Wouldn't that depend a lot
allen lumley wrote:...start out with at least a 6'' J-bend RMH system, Generally anything smaller is an advanced
build, and when an if you get the smaller size working it is too small to do much good ! Big AL
Geoffrey Levens wrote:Thank you Allen, I do get the dramatic size/power decrease. I plan to build at least a couple J-tube test stoves in my back yard, starting simple and get the feel. Eventually I am after a mass heater for my house which will be super insulated and only about 300 sq feet so I have some concern about overheating the space. Once I have done some test set-ups in my yard I can try to ferret out appropriate size info.
allen lumley wrote:Erik Weaver : As Ianto Evans has pointed out in his book with two rocket mass heaters built exactly the same, except for barrel size, they both have to shed
the same amount of heat energy to create the push me pull you magic that allows Your RMHs super draft. Counter-intuitivly, the small barrel will radiate that
heat energy off of the barrels surface at a Higher Temp not a lower one! You may need to give the smaller barrel more space in the room due to its higher
This is the same reason when your 4 yr old is tired and wants up in your lap they are such a good cuddle With a higher mass to surface area than yourself,
in order to maintain a Nominal 98.6ºF they must radiate off the excess heat energy at a higher temp !
Partially covering the barrel will work, as will smaller fires, we still need to plan on reaching the higher Temps that together with our refractory material re-
radiate the heat energy to our combustion core and allow for hot clean fires !
I believe that I understand the Taller gap above the Heat riser is a function of the Horizontally fed Batch rocket, I may be in error there !
For the Good of the Craft ! Big AL
Yeah, I was actually thinking of building a platform of some sort in front, raised area to stand on, funky split level kitchen...
I don't plan to cook any veggies up there (too tall in my set up)
When the air in a bottle gets hot, it expands. If there is any water inside, it will boil and expand 1700 times, so this is a serious danger. Imploding is never an issue. Water vapor is already expanded, and will only expand more if heated.
When I put the first fire in it to dry out the core, this bottle got hot fast and the clay plug kept it from venting, so it blew out the back face with a loud pop/bang. Fortunately it didn't damage anything important.
A little microwave like you show might be small enough to heat with a 3" rocket... but you will need a bunch of mass and insulation around it, and you will need to cut an entrance in the bottom for the hot gases to enter, and make an insulating door. All in all, it seems like a lot more work to make an oven the way you are trying than to make the whole thing of clay/soil cob. The dense bricks would be the right kind of material for the oven floor.
No matter how well you insulate them, the heavy bricks will not work as well as cob or firebrick or insulating refractory. A tiny 3" system needs all the help it can get to work well.
How long are these going to last? Not very long. Off the top of my head I'm thinking aluminum melts around 1800 F and mild steel a little higher, a little below 2000 F. I've measured 1710 F at the entry of my burn chamber (6" system), and it is doubtful that is the hottest point. Under ideal conditions wood is said to burn at roughly 3400 F. The bottom line, is that I think the cans are doomed to fail, and fairly quickly from a heating use (as opposed to some of the flaming cans of death seem on picnic tables in some YouTube videos, heheh).
Doesn't this mean that for the 3-inch can idea to work as a model for space heating, a pourable / castable core material will have to be poured in around the tin can mock up? That would only be using the cans as the form, and letting them burn out is fine after the casting material has set up.