[Stoves] Insulating stoves

[ajheggie at gmail.com]

On Fri, 29 Apr 2022 at 14:59, Graham Knight <biodesigndiy at gmail.com> wrote:

>
> Rocket stoves come in many shapes and sizes but, except for commercial
> stoves and in the USA, they don't prevent the loss of heat to the walls of
> the stove.
> If less heat were lost there would be more going to heat the cooking pot
> and also burn more smoke!
> Is this not important?
>

Yes it is important because it means less heat is lost and hence
temperature is higher in the combustion chamber, this means there is more
chance of the flame burning to completion and hence lower levels of
particulates.

The issue is that of expense.

>
> Maybe the reason that the heat duct is not insulated is concern that any
> fibre glass insert etc will melt if in contact with flames?
> So why not install ceramic fibre insulation which has proven such a
> success stoves in USA stoves for many years!
> It is now available in some SSA countries and is not expensive.
>

Again it may not be that expensive to our eyes but it will be a significant
increase in prices  to others. In use we see kaowool and cerablanket
brands  in direct contact with flames with no problems other than they are
relatively fragile. They can be stiffened with application of calcium
silicate (water glass)  but I had trouble impregnating more than a thin
skin. I never see these fibres being used between steel sheets as Crispin
pointed out they would cause the steel to reach far too high a temperature.

In kilns these ceramic fibre blankets are hung in folds from steel pins,
like hanging washing, to avoid any metalwork fixings being impinged by
flames.

Wood stoves in Europe now tend to use 3/4"(20mm) thick vermiculite boards
to form the sides of the combustion chamber, fittined into a steel or cast
iron stove.. These withstand the high temperature for a number of year's
use but again are a bit fragile. They are relatively expensive too, so a
rocket stove made by pre-forming them and wiring them together would
probably cost over 50$ US.

A TLUD stove gets around the problem somewhat because the downward
traveling pyrolysis front  is at a fairly low temperature and a narrow band
so the steel sides do not get too hot plus the secondary air rising between
the walls is  cooling the steel as it rises.

Andrew

>
>
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