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Post by endrunner on Jul 26, 2013 9:15:58 GMT -8
We were looking for a simple way to build a bell style masonry heater. This build does not use a barrel that is commonly used in rocket heater designs with J-tube style combustion chambers. We decided to try using commonly available chimney flue pipe sizes to construct a quick and dirty masonry heater using a dragon burner as the combustion chamber. The various charts etc can be found on my blog post. Although we will re-configure it for the 2nd round, we were overall impressed by its strong drafting through out the burn, its ability to extract most of the heat, and its dead simple build. Our target exit temperature of around 200F (to avoid condensation problems) was maintained pretty well. We built the whole thing in a few hours. Blog Post on round one of test
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Post by satamax on Jul 26, 2013 23:13:33 GMT -8
Luvley! Endruner, i was wondering if thoses would hold better than the ones you have used? Ok, they might not transfer the heat as well as the ones you have.Tho, would they crack as much? If you have some of thoses on your side of the pond. They might be worth a try. Hth. Max.
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Post by peterberg on Jul 27, 2013 4:33:08 GMT -8
Sandy, The whole stove is made out of chimney liners, you could line it with fire bricks, of course. Not very simple to do, and probably needed in the first bell only, above the riser mouth to be precise.
What do you think of the possibility to line these chimney flue pipe with... another liner? Earthenware will crack, yes, one way to get around this is to prefabricate the fissures and stuff those with superwool. For example, the 13" liner appear to fit inside the 17" pipe. Of course, this shouldn't be a tight fit, there ought to be some room for expansion. And the 17" item would probably fit inside a 20", don't you think? First bell double-walled, second single-walled I would say.
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Post by endrunner on Jul 27, 2013 7:40:43 GMT -8
The second bell definitely had no crack problems and the heat levels where so much lower, we plan to leave it alone.
We are also going to move the heat riser portion outside the bell, adding 2 13x17 flues stacked with their own cap and exhaust outlet of 11x8 into the 1st bell. The heat riser flue will be filled with perlite around the heat riser up to the exhaust. Should be interesting to see how more insulation around the heat riser affects things. It also will insure all the heat goes to the bell. The area above the heat riser serving as an exhaust channel will of course have to be lined with firebrick.
Moving the heat riser out of the bell will, in affect, enlarge the bell by not using the bottom foot for insulation for the burn tunnel, plus the room needed for the riser. By doing this i am hopping to increase heat capture a bit and bring exit temps down.
Pre-cracking the fissures is a good idea. That would work, I am pretty sure. Once the cracks formed they stayed stable and as it cooled, the cracks closed. One fissure might do it. Some of the blocks cracked on 2 sides, but a clean pre-arranged crack might be enough.
Our plan is to line the 1st bell with the 1/2 size fire brick. This is for 2 reasons. One, we wanted to increase the thermal mass of the unit, so it would hold more. The second is using firebricks, which have higher thermal conductance, I am hopping it removes more heat. I would like to see the next run have exit temps hovering more around 180-190, rather than 200. And of course it will shield the liner.
The 1st bell heated up pretty uniformly from top to bottom. The outside temps were only 30 degrees different from top to bottom. It worked like a sold mass. So I think we would need firebricks all the way in the 2nd bell.
We are planning on using fire clay to fill the round corners to speed up fire brick work. I don't think it will take too long, but we will time it and see. I know that this glob in the corners is considered too thick for fire clay, it will crack, but i figured it didn't really matter in this case since it is really working as a kind of insulator for the flue.
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Post by endrunner on Jul 27, 2013 7:53:32 GMT -8
the 13 would fit in the 17, i think. You are suggesting we fissure the 13, then add the 17 with no conducting surfaces between the 13x7, just air? This would reduce the area, but increase the mass and it would be easier to build? Am i understanding?
If the 13 is pre-cut, and inside the bell does it need supper wool?
