[Stoves] Ash mixed with clay to mud in brick stoves

Fri Aug 17 17:43:21 CDT 2018

Dear Kevin

Mud is quite insulative without adding anything. Before assuming anything please check to see if there is some advantage to having a lower density stove body (which will definitely be physically weaker) before recommending it. Make sure the amount of new fuel required to perform some task is consistently less before assuming it is “better” in some way.

Many tests have shown that on average, a high density combustor core outperforms “insulative” chambers unless the cooking time is very short. The reason is that heat must emerge from the walls at a high rate during the late fire cooling period. If this effect is achieved, the CO burns out more completely, the invested heat (some of it) is returned) and the char burns more completely.

If the stove body is ‘insulating’ the gain in thermal efficiency is brief and only at the beginning, give or take a few Watts. Unfortunately an insulating body, even if it contains a large amount of invested heat, cannot give it back to the fire chamber at a rate high enough to sustain the combustion as late or as long. Depending on the stove configuration, the efficiency gain for having a high density combustion chamber is about 1/12th of value which is considerable: 26% v.s. 24%, for example.

When burning dung the effect is far more noticeable to the eye, without measuring anything. The thing to check is how much ‘char’ there is in the large lumps of ash when the fire is out. Using a high mass, dense brick lining for the chamber, it is possible to get dung to burn so completely that you will not find more than one piece of char the size of a pea after burning 5 kg of fuel. All that is left is a fine white ash.

An example (including all drawings) of such a stove is available here<http://www.newdawnengineering.com/website/library/Stoves/Kyrgyzstan/KG%20Model2.5/>.

Regards
Crispin

From: Stoves <stoves-bounces at lists.bioenergylists.org> On Behalf Of K McLean
Sent: Friday, August 17, 2018 2:05 PM
To: stoves at lists.bioenergylists.org
Subject: [Stoves] Ash mixed with clay to mud in brick stoves

In Africa, we are teaching women to make rocket stoves out of 11 standard bricks and a piece of rebar.  You can see it here, called a 3-layer stove:  https://docs.google.com/document/d/1ZryS7gQ1q3zKLZPM2KcXdtIHbOYQp4PbloPqMvrlZ5Y/edit?usp=sharing<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1ZryS7gQ1q3zKLZPM2KcXdtIHbOYQp4PbloPqMvrlZ5Y%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7Cf927dbb0d7754fd5fc1808d6046c458f%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636701260400084277&sdata=q3ZC6QPL34O6NXpg%2FqzGd5yz7Aj%2B%2BA64aN7AZ4YvyQw%3D&reserved=0>

Do any of you have experience mixing wood ash with clay soil to make the "mud" more insulative?  The women like to mud in these stoves.  We want to determine whether to suggest they mix ash into the mud.

Thank you,
Kevin

Kevin McLean, President
Sun24
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