Vortex Stove

[Vortex]

Oct 30, 2020 11:08:26 GMT -8 cork said:

Hi Patamos,
I have been running the stove with about 10% bypass recently which can bring flue temps up to 95 C . I have also made a rookie error in assuming that once the flue gases go past the first exit port that once it stays above csa it will be ok . Recent posts have made it clear the second exit is important as well. When I correct this I am hoping that I will be able to keep the bypass closed. There is also a pinch point where the main body of the stove meets the bench which I hope to improve. James.(cork).

James, did you insulate the bench from the floor and surrounding masonry in the end?

Afterburner exit port (aka stumbler) 52% csa (40 x 230), and Top Chamber exit 78% csa (184 x 75) seems to be the best size for them on mine. That may vary depending on chimney/mass etc. You'll know when you have them the right size because the double vortex will spin easily right from startup till the afterburner goes out during the coaling phase. There seems to be some kind of harmonic relationship between the ports and chambers but I'm still trying to pin it down.

[fishalive12345]

Hi Trevor,
reading through the development and discussion of your stove I am trying (for my benefit and hopefully for others) to summarise my understanding of the components of the current version and their dimensions. The challenge is that this thread documents a long period of time and multiple versions so new components have appeared and names have changed. I hope you don't mind and that you will correct any mistakes.

3 chambers: Fire Box, Afterburner, Top Chamber

3 apertures: (Firebox) Port, (Afterburner) Exit Port, Top Chamber Exit

Dimensions 6 inch or 150mm system. To get the dimensions for a 5" system multiply by 0.833 (125mm) or 0.85 (130mm). For a 4" system multiply by 0.72.

Fire Box: 305H 305W 405D

Port: 50W 175L (39% CSA)

Afterburner: 114H 230W 405D,
the afterburner is made of highly insulative materials but be careful about using ceramic fibre or insulative firebrick if you have a black oven downstream of the afterburner.

Shelf (Afterburner partial roof): 230W 295D,
in development the depth of the shelf was adjustable (forwards, backwards) in order to tune the system to the strength of draught of the individual stove. This depends on the strength of the chimney draught and the size and configuration of the heat recovery system. The dimensions of the shelf are determined by the distance the shelf is set back from the afterburner viewing window.

Shelf thickness: 50mm highly insulative in the current version,
the shelf and all other parts of the afterburner should ensure the highest possible combustion temperature in the afterburner in order to ensure complete combustion. The shelf could be made of thinner, strong, high temperature refractory material ie castable refractory cement, ceramic glass, thin firebrick, refractory kiln shelf (?).

(Afterburner) Exit Port/Stumbler/Stumbling Block: 230W 40H (52% CSA),
located on top of or over the shelf.

Exit Port Setback (from front of shelf): 80mm

Top Chamber: 75H 280W 458D,
the roof of the Top Chamber may, in a cookstove, be a hotplate (ceramic glass or steel/cast iron plate) or the base of an oven. The exit from the Top Chamber is, in the current stove, on the left side (but could presumably be in other locations, right, back, top?).

Top Chamber Exit: 75H 184W (78% CSA)

The CSA is the area of a cross sectional slice of the chimney. There should be no restrictions in the combustion or heat recovery system smaller than the CSA, other than the three apertures; Firebox Port (0.39 CSA), Afterburner Exit(0.52 CSA), Top Chamber Exit (0.78 CSA).

Peterberg is currently carrying out rigorous investigation of a hybrid dsb/vortex stove. I'm following developments very closely as I can't imagine anything more exciting in the world of diy stove building. Thankyou Peter and Trevor in no particular order for sharing.

When building a version, it looks like there is a degree of flexibility with regard to some of the dimensions and materials eg Firebox, but that the dimensions and configuration of other parts (apertures) are critical to achieving the clean, highly efficient burn.

Glad I didn't build last year, but then I could say the about every year since I started following this. Just as well for me that there are some people who say "Glad I've tried, tested and shared lots and lots of ideas."

