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Post by rakettimuurari on Sept 14, 2020 3:36:04 GMT -8
Nice to see it works so well! Is the port really only around 50% of system CSA (4")? My math has been sleeping since the last stove  My summer stove project this year was to build a 4 inch Vortex stove to see how well it behaves compared to the 6 inch. All dimensions are scaled times 0.666 of the 6" / 150mm stove. |
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Post by Vortex on Sept 14, 2020 9:21:37 GMT -8
My math is terrible but I'm pretty sure I got that right: 150mm CSA: 75 x 75 x 3.142 = 17673 mm2. / 2 (50%) = 8836 mm2. / 50mm (width) = 176mm (length). 100mm CSA: 50 x 50 x 3.142 = 7855 mm2. / 2 (50%) = 3927 mm2. / 33mm (width) = 119mm (length). 6" / 150mm port = 176mm x 50mm. 176mm x 0.666 = 117mm 50mm x 0.666 = 33mm There's a 2mm difference in the length because of the rounding to whole numbers. Also the 6" / 150mm stove port is slightly under 50% because of the 'nose', or 'port bow' as I originally called it: donkey32.proboards.com/post/31514/thread. |
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Post by peterberg on Sept 30, 2020 1:25:40 GMT -8
Hi Trevor, because of the apparently scalability I'd like to know more about your rocket variant. I started digging in the vortex thread to looking where and how the primary and secondary air are done but couldn't find it. Proportions seems to be 10% for both 1st and 2nd but if and when I try to build it I need to know more details.
Another question: is there a reason why you made the firebox a lot wider than the afterburner space or is was it dictated by the size of the firebricks to begin with?
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Post by Vortex on Sept 30, 2020 6:51:40 GMT -8
Hi Peter,
The firebox is wider than the afterburner as I originally wanted to keep the same size firebox, so I could just adapt my existing stove. I was experimenting to see what size and shape port and chamber gave the most visually aesthetic double vortex, as I had no testo at the time, and that's what turned out best. I have noticed since though that if the fire is farther from the port, it is less inclined to form the double vortex and testo results are not as good. The wider shorter firebox does keep the fuel all closer to the port than a long thin one.
My 6" / 150mm stove in the house has 20% CSA air, which consists of a 20% csa primary air inlet reduced to 10% by an expanded metal screen (the screen keeps sparks from jumping out, but also shreds the incoming air which really seems to help mix it with the wood gases). The other 10% is all around the sides of the door (there's a two position door catch so it can be completely closed or held open with a 2mm gap all around the edges). It runs better like that than all 20% via primary.
If I was making it now I would increase the maximum available secondary as it occasionally needs a bit more if I'm burning a lot of small wood, and I'd probably make something like your latest system where it comes in around the sides after being heated through a box section door frame.
The 4" / 100mm stove outside needed a fair bit more than 20% air. I was using the glass propped up and leaning slightly out at the bottom so cant say exactly how much it was. I would make it adjustable up to 40%. It's easy to see when you have it right as the double vortex will be completely formed in the afterburner. Too much air and you'll just get a fire fountain, too little air and the flames will stream out of the afterburner around the shelf and up under the hotplate.
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Post by peterberg on Sept 30, 2020 8:58:09 GMT -8
Ahhh... I get it now, actually it's all front air now. About the same direction as Yasin Gach is moving, he implemented an air frame which is fed by a flexible stainless duct that is in de heater body itself. This way, air could be fed either from inside the room as from outside. And since the routing of the flex duct is inside the heater's body all air that's coming in is heated up.
So I understand it's not a done deal that the double vortex will form, air supply volume is an important factor. If and when I give a stab at it, it will probably be a 125 mm version due to size restrains in the two barrel setup I have here to play with. And now I come to think about it, I could use most of the same door setup as was in use for the DSR2 development.
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Post by Vortex on Sept 30, 2020 10:49:22 GMT -8
To do a 125mm version I would scale down all the 6"/150mm dimensions by 0.833. So long as there's sufficient flame the double vortex will form, but if there is too much air it wont form properly and will just be shaped like a palm tree, no spirals either side. If there is not enough air the double vortex of flame streams out of the afterburner up around the shelf and under the hotplate. The testo always shows the best results when the double vortex is perfectly formed within the afterburner. I was only using the bottom air at the end of the burn during the coaling phase, and since going over to the Austrian method I haven't needed it anymore. I made a proper V-shaped firebox floor recently, as the two tiles I used last winter had broken up into pieces.  |
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Post by peterberg on Sept 30, 2020 12:18:06 GMT -8
Yes, that Austrian method of shutting down the heater in coaling phase works remarkably well isn't it?
I'd think the tuning of the air inlet might be a bit tricky and probably differs slightly from one chimney stack to the other. I need to think about how that can be solved in an elegant way. But then: time enough, living in the slow lane.
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Post by Vortex on Oct 1, 2020 9:36:39 GMT -8
I only started using the Austrian method late last winter, so haven't really used it long enough to make a good assement of it yet, but it seems like the logical solution.
