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Post by satamax on Nov 21, 2014 9:23:13 GMT -8
'memory turbulence' - you haven't copyrighted that have you? I'd like to start using it in my work. heheh, feel free to use the phrase if you like Hey guys, what about "wobling of the top" ?  |
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
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Post by morticcio on Nov 22, 2014 1:43:37 GMT -8
I would've thought you'd want any combustibles to have ignited by the time they get to the middle/upper part of the riser so your aim would be to get flue gases out ASAP and not create turbulence.
Is there a thin line between extracting every last kW of energy from the fuel at the expense of causing a bottleneck which would reduce efficiency?
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Post by peterberg on Nov 22, 2014 2:56:33 GMT -8
Is turbulence in the fire riser helpful, for mixing the gases and helping them to burn more completely? Any idea how one would test such changes to the fire riser without access to a gas analyzer? All of the experimental heater cores including sloppy risers I built indicates that the much needed turbulence should be invoked as close to the initial pyrolysis as possible. In the case of the J-tube, that would be the burn tunnel. The best and probably only sequence is pyrolysis, additional preferably heated air, turbulence. The turbulence before air addition will work less effective, definitely. Moreover, when the gases are in a turbulent state in the tunnel those won't be laminar in the riser all of a sudden. Not when rounding a sharp corner just before. And no, you can't see or smell or hear anything at that level of minor changes without an adequate and calibrated gas analizer. The instances that the Testo came up with a completely unexpected result are probably over one hundred. |
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Post by Daryl on Nov 22, 2014 6:13:10 GMT -8
All of the experimental heater cores including sloppy risers I built indicates that the much needed turbulence should be invoked as close to the initial pyrolysis as possible. In the case of the J-tube, that would be the burn tunnel. The best and probably only sequence is pyrolysis, additional preferably heated air, turbulence. The turbulence before air addition will work less effective, definitely. Moreover, when the gases are in a turbulent state in the tunnel those won't be laminar in the riser all of a sudden. Not when rounding a sharp corner just before. Peter, have you tried to add warm air to the bottom of the riser either below or just above the double vortex?
Another question, do you think combustion chambers would ever work on a rocket stove without a bench or are chambers completely out of the question?
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Post by peterberg on Nov 22, 2014 6:45:23 GMT -8
Peter, have you tried to add warm air to the bottom of the riser either below or just above the double vortex? Yes I did, through the side and back wall of the riser. The vortex was still there but not moving as fast and the Testo called it a mediocre testrun. Precisely because of experiments like this I can safely say the right sequence is air and then turbulence. People who are drilling random holes in any stove won't do any good. Another question, do you think combustion chambers would ever work on a rocket stove without a bench or are chambers completely out of the question? This is a very tricky question. Do you mean rocket stoves without a bench, the answer is yes, done quite a couple of times all over the world. But a combustion chamber on a rocket is impossible because the rocket is the combustion chamber. Could you be more specific? |
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Post by Daryl on Nov 22, 2014 7:56:11 GMT -8
I always think of batch box rocket stoves as two chambers - the burn box and secondary combustion chamber (riser). The batch box is built very similar to the down draft gasifiers with refractory cores. When I stand there looking at a rocket stove burning, I think there is such a waste with the riser. Like something more could be done. I'm not sure what though. And maybe it can't. That is why I am asking these questions. I do appreciate and value your knowledge on the topic.
The chamber question was directed at whether or not the riser could ever be slightly sectioned off above the vortex since the draft and energy wouldn't be needed for a bench. Doggy had mentioned something similar to this for a vertical rocket. The riser would be replaced by a horizontal box on top of the batch box.
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Post by erikweaver on Nov 22, 2014 18:07:43 GMT -8
Thank you Peter. I think I'll just leave the fire riser alone then.
Unless I try castable refractory, I don't see how I could easily replicate the swooping "ski ramp" shape at the bottom of the fire riser. One could try to approximate that profile with cut fire brick, and maybe a trip wire in place of your kick. But I believe those ideas have been discussed and experiments you reported on suggest it is past the point of diminishing returns. So, either build the basic J-style, or go to castable refractory for the improved design.
