Hello!
For the past several weeks, we were in the process of building a cookstove that could be constructed in Guatemala. The women there need a charcoal-burning stove with reduced particle and smoke output. To do this, we needed to improve insulation and smoke control from the sheet-metal stove already put in place. We were to use materials that were cheap and locally manufactured.
2/25: design reviews for your original sketches. Start sketch models. Sheet metal intro.
To begin constructing our cookstove, we did research on what cookstoves had already been constructed. The research is presented below.
After, we went into the shop, and Estuardo taught us about the machines so that we could drill, cut, bend, and connect sheet metal.
Goals:
_improve insulation and smoke control
_low cost and local manufacture
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Considerations:
2 grates, furnace (air flow), insulation (ceramic)
size: using charcoal briquettes, pan/pot size
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Our device:
. Used outside (that means we don’t have to worry about inhaling particulate matter). So, standalone. [don’t incorporate into pre-existing stovetime design (wrong diameter, also particular matter going up)].
. Use standalone device (especially if outside).
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To do:
Create a few designs
Make a priorities table and evaluate between them
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Websites:
aprovecho.org
cookstove.net
_enviorofit has the best charcoal stove, $50
_ghana stove (is the older version of the uganda stove)
_thailand bucket
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Envirofit:
Much better idea of how to use it here: http://www.youtube.com/watch?v=6gUvgBw9jVI
So it’s used outside, and you need matches and charcoal and paper. It stands on its own, and you can adjust the fire.
Note: there are three grates here. From bottom to top, I’m saying grey grate, silver grate, and black grate.
The vents are are on the bottom, and adjustable. Then there’s a grey metal grate with airholes. The charcoal sits on top of the first silver grate, and ashes fall through onto the metal grate. Then there’s a black metal grate on top. Everything’s contained in one enclosed pot, so the warmth is insulated.
Easy to clean.
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Uganda Stove: http://www.hedon.info/BP29_HouseholdEnergyActivitiesInUganda
Traditional stoves
...The other stove which is common in the urban areas is the Uganda traditional sigiri. This is a metal charcoal stove similar to the metal Mbaula found in Malawi. It is made of scrap sheet metal obtained from discarded motor vehicles or used bitumen drums. This is a one-pot charcoal stove and is made in many sizes. The Uganda traditional metal 'sigiri' is made by artisans who are found in all the urban areas of the country. This type of stove is inefficient and wastes a lot of charcoal. The stove is portable and uses about 600g of charcoal at a time. Its production dates back to the turn of the century. Most of the Ugandan urban households which use charcoal own this type of stove.
Fig 1 - Sigiri Stove
There are three organizations working on improved cookstoves, all essentially of the same design. This is mainly improved by the addition of ceramics for insulation.
Fig 2 - Usika Charcoal Stove
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Thailand Bucket http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00-0--4----0-0-11-10-0utfZz-8-00&a=d&cl=CL3.28&d=HASH018a1dce7bcc8cf7c408b109.19
Types of Biomass Household Cooking Stoves Used by Rural Families in Thailand
Construction
The stove body and grate are made from a clay/rice-husk ash mixture formed in moulds. After the preliminary moulding they are finished by hand, dried and fired. They are then put in a metal bucket with a protective insulation between the stove body and bucket. The stove is portable and new grates can easily be purchased and installed.
FIGURE
Use of the Stove
The charcoal is lit with kindling and after two to three minutes the charcoal bed is burning and the pot can be put in place. The insulating layer reduces heat loss and keeps the charcoal bed very hot. The chamber only needs to be partially refilled to maintain maximum output. Closing the air inlet door will reduce the burning rate considerably. Left-over charcoal can be retrieved at the end of cooking by putting it into a covered jar or a sand pit to extinguish it.
FIGURE
Specific features of efficient charcoal stove
2/21 Plans:
Potential insulators:
Cellulose (grown in Nicaragua)
Design #2!
Amount of sheet metal we’ll need...
exterior box...91 in by 15 inches... 1365 in^2
each grate: 24 x 22 (x3) = 1584 in^2
t-rods... 15in x4 (x4) = 240 in^2
1365+1584+240 = 3189 = 22 ft^2 worth of sheet metal..
Aluminum sheet comes in 3x3, and is $22... so that’s 9 ft^2, so like 3 of those should be plenty, and we could sort of get by with 2. So, $66.
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Different kinds of insulation: (http://www.appropedia.org/Improved_solid_biofuel_stoves#Improved_cook_stove_materials)
Ceramic tiles
9http://www.homedepot.com/p/t/203223650?catalogId=10053&langId=-1&keyword=ceramic+brick&storeId=10051&N=5yc1v&R=203223650#.UTFhqI5_b50
Mud brick
https://www.engineeringforchange.org/news/2012/04/19/improving_the_improved_cookstoves_standards_test_centers_and_tips.html
In the end, we decided to make a stove based on the envirofit model. Images are shown below.
We initially ordered aluminum sheet metal, ceramic tile, and a long hinge that we didn't end up using.
