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Post by Deleted on Apr 21, 2017 14:15:17 GMT -8
Hi everyone, I recently thought about the possibility of a bell inside a bell.. It would increase ISA dramatically and would reduce the amount of refractory material. Powerful yet compact bell heaters ! Has anyone tried it already ? Results ? I attached here some pictures and the sketchup drawing of a heater that should work on this principle. It's a 250 mm batch. The inside bell is in refractory bricks and the second one in normal bricks or in adobes. The sketchup file is made by layers so you can make each row appear or disappear as you wish. I'll try this configuration as soon as I can and I'll post the results ! Regards, uzume-asso.org/assets/docs/bell_bell/batch250_JSF_V2.skp
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Post by satamax on Apr 24, 2017 23:06:57 GMT -8
Yasintoda. I think i can "sense" the point, but i'm not too sure. IIRC, Peter said that a wall between two bells doesn't count as ISA. Which would be the case here i'd think. If you want something which takes the bulk of the heat, to avoid using expensive refractories. i've had an idea somewhat similar to yours. In the form of a barrel or metal box, over the riser. Just held in the bell. The hot gases would come down along the sides of the heat riser, then back up outside of this flame arrestor. Mixing with colder gases at the bottom of the bell. Thus; may be, stopping the need for refractories in the bell. This is just theoretical. I have never tried. To increase the isa, you could do something like this s-media-cache-ak0.pinimg.com/736x/2c/07/0a/2c070acfc234de972196b9c066829f15.jpgWell, in England, they use one brick thick solid walls. They build two rows of bricks side by side, and every few bricks, put one across. The full brick. I have heard it called spacer brick. You could make a single wall like this, with one brick along the length, one brick across, sticking in the bell, one along the length, one sticking in the bell, and so on at each layer, And with the bricks overlapping, you would have stubs of bricks sticking in the bell. A bit like in the pic above. Each brick stub would increase your isa of 440cm² with 22/11/6 cm bricks.
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Post by satamax on Apr 24, 2017 23:18:37 GMT -8
actually, i didn't have the right words. Remove one row of stretchers, in the thickness of the wall. And leave all the headers, on the Flemish bond type wall.
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Post by satamax on Apr 24, 2017 23:23:59 GMT -8
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Post by peterberg on Apr 25, 2017 0:43:24 GMT -8
Max, what I possibly have said is that a dividing wall between bells is less efficient. It is heated from two sides so it will be "full" earlier. It would be best to make that dividing wall double thick in order to increase not only the heat extracting surface but the mass as well for that particular stretch of wall surface.
Yasin, the concept of a bell in a bell will obviously work. But what you've drawn isn't as efficient as it may look like at first. The inner bell is built against the outer bell for two of the four possible walls. So the lost surface of the outer bell is compensated for by two (outer) surfaces of the inner bell. What's left here to increase the ISA of the whole contraption is the inner suface of the inner bell. (Hope are able able to keep track of the different surfaces and bells.)
When you enlarge the outer bell 10 or 15 cm in two directions all of the outer bell and all of the inner bell, inside and out, is exposed to the hot gases. To make it even better (but also larger) is to double up the outside of the inner bell with bricks, so there will be at least twice as much mass to extract and stock heat.
Max, enlarging the ISA as you suggest is possible but in my view it would be best to realize the gases are streaming in general from top to bottom. So vertical half-columns would be the most efficient, causing minimal turbulence along the walls. One single brick that's sticking out will heat on four exposed sides, front, top, left and right, that's true. The fifth side, under, is in the stream's "shadow", as is the front of the brick directly underneath, thus compensating for the top of the brick above. So it would be best to create those shadows as little as possible.
The above is all my private opinion, of course. Merely backed up by the phenomenon of a horizontal lower temperature band around two stacked barrels. Created by an inward protuding flange which I left when cutting out the lid, so the stability of the circle would remain.
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serg247
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Post by serg247 on Apr 25, 2017 0:56:18 GMT -8
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Post by Deleted on Apr 25, 2017 2:24:48 GMT -8
Peter, I had to make it this way otherwise the ISA would have been too important. Here the ISA equals 12.5 m2 so it's perfect for a double bell with a 250 mm batch. If there was a space all around the inner bell, the ISA would have been way too big ! I also think you're right with making the inside bell twice as thick.. but the most common problem I face with clients is the heater being too big so that was my priority doing this. serg247, nice heater ! It is like what satamax just said.. did you built it already or is it only on sketchup ? satamax, I don't really like the idea of a metal barrel inside the outer bell.. not very good for maintenance. Regards,
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serg247
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Post by serg247 on Apr 25, 2017 2:51:26 GMT -8
только на SketchUp.
