vortex stove 175mm

[martyn]

 I am looking forward to continuing my experiments with the 4” vortex stove, my last attempts using a large top box were showing very promising results.
Reading through my youtube channel comments, and the comments on the forums, seem to suggest that over fueling and the resulting smoky glass are the most common issues that other builder experience. 
Another observations implies that if one follows Trevs design to the letter, the stove will work fine but if you deviate , there could be issues.
I think we all love the design concept and the more people that experiment the better.

I dont see many people having issues with heat output or difficulty starting up etc …it is just the overfueling issues that stop the vortex stove from being the most desirable design out there?

The air supplies are no doupt important but I have found the type of wood , the wind and the air temperature can all require air adjustment on the fly as such, so I feel adjustable air supply is quite important but I feel there is something else that could just change the design to work in more variants, perhaps the larger area top box is worth pursuing?

So many other aspects like a high mass or low mass fire box, hight and quality of chimney, summer and winter can all have an effect.
With the 4” version, running without mass and a short chimney,I have shown that the secondary air supply works very well and I also tested a large volume top box that seemed to also work for me.

So next up will be secondary air and a large volume top box combined together…….

[jonasp]

Dec 5, 2023 3:13:59 GMT -8 martyn said:

 I am looking forward to continuing my experiments with the 4” vortex stove, my last attempts using a large top box were showing very promising results.
Reading through my youtube channel comments, and the comments on the forums, seem to suggest that over fueling and the resulting smoky glass are the most common issues that other builder experience. 
Another observations implies that if one follows Trevs design to the letter, the stove will work fine but if you deviate , there could be issues.
I think we all love the design concept and the more people that experiment the better.

I dont see many people having issues with heat output or difficulty starting up etc …it is just the overfueling issues that stop the vortex stove from being the most desirable design out there?

The air supplies are no doupt important but I have found the type of wood , the wind and the air temperature can all require air adjustment on the fly as such, so I feel adjustable air supply is quite important but I feel there is something else that could just change the design to work in more variants, perhaps the larger area top box is worth pursuing?

So many other aspects like a high mass or low mass fire box, hight and quality of chimney, summer and winter can all have an effect.
With the 4” version, running without mass and a short chimney,I have shown that the secondary air supply works very well and I also tested a large volume top box that seemed to also work for me.

So next up will be secondary air and a large volume top box combined together…….

Hi Martyn,

Thanks for your input! In your large top box version where does the restriction occur is it right after the shelf entering the top box or the top box exit and do you remember the CSA %?
The secondary and primary air video is really insightful!

I love the design of this system I just wish mine was more stable in a wider amount of situations. The amount of heat it produces is just amazing!
After playing some more with my dimensions and not getting the results i would like, I'll probably look into installing secondary air to control overfueling.

[martyn]

The exit can be seen at 4.42 in the second video, it is 100% system size, the same as the entry to the top box 100%.
Always good to experiment just bare in mind my recent experiments are based on a vermiculite 4” stove so quite different from Trevs and your design.
I have lots of rocket stove videos including a 6” cement version on my channel.

edit …there is a small restriction at base the chimney as there is an adjustable flap, even though it runs with the flap open, I would say it works out about 93-5% system size.

[Vortex]

Overfueling on a Vortex stove is just a lot more obvious than on others and harder to ignore, but I think that's a good thing as it shows us how to get it right. When I built the secondary air setup recently I cut out the top part of the metal plate that was blocking me from trying out a larger topbox. I was going to test it out this morning but forgot until after I'd lit the stove    so hopefully tomorrow.

Secondary air on my setup turned out to be a complete waste of time. It initially looks like it works just like in martyn's video above, but if you watch the fire for more than a few minutes after, the firebox gradually gets more smokey, and the amount of secondary air the afterburner needs gradually increases, as the more secondary air you give it the less is drawn in through the primary and the less complete the initial combustion. If you then increase the primary it appears to improve, but there's reduced efficiency due to an increase in exhaust O2.

I didn't notice it before martyn, but in your top vid above at 3:00 minutes you say it's overfueling, but on a testo that would actually be only very slightly raised CO, but anything more than just those tongues of fire licking around the edge of the shelf and the CO does go up very fast.

[jonasp]

I'm getting good experiments the past 2 days. Yesterday I made the top chamber 100% CSA (exit top chamber still 100% CSA too), it was harder to get going and have a fully formed vortex but I could poke the fire to get the vortex even faster and it never overfueled at any point.
Today i made half of the top chamber have a 105% CSA restriction than 120% CSA for the latter part(1shelf) going to 100CSA exit. Beautifully and easy to get a full yellow vortex but overfueled slightly. After slowly adjusting air and observing, I came to the conclusion opening the door a crack bit (1-2mm gap) and closing the primary air more to accommodate the extra air through the door the overfueling got under control.
After the peak fire the top chamber vermiculite board are orange and the vortex is also orange but still fully formed. (is this still a sign of a less clean burn or would it just be the insane temperatures in the afterburner?)

