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Post by swampzr2 on Dec 2, 2014 10:45:35 GMT -8
I'm looking for some suggestions on my build. It don't think the heat is going up into the bell, rather in it and right down through the exhaust. Any and all suggestions are welcome!
Here is info on it: 6" diameter steel exhaust 5.25" x 5.25" fire brick "j tube and heat riser" Mouth opening where sticks go in is 5.25" x 6.25" 14" diameter 3/16" steel cylinder 34" tall (heat riser is ~3" to top) All fire brick is 9" x 4.5" x 1.25" Exit port from cylinder into clay flue is 8"x8" Clay flues are 3/4" thick, 12" x 12"
Here are some temperatures I was able to get after just over an hour of burning:
-Burn chamber maxed out my laser gun so I'd guess just over 1,000 degrees -Outside of burn chamber (outside face of fire brick 450) -Glass 400 -Top of cylinder 500 -Outside of cylinder walls 300 -Bottom of clay flue liner 175 -Middle/top of clay flue liner 110 -Exhaust at ceiling 150
I have a real strong draft going through this thing, even with no fire, it is sucking the air out of the house. I do not have a damper.
Suggestions on capturing more heat in the bell? It seems like the heat isn't rising up into the bell. I planned to add more stone, just wanted to test burn to make sure it worked.
Thanks, Brandon
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Post by byronc on Dec 2, 2014 11:38:28 GMT -8
Nice and neat construction you've got going there.
H'm, most likely your flue liner bell is bypassing. It appears to be way to small (diameter) to support an input of 8x8 inches. This system would have a better chance with 24x24 flue liners. The heat riser will need some attention as well, it needs to be insulated if it is constructed of dense non-insulating firebrick.
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Post by peterberg on Dec 2, 2014 12:19:23 GMT -8
Brandon, Byron is right, your bell is way too small. Its cross section area should be at least 4 times as wide as the inlet opening, preferably more. And that inlet should be the same as the exhaust opening or the chimney pipe immediatly behind it. The inlet is situated higher than the exhaust, that's correct in a narrow bell. But as it is now, it's bypassing big time.
The feed tube, burn tunnel and heat riser should all be insulated with heat resistant material.
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Post by swampzr2 on Dec 2, 2014 12:40:02 GMT -8
My bell is 10.5" square on the inside, so 110 square inches. My burn tunnel is 5.25" square so 27.56" I made my exit from the cylinder 8" because I read that it needs to be much bigger than you think. If I reduce the exit from the cylinder down to 5.25 square, do you think it will heat up the bell more? My bell is 4x the area of the feed tube. I can insulate around the fire brick to retain more heat.
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Post by byronc on Dec 2, 2014 14:04:26 GMT -8
Your cylinder size and flue liner bell size remind me more of a 4" system's components, yet you've got a 6" J-tube feeding it. If you don't want to increase the size of the flue liner bell, or don't have room to do so, then one option would be to rebuild the J-tube (feed, burn tunnel, and riser) to a 4" system size -- like Dragon Heaters, whom use similarly sized flue liners in their 4" castle build RMH. The 8x8 manifold would then need to enter the flue liner bell via a reducer to 4" system size. And as Peter mentioned, the flue liner bell's exit should be the same size as the bell's input. Such a rebuild would of course make for a noble experiment, and may require further modification, such as a baffle plate added to the flue liner bell's floor between the input and outlet ports extending upward etc.
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Post by satamax on Dec 2, 2014 14:10:31 GMT -8
Gap, gap, gap!
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Post by DCish on Dec 2, 2014 16:01:57 GMT -8
As a simple, quick charge experiment, you might try adding a vertical brick after the bell inlet to divert gasses up and see if once directed up the bell functions more as intended.
