Vortex Stove

[ollie]

Thanks for your response Trev, it looks good I think I understand the drawings. 

Few questions: 
1. Would it produce enough heat for people standing around it, would I need to somehow stop the air coming out of the flue. 

2. Would it be possible to have the door where you feed it and the glass window where you view the vortex on opposite sides, like an S shape. Suppose then the flue would be on the side you load. The reason I ask this is because it would be nice for people to see the flames irrespective of what side they are sitting on the stove. 

3. How tall would the flue have to be? 

Thanks again, 
Ollie 

[Vortex]

It produces a surprising amount of heat for it's small size, but if you want a larger version just multiply the dimensions by 1.25 for a 5" version or 1.5 for a 6".

would I need to somehow stop the air coming out of the flue.

I'm not sure what you mean. If you're referring to the resistance of the system then the switchback down the sides of the afterburner under the hotplate seems to be sufficient on the 4" I built but I haven't tried it on a bigger one.

In theory it should be possible to put the afterburner window on the other end (so the vortex is moving away from you) or even both ends, but I haven't tried it.

The flue should ideally be above head height.

Trev

[martyn]

Hi Olly, do you mean you want to use the heat coming out of the chimney to radiate like a gas patio heater?
That would not work but, I do have a 4” patio cook stove and heater, it works very well although it is still being developed and I will be back on it this summer.
A 6” version would be very hot indeed. 
There is a build video on my channel as well.

[Vortex]

I decided that before doing any more top chamber experiments I wanted to remove all the unused secondary air system and return the afterburner back to the full 6" system size (I had reduced it to 5.5" when I installed the secondary air). Everything else would then be back as per the skp file, and I could then be sure the expanded top chamber (as suggested by martyn ) will be compatible with the rest of the basic 2021b skp file design.

It took me the whole day Sunday to remove the top chamber, afterburner and secondary air system, then rebuild it all as it was previously, but with the new expanded top chamber at 1.5 SA:V. (60mm x 295mm = 17700mm2 (1 csa). 295mm + 60mm + 295mm + 60mm = 710mm / 471.3mm = 1.50 SA:V).

The burn was almost perfect except for slightly too much pull on the right side of the vortex, so this morning I removed the vermiculite board on the right side (like jonasp did on his), and the burn was perfect. This gives a lot more flexibility in the design of the top chamber.

[jonasp]

Good to see and read these results! Do you have an issue when the weather is being more mild with the draft not being strong enough? My system was running fine when the weather was 0-5degrees but now when it's 10 degrees outside it's struggling to form a proper vortex even by reducing the top shelf resistance a bit. (Probably need to reduce it even more)

[Vortex]

Outside temp doesn't seem to have any real noticeable effect on my setup, but I have an insulated chimney with only 18" outside above the peak of the roof. The temp of the mass does effect it, if the mass drops much below 20*C, then the start of the burn can be a bit slow. Are you skipping burns on mild days before that's happening? What kind of chimney do you have?

Trev

[jonasp]

Dec 23, 2023 5:34:51 GMT -8 Vortex said:

Outside temp doesn't seem to have any real noticeable effect on my setup, but I have an insulated chimney with only 18" outside above the peak of the roof. The temp of the mass does effect it, if the mass drops much below 20*C, then the start of the burn can be a bit slow. Are you skipping burns on mild days before that's happening? What kind of chimney do you have?

Trev

Hi Trev,
The first meter of the chimney is insulated then goes into an uninsulated chimney put into a rectangle old clay chimney which i filled the gaps with vermiculite.
I did notice there might be a leak at the top which might make the vermiculite damp so that might be the culprit. Can't really fix it at the moment since it's raining too much and i would need to remove some bricks add a normal chimney cowl instead of the current concrete slab. Seal the whole thing with new concrete angled down but first it would all need to dry out first..

My humidity in the house is also around 70% currently which is way too high and might not help either..

Not skipping any days and the mass is for sure higher than 20 c.

I also changed some things to the afterburner exit which makes my burns a lot more stable but need to test some more in more different circumstances before i can conclude anything. (will update on my thread soonish)

How are you liking your afterburner changes so far, did you keep them or changed some more?

[Vortex]

Hi Jonasp,

Sounds like your uninsulated damp clay chimney is the most likely culprit. Why is the humidity high in your house? I live right on the Atlantic coast and my house is next to a big waterfall, the outside winter humidity is 80-100%, inside 50-55%, though I'm in a modern insulated timber house.

I've been doing more experiments; Reduced the afterburner and top chamber to a 5.75"/145mm system size. On the initial test I mistakenly used the 6"/150mm pipe internal circumference to calculate the 1.5 SA:V instead of the 5.75". It overfueled a bit peak burn and didn't feel right, so I rechecked my calculations and saw the mistake I'd made, today I corrected it and the burn was perfect again, so it seems to scale OK.

I'm interested to hear about your experiments with the afterburner exit.

Trev

[jonasp]

Dec 28, 2023 5:37:04 GMT -8 Vortex said:

Hi Jonasp,

Sounds like your uninsulated damp clay chimney is the most likely culprit. Why is the humidity high in your house? I live right on the Atlantic coast and my house is next to a big waterfall, the outside winter humidity is 80-100%, inside 50-55%, though I'm in a modern insulated timber house.

I've been doing more experiments; Reduced the afterburner and top chamber to a 5.75"/145mm system size. On the initial test I mistakenly used the 6"/150mm pipe internal circumference to calculate the 1.5 SA:V instead of the 5.75". It overfueled a bit peak burn and didn't feel right, so I rechecked my calculations and saw the mistake I'd made, today I corrected it and the burn was perfect again, so it seems to scale OK.

