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Post by peterberg on Jan 16, 2009 7:34:34 GMT -8
...First off how would I do any repair work on the rocket once it is encapsulated in brick and mortar? Like for instance if the combustion chambers bricks were cracked and needed replacing? That would be virtually impossible. So I am leaning towards 10 seasons before it will be needed to replace some parts. In that case, you have to rebuild the largest part of the thing. None at all, provided you'll insulate at least the parts outside the bell. Let's assume the bell is 6 or 7 feet high. The input would be best halfway. That happens to be more or less the height of a normal heat riser. Fire clay or not, when there happens to be heat stress in the thing it will crack. So, the best way to do it is building the rocket first. The next step would be building the bell with one wall crossing over the burn tunnel. In this way it is possible to separate the rocket from the bell wall, for example with a layer of aluminum silicate felt or, less expensive, rock wool. The heat riser and part of the burn tunnel will be inside the bell itself, the feed tube and the rest of the burn tunnel will be outside. Now you could build the bell out of ordinary red bricks and clay and sand mix. Single walled, with normal concrete sidewalk pavers as top plates. Another way, to avoid the pavers is closing the top with bricks like larsmith has done. |
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Teach
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Post by Teach on Jan 16, 2009 12:49:29 GMT -8
Thanks for such a speedy reply Peter. If I understand things correctly, heat stresses are caused by different materials expanding and contracting at different rates causing things like mortar to get busted apart. Is this correct?
If yes, then I still think I would prefer to sepparate the rocket from the bell entirely other than by direct connection of the flue from the rocket to the bell.
As over time the materials in the rocket need to be repaired or replaced, the rocket could be rebuilt without having to touch the bell as it should be intact far longer than the rocket if properly built yes? Providing I am willing to sacrifice having two footprints instead of one integral print?
I am building this unit/s in my basement that has a poured concrete floor and concrete walls that are eight feet in height. The chimney is a concrete block chimney that rises more than 30 feet above the basement floor on the outside of the house. The chimney flue exits the basement at the five foot height. If the riser of the rocket is roughly 3-4 feet in height, will this be a large enough difference in height between the top of the riser tube and the chimney flue I would be tying into?
What sort of safe distance could be used for the clearance of the top of bell and the bottom of the main floor's wood framing above? The rocket unit will be an eight inch system.
If for example, I have 12 inches of clearance between the bell and the floor above, could I make the bell shorter but stretch it out from side to side or is height most important? I'm thinking mass and surface area also come into play.
Could concrete cinder blocks be used for the bell? If the use of a paver would be ok for the top I just assume concrete blocks would also be ok for the rest of it? Would you then have to go to a concrete style mortar? Thanks.
Teach....
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Post by Donkey on Jan 16, 2009 16:52:16 GMT -8
You can expect greater durability out of your heat riser if you use heavy gauge steel pipe.
I've used 1/4 inch gauge, 8 inch pipe. I cut the top and bottom off of an old hot water heater tank and used it as a jacket. Between the steel pipe and the tank I poured pearlite mixed with a little clay slip (to keep the pearlite together). Over this arrangement I placed the barrel.
If you plan to loose the barrel, you could junction over with some kind of elbow arrangement.. Either welded or made from fireclay/brick..
I personally would place the heat riser inside the bell in this case.. Steel heat risers aren't going to crack and it should handily outlast the rest. The weak point then would be around the horizontal burn tunnel (assuming it's brick), and up top near where the heat comes out of the heat riser. I'd try to keep it from being too close to the internal walls of the bell..
On second thought, there should be a good 6 inches between the inner heat riser pipe and the outer steel jacket, if you plan to encase the whole thing in brick... It should be enough separation right there.
