Brant Foster wrote:This is my inner form for my RMH combustion chamber and riser. I will be casting with a dense/packed mix of
sodium silicate and sand. Is 4" of casting enough to insulate the riser to get complete combustion? It's a 6" system.
I built this out of scrap wood because it's going to be burned out when casting is done.
Any comments about design are definitely welcomed. The horizontal run is slanted to create an instant draft when getting it started.
Thanks in advance!
Glen Herbert said :
The riser needs insulation to prevent the space around it from being as hot as it is inside; this is one of the "pumps" that drives the draft.
And unless the space around the riser is also freaky hot, you would be losing heat in the riser space where final combustion is supposed to happen.
- - - I just wanted to expand on the last part of Glens comment !
A lot of people in the past have used just Fire clay and Perlite/Vermiculite and they have had mixed results with durability* adding Sand to that mix
will reduce the Insulating qualities but will add strength- producing a lightweight fire brick like material with much greater durability.
Certainly adding Sodium Silicate or the less corrosive Potassium Silicate will add strength.
With the Durability of the inside wall of the Heat Riser taken care of. We still need further protection to assure that there will be a minimum amount of
Heat Energy Transference Through the inner wall of the Heat Riser !
Failure to isolate these Two streams from each other can result in a Balancing or Equilibrium of the temperatures of the Two Streams -Causing
The "Pumping Action'' which promotes the 30'+ Horizontal flow of our hot exhaust gasses through the Thermal Mass to STALL !
This will only be made worse ( I Think ) by your use of a Brick Dome which will retard the Transfer of Heat Energy Through itself - The rapid cooling
of the Hot Exhaust Gasses by Radiation out through the ductile steel of the 55 gal drum is part of that '' Heat Pump !
The Need for insulation to surround the formed Heat Riser can be as simple as a 2'' layer of Mineral wool (rulex )wrapped around the outside of the
Heat Riser !
This is definitely the old-school and cheapest way to go !
Hope this helps and is timely, for the good of the Craft ! Big AL
* There is much discussion about the use of materials like light insulating fire brick in the Feed Tube, Burn Tunnel and Heat Riser, which promotes
rapid heating, and the idea of using a Heavier, Denser, "Kiln Brick with its increased durability and ability to both refract most of the Heat Energy
back into the Combustion Zone while stabilizing the higher temps and resisting Heat Energy Transference !
This usually boils down to what you can afford and what you can get your hands on ! A.L.