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Post by Karl L on Jun 18, 2022 21:19:55 GMT -8
Trev, a while back I saw you were experimenting with increasing the surface area/volume ratio by placing pieces of vermiculite board in the top chamber, aligned with the gas flow. Did that work? Given the width restriction in my situation, I'll probably have to do something like that. The experiments with high surface area to volume ratio in the top chamber, showed that at the highest levels it creates a very stable low CO. burn, but the fire usually runs out of O2 at some point and then the CO. goes vertical. This happens because the high surface area drag leads to a much slower gas flow, which means less air over the fire. Thanks, and sorry, I realise I wasn't being very clear. I guess my question was: can the surface area/volume ratio be increased by adding an internal wall? I wasn't thinking of going for a very high surface area to volume ratio, just trying to get the same value as in your system (1.45), but in a situation where I have limited width. I have only 177mm internal width available for my top chamber. For a 115mm system, to get 1 CSA, the top chamber has to be 59mm high. The sa/v value for this is about 1.3. I was thinking that I could place some vermiculite board as a central divider, so the top chamber becomes two channels, with increased surface area/volume. Then, by making the divider less than full height, the surface area could adjusted to get the right sa/v value. Does that sound reasonable?
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Post by Vortex on Jun 19, 2022 2:45:52 GMT -8
Apologies Karl, I was really tired and missed that. Looking at your dimensions you should be able to get close enough by raising the height of the top chamber 2mm to 61mm and placing a 23mm high 20mm wide vane down the middle. 10388 1 csa of 115mm pipe. internal circumference / perimeter = 361.33 177 x 61 = 10797 minus the vane 23 x 20 (460) = csa 10338 Your top chamber ideally needs a perimeter length of 524mm so: 177 + 78.5 + 78.5 + 61 + 61 (chamber) + 23 + 20 + 23 (vane) = 522mm 522 / 361.33 = SA:V 1.445 Surface Area to Volume Ratio (SA:V) donkey32.proboards.com/post/36899/thread
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Post by Karl L on Jun 19, 2022 8:49:42 GMT -8
Thanks - that's really useful!
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Post by martyn on Jun 22, 2022 11:46:35 GMT -8
So after a few days of trial and error I have a few bits to report … I have found that the fire burns quite well with the bottom door open but you need to close it near the end or you are left with a fair but of charcoal and even unburnt wood. The main advantage for me is, with the door open it burns quite a bit cooler and surprisingly slower than with the door closed. However I can tell it is not so clean burning, I cant see any smoke but I can smell something in the air.
So the best burns so far are with the door open for the first 10 minutes then close the door for the duration. It will work fine with the door closed from the beginning but takes longer to get up to speed. I discovered that by fitting an extra layer of vermiculite on the floor, the fire does not burn as well. I tried it for two burns with as much wood as I could fit in and although the vortex was present it was not as spectacular. I removed the extra vermiculite and the fire burns much better, I think this is because the double layer of vermiculite prevents the air supply heating up as it travels under the floor?
I tried a few options of secondary air with very mixed results, my first attempt was drilling two 12mm holes in the back of the afterburner right where the center of the vortex would be. The holes are feed by cooper pipe that runs across the fire box roof but my Heath Robinson set up requires the door to be open throughout the burn.
That worked so well that I could not stop smiling as I could see a blue flashing air stream instantly mixing in with the vortex! Unfortunately it did not last long and I have not got the blue to show again. I think that might be effected by the type and condition of the fuel wood? I then tried mutable small holes in the back but that to upset the vortex and smoked up the glass.... I think because I could not work out a way to pre heat the air without destroying my whole stove....it is already looking a bit worse for wear with various holes and repairs !!
I feel I need to really heat up the secondary air supply and use more of it?
I have fitted various bits of vermiculite and glass in the top chamber with some positive results regarding a more equal temperature across the hotplate.
To be honest the first burn I did with two doors in place was the best and the most simple to operate .... light blue paper, stand back and watch... However is was too hot and fast for my use, of course as a heater, this basic format might be perfect for some folk.
As always this a steep learning curve but, next up will be more secondary air and adjustable fire box air...
On a positive note the stove does indeed work and it was a simple and quick build useing the vermiculite board. The board its self is holding up well, apart from numerouse holes there is no other noticable deterioation that I can see!
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Post by Vortex on Jun 23, 2022 1:57:22 GMT -8
If you need the door open it needs a larger primary air supply.
I found that running the stove with less primary and more heated secondary air directly into the afterburner resulted in less heat uptake into the mass, but that might actually be a benefit for your needs.
Only place I've had vermiculite board crack is in the firebox, the afterburner pieces seem to go on for years without much sign of degradation.
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Post by martyn on Jun 23, 2022 12:17:57 GMT -8
Video update, crazy temperatures for such a small stove must be on the limit of the glasses integrity, cooks great food faster than a microwave!……!
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Forsythe
Full Member
Instauratur Ruinae
Posts: 208
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Post by Forsythe on Jun 24, 2022 3:32:13 GMT -8
I really appreciate and enjoy getting to see all the various iterations' progress reports.
It's awesome to see when a plan comes together — but even when things don't go quite as planned, too — and I get to watch the improvisational problem-solving. I feel like I learn something equally valuable from the content and the subsequent conversations it sparks, either way.
So: thank you to everybody posting results in the forum, for sharing your findings. Much appreciated.