I'm interested to hear about your experiments with the afterburner exit.

Trev

The house will be renovated in April and we have no ventilation yet so there are many "cold" bridges (not sure if that's the correct English term) where it's condensing. There're also some small leaks and some parts are not insulated. Also the basement has water problems. So many different parameters is making the humidity high I presume.

Good to read yet another successful change!

There has been a lot of constant wind lately (we don't get them often though) so it's hard to adjust when the pull of the chimney is so high.
What's your effect on the vortex when you have strong winds? What I observe is way to strong pull which tends to make a full vortex hard (keep in mind I don't have any cowl that can limit the wind pull).
The uninsulated part is also another 4-5meters high

(I made another CSA exit (50% CSA) on the other side of the shelf, so now the airflow will split to 2 exits. The draw is very good but I'm waiting for no wind to observe how the system will work)

[Vortex]

As the vortex in the afterburner is a balance (between the push of the expanding gasses in the firebox and the pull of rising hot gasses in the chimney) any extra draw on the chimney from wind or reduced draw from down-drafts will affect the vortex.

I live in a very windy place so it's always been an issue for me. I did a lot of experimenting with different chimney cowls and ended up making my own as most commercial ones weren't very good, they either created too much resistance to gas flow, let the rain in, or had no/limited effect on wind problems.

After a couple of years the one I made got wrecked in a storm, and a neighbor loaned me one which turned out to be slightly better than mine and so I'm still using it. I'd not tried this brand before as they're expensive and ugly looking, but very effective. Windkat: www.windkatcowls.co.uk/

I also researched draft regulators which are mainly used on gas/oil heating systems, they're a balanced flap in the chimney that opens when there is increased draw from wind and allows some air to enter the chimney instead of extra air being drawn through the stove. I find it really helps with the extra wind draw, but they have no effect on down drafts so work well in combination with a good cowl:


www.vftshop.com/images/others/Stove/draftreg.jpg

www.vftshop.com/images/others/Stove/cowl.jpg

www.vftshop.com/images/others/Stove/antidowndraftcowl.jpg

www.vftshop.com/images/others/Stove/stormcollar.jpg

[jonasp]

Thanks again for sharing your experience, very interesting.
That's a steep price for a chimney cowl but better spent once a bit more than having to change later.. Did you ever try the cilinder rotating cowls?

I have a temporary fix for small leaks into the chimney vermiculite insulation, curious how it will affect my setup.

I had a fire when there was not much wind and the vortex was excellent, I only saw some small overfueling smoke flares but lasted only 2min. When there's a lot of wind the system struggles to form a nice vortex but no overfueling at all.

I do think when my setup is going for the first 30-45min the draft is a little bit lacking due to resistance of the bell or the chimney which makes the vortex go too slow and a higher chance of overfueling since the heat stays longer in the afterburner. (It's not the resistance on the shelf, neither the shelf exits which makes the draft slow) maybe it'll be better now there shouldn't be a chance the insulation getting damp. I assume this because when it's running full blast I see the vortex going faster and mostly no overfueling.
It was the same sort of effect when I did get overfueling and opening the door a crack bit the vortex spins faster and fixes the overfuel situation. (Opening more primary air does not make the vortex spins faster)

Just some thoughts and conclusions(still just guessing, who knows what exactly goes on) maybe should've shared it on my thread but was answering you hehe

[Vortex]

Yeah luckily I didn't have to pay for the windkat cowl, the neighbor who loaned me it moved away and didn't want it back. I've never tried the spinny rotating cowls, though I'd be interested to see if they're any good. I worry though that on a timber house like mine it might sound like someone cycling around on the roof

Contrary to what you might expect, wind causes the vortex to be only partially formed and palm tree shaped, this is because the wind increases the gasflow, and so increases the amount of air being drawn in through the primary air inlet. A down-draft causes the vortex to spiral all the way to the front of the afterburner, as the slowing of the gasflow means less primary air is being delivered to the firebox, and so it briefly overfuels.

A rule-of-thumb I've been experimenting with is- Presuming all the other stove parameters including air, fuel and weather etc are all correct, then if the afterburner is overfueling and more primary air doesn't change it, you have too much resistance - if more air does change it then there isn't enough resistance.

Your idea of having two top chamber exit ports is interesting. I would think so long as the overall csa and SA:V are right then it should work the same as one, unfortunately I don't think I have enough room in my top chamber to try it out properly.

Trev

[hof]

[fishalive12345]

Hello Trev and Vortexers,
I started planning a vortex stove lookalike a long time ago. I even cast the firebox and afterburner but didn't get much further other than to periodically follow developments on this thread. Last year I installed a 120mm stainless steel chimney liner and made a first attempt with the help of my brother in law at starting to build the stove.
The plan is to build a 100x60cm cookstove which is 86cm high. The firebox and chimney on the right and the mass (dense firebricks with smoke path channels) on the left. Originally I planned to include an oven on the left side but abandoned that idea because there isn't enough space.
Over time my plan has become more and more similar to Trev's stove. I abandoned the oven idea and have decided to use the firebricks without mortar inside a steel sheet skin held together in a steel frame.
I have a number of unresolved questions and Id like to ask for advice about them. Thanks in advance to anyone who takes the time and trouble to answer. Thanks in particular to Trev and the regular contributors for generously sharing their experience and accumulated expertise. Multiple gold stars to you all.

[fishalive12345]

A sideview sketch of the stove
imgur.com/gallery/kWQhwen.