tferr
Junior Member
Posts: 69
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Post by tferr on Dec 19, 2021 5:22:19 GMT -8
patamos very kindly sent me THIS VIDEO of the finished Vortex stove he's built for Brent in Canada, and the description below: The various iterations with the steep V-sided floor never quite worked out. Even once I thinned its mass to 2" and added big air slots front and back it kept bogging down to incomplete burns. Glass was sooting up and big chunks of unburnt wood were leftover. Not happy... Tweaks to downstream aspects of the system were helping - particularly extending the tongue in the backrest-bell to make it more of an upper-lower flue run... Super glad I put that in, and big thanks to everyone who chimed in response to my questions about what to do there. But things were still way off, and my sense was that too much air was bypassing the fuel up the side walls. Unburnt O2 running past (rather than into) the flame is just a bunch of cooling ballast gas clogging up the system... Next tweak was to close off the side wall air ports which improved the coaling phase, but still things were sluggish. So we then reopened some side air at the front and back. Again, minor improvement, but still soot covered the glass from mid burn onward. With each tweak it grew clear that the V was not going to work out because we had no way of concentrating the air flow where we wanted it to go when we wanted it to. We could prevent early stage bottom air supply by placing a chunk of 2x2 in there. I thought I was a pretty smart fella for coming up with that idea. But evidently I was more of a fart smella... Residency time in the fire chamber was not too slow, but temperature was too low and turbulence was still way off. The door had about 2" of CSA but this had little effect and I wasn't interested in modifying a store-bought cast iron unit. So I rigged up a metal floor with air slots front and back and along the sides. And we loaded up a bunch of not so dry wood... and voila. She started hummin. That video is about 20 minutes in and the mild soot on the glass from early burn was still cleaning up. This variation of metal floor 'bottom air' supply is spread out mostly over 3" across the back and 3" across the front (with numerous 1/2" holes), and along the bottom corner side-walls via 1/2" x 12" spaces. There are no air holes in the middle area of the floor so as to encourage the fuel to burn from the ends and perimeter towards the middle. Otherwise that mid-region of fuel (which is directly under the ceiling exit port) will burn first, creating a(nother) situation in which the air supply would be blowing past the fuel... All in all, i think this kind of air-port layout may be as good as we can get with a non-adjustable air supply system. Once things get to coaling phase one can rake the coals forward and/or back onto the ports to turbo blast them. We may play around with the floor-air configurations a bit. This is just a thin piece of 16 gauge mild steel I had kicking around. Once I think we have nailed it I will make something out of 1/4" btw - the 2mm piece of mild steel I have in the floor of my tauran triple shoe box is still holding up after 4+ years. Must be the cooling effect of under-air flow. Now that we are getting closer to ideal temperature and pull, we might tune down the ceiling port which I hogged out to 6" x 2.25" (knowing it would be way easier to shrink that down than get in there and carve out again...). In the video we had shrunk the length by 1", but we might cut up some old 3/4" thick kiln shelf to narrow the sides and raise the floor closer to Trev's specs of a 5" system size. I think first though Brent is going to place a divider across the midsection to see what happens with a sideways tauran double port. Should be fun to watch One last thought for now: I think Trev is right about the downstream harvesting dynamics having negligible impact on combustion dynamics, particularly when the fire is really cranking. When our combustion process was staggering the bypass port in the backrest was very influential. But once combustion was in the happy zone the bypass adjustments had very minor and gradual effect Patamos ...what is the cook top made of ...did youput the "Swirl" circle in it.
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Post by patamos on Dec 20, 2021 13:06:10 GMT -8
The cook top is a cast iron unit with frame, removable deck and two removable disc/plates. I bought this one from max Edelson (firespeaking.com) who is the N.A. importer and distributor for a Chinese company called 'Fireway' The firebox door is also from them. Both part of a larger shipment I had arranged 2 years back. Pretty good quality all in all.
Can't imagine what the supply line is looking like these days. I hear talk of highly inflated bidding wars for cargo space on sea-containers
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Post by martyn on Dec 20, 2021 13:19:15 GMT -8
Having removable plates is an important factor to avoid warping, in my case I have found that by having a central plate, my 10mm mild steel top becomes slightly concave but the sides dont move. So I dont even need to fix the plate down, it just sits on a rope gasket.
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tferr
Junior Member
Posts: 69
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Post by tferr on Dec 20, 2021 17:54:08 GMT -8
I'm kickin myself for scrapping an old beat up Findley Oval a couple of years ago. I could have easily made those top plates work
Thanks Patamos I checked outthe site Are those prices Canadian
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Post by patamos on Dec 20, 2021 20:51:13 GMT -8
Ya cast iron anything is worth holding onto. Even small sections might become a griddle for something somewhere
Prices are USD, and to get them into Canada you have to sort out the duty and customs yourself. Easy to do in person at the border, but all kinds of emails, phone-calls, and scans/faxes otherwise.
