morticcio
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"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
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Post by morticcio on Jan 31, 2012 16:01:43 GMT -8
 Something like the one in the picture. It will form a usable trip wire, although not with a smaller than 90 degrees angle to the air stream, that will be a tad more complicated. So, the "bluff body" itself is quite small but adequate, a 1/4" or even smaller will be all you need. It will perturb the boundary layer without too much friction in the air path. Great thread... Regarding making a wirebrick, there are fire bricks with different sized sides that are used to form an arch (usually for outdoor pizza ovens). Available sizes (in mm) here in UK are as follows: 230 x 114 x 76/70 mm - 3 mm exposed with 3 deg slope behind 230 x 114 x 76/64 mm - 9 mm exposed with 6 deg slope behind 230 x 114 x 76/57 mm - 16 mm exposed with 9 deg slope behind 230 x 114 x 76/52 mm - 21 mm exposed with 11 deg slope behind I have allowed 3mm for mortar. With only 3mm exposed it may not be possible to use the 76/70mm brick. The brick would have to be laid with 114mm side down (as opposed to 76mm side) for this to work as this would allow right angles between the sandwiched bricks. Using these bricks will help to reduce the amount of cutting - only the 20mm (approx.) wide slice at either end. However I'm not sure what effect it will have on the profile of the tripwire/Peter Stream as it will be a shallow angle behind. I've attached a rough sketch of the "profiled" brick sandwiched between two normal ones. Attachments:
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ernie
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Post by ernie on Jan 31, 2012 21:31:25 GMT -8
Cool Peter; Someone pointed me to the testo data the other day and i should have known it was yours. So to sum up the trip wire is a small ridge at the top of the burn tunnel to provide added turbulence and the peter plate is a gap in front of the first bridge brick to cool and allow a secondary air intake. the gap needs to be as close to 1/3 rd of an inch. the wood laying /leaning on the front of the burn tunnel causes a slightly dirty burn and fire climbing. Cool I will put that into my test bed and fiddle with it a little. I will credit you anytime i use or mention it. would be allowed for me to write it up and draw it up in my stove designs after i have tested it for a year? Would it be OK with you for me to see about making the peterplate from masonry?
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Post by peterberg on Feb 1, 2012 4:26:47 GMT -8
morticcio, It's possible to use these bricks to fabricate a trip wire of some sorts. With a mortar thickness of 3 mm, you have to use the 9 mm overhang as a minimum. The wire isn't ideal, being at right angles to the air stream. It's the better solution to have it at an angle, i.e. as an arrow pointing to the riser side. There's an error in your drawing: the flow direction is wrong. The air stream has to go from left to right, not the other way around. Besides that, the best location for the ridge itself should be 50 to 100 mm away from where the air comes in, depending on the size and length of the tunnel. So this special brick need to be the first brick bridging the tunnel. That particular one will get awfully hot, I don't know how long it will last. Perhaps you could place another brick on top of it to divert some of the highest heat? I have to admit, adding the feature which Donkey elegantly christened as "Peter Channel" could help by cooling this first brick. But that's theory only, nothing has been proved yet.
