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The development of the stove for the project
We started by first to test a stove design based on the “Rocket Elbow Principles”. The Rocket Elbow comprise of a horizontal chamber for firewood and a vertical chamber in which the burning is taking place and where the heat are channelled to the pot.
You can read more about the “Rocket Elbow Principles” here.
You can also find 10 design principles for firewood stoves here.
We were from the start aware of that a stove build of local materials bricks, clay and stone would have the problems that a lot of heat from the fire would be absorbed by these heavy materials and stored in the stove itself, thereby taking energy away from the pot. This could only be avoided if the firebox was made of materials there have an insulating effect.
The only insulation materials we can find locally are pumice. Pumice is a material of volcanic origin it contains a lot of small air pockets, it is the air pockets which gives the pumice its insulating effects.
Pumice is found at the base of the volcanic mountain Mount Meru. Pumice is here excavated out and used in the nearby town Arusha as materials in lightweight concrete blocks. Pumice is in this way available 130 km away from Karatu. As Pumice only shall be used in small quantities in each stove and it is a very light material, we found that the transport expenses in relation to each stove would be small, and that it in this way will be feasible to use the pumice.
The greatest of the firebox, build on the basis of pumice, is achieved by ceramic blocks which are made by mixing pumice with clay and water, shape it in to blocks and burn them as ceramics.
In the start of the project we did not have the possibility to make ceramic blocks of pumice, but we could make blocks for the firebox out of pumice and cement. Such blocks have nearly the same insulation effects but not the same strengths against heat.
We started the development work by using pumice / cement blocks for the firebox.
In our stove workshop in Endabash we build 2 prototypes of new stoves based on the “Rocket Elbow Principles”
For comparison we also build a clay stove of the “Lusotho” type, a stove that earlier have been used in the area, without greater success, but still are used by e few households. We also made a traditional 3-stens fireplace.
The two prototypes of a new stove was build one as:
A stove for one pot and a elbow firebox, but without iron plate as a shelf for firewood. In this stove the pot is placed on top of the stove, and there is no chimney to the stove.
The second prototype af stove was for 2 pots, with a elbow firebox with iron plate as a shelf for firewood. In this stove the pots was lowered down in the stove to allow the fire from the stove a greater area of the pot to lick around. There was connected a chimney to the stove.
The stoves were build with a framework of bricks with clay mortar. Inside this frame there was filled with sand in which the firebox of pumice / cement elements was placed. The top of the stove was build as a layer of cement mortar.