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Post by peterberg on Jan 17, 2009 10:37:19 GMT -8
...If I understand things correctly, heat stresses are caused by different materials expanding and contracting at different rates causing things like mortar to get busted apart. Is this correct? Yes. If I understand correctly, you mean the difference between the 30 feet chimney and the 4 feet riser? In that case the answer is yes. Better to make the bell wider and deeper, to give it more volume. Beware though, the top of the bell need to be at least 3 feet away from the end of the heat riser. More volume means automatically more mass and weight. Concrete blocks would be OK, provided they are not hollow. It is better to use clay and sand mortar and thin seams. Clay is much more flexible than cement. |
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Teach
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Post by Teach on Jan 17, 2009 14:37:43 GMT -8
Hmmm, wish I knew how to work the quote function. On the heat stress - great. What I was trying to get at with the different heights was ...I'll try again. In the basement where the stove will be built......from the concrete floor up to the exit hole leading into the chimney is 5 feet. If the top of the riser tube is roughly at the 4 foot mark, then there is only a difference in height between these two points of 1 foot vertically. Once the gasses travel out of the riser tube up into the bell, then back down to the exit at the floor level (single bell) they make they're way back up to the exit leading into the chimney which is at the 5 foot mark. After all is said and done, of the gasses rising and falling........the end result is only a 1 foot rise between the riser and the exit. By contrast - your setup in the pictures shows your stove pipe coming out of the bottom of the bell and then up at least 10 feet or so to exit out into the chimney. Will one foot of rise be enough? or will the fact that the gasses continue out and up the chimney make this a non issue? I think I may have just answered my own question  The reason I was wondering about the height of the bell and the distance between it and the wooden framed floor above it is for fire hazard reasons. Could it ever get hot enough to start a fire if there was not enough room between the top of the bell and the floor above? If I require 3 feet between the top of the riser to the underside of the bell then I could very well be over 7 feet to the outside top of the bell. Fire concern once again. Or will it not get that hot on top of the bell? Now, can I build these units together from the concrete floor up or will I have to lay down a coarse of bricks on top of the concrete floor upon which the rest of the units will be built? Will I need a full layer of bricks for the bottom of the rocket to be built on or from which the walls of the bell will be started from? Could I build both directly from conrete up with no brick floor for the units? I understand the affects of mass for storage. When I asked if the bell could be stretched out from side to side......what I was getting at was if you had a bell that had a foot print of say 3 feet wide x 4 feet deep and 7 feet tall................could you make it say 13 feet wide x 4 feet deep and 7 feet tall? Or do you end up with a similar situation like with the benches where you could pull too much heat out of the gasses? Trial and error seems to be the only way to really find out! What really appeals to me about the double bell is the possibility to heat two separate areas on two separate floors.......one bell in the basement and the second going up through the wooden floor to warm the area of the house directly above also. |
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Post by peterberg on Jan 19, 2009 12:19:01 GMT -8
or will the fact that the gasses continue out and up the chimney make this a non issue? I think I may have just answered my own question. Spot on. that's the answer. I'm afraid it's quite possible. Stay away at least one foot from the ceiling with the top of the bell and adding a thick layer of insulation on top would be sufficient, I do think. It will quite warm there, of course the hottest place in the bell. You could decide to build the heat riser shorter than 4 feet. The closer the heat riser will come to the top, the hotter the top will be. The bottom of the bell can be straight on the concrete floor, that would be no problem. Insulation underneath is better, but not a necessity. The rocket on the other hand have to be shielded from the concrete with fire brick and insulation because this one is going to be very hot. Not limitlessly, no. That situation still applies, yes. If you extract too much energy from the gases the rocket will be very difficult to start. And when it is finally going, you running the risk of having your whole basement full of smoke at some point or other. It is not easy to give exact details of how large the thing can be, it is depending on how good the chimney is, among other factors. In that case, you have to know that the second bell is much cooler than the first. A way around this is: make the first as small as possible, and the second large. But if you plan the bells on top of each other through the wooden floor, why not a large single bell? In that way it is possible to have the bell build through the floor. The top is hot first, you don't have restrictions because of the usable height and you can have the fire downstairs with the associated dust, wood chips and splinters. The first iteration of the rocket/bell was still working nicely with a height of 8' 6"! Plus you could have a convenient primer box downstairs as well. Ideal situation, I would think. |
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Teach
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Post by Teach on Jan 21, 2009 18:32:50 GMT -8
I agree Peter. That would be ideal.
