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What is wrong with my design?  RSS feed

 
Posts: 11
Location: Istanbul
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I tried a rocket mass heater demo with the fire brick I had.

I followed the ratios 1:2:4 | feed tube= 20cm, burn tunnel=40cm , heat riser=80cm

section area is 12x20cm ( equal to 7" system)

when I set the fire it is not burning sideways, flames and smoke all coming out of feed tube. no flow through the heat riser.

where is the problem?

thanks.
rmh.JPG
[Thumbnail for rmh.JPG]
rmh2.JPG
[Thumbnail for rmh2.JPG]
 
Burak Unver
Posts: 11
Location: Istanbul
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This is how it looks like in real
rmh3.jpeg
[Thumbnail for rmh3.jpeg]
 
gardener
Posts: 1272
Location: latitude 47 N.W. montana zone 6A
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Well your feed tube is  200 mm x 120 mm  they must be square same size. The burn tunnel and the riser must ALL be the same.  Also i see no mud between the bricks so I am guessing your are sucking air in thru the gaps.
Edit)  I see your calculations say 200x120 is same as 7.5x7.5"  I have my doubts but I will take your word for it.  You Do need to mud your bricks together though.
 
Burak Unver
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Location: Istanbul
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I didn't apply mud becasu I wanted to see how it works, It didnt work at all.. Should it be a square? Is it a must that edges should be the same size?

My feed tube, burn tunnel and heat riser are all have the same section area, I thought that It's enough to have the same area.
 
thomas rubino
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I suspect that your burn tunnel is the problem , either too low and wide or too tall and narrow.   If nothing else smear mud over the exterior to temporarily seal it for a test burn . If it still does not work then rebuild using a square configuration.
 
gardener
Posts: 2581
Location: Upstate NY, zone 5
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It is recommended that, if the cross section can't be square, that taller is better than wider, so I'm not sure the shape is the main issue. I do suspect that air gaps are a good part of it. A thin layer of mud all over the outside would show whether this is true, or if you need to look farther for answers.

I suspect that the shape combined with the relatively short feed tube mean that the near half (away from the burn tunnel) is getting little of the draw, and easily overpowers it. When flames come up out of the feed, where do they start and burn most strongly?
I would try adding a brick of height to the feed and seeing if draw is more consistent. That would give proportions more like 1:1.5:3, which I have and find to work well (with a square cross section).

Using wood short enough to fit completely inside the feed, and partly covering the feed with a moveable brick or two, will make a big difference. The fire will generally burn well with only a third of the feed open, and not have excess air cooling the flames.
 
gardener
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Location: +52° 1' 47.40", +4° 22' 57.80"
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The 1:2:4 proportion measured along the centerline is correct in my view. The rectangle size of the system is not ideal but should work. You say you didn't use mud because you do want to see how it works. Well, it won't until you seal all the leaks with whatever you have at hand.
My first J-tube setup out in the garden didn't work because I stacked it dry, just like yours. I used a clay/sand mixture to do it over again, properly sealed and it ran like a champ after that.
I would recommend you do the build properly and it should work properly.

Edit: When you start it up push some burning paper in the tunnel to the riser to initiate the draft.
 
Glenn Herbert
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Aside from the rectangular shape not being ideal, looking at the photo reminds me that that stacking method is inherently unstable. At the expense of cutting two bricks a bit shorter and using an extra layer's worth of bricks reoriented at the base, you could rearrange the core to be square and much stronger.
Replace the bottom vertical row of the core with two layers set horizontally, giving a smaller height, and run the heat riser bricks in pinwheel fashion, alternating direction with each course. The bottom course of feed and riser would need a brick cut shorter by the thickness of a brick, so the burn tunnel can be safely bridged. Do that, with the joints clayed up, and I bet it will rocket. You would also need another course of bricks laid flat and pinwheel fashion on the top of the feed, to make up the height lost by the flat layers at the base. This would have the side benefit of giving a wide flat top to the feed surface for more stability (once it is supported by cob enclosing the core.)
 
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Location: North Alabama
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You don't mention how you attempted to "FORCE" the air flow to follow your desired path. Did you blow vigorously down the feed tube??? Maybe even with a leaf blower?? Compressed air??? Also, you could wrap the exterior with aluminum foil, duct tape, or even brown paper, to "seal" up all the gaps between bricks enough to actually get some draw. The shape won't matter all that much if you get it sealed.
 
Burak Unver
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Location: Istanbul
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Glenn Herbert wrote:Aside from the rectangular shape not being ideal, looking at the photo reminds me that that stacking method is inherently unstable. At the expense of cutting two bricks a bit shorter and using an extra layer's worth of bricks reoriented at the base, you could rearrange the core to be square and much stronger.
Replace the bottom vertical row of the core with two layers set horizontally, giving a smaller height, and run the heat riser bricks in pinwheel fashion, alternating direction with each course. The bottom course of feed and riser would need a brick cut shorter by the thickness of a brick, so the burn tunnel can be safely bridged. Do that, with the joints clayed up, and I bet it will rocket. You would also need another course of bricks laid flat and pinwheel fashion on the top of the feed, to make up the height lost by the flat layers at the base. This would have the side benefit of giving a wide flat top to the feed surface for more stability (once it is supported by cob enclosing the core.)



Do you have a photo or drawing that you mention above. That would be very helpful.

I made that design because I have that amount of bricks and I didn't want to struggle with cutting the bricks, so I wanted to try if it works.
 
pollinator
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Burak

After temporarily sealing most of the gaps in the bricks as suggested above, then, as you have the heater roughly set up outside and you have access to the heat riser mouth, why not light some paper and fine kindling in the riser itself - just to get the draft going and then feed in additional paper/fine kindling into the feed tube as you would normally. It should work...
 
thomas rubino
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Burak:  Have you smeared mud over your RMH yet?   Until you do you are going to fight it. 
 
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