1. Three 3x3 sheets of aluminum sheet metal: $66. Purpose: structure of containers. Any sheet metal that doesn't burn will work.
(Calculations:
exterior box...91 in by 15 inches... 1365 in^2;
each grate: 24 x 22 (x3) = 1584 in^2;
t-rods... 15in x4 (x4) = 240 in^2
1365+1584+240 = 3189 = 22 ft^2 worth of sheet metal..)
2. Three 12inx12in ceramic tiles: $9. Purpose: cheap insulation, fire proof.
3. Long hinge. $9. Purpose: connecting outer grate to external box. I have no idea how to construct a hinge, and I can't remember how the Ghana stove did it (and can't find it online.)
Then, after attempting to create a frame with the thin sheet metal, we realized we needed thicker sheet metal, and bought 1/4 in sheet metal. We used this for our frame.
Our model was originally many parts, because then each of the grates (there were two) could be adjusted based on the style of cooking. We decided that that would mean too many parts and excessive complications, so we made the inner frame non-adjustable, and then we had three parts (the outer box for insulation, the inner frame, and the upper grate). Prof. Banzaert told us that it would be better if we could reduce the amount of parts, so we connected the top grate to the outer box. Thus, we finished with two parts, the outer box, and the inner frame (though the upper grate was removable.)
2/28: design reviews for your sketch models. Start to build.
Our greatest challenge in building was realizing the aluminum sheet metal wouldn't be strong enough to support the pot. We solved this problem by using the chicken wire from another group. If we had not had this available, our grates would have collapsed from beneath the weight of the charcoal and pot.
We spent a lot of time planning dimensions, and from there a lot of time measuring and cutting. It was very successful because of the time we had taken to make the dimensions how we wished them to be.
Because we had ceramic tiles that were 12 inches, our box ended up being 12 inches because the tiles would have been almost impossible to cut. The dimensions of the rest of the box and frame emerged from this basic parameter.
We constructed the bottom grate out of two sheets of metal, which were riveted together. The second and top grates were chicken wire, with sheet metal woven in that we could use to rivet to the outer frame, which was made of heavier metal.
We constructed the outer box on the first day, making sure the dimensions of the sheet metal surrounding the ceramic tiles were correct. It barely was, so that the tiles stuck very tightly into the box. This was a good thing, since we then didn't need to use adhesive. In Guatemala, it would be expected that their ceramic was made out of a mold, or that they would press clay into the sides of the box.
3/4, 3/7: continue building, testing, probable field trip one day.
Our main building process was to measure and mark metal, cut it, bend it, and do a lot of riveting. It was a rather smooth process, and we only had to come in outside of class for an hour. It was also smooth because we divided the work fairly evenly after our initial group work with the outer box. Because we had spent so much time planning together, it was pretty easy to work by ourselves on the actual building process. Estuardo was very useful in aiding us in the construction process.
3/11: final testing, final design review.
Our stove didn't end up boiling water (it turned out to be pretty open on top, and the wind didn't help), but the water was bathwater temperature, which wasn't bad. We had hoped that the increased insulation and improved design (the hallmarks of the envirofit design) would reduce airborn pollution, but this didn't turn out to be the case. Our pot was black by the end of the fire. We meant our pot to be used outside, but we didn't have a good grasp of how to reduce emissions, besides copy the envirofit design. It was difficult to discern the exact reasons for why the envirofit design reduced emissions, because that information wasn't available online. In the future, we should find out exactly why it was effective. We also should have considered that our design was more open than that of the envirofit (because of the constraints of using square ceramic tiles) so that mitigated the beneficial effects. We could have used a more obvious method to reduce pollution, like make a tunnel like one of the other groups did. The overall problem for all of the stoves seemed to be an incomplete grasp of WHY all of the example stoves reduced emissions.
See resources for some useful links. Remember the basic design process discussed in class:
In defining the problem, we probably placed less emphasis on emissions than we should have, because we didn't understand the problem. Nevertheless, our stove wasn't terrible in final design, as it had good airflow, strong grates, and was easy to clean and use. It was a bit rickety because it contained an inner structure that was removable, but we liked the outer box sheltering the inner structure design.
We placed emphasis on low cost and manufacture (we were able to construct it fairly quickly and cheaply, which is a good sign), and in modeling the envirofit design with good insulation and airflow.
- System-level Design
- Detail Design
- Testing & Refinement
A lot of decisions were made along the way, and I enjoyed how it was a flexible process. Overall, however, we stuck pretty closely with our original design. If we were to work on this stove in the future, we would need to have multiple versions of the stove instead of basically sticking with our original concept.
all of which probably require:
- research
- brainstorming
- selection (Pugh Chart)
- prototyping
We made a cardboard version of our box before we constructed the metal version. For the metal version, we added a central metal frame that was different from the envirofit and our original design.
- experimentation
- evaluation
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pics from the final day: Roshan, me, and Melody. We had our stove stuck on logs, but our original concept was to use bricks.
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