I have been doing a lot of research on rocket mass heaters
. I am quite certain I understand all of the principles to build rocket mass heaters as they have been built for the purpose of heating larger homes/spaces.
I have a few questions on materials and theory so that I may experiment with some variations on the theme. Hopefully they will spark some new dialogue and possibly forays in to new territory.
First question has probably been covered before but I have not found a definitive answer
1. Is there a simple tried and true formula/ratio to create ideal refractory material for a chimney/heat riser? Ideal meaning high temperature, resist shrinking/cracking etc. Is this formula also the same if one wants to cast the entire core and heat riser from the same material? (different sections though) And if I pour a j-tube, is there a formula that will not require waiting 4 weeks before the unit can be used?
I would love to figure out a homogenous material I could cast the core from, I plan on casting it in a small galvanized feed
type tub. For simplicity sake it would be great to come up with a simple j-tube form to hang in the tub and do a SINGLE simple pour in to the tub, rather than all of the multiple stages/materials that are used to currently build the cores.
I keep seeing people
build these 2000 degree furnaces in a wood
box. Metal seems like a much more suitable material to contain fire. Wat up wit' dat?
I have seen all manners of materials and ratios for heat riser. I understand firebrick wrapped with stovepipe and stuffed with insulation works best, but I am experimenting with MUCH SMALLER units, and the firebrick method requires too much space basically forcing you to use a huge drum as the final shell which creates a huge footprint
I like the idea of perlite and clay mixture, that seems the most "rock like".
2. What kind of clay? where do I get it? I need to be able to purchase these materials, I can not dig any up.
3. if I decide to use a sacrificial metal liner for the riser, that burns off, leaving the refractory material, what happens to that material? do any toxic compounds become embedded in the refractory material to be slowly released in exhaust over time? The reason I ask is because one of the applications will be exhausted very close to a chicken coop
. I do not want zinc or other metals being exhausted in to their environment/runs.
I also wondered about perlite in the heat riser. Does the surface of the riser release particles of volcanic glass in the exhaust? Are exposed bits of perlite in the heat riser and exhaust run a health issue for any humans who may be very close to the exhaust flue? This question also applies to COOKING rocket stoves people pour in 5 gallon buckets. Are they breathing in small particles of volcanic glass rocketing up in to their food and lungs?
4. Is there an ideal ratio for the inner dimensions of the core/heat riser/exhaust? Are there any rules dimension-wise which are especially critical while there is room for experimentation elsewhere? In particular, is the diameter of the airflow path the SAME ALL THE WAY THOUGH the system? Or do you need the exhaust portion of the path to have larger diameter than the core/riser to create lower pressure on the back end, to let the gasses slow down and get burned rather than being rocketed out the chimney cap before getting burned.
All of my designs will incorporate very tall heat riser to amplify the front end updraft as much as possible.
For smaller applications I may or may not be that concerned with a long exhaust run/large thermal bench. I will be trying to use a few horizontal runs made from metal to release the heat inside the dwelling rather than a huge slab of permanent cob
using up all the floor space. I completely understand that less thermal mass means more fluctuation and fire tending. This is fine for my applications. Plus I have an idea to keep the fire burning unattended with zero thermal mass in the system which I will present as it's own topic.
Thanks for any help, and thanks to all who have pioneered these devices. The efficiency and ability to use scrap twigs and branches that are useless in conventional stoves is truly an evolution in heating technology.
Huge chunky cord wood trees
could be put to much better use than belching heat and smoke out in to the cold night air!