Tomorrow I might try to loosen the door so when it's closed I still have a small gap and or adjust the top chamber to be fully 105% CSA. (wondering if having 2 restriction with an area for slight expansion will influence things, might be an area where pressure will buildup to get easier through the last exit. Just an uneducated guess though)

It's good to finally have more predictable results and see what tiny changes can do.

[Vortex]

The top chamber should be around 100% csa right through including the exit, but also should have the correct surface area to volume ratio. The higher surface area creates resistance without an actual restriction.

www.google.com/search?as_q=vortex+stove&as_epq=surface+area+to+volume+ratio&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=https%3A%2F%2Fdonkey32.proboards.com&as_occt=any&as_filetype=&tbs=

Glowing vermiculite shows you are getting high temps in the afterburner which is good, but to be sure it's clean I'd need to see a video. Red-orange is high O2, golden yellow is what you want to aim for.

A fixed open air supply is OK for experimenting with but if a permanent feature it will always be leaching your heat out of the system.

Experimenting is good I think, it helps you understand your system and what all the variables do so you can get the best out of it.

[jonasp]

I don't understand how you can increase surface area to volume ratio in the top chamber or the opposite If we want to keep the whole top chamber 100% csa, doesn't it scale linear? (increasing depth will scale both volume and surface area?) The only thing i see which has influence is the gasses will have a longer time of resistance if you increase the depth of top chamber.
I feel like I'm missing something but not sure what..

edit: oh ofcourse i see, you can put in some divider or standalone vermiculite parts which will increase surface area, I'll check my ratio and try to get as close as your 1.45

Yes good point, it would be purely for experimenting first and then probably make permanent adjustments to the door design.

I'll make a video tomorrow of the orange vortex

Video right after the small overfueling fix
drive.google.com/file/d/1QNn-K07f4WdIRJTxAeSesCmQCqAEtZGA/view?usp=sharing

[Vortex]

I'm terrible at math, not academic at all, I work intuitively, so please if you see a mistake in my calculations point it out, as I find this kind of stuff very difficult and cant hold it in my head for more than 5 minutes, lol

I don't use vanes in the top chamber. Different shaped chambers have different internal surface areas, even when they are all the same csa. Forget the depth/length, to simplify we can just do a simple cross-section and measure the internal perimeter;

A 6"/ 150mm system csa is 17673mm2 and the perimeter (internal circumference) is 471mm. So a square top chamber 133mm x 133mm is also 1 csa, and the total length of the perimeter is 532mm. Now if we make that same 1 csa top chamber a low and wide rectangle, say 65mm high x 272mm wide then the total length of the internal perimeter is 674mm.

That video looks fine, nice color vortex. It's normal for the vortex to not be quite fully formed at startup, until the afterburner heats up.

[jonasp]

ooh wait I understand now, i think.
So we're making a ratio of the top chamber circumference vs the circle circumference system size?

I was under the impression we're calculating top chamber surface area / volume area of the top chamber.

If we take the example of the cube 13,3cm top chamber
surface area (neglecting exit port) it would be 13,3*13,3mm*5 (cube has 6 but 1 is open so 5) = 2352,637cm2
volume 13,3*13,3*13,3 = 884,45 cm3
ratio would be 2352,637cm2/884,45 cm3 = 2,66 cm-1

while the top chamber circumference vs the circle circumference system size is different.

Not sure if i make any sense and or if I'm completely wrong here but I'm just following my logic


edit: I seem to remember I've read something that if you made your top chamber port more square it influenced the vortex too. the circumference of a square is also less than circumference of a rectangle. (so more resistance in top chamber because of longer rectangle resistance and easier exit because of rectangle so less resistance)

keep in mind I'm just throwing uneducated guesses here

edit2: oh now i completely understand why you call it SA/V (you calculated a cross section of chimney SA/V compared to cross section top chamber SA/V) or in my mind how i understand it better cross section area/cross section circumference of the chimney vs the cross section area/cross section circumference of the top chamber.
Did you do any tests by making the depth of the top chamber longer or shorter?

sorry for all my rambling and edits trying to wrap my head around it hehe

[Vortex]

Dec 7, 2023 6:44:03 GMT -8 jonasp said:

ooh wait I understand now, i think.
So we're making a ratio of the top chamber circumference vs the circle circumference system size?

I was under the impression we're calculating top chamber surface area / volume area of the top chamber.

Yes I was referring to a normal 6"/150mm round chimney pipe there.

