[Stoves] Dimensions for the Ethiopian Mirt stove
Ronal W. Larson
rongretlarson at comcast.net
Wed Oct 7 11:35:33 CDT 2015
Stephen, Christa et al
1. I concur with Christa on the diameter. My recollection is that the thickness is about 2 cm. I have no idea what temperature they are fired to - but that is probably around in the literature. It will make some difference in the heat transfer characteristics. I think every village or small market region all over Ethiopia probably has a few families making the mitads - as well as other needed ceramic objects (especially for making and drinking coffee). When entering these markets you can always find the mitad/ceramic area from the “clinking” noise as buyers try to determine the quality of the different ceramics.
2. My work on char-making enjira cookers was for a few months in 1995 - and I have forgotten most. Here are a few recollections:
a. I vaguely recall that I was working with a can of roughly 5 gallon size - maybe 30 cm diameter and a little more in height. So the flame traveled under the mitad some 15 cm before turning up. The gap between the can top and the mitad was probably a few cm. Probably not too critical, but you should allow some variability as you further develop.
b. Most housewives cook enjira every two or three days - not every day. With a char-maker you therefore need to have enough fuel to last the hour or more she will be cooking. I think mine lasted 1.5 hours or more. Each enjira “circle” probably took 3-5 minutes to cook. There are (or were) some excellent Ethiopian cook stove developer NGO’s around Addis. I would seek them out before going into this is detail. 20 years ago, none were working on char-making. Probably are doing so now; I vaguely recall reading of one 10 or more years ago.
I tried converting dung to char under the mitad - and (fortunately) had zero success. Better that go into the ground.
c. The housewives are skilled in pouring out the batter - able to control thickness quite well (I never got to that level). Probably can start pouring from either outside or center depending on heat distribution. I can only guess now, but they probably learn from their mothers how to control the heat distribution by varying the wood and coals below. I can’t recall their typical fire diameter but probably closer to 50 cm than 30 cm. I think normally the mitad is supported on 3 rocks. These dimensions and typical wood consumption per injera should be in the Ethiopian stove literature. I guess over 5 kW needed. There is probably good data on kg wood per kg enjira. Wouldn’t surprise me that you can halve those numbers for traditional cooking. A big plus will be in your ability to quickly control the power levels.
d. The traditional 60 cm ceramic mitad could probably be replaced for better lifetime economics. I think the average lifetime is less than a year, even though they of course try to keep a good one as long as possible. A key feature is being able to soak up a mustard seed oil. But commercial enjira factories (I visited one) use electric resistance coils integrated into an (I recall) Aluminum mitad. I presume the coil spacings have evolved to give a satisfactory temperature distribution - maybe even recommending a pour from inside to outside. I think not considered as satisfactory for flavor as the traditional ceramic/oil approach - but maybe (now twenty years later) there is a sintered or other material you would want to work with. I think I can buy an electric version in Denver - maybe Sydney. Would be worth it.
e. A key part of the cooking is placing an insulating “cone” (name forgotten) over the enjira as it is cooked. The only material I ever saw was dung. Value in keeping the humidity higher as well as reducing radiative and convective heat losses. I burned up several. Although these are super cheap in the same markets selling the mitads, I guess there is room for cost saving improvements in this “insulation”. I have vague recollection that the commercial enjira cooking factories probably used an aluminum “hemisphere”.
f. I gave a demonstration once to the Ethiopian Minister of the Environment. She was supportive, but her main reaction was that everything was too bulky- it had to be foldable against the wall. She noted the typical village home was too small to store in place, if cooking was indoors (but I think most is out of doors). I did switch to a foldable tripod supporting the mitad.
g. All the enjira makers take care to collect the unused char. I once watched a woman hired to do testing of wood use at an Addis stove NGO scrape up all the char at the end of her testing day - as that was considered part of her entitlement. But Ethiopia (like Sudan which has some similar cooking practices) wastes a lot of wood as they make char. So there will be competition for the char for cooking vs biochar for soil and atmospheric improvement. When I was doing this work 20 years ago, I had never heard of biochar (or terra preta , etc). What you are doing is very important to save forests - even if little gets used as biochar.
h. I recall seeing some work out of Lawrence Berkeley (?) on similar cookers being used in Darfur.
i. I presume Australia has a few immigrant skilled Ethiopian women who still remember how to prepare/cook enjira. I would make every effort to hire such guidance.