I'm a little unclear as to what these primer boxes are. I understand perfectly what they do.........just not sure of how they are configured. I know they are used to prime (so to speak) the draft of the chimney to get the updraft moving before lighting the stove and filling the room with smoke due to overpowering downward cold airflow. In my mind they would be placed low in the scheme of things but how are they built? If using pipe are they configured with a T for example with the bottom of the T capped and removed for priming? Or with the chimney for example.....do you build or modify the chimney by putting in a box (access port) of some sort below the feed point of the stove pipe?
In an earlier post by Lars entitled Design theory, Donkey had a post that got me thinking similarly to what I was thinking earlier and similarly as above when I asked if the stove could not be built outside of the bell.
What I am thinking is to build a mass rocket heater complete with barrel. Then rather than build a bench or other type of built in furniture to act as a heat sink or battery, I was thinking of using the bell technique of trapping and holding the heat while allowing the cooling gasses to take out the smoke
........not that there will be much with the rocket.
Another benefit of this is that if the rocket was removed or to be rebuilt, a steel box stove could be slid into place and plugged into the bell just as easily to take advantage of the heat exchange rather than allowing it to go up the chimney?
In the design theory post you mentiond that both the feed and the exit could both come in at the same level but preferably with the feed from the firebox coming into the bell slightly higher than the exit. I'm assuming that this is to allow for an easier separation (less intermixing) of hot gasses vs cooler gasses?
Within the bell itself...........would there be any advantage for say (heat storage) that would not be detrimental to the function of the bell to fill the cavity of the bell up to the point of where the heaters gasses enter the bell? Seems to me that you are going to have a lot of heat in the bell anyway, with the hottest gasses moving upward from the heaters exhaust ..........why not capture some of of the heat within the bell with say rocks of a diameter of roughly 12 to 16 inches below the point of entry of the heaters gasses?
You are aware of my height restrictions. Care to take a stab at the allowable length and width of a bell for a rocket heater of 8" if the bell is only 5-6 feet high? I'm thinking perhaps 4 feet deep x 6 feet long by 6 feet high? Or better yet, 3 feet deep x 7-8 feet long by 6 feet high?
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ernie
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Post by ernie on Jan 21, 2009 22:28:57 GMT -8
interesting concept, looks to me like the heat torus in the first bell is erratic. you could put a block in to break up the stream (the clean spot on the roof of the bell). I think this would jump your efficiencies a bit more. if the heat column is correct you will not see any blacking in the corners. to rid you of the spikes at each in the the combustion cycle you might think of potting self closing flaps in the air inlets. if made from aluminum or other lite material it should self regulate the amount of fresh air you can draw. this in tern should cut those Co2 spikes out since the fire would get the proper amount of air at each stage.
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Post by peterberg on Jan 23, 2009 5:28:59 GMT -8
I'm a little unclear as to what these primer boxes are. I understand perfectly what they do.........just not sure of how they are configured. Personally, I don't have any experience with primer boxes... but donkey could tell you all about it. And Ernie probably as well. Instead of a bench! That would be quite nice. The exit of the bell lower than the input is to avoid a straight path between those points. Mixing will take place all the time as long there is flow. About introducing more mass in the bell itself: That could be done, but the best place is not at the bottom. The idea which springs to mind is to make the walls of the bell gradually thicker higher up. In that way the bulk of the mass is at the top and at the hottest place as well. I've seen a 6" rocket/bell combination working with a quarter of the volume you mention. You are aiming for an 8" system, which is 1.75 times as big... So half of the volume you propose would be sufficient, probably. Say anything between 70 and 80 cubic feet. Otherwise you'll run the risk of having a stove with water condensation in the flue gases. Keep in mind that a bench system is a tunnel with the center of the gas stream hottest. So giving off heat to the wall of the tunnel is not very good. In a bell there isn't such a thing as a stream in a specific direction. |
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Post by Donkey on Jan 23, 2009 8:40:46 GMT -8
Somewhere, (probably in one of my physics texts) I've read that (in a bell type system) every molecule of heated gas will touch every square inch of surface of the inside of the bell before finding the exit.
