUD that will be used to burn wood chips for which he requested the assistance of Stove Camp participants. Jordan sent a list of specifications that the winning TLUD design must reach. This prize was awarded to Mick Black and Jeffrey Santiago who tweaked Paul Anderson's Quad 3 stove until it cleanly burned the wood chips and lasted long enough to make posho , a typical meal in Malawi. 

Dona_DoraThe other prize was for any stove that met the Tier rating of 2-3-3-3-3 (Thermal Efficiency, High & Low power PM, and High and Low power CO). Many stoves met this criteria so participants were allowed to vote for their favorite. The prize was awarded to David Evitt with his Guatemalan Doña Dora stove which he toiled to improve all week. 

During camp there was a ‘shotgun’ approach of many individual tests done by many operators. For this we had three testing locations set-up. The two Laboratory Emissions Monitoring Systems (LEMS) in the lab and a new configuration we are calling “IAP-in-a-Box”, which is a test kitchen with a basic hood and collection chamber that holds the Indoor Air Pollution Meter (IAPM). This system was set up with the idea that testers can watch the live output from the meter and gauge their design’s progress without having to do a full test with the more complicated LEMS equipment. The “IAP-in-a-Box” is being documented for those who wish to test total stove emissions using the small, portable, IAP Meter. Please contact us if you are interested in getting a system. 

Dr_TLUD_GraphLast summer people did many tests on charcoal stoves and it was obvious looking at the results that although charcoal stoves emitted a lot of CO they were almost all very low for PM. This year we created a large graphic representation of all the tests on the wall and added to it everyday. The conclusion was that TLUDs generally produce lower amounts of PM than Rocket stoves but there seemed to be two classes of TLUDS: really clean ones and only moderately clean ones. Both Rockets and TLUDs were improved by paying greater attention to heat transfer. Even though getting excellent heat transfer is well described and doesn’t have to cost more it is amazing that getting more heat into the pot is so frequently ignored. As Dr. Winiarski and Dr. Baldwin point out, optimized heat transfer is a vitally import element in a good stove. 

StoveCampFoodThe progress with the TLUDs was impressive. Several of the stoves worked well with different fuels and had adequate turn down ratio. Paul Anderson helped everyone to understand TLUD mechanics and air control. He was joined by Ron Larson, Art Donnelly, and others who are evolving the TLUD approach. 

There is so much work that any motivated person could do, solving problems of the poor and moving humanity towards a more fulfilling and elegant future. Dean joked that even a monkey could follow the iterative design method and would eventually come up with innovative solutions to issues such as food drying, desalinization, solar heating, and stoves. All it takes is making a change or two per day in the prototype and seeing if it performs better or worse. That’s what we do here at Aprovecho and we hope that it catches on. 

Sincerely, 

The Aprovecho Team 

Photos by Simon Anderson and Sanya Detweiler. Aprovecho Research Center is a lab based in Cottage Grove, OR--visit the main website for more information. Please email sanya at aprovecho.org regarding subscription to these updates. 

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</blockquote>

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