Best of luck.
Ron
On Oct 7, 2015, at 3:04 AM, CHRISTA ROTH <stoves at foodandfuel.info> wrote:
> Hi Stephen, you need to have a firechamber/ heat exchanger to be able to heat the ceramic plate on top, the mitad. there are various diameters, but you should aim at something between 55 and 65 cm diameter.
> regards
> Christa
>
>> Am 07.10.2015 um 09:25 schrieb Stephen Joseph <joey.stephen at gmail.com>:
>>
>> Hi Ron et All
>>
>> Does anyone have the dimensions for the Ethiopian Mirt Stove for cooking Injera. I am trying to adapt to make biochar
>>
>> Thanks
>> Stephen
>>
>>
>> On 5 Oct 2015, at 11:41 am, Anand Karve <adkarve at gmail.com> wrote:
>>
>>> Dear Stovers,
>>> LPG is one of the most user friendly fuels for a stove. I was told that it is a by product of the petroleum refining process. Formerly it used to be burned off, but nowadays it is used as fuel. The cost of LPG is mainly the cost of bottling and bringing it to the user, plus some taxes. As far as the village inhabitants are concerned, the city dwellers are their role model and they would like to have the same life style. When we try to sell our improved biomass burning stoves, which are of course costlier than the home-made mud stoves, potential users refuse to buy them, because they feel that by spending a little more money, they can get a LPG stove It is only the do gooders like the Rotary Club and similar other philanthropic organizations who buy improved stoves for free distribution to villagers. We have therefore stopped selling them to villagers. Our main buyers are city dwellers, who occasionally cook on wood or charcoal, just for the fun of it. Our urban household biogas plant is however quite popular, mainly because the municipalities have stopped accepting biodegradable wet garbage (vegetable waste, fruit waste and food waste).
>>> Yours
>>> A.D.Karve
>>>
>>> ***
>>> Dr. A.D. Karve
>>>
>>> Chairman, Samuchit Enviro Tech Pvt Ltd (www.samuchit.com)
>>>
>>> Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)
>>>
>>> On Sat, Oct 3, 2015 at 11:54 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
>>> Dear Anh
>>>
>>>
>>>
>>> In Central Java people ‘too poor’ to use LPG are often seen with a 3 kg cylinder (subsidised) and consume that amount in 3 months. It is used for particular things, mostly making tea and re-heating food at short notice.
>>>
>>>
>>>
>>> It is nothing close to being their ‘primary cooking fuel’ but 70% of the population has and uses LPG. About 40% use it ‘primarily’. Of those who do, 70% use wood to heat water, plus the 100% who cook primarily with wood.
>>>
>>>
>>>
>>> Where the mix is strong, there is a clean kitchen and utensils, and a dirty kitchen with its utensils, tending to be outside or near the door. There is a market opportunity to use a dedicated water heater that is clean enough to be used in the ‘clean’ kitchen. No offers have been received yet…
>>>
>>>
>>>
>>> Crispin
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Dear All,
>>>
>>> I dont think that would solve anything. There are 2 problems with the poor, access to service and afford service. I dont think a poor family having lpg stoves would meant that they will switch to use lpg for cooking unless lpg is the cheapest or at least highly affordable compare to the income.
>>>
>>> Vietnam has very good lpg stoves coverage, ~95% rural family that we talked to has lpg stove using 12kg plg tank. But most of them use that 12kg for 3-6 months, some cases up to 12-18 months while city folks use same tank for 20-30days.
>>>
>>> That a good thing that the Indian PM do but that is not enough to solve the root of the problem, not yet.
>>>
>>> Anh
>>>
>>>
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