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Post by peterberg on Apr 25, 2017 5:16:43 GMT -8
Peter, I had to make it this way otherwise the ISA would have been too important. Here the ISA equals 12.5 m2 so it's perfect for a double bell with a 250 mm batch. If there was a space all around the inner bell, the ISA would have been way too big ! I also think you're right with making the inside bell twice as thick.. but the most common problem I face with clients is the heater being too big so that was my priority doing this. Ahhh... I didn't calculate the whole thing, or even checked the size. So 12.5 m² is already quite sizeable, now I see that in order to achieve the same with a single bell it would be a lot more voluminous while retaining more or less the same mass. It might be that the heater is different from others heat-storage wise. For example it could fill up quite slow at first and all of a sudden the end temp could rise, signalling the heat storage is at its limit. Or maybe even the normal rule for double bells doesn't apply here. Just a thought, no experience or theory pointing in that specific direction. Curious; this could be a major development creating another type of bell construction, a larger part of the total mass as inexpensive bricks or adobe in a compact shell. You could even use ordinairy concrete slabs to cap the outer bell!
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Post by Deleted on Apr 25, 2017 6:55:51 GMT -8
Yes right on Peter, that's why I'm excited about it ! To me it really feels like contraflow heaters. On the version I built from plans the gap between the first skin and the core was 8 cm.. I wonder how close in this bell version the two walls could be without adding too much friction ?
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Post by satamax on Apr 25, 2017 7:05:04 GMT -8
Yasintoda, i think you're missing something in your equation. Outside radiating surface. If your isa is huge, and you can't shed the heat due to a small outside surface. Where's the point?
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Post by peterberg on Apr 25, 2017 7:28:58 GMT -8
Dictated by law of physics, heat flows from high to low. Which means once a spot is heated up, the stream of hot gases will divert its course slightly to a cooler place in order to heat it up. Until it's warmer than the spot next to it and change course again, and again. The wider the bell, the more frequent the hot stream is diverted. We've seen that effect in North Carolina during the MHA 2015 meeting. By measuring and noting down the temperature levels of several rings of points around the main (single walled) bell every 5 minutes we could see the hottest spots were moving around all the time. As a result, the heat distribution in a bell is excellent, very uniform in any given horizontal plane.
This could mean the following: when there's a sufficient large void where the hot gases are slowed down the smaller spaces should get their heat distributed from there. Just two slits like in a contraflow is different, the benefits of lower gas velocity would be lost by that. So the situation in your drawing might be just what it takes to make the above effect happening. That's why it's so interesting.
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Post by peterberg on Apr 25, 2017 7:40:34 GMT -8
Yasintoda, i think you're missing something in your equation. Outside radiating surface. If your isa is huge, and you can't shed the heat due to a small outside surface. Where's the point? More mass in the same shell would mean longer radiation at a stable temperature, I'd think. Bells would be shifting a bit more into the direction of contraflows, which are quite a bit more massive than single empty bells, don't you think?
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Post by drooster on Apr 25, 2017 11:01:26 GMT -8
Hang on. Won't the inner bell get so hot that it will not act efficiently to descend/cool the HOT gases coming out of the riser?: thus slowing the riser flow potential. A standard RMH with steel barrel sheds a lot of heat from the barrel surface into the room to maintain its ability to cool those gases, I just think a masonry or metal bell inside a bigger bell will lose a lot of rockettyness because the inner bell will get too hot too soon.
Maybe.
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Post by satamax on Apr 25, 2017 12:20:12 GMT -8
Yasintoda, i think you're missing something in your equation. Outside radiating surface. If your isa is huge, and you can't shed the heat due to a small outside surface. Where's the point? More mass in the same shell would mean longer radiation at a stable temperature, I'd think. Bells would be shifting a bit more into the direction of contraflows, which are quite a bit more massive than single empty bells, don't you think? Well, Peter. It's just gut feeling. To me contraflow heaters, have a huge ISA, but also they are quite big outside,usually. And i'm wondering if we build a bell with far more ISA, than outside surface area, wouldn't it choke the heater? I mean restrain it's ability to release heat in the surrounding atmosphere? I'm just wondering. Hang on. Won't the inner bell get so hot that it will not act efficiently to descend/cool the HOT gases coming out of the riser?: thus slowing the riser flow potential. A standard RMH with steel barrel sheds a lot of heat from the barrel surface into the room to maintain its ability to cool those gases, I just think a masonry or metal bell inside a bigger bell will lose a lot of rockettyness because the inner bell will get too hot too soon. Maybe. Well, i think the cooling effect is only marginal. What produces the draft, is the chimney. Proof, horizontal chimney rockets are generally extremely fussy.
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