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Post by patamos on Dec 20, 2021 20:55:42 GMT -8
Having removable plates is an important factor to avoid warping, in my case I have found that by having a central plate, my 10mm mild steel top becomes slightly concave but the sides dont move. So I dont even need to fix the plate down, it just sits on a rope gasket. One cook-stove heater i built with a mid-size firebox and a mild steel cook top 16" x 20" x 1/4". Every firing it warps up about 10mm and you can see into where the flames are rounding the top shelf. It was only meant to be temporary til I found a ceramic glass top, but the clients liked the dynamic, and it has never smoked back on them in the 8 years since.
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Post by martyn on Dec 21, 2021 0:20:15 GMT -8
Yes my first steel tops warped like mad but as soon as I cut a hole in the middle for a removable plate it seemed to remove the cross tension and rectified the problem.. My cooking top reaches 550c and only concaves a little but it is a round cooking plate.
The ceramic glass tops I have used are no use to me as they simply let to much heat through, the centre above the riser would reach 500c in the first few minutes but the edges would only go to 200c even the barrel edges would get hotter than the ceramic glass edge. The other issue with ceramic glass is that I was always very wary of breaking it and that does not suit my cooking style.
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Post by Vortex on Dec 22, 2021 14:27:23 GMT -8
Carrying on from my experiments with secondary air in the afterburner, once I'd established the best way to do it I wasn't quite sure where to go with it next, so I played around the 3 air controls to see what effect different ratios at different stages had. While I was doing this I realised that the afterburner secondary air is self balancing with the primary, when you close the primary the drop in pressure increases the flow through the secondary, and with secondary air to the afterburner, theoretically once it's hot it should keep running even if the primary air is completely closed - so I tried it There is a VIDEO HEREafter the first clip from that video I opened the primary a tiny amount, just enough to get a finger nail into and waited to see what would happen. The stove overfueled badly for a while then gradually settled down into a beautiful long lazy gasifying burn with very low carbon monoxide, low exhaust temps (because of the reduced air flow), and a short coaling phase (the lower gas flow seems to burn off the volatiles slower, so you have more left to help burn up the coals at the end). Over the following 3 days I set about trying to create this kind of burn from as close to the start as I could. My first couple of attempts were rather messy but both eventually settled into the nice gasifying burn. On the 3rd attempt, I tried starting off with a little primary air, the secondary full open and very little kindling on top of medium then large sized pieces at the bottom. This was a lot better, it did overfuel very briefly but then settled nicely. By the 4th try I was getting the hang of it, I ran it as the previous one except with less primary air from the start. With the reduced firebox size and larger primary air my burn times had drop to around an hour, with this setup it's back up to 2 hours. The chimney temps are lower, it only takes a tiny amount of kindling to light so there's less wood splitting, and a shorter coaling phase. Apart from the initial hassle of making the secondary air setup, I cant see a down side to it.
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tferr
Junior Member
Posts: 69
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Post by tferr on Dec 22, 2021 16:18:05 GMT -8
Bravo! As a novice starting my build just a month or so ago, reading all the info in this forum makes me feel like a cherry picker sitting on the blue line
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Post by patamos on Dec 22, 2021 22:12:35 GMT -8
Beautiful work Trev!
And the slower burn rate is giving your mass longer harvest/residency times to boot.
I'm curious to hear your thoughts on ideal routing for the secondary air?.. (Thinking of how to retro fit something into a few recent builds...)
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Post by Vortex on Dec 23, 2021 3:27:44 GMT -8
Thanks guys.
The mass heat capture seems slightly better, had to have the house door open again all last evening. I don't know what the temps in the afterburner are like compared to before, as the hole I previously used for the thermometer probe I'm now using as the secondary air inlet. Visually it looks about the same though.
I've been thinking a lot about the best way to implement the secondary air. Most ideas seem quite complicated compared to what I have now. Not sure how much or if any benefit there would be to a longer heating path, as those vermiculite boards are glowing red hot and the air travels behind and through small holes in them. I guess that's next to figure out.
The only problems I have with that present secondary air setup are, one side is closer to the inlet hole, so I've had to restrict that side to get a better balance. Also the pieces are not fixed and they 'walk' quite fast, having to push them back into position almost every burn, not sure how best to hold them in place. They seem to cope with the abuse very well though.
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Post by hof on Dec 23, 2021 18:35:57 GMT -8
What was primary and secondary air cross sections?
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Post by Vortex on Dec 24, 2021 2:35:17 GMT -8
For that last graph above it was:
Primary 11% for kindling phase, then 3% for rest of burn.
Secondary 9% until 70 minutes, then 4.5% for rest of burn.
Coal-burn air opened 1% from 35 minutes, then 3% from 100 minutes until coals all gone.
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Post by hof on Dec 24, 2021 7:16:00 GMT -8
Got schamote plates 20 mm thick. How do you think, is it realy need 40 mm thikness of 20 will be enough? If not, where is better to glue ribs: on upped side or on bottom side?
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Post by Vortex on Dec 24, 2021 13:11:55 GMT -8
I used 20mm vermiculite boards on my 4" stoves. The 40mm thickness on the 6" is just for strength. I've thought about doing it next time with two 20mm layers of kiln shelves, with the top layer with the join across in front of the port (so the top layer would be in 3 pieces).
What are the ribs for? I wouldn't put them on the top as it would interfere with the vortex, on the underside should be OK, might even add a bid more mixing for your secondary air.
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