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Post by martyn on Jul 3, 2023 9:29:08 GMT -8
Refractory casting mix is very dry compared with standard mortar mixes.
I am using large amounts so I use an electric cement mixer but mixing in a barrow with a trowel is fine.
What we want from the vibrating, is a solid dense mass with zero trapped air.
You will just have to do your best with whatever method you can, basically you vibrate until no bubbles rise.
On a hight frequency vibrating table (very expensive machine) it would take about 5-10 seconds with a diy table maybe 60-120 seconds and with a hammer drill, as soon as the bubbles stop coming to the surface?
Its all good fun……
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Post by martyn on Aug 18, 2023 22:56:17 GMT -8
I have been helping Michele customise his 4” vortex stove to suit his use and he has got it working very well …..
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Post by Vortex on Aug 19, 2023 8:55:38 GMT -8
Excellent! Would be interested to know the secondary air setup on there - plan to do some more research on the secondary air system on mine this autumn.
Trev
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Post by martyn on Aug 23, 2023 5:13:10 GMT -8
The secondary air design is the same as mine but I am not sure what the actual gap around the vortex slot is, but there are a few things we have established.
The air should only enter from the sides on the vortex slot and not the front, in my case I settled with 12mm down both sides and a 25mm gap between the fire box roof and the vortex chamber.
The other thing seems to be a large space Immediately after the vortex chamber really does stabilises the burn and allows re loading a hot fire box.
I have not found a limit or ultimate volume just that…. so far the bigger the space the better!
What I now need to test is the secondary air, plus big top box……
We have also tried mini risers coming out of the normal size top box, a mini riser of 100x100mm 200mm hight (100mm system) seems to also help with adding wood to a hot fire. Not quite as good as a big top box but quite a good improvement.
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Post by Vortex on Aug 23, 2023 10:00:39 GMT -8
If that's still a 4"/100mm system then the 12mm each side of the port should be providing just over 38% secondary, which is almost the 40% theoretically needed to provide the equivalent of 10% at room temperature, (as the air expands about 4x at afterburner temps but still only contains the same amount of O2). What width is your 25mm gap between the fire box roof and the vortex chamber? To get 40% it'd need to be about 125mm wide. I also found secondary air from the front messed up the vortex. The other thing seems to be a large space Immediately after the vortex chamber really does stabilises the burn and allows re loading a hot fire box. I have not found a limit or ultimate volume just that…. so far the bigger the space the better! Is that between the afterburner and top chamber at the front behind the glass or the top chamber itself? I've been limited by the outside dimensions of the stove so have never had much spare room to experiment with large top chambers. Trev. |
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Post by martyn on Aug 24, 2023 22:42:44 GMT -8
I would like to combine last years big top box with this years secondary air, it is just finding the time……
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Post by Vortex on Aug 25, 2023 1:42:01 GMT -8
If I remember correctly neither yours or Michele's has any mass bell or contraflow system? I think that will have a big influence on what the best configuration beyond the afterburner is.
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Post by martyn on Aug 25, 2023 4:51:08 GMT -8
No we have both tested with contraflow, I have already posted videos featuring an old filing cabinet that worked perfectly well and Micheal has his unit inside a brick construction with a bottom exit.
However i do believe you need to tune each one to suit the design,, things like tall insulated chimneys are certain to make a difference.
we have both suffered bad start ups and bad reloads, it is getting the ‘every time consistency’ that is difficult.
I have high hopes for a big top box and adjustable secondary air…
There are several other people trying the 4” vermiculite version, but I have not had much feedback so far…..
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Post by Vortex on Aug 25, 2023 9:19:29 GMT -8
Oh that's good - now you mention it I remember your filing cabinet video, I'd forgotten about that.
Measured up mine today and there's just enough room to put in a 40% csa secondary from the front above the door to the sides of the afterburner, I can do it using one of my kiln shelves for the firebox roof and pieces of old stoveglass for the afterburner floor.
Only way I can see I could increase the size of the top chamber would be to expand it sideways up to the bypass. Did it work wide and shallow for you or did it have to be higher?
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Post by martyn on Aug 25, 2023 12:02:33 GMT -8
I have only tried the two big top box versions, earlier this year I worked on lots of top box configurations but the very first design seemed to be a lucky success!
I just don't know or understand how it works but it appears that if the vortex immediately goes into a big space the stoves runs very cleanly.
However as you point out those test did not have any mass or downward flow.