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Post by endrunner on Jul 27, 2013 10:57:36 GMT -8
So we have thought about the approach of a double wall bell and checked the fit. I think the easier build, may out weight the superior properties of the fire brick. Making a single slice, on 7 flues, is not too bad, labor wise. The small one inside the larger one leaves about a 1" gap. I am thinking we should fill this gap with crushed granite (which will easily compress during heat expansion) to supply better conduction of the heat from the inner bell to the outer. The double wall will have less interior surface area, but would provide a 3" wall and be easy to build. So it should store a fair amount of heat with a good release curve. The fire brick i think would be a bit better, but it may not be worth the additional cost and labor.
How does this sound?
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Post by peterberg on Jul 27, 2013 12:09:43 GMT -8
Please don't fill up the space between the inner and outer wall. Leave open that 1" gap, otherwise the inner liner will expand and crack the outer wall sooner rather than later. The outer wall will get hot nonetheless, there's not much conduction between the two but radiation is just as good. Close the gap between the two liners by means of the top plate only, you don't want convection in there.
In short, leave expansion room and everything will be alright. The double-walled bell will be just as warm outside as the single-walled second bell. Even heat distribution and a longer stretch of time before all the heat is radiated out into the room, that's what you want isn't it?
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Post by endrunner on Jul 27, 2013 13:55:26 GMT -8
In short, leave expansion room and everything will be alright. The double-walled bell will be just as warm outside as the single-walled second bell. Even heat distribution and a longer stretch of time before all the heat is radiated out into the room, that's what you want isn't it? Yes, I was hoping to have a masonry stove type heating pattern. The flues do radiate quite well, and its easier to build without filler. We will leave the space empty and give it a go. I look forward to seeing the numbers!
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Post by endrunner on Jul 27, 2013 13:57:14 GMT -8
Do you think it matters if i line up the splits on the inner flues or should they be staggered?
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Post by peterberg on Jul 28, 2013 1:01:02 GMT -8
Do you think it matters if i line up the splits on the inner flues or should they be staggered? Good question. When only one side of each module is split, line them up, I would say. Because the bottom and top ends are fitting together with male and female ends. When each module is double split at opposite sides, I do feel staggering would be better and a lower chance of things going wrong as a whole. Good luck!
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Post by endrunner on Jul 28, 2013 7:26:12 GMT -8
Do you think this arrangement of the flues, having the heat riser flues in front there will block too much heat? Or would it be okay, it will all radiate out? This arrangement looks better than any other combination I could come up with. Attachments:
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Post by peterberg on Jul 28, 2013 7:56:53 GMT -8
This will be okay, in this arrangement there's more mass in the center of the stove. The inside will stay the same size, so aborbing heat will be the same. Heat retention on the other hand will be longer. Eventually, all heat will radiate out, no question about that.
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Post by peterberg on Jul 29, 2013 6:20:28 GMT -8
Using clay flue liners to build a stove has been done before. I had to dig in the Masonry Heater association's archive, but here it is.This is a simple stove, of course, but it shows the possibilities. In another workshop they used the same kind of liners in the inside of a stove to form the downdraft channels, hasn't found the report as yet.
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Post by endrunner on Jul 29, 2013 8:18:03 GMT -8
Great link, seemed like someone was bound to have tried before. A smokey combustion, but maybe it was early in the burn. I like the large flues, they are hard to get around here, but we can try a bit harder.
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Post by endrunner on Aug 4, 2013 15:31:06 GMT -8
So here is the revision #2 for the chimney flue build. Notes on the build are here. blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-2/And the charts for the build here. blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-3/We think the exit temperatures could be a bit higher, but we were running this at over 93°F ambient, not exactly cool weather. Draft should increase during more realistic winter conditions. The temperatures outside the heat riser column rose to over 350°F even with the firebrick lining. It was not logged well because the adhesive on the tape holding the thermocouple failed and it would not stay on the flue. In order to lower the temperature on the flue surrounding the heat riser, we will do an additional revision. We will change most of the interior liner from fire clay brick to insulation. Making this area cooler will to allow for skinning the stove in tile or stone. It will also force a bit more heat into the bells, which have plenty of capacity for additional heat. With the change to insulation around the heat riser exhaust, we are hoping to push the exit temperatures a tad bit higher. In general, we were pleased with its performance and think it is a winner. It Drafts well even in summer Low CO emissions High efficiency Captures all of the heat Can be constructed in a day Inexpensive to build Attachments:
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