Hope I've got that mostly right (smiley face)

[Vortex]

Hi Brian, That's an excellent summary, thank you for writing it. I have recently updated the first page of this thread to try and give an overview with quick links to the various parts, inc videos and drawings etc. and will try to improve that further. If you don't mind I will include this summary with a few clarifications:

The 4" version scale is x 0.666.

6"/ 150mm system:
Firebox depth is 420mm (not inc the door frame)
Afterburner port is 50mm x 175mm (approx. 50% csa)
Afterburner Chamber is 114mm high, 230mm wide & 420mm deep. (Experimenting with it 445mm deep at present)

Afterburner should be low mass and well insulated. I do not recommend using ceramic fiber products in any stove if you can avoid it, but if you have to, then enclose them so they are not releasing fibers into the gas stream. Insulating firebricks I believe are ok as they do not contain fibers.

Afterburner Shelf (roof of the Afterburner / floor of the Top Chamber). I originally made this adjustable (forwards / backwards) because at the time the gap between the front edge of the shelf and the inside of the glass was functioning as the Exit Port. That had the downside of the glass getting 'etched' from the intense heat against it, so I moved the Exit Port up on top of the shelf and found the increase in size of the afterburner was also an improvement. A gap of 110mm between shelf front and glass seems to be good, as it is large enough to avoid damage to the surface of the glass, but close enough that if the stove overfuels and smoke deposit is left on the inside of the afterburner glass it burns of clean again quickly.

The roof of the afterburner should be made of an insulating or low mass material. Ideally I think a material that will glow as quickly as possible would be the best. A kiln shelf or ceramic glass may be ok, but I haven't tried.

The top chamber exit can be at the rear middle, left or right hand side.

CSA = Cross Sectional Area. ie on a 150mm system: (the radius) 75mm x 75mm x Pi (π) = 17673mm²
Port (0.50 CSA), Afterburner Exit (0.52 CSA), Top Chamber Exit (0.78 CSA).

[fishalive12345]

You're very welcome. Pleased to be useful in a small way and thankyou for the clarifications.

I'm moving towards actually building early next year. I'm thinking whether it will be possible to adapt the 5" parts I cast last year to build a 4" system for the reason you mentioned, to be able to light up more than once a day depending on outside temperature and cooking requirements. Also hoping to be able to share a sketchup of "my" stove soonish. At least before I start building so that any foolishness can be pointed out. In the meantime I will be following the insights that you, Peter and others come up with in order to incorporate them into the build.

[patamos]

Oct 30, 2020 11:08:26 GMT -8 cork said:

Hi Patamos,
I have been running the stove with about 10% bypass recently which can bring flue temps up to 95 C . I have also made a rookie error in assuming that once the flue gases go past the first exit port that once it stays above csa it will be ok . Recent posts have made it clear the second exit is important as well. When I correct this I am hoping that I will be able to keep the bypass closed. There is also a pinch point where the main body of the stove meets the bench which I hope to improve. James.(cork).

James, I'd still guess it is due to the pinch point you mentioned.  I say this because the last vortex i built with a massively oversized ISA (see: amosclayworks.ca).  12' of 6" x 9" flue run, opening into 90sq.ft. of bell chamber.  It has the low bell exit port as usual, but also an adjustable bell-exit port near the top of the bell into the chimney.  The idea was to experiment with major oversized harvesting mass, and be able to tune it back down.

At first i had to keep the bypass open about 10%, and the upper bell exit at 40% but after adding another 3' of chimney flue and some pebble rock atop the cooktop surface it can now run with bypass closed and upper bell exit at 20%.
All this to say, tuning the downstream gas flow dynamics can be a major factor...

[martyn]

I dont think ceramic glass would last long as a shelf material, I tried lining a J tube fire box with it, the bottom piece cracked in about 45 minutes shortly followed by the side pieces.
It seem to be ok up to around 600c but starts to deteriorate and get pitted at around 500c If exposed to flame.
There are a few highbred refactory mixes being used in the pizza oven world ... a 50 50 mix of dense and insulating with added carbon fibre strands or very fine carbon fibres.
I have been following the progress of these mixes and i may well do some experimenting myself.