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Post by peterberg on Feb 1, 2012 4:50:32 GMT -8
So to sum up the trip wire is a small ridge at the top of the burn tunnel to provide added turbulence and the peter plate is a gap in front of the first bridge brick to cool and allow a secondary air intake. the gap needs to be as close to 1/3 rd of an inch. Hi Ernie, Yes, that dimension is correct for an 8" rocket like the one Donkey tried it on. The trip wire could be at right angles to the flow direction, but it's better at an angle of 10 to 15 degrees as an arrow pointing to the heat riser. The right angle trip wire will work nevertheless, only not as efficient. I will credit you anytime i use or mention it. would be allowed for me to write it up and draw it up in my stove designs after i have tested it for a year? You are very welcome to use it in every application you like. To credit me for it will be nice, thank you. Would it be OK with you for me to see about making the peterplate from masonry? It will be OK with me, but I have to emphasize the fact that the opening should be very, very close to the feed tube. I'd think that making it all from masonry would be difficult. In fact, I've tested it with the opening about 2" from the feed and the desired effect, according to the Testo, wasn't there at all. |
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morticcio
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"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Feb 1, 2012 5:44:16 GMT -8
morticcio, It's possible to use these bricks to fabricate a trip wire of some sorts. With a mortar thickness of 3 mm, you have to use the 9 mm overhang as a minimum. The wire isn't ideal, being at right angles to the air stream. It's the better solution to have it at an angle, i.e. as an arrow pointing to the riser side. There's an error in your drawing: the flow direction is wrong. The air stream has to go from left to right, not the other way around. I've modified the drawing and corrected the air flow - is this what you mean by arrow pointing towards the riser? Attachments:
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Post by peterberg on Feb 1, 2012 6:19:54 GMT -8
I've modified the drawing and corrected the air flow - is this what you mean by arrow pointing towards the riser? Yes, that's what I've meant. Too little wire close to the wall of the tunnel, however. The angle could be as small as 10 degrees, i.e. 80 and 100 degrees to the flow direction. I've recognized this height problem last summer, so I've made the ceiling of the burn tunnel slightly like a tile roof, with the ridge pointing to the riser again. By this way, the trip wire will be at an even height the full width of the tunnel. But there's only a theoretical difference in the overall effect, so one at right angles might work satisfactorily as well. Not tested, by the way, I've been following the theoretically best layout. |
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Deleted
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Post by Deleted on Feb 19, 2012 5:08:47 GMT -8
peterHave you tried to let the arrow point in the other direction ? It would then also work similar to a flame ring in a pot-style burner by providing an hot edge.
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hpmer
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Post by hpmer on Feb 19, 2012 5:46:58 GMT -8
That's actually how I thought it was originally, the abrupt edge against the heat flow and tapering towards the heat riser. Guess I had it backwards.
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Post by peterberg on Feb 19, 2012 11:13:14 GMT -8
Have you tried to let the arrow point in the other direction ? Yes, I did. There happened to be a minor difference. With the arrow pointing to the riser the stream is more or less split in two, diverging to the walls on both sides. I would consider that a good effect, I'd expect the slight roof shape of the tunnel ceiling normally would prevent that. The vortex end of the tunnel do the opposite, converging the gases again. All together an excellent mixing of the unburnt gases and fresh air. Not very vigorously, but effective. Too much turbulence can be the cause of friction as well, don't you think? |
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Deleted
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Post by Deleted on Feb 20, 2012 1:21:33 GMT -8
Causing friction in the boundary layer is the task an turbulator is intended for. But more friction in the boundary layer does not mean there has to be more friction in the system too. For example an helical turbulator in a round tube raises friction in the boundary layer, but lowers friction of the whole system. www.youtube.com/watch?feature=endscreen&NR=1&v=WG-YCpAGgQQwww.youtube.com/watch?v=4XZgxbBFS34&feature=channelIn a system with a round cross section creating a vortex in this way would very likely be beneficial and could allow an even longer burn tunel respectively heat riser. Placing removeable spirals in the bench tubes and maybe the lower part of the barrel or the upper part of the riser where the flow becomes less turbulent could make sense for increasing throughput, heat transfer and preventing deposits of creosote. |
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Deleted
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Post by Deleted on Feb 20, 2012 3:21:38 GMT -8
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Post by peterberg on Apr 17, 2012 4:01:50 GMT -8
