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Post by peterberg on Apr 25, 2017 13:18:16 GMT -8
The proof of the pudding is in the eating, only a heater built like that will show whether it'll work or not. My guess: the heater won't be choked as long as it is coupled to a proper chimney. Most likely, there are some surprises down the line like what I mentioned above, but that's only to be expected.
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Deleted
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Post by Deleted on Apr 25, 2017 21:50:06 GMT -8
satamax the contraflow heater in the sketchup drawing is made by David Szumilo of Oxalis in Haute-Savoie, close to you. They have made a LOT of them and : - their outside radiating surface is small compared to a single bell of the same power. The one in the drawing is 99x88cm on the ground and is 195 cm high. It's an 8 kw and the sketchup file is here and a picture below : uzume-asso.org/assets/docs/bell_bell/23212_8Kw.skp. In comparison, an 8 kw batchrocket (a 250mm) single bell and single skin measures 132x122 cm on the ground and is 193 cm high (I've build one). It's a really huge heater. - they work very well but they do need a very good chimney stack. In my opinion, it is partly because of the contraflow system and the friction it generates and p artly because of the fact they don't have a starter. I think a bell inside a bell like that could work with a normal chimney stack as long as there is a starter... but as peter said, the proof of the pudding is in the eating !
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Post by satamax on Apr 26, 2017 9:05:56 GMT -8
Yep, off you go. It's prototype time.
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terry
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Post by terry on Apr 29, 2017 19:21:28 GMT -8
One thing that possibly should be considered is the radiating area of the final bell, ie the SA that radiates heat into the room.
For a given heat input to the system, (usually fixed), a single skin/single bell will reach working temperature. To keep that temp to 'acceptable' levels (eg not too hot) the SA has to be larger to keep that temp down. That is also a good thing because to get enough heat into the room a lower temp body must have a larger surface than a higher temp body.
Putting a bell within a bell is presumably done to lower the footprint of the bell in the room which is understandable. It then also follows that (for the same given, fixed, heat input to the system ie the firebox) the radiating skin temp will be lower. The lower the radiating temp of the surface the greater the surface area needs to be to radiate the same heat to the room.
At least that is how I intuitively see this working. It is not necessarily a problem (if my gut instinct is correct) but it does need to be known about when considering.
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Post by peterberg on Apr 30, 2017 0:18:08 GMT -8
In my view, a matroesjka bell adds more mass into the heater. Much like the Russian system where inside the bell columns are built to allow the top to be closed with bricks. The advantage of this system deminishes the fact that a bell has its mass almost exclusively in the outer shell. Something like that is happening when introducing a bell in a bell.
Imagine a bell heater equipped with a 150 mm batchrocket, the bell exactly up to the maximum of ISA. This imaginary heater is well sized for the imaginary room where it's placed, output-wise. Introducing another bell inside will extend the ISA suitable to, say, a 180 mm system so the same (outer) bell could house a bigger core. This bigger core is capable of burning more fuel in the same span of time, which incidentally is also needed to charge the larger mass in one batch. The net result would be a heater with the same surface temperature, thus yielding the same amount of heat.
The difference here is the amount of hours that can be bridged without charging the mass again. In my view this is a good thing, though the formula provided by Yasin won't do anymore. So there need to be a new spreadsheet to calculate the size and ISA of a matroesjka bell. Before anyone could do that there should be a lot more experience with the concept I'd say.
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terry
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Post by terry on Apr 30, 2017 15:06:10 GMT -8
Pretty sure I understood what you were saying, and yes it kinda looks at what I said from the other side of the lens. Note that I held the firebox 'constant', which led to the overall lower skin temp of the external bell. Having recognised that phenomenon leads to, as you say, realising that to have the same skin temp necessarily means having a larger firebox.
Both our approaches from either side of the lens is simply fleshing out the consequences of the question 'what about a bell within a bell?'
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Post by peterberg on Apr 30, 2017 23:24:57 GMT -8
Nicely worded, thank you Terry.
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Post by pyrophile on Aug 12, 2017 10:08:48 GMT -8
I come back to this subject.
I am thinking about a high and empty column into a bell that could have its own surface roughly doubled, if needed, thanks to a damper. This narrow but high column (20x20cm wide, 30x30cm or more)would be open on top and at the bottom. The damper would be on top, opening or closing this column to hot gases and would be activated from outside the stove. This column could be built quickly with normal ceramic flue blocks filled with clay (liquid or solid). The damper should resist to heat (a refractory slab, a thick metal part, etc. It would not be exactly a bell but it could lower the external surface. Of course, the external surface of this column would always absorb heat and should be added to the total internal surface of the bell.
Sorry, I can not make a drawing...
Benoit
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Deleted
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Post by Deleted on Aug 14, 2017 6:33:03 GMT -8
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