SA:V is used a lot in other things and was the closest I could find to express the relationship, but for our needs circumference or perimeter to cross sectional area is all we really needed (P:csa), as the length/depth of the top chamber was already defined.

edit: I seem to remember I've read something that if you made your top chamber port more square it influenced the vortex too. the circumference of a square is also less than circumference of a rectangle. (so more resistance in top chamber because of longer rectangle resistance and easier exit because of rectangle so less resistance)

keep in mind I'm just throwing uneducated guesses here

I think the square exit port only worked better because the changes I had to make to get it in, happened to increase the surface area while maintaining the csa.

edit2: oh now i completely understand why you call it SA/V (you calculated a cross section of chimney SA/V compared to cross section top chamber SA/V) or in my mind how i understand it better cross section area/cross section circumference of the chimney vs the cross section area/cross section circumference of the top chamber.
Did you do any tests by making the depth of the top chamber longer or shorter?

sorry for all my rambling and edits trying to wrap my head around it hehe

You got it. My stove is quite limited in what I can do with the top chamber, so I was only able to make it a couple of inches longer which is how it is now on the skp file, but that was the only change in depth.

Yesterday I tried martyn 's suggestion of making the top chamber wider, by taking out the left hand side, so the top chamber is now much wider and the exit is formed between the internal chimney and the front wall (where the bypass flap control is on the outside).

Yesterday's fire I purposely loaded with a lot of small sticks and kindling to see how it would cope when overfueled, it was about the same as the standard skp file design. Today I lit it as normal and if I didn't know I'd made the internal changes I wouldn't have noticed any difference, so it is at least as good as the best I'd previously found.

[jonasp]

oh yes i completely understand now why you call it SA:V since it's essentially that what you refer to. My misunderstanding was how you calculated it.

So your experiment yesterday made the top chamber have a bigger csa and more surface area? Did the fold over exit also change? (where the gasses enter the top chamber).

Today i had a worse overfuel than yesterday and the only changes that were made, i cut the original 100csa board down to 107% csa but with more surface area than yesterday 105% csa (although there might be more resistance because I placed offcuts next to each other with tiny gaps since it's not 1 piece) interestingly the offcuts i placed in yesterday were roughly 50% depth of the top chamber.
Tomorrow i'll place another piece to lessen CSA % and add a bit more resistance.
Hopefully i can find the sweet spot of the amount of resistance my system needs.

Thanks again for all the input!

[Vortex]

My experiment yesterday was just the removal of the left-hand side of the top chamber, so that the top chamber width was expanded from 280mm wide to 540mm wide. The top chamber exit was then formed by the approx. 1.1 csa gap between the internal chimney and the front of the stove. The 'fold over exit' from the afterburner into the top chamber remained unchanged at 1 csa.

Today I removed all the vermiculite boards from the top chamber so it was maximum size (540 x 400 x 115), the height expanded from 65mm to about 115mm, and I reduced the exit from about 1.1 csa to exactly 1 csa. The weather was very windy and I loaded a normal batch of wood. The vortex was very nicely formed and the fire ran well, it briefly overfueled at the peak but nothing I wouldn't expect with the strong wind. I will run it the same again tomorrow, hopefully with less wind and see how it goes.

vftshop.com/images/others/Stove/exptc1.jpg

vftshop.com/images/others/Stove/exptc2.jpg

vftshop.com/images/others/Stove/exptc3.jpg

vftshop.com/images/others/Stove/exptc4.jpg

[fruitbat]

Very interesting that such a huge change had so little effect on performance. I suppose the question now is would the effect be the same with a Vortex core in an open bell, or is your labyrinth channel mass now having an even more important restricting effect to regulate combustion...

[Vortex]

Hi fruitbat, I'll answer your question in the Vortex Stove thread as this is jonasp's and I dont want it to get off topic.

[jonasp]

So interesting! I responded on your thread.

Today I did a similar experiment. Changed the top chamber fold over exit to 1 CSA and removed the boards behind that.



I also removed the grid at the primary air (felt like the holes were too little) and replaced them with some vermiculite. Bit of a sloppy job but just testing..



Very slow start up, I also used a bit less wood. When the fire got going and was at the peak It did overfuel a tiny bit a couple of times.(just some flares of smoke going over the fold over and then got back to stable)
I way prefer this type of slower fire than a better faster vortex but overfuel. Once the vortex get too much orange color I do increase primary air and it goes back to more yellow/orange color

Video around the peak
drive.google.com/file/d/1JtVpClqolqMkoBwKxqIRijCef2EwHmGZ/view?usp=drivesdk

Further thoughts, the restriction above the oven may be too much and might slow down the startup (it is a very wide but low in height gap and I don't know the exact CSA, definitely more than 100). I will keep everything the same but might remove some of the wool to eliminate that restriction.


I'm also wondering if the ceiling top chamber is better to have a material which can conduct heat faster as a sort of controlling the temperature better since overfueling/thermal Runaway is essentially temperatures that keep going up and up. (Just a random thought)

Further random thoughts if I get a faster air flow the vortex spins faster and the hot air moves faster so less heat building up so less chance of thermal Runaway.