Today, I've shot two video-clips, using my wife's mobile phone. The clips are low-res, but the sound is about right. During the first clip there's a very audible metal-like clattering, caused by the bung hole which wasn't screwed down at the top of the uppermost oil drum. I've tried to shorten the start-up time with a paint stripper, but that wouldn't work. After I've changed it for a very antique hair dryer, blowing cold air only, things went a lot smoother. Total start-up time up to the required temperature went down from 40 minutes to 15 minutes. The second attempt took a while longer to my surprise to get it up to the desired mode. Nothing more to tell, really. It kept on going this way as long as it has been forced fed using very thin pieces. More about pulse jet perils in the thread Hypothetical stove. |
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Post by peterberg on May 2, 2012 12:02:52 GMT -8
Another guy in the Netherlands is busy with a small rocket in his spare time. Last Saturday I've been there and we've put his creation to the test(o). We performed several test runs, each in another configuration. The feed tube and heat riser the same, with different turbulators in the burn tunnel. And one run using a straight tunnel in order to compare the effects. The goal was to determine which configuration generated the best combustion quality. This is the set-up, done in a greenhouse.  The drums are there to protect the temperature sensor of the Testo, the lower drum has been used on its own first, hence the scorched paint. The core components were made of ceramic paper, impregnated with a very wet kaolin-slip. Here are the different turbulators:  We've used the left one first, which is like a swirler. This is the graphic it produced:  Large image.As is visible, the CO line went down at a certain point to stay there for 16 minutes. After that it went up despite our efforts to get it down again. The second one has got two strips behind each other in the upper quarter of the tunnel. Less obstructive and done following my assumption that most of the combustible gases are against the ceiling of the tunnel.  Large image.In this instance, the low valley (very, very close to zero) happened to be 20 minutes long. After that all the pleasure dwindled and whatever we did, the CO levels wouldn't go down again. We tried a bit longer, so this graphic do span 105 minutes. The null metering hadn't been done yet, so we decided to do that right away. Started not bad, within 10 minutes it did enter its own valley which lasted 2 full minutes, and went up to never come down again. There's a certain upwards trend visible.  Large image.Fourth run has been done with a little strip in the top segment of the tunnel. About 1/4" high and spanning a quarter of the circumference, see the third ring in the picture above. As such, it could be qualified as a coarse trip wire. Started on top of some glowing charcoal. Because of that, the whole warming up phase was skipped and the CO line began a march close to the bottom of the graphic. Very, very close, the value of zero came by fairly often.  Large image.The thin and relatively short peaks were due to not providing fuel in time, because we were talking to some visitors. Adding fuel moved the line down easily. Another run has been done, with a complicated set up, mainly consisting of two horizontal strips and a lower piece.  This performed well, but the fire kept creeping up, resulting in the highest peak of the day, 8600 ppm. Demolishing the middle strip improved matters some what, but creeping up was still very much there.  Large image.This last one is probably as good as the trip wire, albeit at the cost of difficulties to keep the fire down. The filters were anything from dark grey to white. See the picture below, run 1 to 5 from left to right.  None of the configurations used a P-channel, by the way. Instead we've been very anxious always to provide some air on the side closest to the heat riser. Conclusion drawn at the end of the day: the bulk, maybe all, of the combustible gases are streaming close to the ceiling of the tunnel. That is to say, using this contraption. ;D It was awesome, we've had a wood stove inside a greenhouse, having it run for nearly 7 hours. Because there happened to be no stack to outside, we've had 100% efficiency inside! |
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hpmer
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Post by hpmer on May 12, 2012 4:26:24 GMT -8
Peter,
Although not as elegant as your described tripwire, would a flat projection, of say 3/8" across the entire burn tunnel, work adequately? I'm thinking of hanging a piece of tile vertically behind the first brick and allowing it to drop slightly below the bricks to create the air flow disruption. Or is there magic to the tapered version that this simplified version lacks?
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Post by peterberg on May 12, 2012 8:29:46 GMT -8
Although not as elegant as your described tripwire, would a flat projection, of say 3/8" across the entire burn tunnel, work adequately? I'm convinced it would work, see the test above. 3/8" is maybe a little too large, 5/16" is perfectly adequate. One proviso: the thickness of the tile need to be less than the overhang. Otherwise the turbulence will happen under the ridge instead of behind it. For best performance, you'll need the P-channel as well. Or is there magic to the tapered version that this simplified version lacks? The tapered and angled version is optimized, nothing more. No magic, witchcraft, sword or sorcery. Keep us posted, I'm still in dire need of more confirmation. |
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