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Post by byronc on Dec 4, 2014 5:36:47 GMT -8
ISA = Internal Surface Area
Dropping another flue liner on top of the existing two for greater height will increase the effective ISA, and obviously result in some more heat capture in the mass of the bell etc.
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Post by swampzr2 on Dec 4, 2014 5:49:01 GMT -8
I was thinking of adding another foot of flue to make it look right, but wont that lower my exhaust temperatures even more? Mine are already under 150. Is that a concern to be that low? I don't want moisture problems, and low draft problems etc... ISA = Internal Surface Area Dropping another flue liner on top of the existing two for greater height will increase the effective ISA, and obviously result in some more heat capture in the mass of the bell etc.
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Post by byronc on Dec 4, 2014 5:55:02 GMT -8
150° F, is that the surface of the stove pipe, or the gas stream in the center hottest most area inside the pipe?
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Post by swampzr2 on Dec 4, 2014 6:16:39 GMT -8
150° F, is that the surface of the stove pipe, or the gas stream in the center hottest most area inside the pipe? That is the temperature of the stove pipe, from my laser gun. It is just under 150 now.
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Post by patamos on Dec 4, 2014 21:12:14 GMT -8
The centre of your gas stream is bound to be a lot hotter than the surface of the stove pipe.
The recommended ISA fora 6" J-feed is around 4 square meters. So you have potential to add on a much bigger (or second) bell if you like.
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Post by matthewwalker on Dec 4, 2014 22:53:57 GMT -8
Internal temp will be roughly double what you read on the outside, in my experience.
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Post by satamax on Dec 4, 2014 23:55:38 GMT -8
Myself, i have a question, how is that blady heat riser insulated? Even if thoses are insulating firebricks, they look a smidge thin! Therefor, if you add insulation, your "edge of heat riser gap" will be too narrow. Anyway, there's a build a bit along your lines, for which i have used the picture of your flow diverter. www.permies.com/t/41795/rocket-stoves/Russain-Rocket-stove-built-running
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Post by swampzr2 on Dec 5, 2014 5:01:09 GMT -8
The centre of your gas stream is bound to be a lot hotter than the surface of the stove pipe. The recommended ISA fora 6" J-feed is around 4 square meters. So you have potential to add on a much bigger (or second) bell if you like. I was hoping to get a second bell in there, but space is limited. My hearth is 4'x4' in that corner. I may slice some of the flues in half and cement them together to make a bigger bell to capture more heat. At any rate, this sure beats my old cast iron wood burner. That thing would burn 4 face cords of wood in a month!
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Post by swampzr2 on Dec 5, 2014 5:09:54 GMT -8
Myself, i have a question, how is that blady heat riser insulated? Even if thoses are insulating firebricks, they look a smidge thin! Therefor, if you add insulation, your "edge of heat riser gap" will be too narrow. Anyway, there's a build a bit along your lines, for which i have used the picture of your flow diverter. www.permies.com/t/41795/rocket-stoves/Russain-Rocket-stove-built-runningThe heat riser isn't insulated at all actually. I used the Vogelzang fire bricks dimensions 4-1/2" x 9" x 1-1/4". I could put a 10" stove pipe around the heat riser, and stuff insulation in between that and the heat riser. What exactly will that help however?
Other questions I have:
1. If I put a 10" stove pipe around the heat riser, what is the best insulation to fill between the pipe and the heat riser? 2. How should I insulate the feed tube and the burn tunnel? I plan on adding stone around it. 3. How hot can clay flues get before you crack or damage them? 4. How thick of stone should I wrap the clay flues with? They are 3/4" now.
Thanks
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Post by pinhead on Dec 5, 2014 7:27:40 GMT -8
From what I see, your current "barrel" is the right dimensions for the outside of the riser (with insulation stuffed between) and your new barrel should be around that.
As-is, your "plenum" at the exit of the "barrel" is too small/restrictive, IMO.
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Post by swampzr2 on Dec 5, 2014 7:34:33 GMT -8
From what I see, your current "barrel" is the right dimensions for the outside of the riser (with insulation stuffed between) and your new barrel should be around that. As-is, your "plenum" at the exit of the "barrel" is too small/restrictive, IMO. The exit from my barrel is 8" x 8". You think that is too small?
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Post by pinhead on Dec 5, 2014 8:46:03 GMT -8
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Post by swampzr2 on Dec 5, 2014 9:26:08 GMT -8
If you do the math on mine I think I'm OK...
5.25" x 5.25" feed tube, burn tunnel, and heat riser = 27.56 square inches 6" stove pipe exhaust = 28.26 square inches 8" x 8" exit from barrel into flue liner = 64 square inches
So I think it is big enough. It has been drafting really good, and capturing lots of heat since I put the dividing wall diagonally in the flue. Now I just need to insulate and wrap more mass around it.
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Post by DCish on Dec 5, 2014 12:59:37 GMT -8
If Matthew is right and your exit flue gasses are running at 300ish degrees (verifiable with a probe thermometer), then I would definitely see if an ISA increase would be possible (either the taller bell idea or the larger diameter bell idea, given your restrictive footprint).
When you have a good chimney providing draft the burn chamber and riser insulation have a less noticeable effect on its ability to start and burn, though you can expect to still have a less complete burn due to lower combustion temps and a longer warm-up time. This may mean an accumulation of soot/tars in your system over time. A great insulation to pour into a gap is perlite.
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Post by satamax on Dec 5, 2014 23:56:39 GMT -8
Insulation around the feed, burn tunnel and heat riser is there to help burniong the last volatiles. To me, a rocket without insulation, isn't a rocket. Your flues are designed, i think, to whistand 400C°, and 1000C° for half an hour. So at 400C° continuous they should cope.
Swamp, the gap on your "plenum" isn't calculated as total ISA, but gap's ISA, or ring projection. 4x8=32 linear inches x your gap let's say the final gap when you will add insulation will be 2 inches. so that's 64sqin as well. To be sure, you take you system ISA x1.5, to account for friction and changes of direction. So, 28.26x1.5= 42.39sqin.
To me you should be good. Tho your gap shouldn't be less than 1.5 inch.
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