Re: Tuffa vs Approvechite

["Kevin Chisholm" <kchisholm@ca.inter.net>]

Dear Tom

 

The insulations can have a relatively high melting point, if they do not contact ash..... the ash fluxes the insulation. While the Mullite is an aluminum silicate, wood ash can introduce potassium and calcium oxides.

 

Sadly, for durability considerations, I would suggest that the wall profile of a stove must be as follows:

    1: Steel outer jacket

    2:  Liner of insulating refractory INSIDE the steel.

    3: Hard refractory inside liner, to prevent ash and flame contact with teh insulation.

 

Now, this is not all bad.... the good result here is that the insulation that is protected with a refractory inner liner can be of lower quality. A lower grade "rock wool insulation" could be used.

 

Kindest regards,

 

Kevin Chisholm

 

----- Original Message -----

From: Tom Reed

To: Dean Still ; Stoves ; Agua Das

Sent: Thursday, October 24, 2002 6:12 AM

Subject: Tuffa vs Approvechite

Dear Dean and All:

 

Tuffa sounds great.  However, it doesn't occur everywhere and would require shipping in big chunks, so costly. 

 

Here's a challenge for Aprovecho. 

 

The ideal stove insulation would

 

o  have zero mass

o  have a melting point over 1000 C (white heat)

o high strength,

o be easily formed into elbows, liners, cones etc

o be cheap 

o be available worldwide for local fabrication. 

 

We know that spun Mullite (an alumino silicate, inherently cheap and available worldwide under names such as Kaowool) can withstand 1600C.  We'd like to know more about rock wool, also widely available in various forms, probably doesn't withstand more than 1100C but may be adequate.  I think it is made from spun slag, but start research at

http://www.amerrock.com/news.htm.  (It's also used for hydroponics.  We know that fibreglas melts at 600C so would NOT be adequate.

 

We also know that Mullite and rockwool can be formed with a mild vacuum into sleeves (riser sleeves), crucibles, board etc.  (Starch binder?)  We also know that Mullite can be hardened with an amorphous silica surface (commercially expensive, but probably cheap, made from water glass, also worldwide available.)

 

So I hope that Aprovecho can use some of its creative minds to put together a good insulation program that can be implemented in villages, towns, cities around the world to make ALL shapes of stoves. 

 

Forget clay for the fireside insulation.  OK for the outside. 

 

Your booster/pusher,                                TOM REED                                   Biomass Energy Foundation

----- Original Message -----

From: Dean Still

To: ethos

Sent: Thursday, October 24, 2002 7:11 AM

Subject: [ethos] Fw: Tuffa

Dear Friends,

 

Tuffa sounds like Larry's dream material: chunks of pumice large enough to carve out a Rocket elbow!! In our part of the world it is rare to find rocks big enough but I'm hoping that tuffa will be great for combustion chambers... Roberto, please keep us informed! Y buenas suerte, socio!

 

What a great heating, cooking stove you could make from really big tuffa rocks! I imagine the rock glowing in the darkness.

 

Best,

 

Dean

-----Original Message-----
From: Roberto Escardó <robertoescardo@arnet.com.ar>
To: Dean Still <dstill@epud.net>
Date: Wednesday, October 23, 2002 8:23 PM
Subject: Tuffa

I was today with a geologist in our University and she eplained me that TUFFA is   CONSOLIDATED PUMICE !!! (In  fact they are the same material)

I hope to get some samples and try it for combustion chambers. Looks promising.

Un abrazo

Roberto

 

I also get some values for thermal conductivity of pumice: about 0.2 kcal/mh °C. It corresponds to a coefficient of thermal transmittance K=0.58 Kcal/m² h °C.  ( When I find my table I will give you an R equivalent)  It depens on granulometry.