Chimney draw and mass resistance are going to be different in every stove, but with the afterburner window you have the perfect gauge of how well tuned the air is to the stove in real time. I'm not into electronics in stoves, but if you were I'm sure you could implement a system of electronic air controls based on the amount and position of flame in the afterburner, using either the fish-eye sensors used in heating oil burners or the changes in resistance in a nichrome wire across the flame path. Personally I prefer the simpler more elegant solutions.
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Post by peterberg on Oct 1, 2020 10:36:39 GMT -8
Personally I prefer the simpler more elegant solutions. Me too, me too. |
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Post by martyn on Oct 3, 2020 0:38:18 GMT -8
Hi Trevor, I love the visual effect of your design and I am keen to build one.
You seem to have done a fantastic job and I dont think I would need any more heat than you are getting from a four inch system however as I already have a 6’’ chimney in place I think a 5’’ version will be good?
Before I start, could I ask .... if you were starting a fresh, would there be any minor improvements you would make?
Perhaps some rounded corners or dimension changes that sort of thing.
I feel confident to mold any shapes or details Into the construction if you feel it would play any benefit.
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Post by Vortex on Oct 3, 2020 14:19:03 GMT -8
Hi Martyn, That's a good question. If I was building it now I would probably make a 5" version for myself. The stove is so efficient that the 6" is a bit too much for my cabin. The stove runs best on full loads, so I only have one fire a day and I often end up with the window or door open as its too hot. I could probably manage on the 4" and have a couple of fires a day. The distance from the fire to the port is quite important and is more noticeable in the larger stove, I think that's because you're more likely to run it on less than a full load. It seems like when the fire is too far from the port too much of the wood-gases get burnt in the firebox and there isn't enough left to form a full double vortex in the afterburner. Today I raised that new V-shaped floor I made by 3/4" as it was lower than the previous one, it's surprising how much difference it makes. Yesterday I took the afterburner apart to replace a couple of cracked insulating firebricks. I discovered that the underside edges of the port are disintegrating after just 2 seasons of use. I was surprised as my previous firebox roofs have been perfect even after 10 years of use. I would have thought the top would be a more aggressive environment but they were still OK, so I turned the top over and repaired the edges with some calcium alumina cement. While I was in there I made a slight change to the afterburner that I have wanted to try out for a while. I made the afterburner chamber 1" deeper than the firebox and made a sloped back edge to the port and a bigger 'nose'. The idea is to throw the double vortex towards the rear of the afterburner to give it a bit more time there for complete combustion.    |
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Post by martyn on Oct 4, 2020 0:22:31 GMT -8
No doubt your fire is running at cement destroying temperatures!
I already have a very nice stove but it lacks the visual experience so I am very tempted however I was planning on having it running on just producing radiant heat so I could keep the effect going for at least two burns in a row.
Maybe the 4” system would suit my needs better.
I use stainless steel needles and plastic burn out fibres in my refactory mix. In theory the needles help to strengthen the mix and the fibres allow moister to disperse and also allow a certain amount of expansion. I can’t really say how effective these additions are but I have cast several large pieces with no cracking after many years of use.
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yasin
New Member
Posts: 33
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Post by yasin on Oct 4, 2020 2:57:15 GMT -8
If you are testing this core, will you test it insulated or uninsulated ? I would be very interested to know if my test of this core without insulation replicates or not. Insulation is very problematic to me when it is in direct contact with the flames because of the cooking of food in the oven.
Anyhow it is just a suggestion..
Kind regards,
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Post by peterberg on Oct 4, 2020 6:53:16 GMT -8
Hi Yasin,
At the moment there's no testing in progress. Plans for the coming week or weeks are to partly demolish the DSR2 reference model and rebuild the top box according to Trevor's specifications. I don't own a wet saw and I have some 50 mm CFB leftovers from the development stage. So it will be insulating from the firebox' ceiling and up, only the shelf in the top box will probably be a refractory cast piece just because I have that laying around. The firebox won't be like Trevor's but the air supply is.
To help you with your specific question: once the DSR2 development core was ditched and the reference model built up, it behaved exactly the same. The only difference was that it took quite some time to reach a decent temperature while the insulative model got hot in minutes. Mine happens to be a 125 mm model, yours is bigger, 180 mm I believe? The larger the core, the less it is influenced by the materials of the walls. This is due to the volume is scaling up faster as compared to the wall area. I'd think you wouldn't see much of a difference, and according to the 2022 EU norm the heater should be at operating temperature before the test is started anyway.
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Post by Vortex on Oct 4, 2020 9:49:06 GMT -8
martyn , If it's for an outdoor radiant heater then I'd go with the 5", indoors it would depend on the size of the room and how well insulated. yasin , I'd like to move away from using ceramic fibre products all together. I would think the insulating firebricks are OK and no problem near foods though. peterberg , So long as you run it on a full load I doubt the difference in firebox shape will interfere with it. All my tests have been run from startup, but the whole of my afterburner is made of insulating materials, except the floor. I would think the roof of the afterburner being insulated would be quite important for cold-start efficiency, but if the test is not run until it is really hot then I cant see it making much difference then. If you have an old piece of ceramic glass you could use that with ceramic fibre blanket on top for the shelf. I used Vermiculite board on the 4" which works OK so long as it's not for permanent use as larger pieces tend to crack up after a while.
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