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Post by Vortex on Aug 26, 2023 4:52:49 GMT -8
If it worked well in the low wide configuration in that video, then I could try expanding my top chamber to half or all of the top of my stove. Here's an old pic but shows the space available:  |
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Post by peterberg on Aug 26, 2023 6:43:06 GMT -8
The other thing seems to be a large space Immediately after the vortex chamber really does stabilises the burn and allows re loading a hot fire box. I have not found a limit or ultimate volume just that…. so far the bigger the space the better! , about two years ago I've found the same phenomenon, very interesting you are aware of the same. At first, my development model didn't allow a larger back fold above the vortex shelf. Whatever I did, I wasn't able to repeat the results of Trevor. Later on, I switched to a round ceramic tube which left more space around it in the same total space. More experiments with the end port resulted in one that was 100% of system csa, while the cross section area of the backfold happened to be nearly 170% of system csa. donkey32.proboards.com/post/36420/threadDon't know about volume, the process as I understand it: a space which allows the hot gases to expand, followed by an exhaust opening which is narrower again. So cross section area could be the magic word, as far as I am aware of. The later pre-production model (the only one to date!) sported a slightly larger expansion space and also behaved like it should. The net result is a combustion core which is very stable, it won't go into thermal overdrive just like that as before. To date, about 15 upscaled versions are built which are all behaving exactly like my development model. I presume Trevor's core/heater is built in such a way there is enough back pressure further down in the system to prevent overfuelling. |
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Post by Vortex on Aug 26, 2023 8:56:56 GMT -8
The back pressure of a mass / contraflow system definitely helps resist overfueling. When doing the initial Vortex afterburner experiments outside in 2018, I discovered that an end port also really helped reduce it. I later discovered that a high surface area to volume ratio of the top chamber improved this even further. I think that's because there is more exhaust gases in contact with the surface creating more resistance but without restricting the flow.
My present setup is very stable with the small top chamber with high surface area, end port and contraflow mass, but I'm always interested in the how and why things work the ways they do, and a large top chamber is something I have never tried out before. I'll definitely give it a go once we're back into the fire lighting season.
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aleks
New Member
Posts: 6
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Post by aleks on Sept 5, 2023 23:49:03 GMT -8
Hi There, I got very much intrigued by the vortex stove after seeing the one jojohannes build and feeling it's remarkable heat. We are building one in our Italian mountain hut, just 10 minutes from Johannes with similar isolation values but a much higher ceiling so we decided to build the 6 inch version. Just to have a clear view on everything I decided to read all the 87 pages of replies but there were some detailed subjects I didn't take proper notes one. To spare me the effort of reading the 87 pages again I thought I ask my questions here. I'm making the foundations now and have started building the casts. Regarding the floor of the firebox: what is the correct size of the whole where the ash goes trough? is it 40 x 200? I saved this drawing of the floor but can't make out the size of the gap www.vftshop.com/images/others/Stove/V-floorscan.jpgRegarding the battery: have there been any updates on the battery since this design? www.vftshop.com/images/others/Stove/Vortex%20Stove.pdfAnd is there any objection in making a bigger battery? we are planning to make a bench of about 90 cm so should we make the battery bigger as well? And is there any objection in lowering the battery considerably from the firebox (for esthetic reasons) I've seen that the inflow in the battery is somewhat lower in the original design donkey32.proboards.com/thread/703/vortex-stove but I might want to add an extra 10 cm on that. Lastly: what is the latest wisdom on the wholes in the secondary burn chamber? I've lost track a bit during my reading there. But what's the advice, holes or no holes? Thanks for your time and all the great work you have been doing in the last ten years. I will send you some pictures after the build in Oktober. |
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Post by Vortex on Sept 6, 2023 1:58:43 GMT -8
Hi There, I got very much intrigued by the vortex stove after seeing the one jojohannes build and feeling it's remarkable heat. We are building one in our Italian mountain hut, just 10 minutes from Johannes with similar isolation values but a much higher ceiling so we decided to build the 6 inch version. Hi aleks, Welcome to the forum. Glad to hear Johannes' stove is still going well. The width of the new ash trap slit is 13mm. It was not clear on that image as the 2 scans were misaligned and so looked like 1313mm, I've corrected it now. The length is 365mm. This post explains the new ash trap well: donkey32.proboards.com/post/35088/thread I use the poker to clear that last bit of ash through it from the previous fire before loading the wood. In the new stove I changed the 'battery' design to maximize the efficiency for it's small size as my space is very limited, but this wont work well on a larger scale, so you can just build the original style bell with a bench if that's what you want. You may need to tune the top chamber of the stove to your bell/bench to get the best results though. The new stove is a bit higher than the original, but the inflow was at the top of both, you can lower it by 10cm without any problems. The sides of the port seem to be the best place to introduce secondary air. The optimum amount is still a bit unclear. I would try to make it large <40% csa and make the entrance adjustable. I will be experimenting with this myself again soon. Thanks, I look forward to seeing the pictures  Trev |
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