I do wonder about the port on the batch system you designed - might that also be effective in the basic J-style rocket stove? But I seem to recall that you reported while technically feasible, in a real-world practical use, it didn't work very well, because the balancing act required of the primary air in-take was too unpredictable (which changes as the wood fuel is consumed, changing the air in-take ratios).
Did I get those points right?
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Post by Donkey on Nov 23, 2014 1:11:17 GMT -8
I wonder what would happen if the inner surface of the riser were dimpled, like the skin of a golf ball?
Here I'm thinking of reducing drag, rather than fuel/air mixing. Get it to slide through faster, maybe increase velocity of flow.
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Deleted
Deleted Member
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Post by Deleted on Nov 23, 2014 2:19:29 GMT -8
Dimples are vortex generators. The vortices reduce friction similar to ball bearings and may even improve combustion in the border zone. Likely dimples will also increase thermal stress. www.dtic.mil/dtic/tr/fulltext/u2/a469906.pdf |
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Post by peterberg on Nov 23, 2014 2:31:42 GMT -8
The chamber question was directed at whether or not the riser could ever be slightly sectioned off above the vortex since the draft and energy wouldn't be needed for a bench. Doggy had mentioned something similar to this for a vertical rocket. The riser would be replaced by a horizontal box on top of the batch box. I've been very busy with these heaters for a couple of years. Moe or less inevitably I've tried that too in combination with a syphon. It seemed such a good idea to make the thing compact but it didn't work out. I tried both rear and front exhaust opening to no avail. Even with air ducts to the entrance of the syphon. Spent about a week to rebuild and test the thing and regarded it as a dead end street. |
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Post by peterberg on Nov 23, 2014 2:36:15 GMT -8
I do wonder about the port on the batch system you designed - might that also be effective in the basic J-style rocket stove? Yes, during the Innovators Gathering I told Ernie and he though it a tantalizing idea so he worked it out in different shapes. We even tested it in an 8" J-tube but it didn't do anything good for us so the idea was ditched. |
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Post by Daryl on Nov 23, 2014 6:21:23 GMT -8
I wonder what would happen if the inner surface of the riser were dimpled, like the skin of a golf ball? Here I'm thinking of reducing drag, rather than fuel/air mixing. Get it to slide through faster, maybe increase velocity of flow. If you are having problems with finding a faster flow through the riser, then maybe cut back the double vortex to a single vortex? It would make sense that less turbulence will lead to a better speed. These stoves are pretty efficient on their own that maybe not so much turbulence is needed.
BTW, for those lurkers who have never seen a single vortex, it occurs when the venturi is moved to the far right of the back of the burn box instead of being in the middle.
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Post by pinhead on Nov 24, 2014 6:55:35 GMT -8
I wonder what would happen if the inner surface of the riser were dimpled, like the skin of a golf ball? Here I'm thinking of reducing drag, rather than fuel/air mixing. Get it to slide through faster, maybe increase velocity of flow. If you are having problems with finding a faster flow through the riser, then maybe cut back the double vortex to a single vortex? It would make sense that less turbulence will lead to a better speed. These stoves are pretty efficient on their own that maybe not so much turbulence is needed.
BTW, for those lurkers who have never seen a single vortex, it occurs when the venturi is moved to the far right of the back of the burn box instead of being in the middle.
IIRC, Peter tried this "single vortex" and it didn't burn nearly as cleanly as the double-vortex. |
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Post by shilo on Nov 24, 2014 7:40:43 GMT -8
a lot of black smoke
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Post by Daryl on Nov 24, 2014 11:23:58 GMT -8
I don't know. I mean i have built single vortexes outside and they seemed to do pretty good. I've been thinking about this since yesterday. For an outdoor oven I would prefer the heat transfer and speed over a super efficient stove. I work with outdoor ovens so that makes a difference. Downgrading the vortex might be a great way to shorten the riser.
No matter what, i will give it a try this spring or summer and see how it goes.
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