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Post by swampzr2 on Dec 2, 2014 19:14:17 GMT -8
As a simple, quick charge experiment, you might try adding a vertical brick after the bell inlet to divert gasses up and see if once directed up the bell functions more as intended. DCish, I was thinking the same thing.... reduce my 8x8 down some. I cut a brick 8" long by 2.5 inches tall. So no the inlet to the clay flue liner is 8x5.5. The overall temperatures were slightly lower (instead of 500 on the top of the metal cylinder it reached 400-450) but the clay flues didn't get much hotter than 110 at the top. Maybe I will just use the clay flues as part of the exhaust, and route the 6" black pipe out the top of it (instead of out the bottom side). Then I could really wrap the outside of the clay flues in stone to absorb the heat and radiate longer. Is that a good idea? I don't want to rebuild the J tube, and I already spent allot on the clay flues. I hate to buy 24x24's!
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Post by DCish on Dec 2, 2014 20:20:36 GMT -8
I can't quite visualize what you did... Did you just restrict the opening into the bell? I was trying to convey something that would make a sort of "L" shape to force gasses up to eliminate the direct pass-through of gasses from the inlet to the outlet. Here's a little sketch...
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Post by swampzr2 on Dec 3, 2014 5:48:43 GMT -8
Here is a drawing of what I tried....
I think if I create a vertical wall 75% of the way up, dividing the clay flue into two sections, I may be able to salvage this with little effort (which is similar to what your picture shows).
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Post by byronc on Dec 3, 2014 6:05:17 GMT -8
That will work, and I'd stack the brick "wall" up on the diagonal, caddy-corner to caddy-corner. Mortar (clay/sand) the bricks, especially at the flue corners, to seal the up and down gas channel. Then the flue liner becomes a vertical flue run instead of a bell, but it will heat up much like the horizontal bench runs of a typical RMH.
You could even do a second up/down flue run (add another vertical flue liner stack next to the first) to harvest even more heat from the exhaust gases, but I suspect a bypass may then be needed for cold starts etc.
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Post by DCish on Dec 3, 2014 6:50:37 GMT -8
A fun experiment might be to try the low wall first, then if you're not satisfied with heat harvest, try making the wall taller as byronc suggests, and see which gives better results.
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Post by patamos on Dec 3, 2014 17:17:16 GMT -8
I agree with DCish. Start off with a low divider. Kitty corner. Just a few inches taller than the top of the input. That might be enough to give all the turbid gasses coming out of the downdraft barrel a chance to float up in to the bell without being affected by the strong exit vacuum of the chimney.
A simple way to increase your bell ISA to some degree would be to keep stacking flue liners on top of the existing bell. I'm not sure how easy/free a time the gas movement will have in that narrow a space, but it is a small step that will tell you a lot...
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Post by swampzr2 on Dec 4, 2014 5:07:47 GMT -8
So I decided to put the divider 3/4 of the way up (3 feet high on the 4' high bell). I found that a 12" patio block fit almost perfectly in there with only 1/2" gap. So I put 3 of them in there, put some k-wool around the burn tube, and fired it up. Here are the temperatures I achieved after a 2 hour burn.
Top of cylinder above heat riser 500 degrees Clay flue liner bell 200-250 degrees Exhaust just before it exits the ceiling 140 This has been the best burn yet for capturing heat.
The draft was not as strong, and I hope if I take out (2) 90 degree exhaust bends and replace them with (2) 45 degree bends, it will give me a stronger draft. A few questions I have for you veterans: 1. For insulating the feet tube and burn tunnel.... what is preferred K-wool or the light soft fire brick? I want to put nice looking stone over it to finish it off. 2. How hot can these clay liners get before they crack? 3. How much stone would you wrap the outside of the clay liners with (how thick)? The clay liners are 3/4" thick now.
What do you think??
Thanks, Brandon
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Post by swampzr2 on Dec 4, 2014 5:16:05 GMT -8
I agree with DCish. Start off with a low divider. Kitty corner. Just a few inches taller than the top of the input. That might be enough to give all the turbid gasses coming out of the downdraft barrel a chance to float up in to the bell without being affected by the strong exit vacuum of the chimney. A simple way to increase your bell ISA to some degree would be to keep stacking flue liners on top of the existing bell. I'm not sure how easy/free a time the gas movement will have in that narrow a space, but it is a small step that will tell you a lot... What do you mean by "A simple way to increase your bell ISA to some degree would be to keep stacking flue liners on top of the existing bell."
What is ISA?
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