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Post by martyn on Jun 25, 2022 23:41:18 GMT -8
I have seen the first crack in the vermiculite, it is on the lowest part of the floor and not an issues at all. All the other components are fine. I have removed my secondary air and reduced the vortex port, just a little bit but the display is even better than ever…. and now longer lasting ….and the stove is running in a more sedate fashion. Yesterdays last fire, lasted around 80 minutes with the vortex showing for 55 minutes, the coals were still glowing after two hours. I have tried feeding the fire on top of the coals but it does not behave very well with some smoke and then a furious bust but to be fair I have to do a few more trials on that aspect. I must say I am hugely impressed with the vermiculite, it was so easy and quick to work with!
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Post by marcios on Jun 26, 2022 5:40:15 GMT -8
I have seen the first crack in the vermiculite, it is on the lowest part of the floor and not an issues at all. All the other components are fine. I have removed my secondary air and reduced the vortex port, just a little bit but the display is even better than ever…. and now longer lasting ….and the stove is running in a more sedate fashion. Yesterdays last fire, lasted around 80 minutes with the vortex showing for 55 minutes, the coals were still glowing after two hours. I have tried feeding the fire on top of the coals but it does not behave very well with some smoke and then a furious bust but to be fair I have to do a few more trials on that aspect. I must say I am hugely impressed with the vermiculite, it was so easy and quick to work with!
Nice stove Martyn!
How the final dimensions turned out: firebox, port and afterburner?
Do you intend to keep it without any secondary air?
Is the vermiculite plate one of the most resistant made with potassium silicate? Which is the producer?
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Post by martyn on Jun 26, 2022 13:51:42 GMT -8
Hi Marcios, I am still messing around with the dimensions and to be honest I do not know exactly who makes the vermiculite board as I just picked it up from my locale supplier but I will find out for you…. I am going to buy one more sheet as I plan to make a free standing oven encloser above the hot plate with a Rotisserie facility.
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Post by martyn on Jun 27, 2022 11:35:16 GMT -8
The vermiculite board that I used is called Skamolex stove board and is rated for 1000c service temp and a max of 1100. They are not the cheapest board at £58 for a 100 x 61 x 2.5 cm sheet the standard 20mm thick vermiculite board is £38 so quite a bit more but the guys at the stove shop say it is better lasting product for use inside wood burning stoves. The also make a blue water glass coated coated board rated at 1200c. My stove used exactly two sheets and one tube of Skamolex glue, total cost £130. Prices may vary as I live on an expensive island but I do get 20% trade discount.
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Jun 28, 2022 2:19:46 GMT -8
Interesting build Martyn , the vermiculite board seems to be a good alternative to CFB.It will be interesting to see how it lasts.Im glad to see you're still experimenting.
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Post by marcios on Jun 28, 2022 7:01:50 GMT -8
Martyn, In fact, it seems that Skamolex has a very good reputation. On the Skamolex chemical they say 10% potassium oxide. Vermiculite itself in general is below 6%. So I guess it is with potassium silicate as binder, as in the best. How I have vermiculite and some potassium silicate, I plan to try it, but I don't know the details of pressing and curing yet. Sorry about "final dimensions", I'm just wondering about the last dimensions, assuming ongoing experiments, especially of the reduced port that sedate the stove. Translated with www.DeepL.com/Translator (free version)
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Post by martyn on Jul 26, 2022 23:12:05 GMT -8
I am still playing with the 4” stove, I tried out a much taller top box by just adding some 4” strips of vermiculite making the top box 7” tall. I bought a 8mm steel top and welded (paid someone to weld) 30mm angle all around and one more piece longways underneath. The stove worked fine with a far more equal temperature across the whole top although still with a hot spot above the afterburner exit point! However it looked terrible and was 4” above the surrounding worktop space, so I am back to the original 3” tall top box. The steel top is a massive improvement for cooking purposes. The vermiculite has some cracks, the most obvious one in in the base of the firebox where the board is cracked from one end to the other but the crack is not open or causing any performance issues. Other hairline cracks have formed in the afterburner floor and roof, these are very tight and not even obvious unless you are searching. So overall the vermiculite is holding up extremely well, I did paint all sides and with waterglass, this might be protecting the surface a bit but there is no physical damage to the firebox as yet! The stove is in use most days and is good for cooking at around 15 minutes after lighting, I have also made a vermiculite oven to fit over the hotplate with a rotisserie and glass viewing window, this is great fun….. If I had more time and more money I would love to do a rebuild with the new knowledge I have gained but I don't have either at the moment ha ha…
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Post by martyn on Jul 31, 2022 5:01:43 GMT -8
I think I spoke too soon as regards the steel cook top as it has now deformed quite a bit! I will post some picture in the next video but, the top is quite massive with lots of angle iron welded in place, it is so heavy I can barely lift it! The top has been stable for the last weeks of cooking but, yesterday I used some smaller offcuts of softwood and the increased heat has warped the top making it impossible to straiten back into a flat top! Interestingly my other stove in my partyhouse has a 8mm steel top that has been in use for about 5 years and is still functioning perfectly, this is because it is round and the heat source is in the middle. This means that although the top does deform it is deforms equally around the edge so it still sits on its gasket seal, the middle in fact conclaves but always returns back to flat. The vortex stove has a rectangle top and is heated near the front edge making the outer corners lift up even with its massive construction.
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