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Post by drooster on May 4, 2016 12:36:52 GMT -8
Here : let me type this in English.
There's a J-tube or batch box full of burning wood,
there's an insulated riser creating a very hot combustion,
then ...
normally there's a metal barrel to cool the gases as they descend around the riser to a flue going to a mass/exchanger and then to some exit.
My question : atop the riser does the hot gas need to descend?,
or could it go up/sideways to the mass/exchanger without descending inside a barrel?
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terry
Junior Member
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Post by terry on May 4, 2016 19:54:50 GMT -8
The only thing needed is that the gases cool. Hence descend to the exit. How you get that to happen does not matter. As a thought experiment (ie DON'T do this!) just imagine the core burning in the room you want to heat, sealed room of course, with an exit flue somewhere. As long as you have draft up the flue, the core will burn normally and gases will go out the flue.
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jrl
Junior Member
Posts: 101
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Post by jrl on Dec 7, 2016 9:33:56 GMT -8
How much truth is there to the suction effect created by having a barrel? I read in a lot of places that the rapid cooling of the gases in the barrel on top of the riser accelerates the rocket effect. If you're just venting into the mass the cooling effect would in theory occur much slower.
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Post by drooster on Dec 7, 2016 11:08:42 GMT -8
My original question back in May was answered in my own head after reading more and more unconnected threads.
The answer was NO.
However to extract heat from the efficient burn an efficient cooling descent is best, and shock-horror the big ugly old 55-gal steel barrel is about ideal!
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Post by patamos on Dec 9, 2016 9:21:58 GMT -8
The barrel per se is not necessary, but any time you can increase the difference in temperature between the gasses inside the riser and the atmosphere just outside the exit of the riser or flue, the gasses will be relatively more buoyant and therefore the draft will be stronger.
I have noticed this when i place an electric fan on top of the barrel of my 6" J-feed. When the fan is on, and drawing heat away from that surface, the combustion process accelerates.
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Post by rabivens on Feb 13, 2017 16:29:06 GMT -8
My understanding is that the main purpose of the barrel is to create more turbulence and a more complete burn of the gasses, thereby increasing heat which is then radiated out of the barrel and stored into the mass before it escapes through the chimney in a much cleaner (less smoke) exhaust.
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Post by patamos on Feb 13, 2017 19:13:33 GMT -8
So far as i have heard, the notion of gasses reburning around the top of the heat riser is proving to be false. Only on vary rare occasion, or with special setups like Matt Walker's split riser does the flame reach the top of the riser.
my 2c
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Post by pinhead on Feb 14, 2017 10:29:24 GMT -8
My understanding is that the main purpose of the barrel is to create more turbulence and a more complete burn of the gasses, thereby increasing heat which is then radiated out of the barrel and stored into the mass before it escapes through the chimney in a much cleaner (less smoke) exhaust. Patamost is correct; the only time there is flame in the barrel (outside the confines of the heat riser) is during the very peak of the burn where the flame extends into the barrel, though there is no "re-burn" in the barrel. For max efficiency, all combustion must be complete before it exits the heat riser. After all, the entire reason the heat riser is insulated is for complete combustion - and the barrel is the exact opposite of "insulated." There can be an argument made for the venturi effect which can be tuned by the barrel-riser gap, though IMO it doesn't constitute any secondary burn. In every rocket I've built, the larger top-gap the better the draft. My current batch box has a 12-inch top gap. Also, it takes energy to force the exhaust to fight against natural buoyancy - hence reducing draft. A "max-draft" rocket stove is simply a super-tall heat riser. You could, for example, build a rocket in the basement and extended the heat riser to the first floor where it is directed into a bench - thereby eliminating any down-draft - and exit at the far end at the chimney which, then, further extends upward. This would likely produce so much draft it would blow the flame out. Would definitely be a fun experiment, though! |
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Post by patamos on Feb 23, 2017 8:31:14 GMT -8
A "max-draft" rocket stove is simply a super-tall heat riser. You could, for example, build a rocket in the basement and extended the heat riser to the first floor where it is directed into a bench - thereby eliminating any down-draft - and exit at the far end at the chimney which, then, further extends upward. This would likely produce so much draft it would blow the flame out. Would definitely be a fun experiment, though! I've been wondering about this possibility - everytime some one asks met about placing a heater in the basement to warm the second floor area. I recall Donkey once wondering if too much of the heat would be lost in the mass of the riser. But with low mass materials that would be way less of an issue... I mentioned the idea to one of our local building inspectors a while back. But he was nervous enough OK-ing a regular masonry heater... |
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Post by drooster on Feb 23, 2017 9:58:54 GMT -8
A "max-draft" rocket stove is simply a super-tall heat riser. You could, for example, build a rocket in the basement and extended the heat riser to the first floor where it is directed into a bench - thereby eliminating any down-draft - and exit at the far end at the chimney which, then, further extends upward. This would likely produce so much draft it would blow the flame out. Would definitely be a fun experiment, though! I've been wondering about this possibility - everytime some one asks met about placing a heater in the basement to warm the second floor area. I recall Donkey once wondering if too much of the heat would be lost in the mass of the riser. Surely in the specific case of a very tall riser, there would be almost NO heat lost in the mass or the riser, as almost all of the heat would be eventually given up to the house ... unless you are talking about a problem with getting the interior of the riser up to proper temperature? |
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Post by pinhead on Feb 23, 2017 10:40:21 GMT -8
With a heat riser made of something such as ceramic-fiber blanket of sufficient thickness, I wouldn't predict much heat "loss" through the riser.
But as drooster said, the heat going into the house in this case wouldn't necessarily be a negative - provided the riser is insulative enough to maintain complete combustion.
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Post by patamos on Feb 26, 2017 9:04:55 GMT -8
Oh ya i agree. It is just a matter of making sure there is enough heat remaining to warm up the mass you want to. If the riser is low mass CFB or fire brick or the like then no problem. But if it is full size brick, then at some point up the tunnel it begins to count as flue run ISA. Which is not necessarily a problem...
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