[Vortex]

Those experimental mixes sound interesting. There are different grades of ceramic glass, the stuff used for stove doors is rated at 800C, and the surface starts to etch at around 850C. patamos uses a piece for the roof of his firebox IIRC, and Peter used a piece for the cooktop on the DSR1. It's what they make ceramic cooktops out of. The pyrex borosilicate glass is rated at 500C though. I've broken a few pieces of that getting them too hot. I have a few small stove glass off-cuts, I'll put one in the afterburner today

[fishalive12345]

I was thinking about the possibility of using castable for the shelf and as a lining for the secondary combustion area but wasn't sure that it would be rigid and resistant enough. How thin do you think you could go with castable as a slab rather than a lining? Martyn?


In the end I decided I'll probably go with cordierite kiln shelves to line the afterburner and top chamber. Rated at 1250 and 13mm thick. Cordierite and mullite shelves, 16mm thick, rated at 1300 are also available. More expensive than castable for sure though I've found a supplier who sells ceramics kilns and kiln furniture. Their prices seem reasonable and they can do up to 2 cuts on a 500 x 600 piece.

Planning to make the whole combustion area out of dense outer layers and insulating inner layers. Thin and dense in contact with flame and thick and dense structural exterior with a sandwich of insulating firebrick and cf board. The cfb will be waterglassed and wrapped in aluminium foil and will, in any case, be buried well away from contact with air, flame or touch.

[martyn]

I made my box up from 30mm (1.1/8”j components but I was very carefully to accurately mix and vibrate the the refractory.
I think you could go thinner if you except the shelf as replaceable component and be prepared to replace it but of course I don’t actually know until I get my fire up and working.
The glass I use is all stove glass, I get it as free off cuts as I have a good working relationship with the locale wood burning stove centre.
I have a couple of striped down ceramic hob tops waiting to be tested.

[Vortex]

Today I removed all the ceramic fiber board and blanket from the afterburner and rebuilt it with a double layer of vermiculite board. Also put a small piece of ceramic glass in the hottest part of the afterburner. Had it all glowing orange for about an an hour. Cooled down now and still looks as good as new after the first burn. Have to see about getting some kiln shelves to try out.

[cork]

Trev, Yes I did insulate the floor of the bench and the wall behind with 2" calcium silicate board. My thermometer is also a BBQ grill probe type which measures to 300 C sold as accurate to +/- 1%. It seems ok as on reading at 80C I measured 50 C with greenhouse thermometer just below the umbrella cowl with small trace of condensation at top of the flue. On a reading of 90 C flue was completely dry. I changed my top chamber exit to 78% csa today and tried a burn. It started very well but the high wind affected the burn. I think my next step will be to change my cowl.

Patamos, I looked up your build it's very impressive. My pinch point is from a down draft chamber 610 x 145mm to a horizontal path 135 x 230 mm with 230mm being the vertical dimension. I should be able to widen the path from 135 to 160 mm and chamfer or radius the bricks on the corners of the turn. James.

[patamos]

James, ya that should help. I'm curious to hear how it affects the flow.

Martin, Trev is correct. I used stove glass as the roof of my main firebox for a year. Then replaced it with CFB when i reconfigured the set up.
I have continued using two small pieces of stove glass (6" x 4") as the shelf between the upper shoeboxes. After 3 years they are getting brittle and starting to flake. Kind of like they are degenerating to silica sand.
I also had a 1.5" x 8" stick of ceramic glass protruding into the throat (inverse aryan set up). But under those conditions it only lasted 1 season.

[martyn]

Hi Trev, how is the vermiculite holding up.

[Vortex]

Hi Martyn, I took it out and checked it for cracks 2 days ago and it's still as perfect as when it went in. It was up to 900C a couple of times, but that's well within it's operating temperature of 1100C. The spec sheet is here: www.dineensales.com/downloads/dinboardSheet.pdf

[martyn]

I use it to line the back of wood oven doors and have been doing so for many years although the max temperature is never more than 500c, the vermiculite will last until it gets damp or bashed around.
It does degrade over time and gets crumbly but often it last for years...
I have never used it in a rocket stove because i have read numerus times that it will quickly fail... it seems to be an easy and safe option to use for many applications ... I will be giving it a try myself.