This may not be strictly true, though true enough to imagine how good heat distribution can be in the bell system.
Peter.. Do you think it would be possible to introduce some kind of mini bell type system, or chain of bells within a bench?? Cause the nice thing about benches is that the heat is in a most convenient place.
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Teach
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Post by Teach on Jan 23, 2009 17:23:44 GMT -8
LOL, Donkey I was thinking this same thing not so long ago but dismissed it as being unsuitable as the bench height would be so high that it would no longer be comfortable to get on and off of. Otherwise if it was not that tall the the bench would get too hot for sitting on as the top of the bench would be too close to the heat of the bells underneath.
But, what about an elevated bed?
Or, simply use a bell for the bench?
However if you were to keep with the idea Donkey, what about using clay/ceramic pots upside down placed above in such a manner as to form part of the flue channel and within the bed. From the side it might resemble a picket fence with pickets that were flat on top rather than pointed. The gasses could move through the flu underneath the pots while the pots captured and held heat Not sure how well that would work as it would create a lot of friction and inhibit the movement of gasses along the flue. I think a person might possible gain more from using a more narrow and rectangular flue similar to what Lars did within his heater that would more efficiently give up heat to the bed. Certainly worthy of more thought though.
If a person used a bell for the bed/bench the surface on top would be more uniform in heat levels and you could easily incorporate more insulation (like cob) on top to prevent the top from getting too hot and successfully add more mass to the bell.
I'd like to know if the bell would perform well if it had a height of only say 3 or 4 feet but a length of say 6 feet. Same volume as Peter mentioned about but lower in height to accomodate a bed/bench .
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Post by peterberg on Jan 24, 2009 2:28:44 GMT -8
Peter.. Do you think it would be possible to introduce some kind of mini bell type system, or chain of bells within a bench?? Cause the nice thing about benches is that the heat is in a most convenient place. Unfortunately, I don't have any experience (yet) with a low and wide bell. But according to prof. Groume-Grjimailo, who described the system in 1923 it should work in a shallow bell as well. Here is a rather large document containing scans of an earlier book by the same professor. heatkit.com/docs/shabaldin/grimailo.pdfNorbert Senf of the Masonry Heater Association did some work on small bells in a row and it worked. see link: heatkit.com/html/lopezn.htm Of course I don't have the foggiest idea about the difference in temperature between first and last small bell if the row is, say, 10 bells long. My guess would be: an open shallow bell as the best system of the two. |
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Post by peterberg on Jan 24, 2009 2:41:17 GMT -8
interesting concept, looks to me like the heat torus in the first bell is erratic. you could put a block in to break up the stream (the clean spot on the roof of the bell). I think this would jump your efficiencies a bit more. if the heat column is correct you will not see any blacking in the corners. Ernie, I think you are referring to some of the pictures. The inside of the bell is not visible there, it is the combustion chamber. In the combustion chamber only pyrolysis takes place most of the time. This will result inevitably in black patches. Later on, after repeatedly firing, all the black spots disappeared. Mind you, the highest temperatures are reached in the rocket derivate behind the combustion chamber. That part of the stove is always very clean, of course. I'm inclined to give a new name to this type of afterburner, just to avoid confusion; for example "rocket siphon". |
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ernie
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Post by ernie on Jan 24, 2009 12:47:59 GMT -8
ahhh ok
it looked to me like you had blackening in the corners. my focus is to get as much of the soot and gases burned as passable so the exhaust has little or no unburned fuel. I think rocket siphon would be a good name for it.
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Post by peterberg on Jan 28, 2009 11:53:33 GMT -8
I've seen a 6" rocket/bell combination working with a quarter of the volume you mention. You are aiming for an 8" system, which is 1.75 times as big... So half of the volume you propose would be sufficient, probably. Say anything between 70 and 80 cubic feet. Teach, I'll have to rephrase this quotation. The cubic feet I do mention here is far too large. Mainly because the rocket stove you are planning is not inside the bell, but entirely outside it. On top of that, the barrel over the heat riser will distract a lot of heat as well. So I think in your proposed configuration 40 or 50 cubic feet for the bench/bell would be all you'll need. |
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