Vortex Stove

[martyn]

Hi Dave, I would definitely insulate under the fire box, I think the kiln shelve ‘might’ work but I dont think they have been tried and they wont offer any insulation properties!
We do know that an insulated afterburner does work and I would suggest you go down that route, insulating fire brick or vermiculite are good choices.

[dcoyote]

Vortex, I have been following these threads for several years.  I have build one vortex stove but then saw your "gasification" design with the port at the front above the door.  I was excited about the longer burn times this promised.  Then that design seemed to disappear from the discussion.  Did it move to a different thread, or what?

[Vortex]

Hi dcoyote, I have only one Vortex thread. The first post is used to keep an updated overview of the latest design so it's easier for people to find, but after that it starts with the original stove that you're looking for, which then gradually evolves over the next 10 years into the present core.
Trev

[Dan (Upstate NY, USA)]

over the next 10 years

important words...

[dcoyote]

Trev, I understand that the design has evolved, but I am still trying to figure out why the gasification design was abandoned.  Was it less efficient?  Earlier posts suggest just the opposite.  Harder to build?  
Please explain.
Thanks,
David

[Vortex]

Hi David, I discovered a downside to that way of running the stove to get the slower longer gasifying burns, the lower flue gas temperatures lead to less heat transfer into the mass, and so overall heat output from the stove is lower, as the larger the difference in temperature between the flue gas and mass the better the heat uptake into the mass seems to be.
Trev

[dcoyote]

Trev, thanks for the reply. My stove project is slightly different in that I am setting a cast iron heat exchanger from a hydronic boiler in place of the cook top. I am heating water to go into a large storage tank, from there via a heat exchanger into a closed loop system going to radiators. The flue gases pass through the heat exchanger and then out the chimney. There is a 16' run rising 2' before going into a 30' insulated chimney.

When you say the flue gases are a lower temperature, how much lower are we talking about? A slightly lower temp may actually work better for me. However, I do want to keep the burn clean and efficient.

David

[martyn]

David, I can run my J tube in a gasifier mode by restricting the main air to around 2-3% and just using about 20% secondary air.
It works well and looks fascinating to see the smoke catching fire but only works when the fire has been running full bore and everything is very hot.
I would be interested in experimenting more with gasifier methods but there is not a lot info about DIY stoves.

[solobird]

Hi guys, hi Trev, happy to be reading on your work and experiments.

Do you happen to know the expected temperatures on the top plate for the 4" dedicated cookstove ?
Particularly just above the port where I guess they're the highest.
From the following videos martyn vortex stove, martyn stove deep top box, which I think are from martyn and show a "regular" 4" vortex stove (longer distance from port to top), I wonder how you could achieve a moderate, say 200C temp with the dedicated version ?
So either go with the regular (and heighten the top box under the plate) or try to protect the underside of the cook plate just over the port on the dedicated version using split brick or vermiculite.
Plan is to use a cast iron cook top which would give a better distribution of temperature all around but would also be prone to warping or cracking.

Would there be a way to regulate temps other than raise or reduce primary air intake with maybe a small sliding door ?

[Vortex]

IIRC the dedicated cookstove top was 350C to 500C. The original cookstove top with the separate top chamber was lower around 200C to 350C, but then without a mass to catch the extra heat you're just wasting it out the chimney - same with adding more top layers. Raising the height of the afterburner will reduce the temperature but you'll lose the vortex and complete combustion. Attempting to use the primary air control to regulate temp will work but not give you a clean burn, so the glass will just soot up.

[solobird]

I see what you mean about the clean burn.
Stove would be built outside, no mass, also need an oven for baking (mostly) bread. Currently in the planing stage.

Cook plate would mostly be used for canning so nice to haves:
- ash pit (previously built a Walker riser-less without the ash pit and needed to remove coals on extended burns)
- 70-80 cm height
- ability to burn sticks or wood that is not ideal (maybe increase the firebox a bit), tending/adding wood as rarely as possible
- insulated, least mass, all heat into top
- temperature withing 180-250 most of the time without tuning air or using less wood than designed for. Could sizing the port and post-port part to maybe 3-3.5" and the firebox to 4.5-5" work on the dedicated to reduce top temps ? What about placing 2 split firebricks over the port exit so the vortex does not hit the cast iron top directly ?
Oven mostly for bread baking, nice to haves:
- fast start (low mass firebox and least in oven box, insulated outside) with least wood
- even temperature on all sides (gas flow from under + top exhaust / bell-ish white oven with low exhaust)
- least temperature fluctuation inside oven during burn (maybe a little mass needed in oven or make it from thicker steel)

Of course the vortex core already covers a lot of these, others could be solved by design (ie ash pit).
Thinking of routing the exhaust of the dedicated vortex to the inlet of an insulated barrel (oven). And maybe having a separate firebox under the oven when only needing to use the oven www.youtube.com/watch?v=h4WDZMmkDeo. Single chimney.

Thanks.

[Vortex]

With the dedicated cookstove top with the side channels you could put the white oven over the central afterburner, and have 2 hotplates either side over the side channels where the temperature would be lower. You could also try making the side channels wider and shallower to get more space for cooking surfaces.

[solobird]

I guess that if I let the gasses flow between the interior/exterior walls of the white oven structure placed right above the afterburner, that is surely going to change the surface to volume ratio, so alterations would need to be made to dimensions. Read on your work on the top box surface area in order to get the fire vortex just right. Material choice is also going to have a part to play in this: dense, insulated or not (ie steel vs dense brick vs vermiculite).
Need to get a piece of heat resistant glass and experiment as soon as there's +0C at night.
What are the temperatures on the glass in front of the vortex for the dedicated ? Would an oven door glass hold ? That should be tempered with maybe a little Al oxide added so 300C ?
Thanks.

[Vortex]

I would only heat the bottom of the oven and just insulate the sides, if the oven body is made of steel it will conduct the heat up the sides anyway.
Never measured the temp on the inside of the cookstove glass but the inside Vortex stove glass is up to 800*C+, so only a good borosilicate stove glass like Robax or Neoceram is going to work there - will be well over 300*C for sure.

[solobird]

A couple of more questions have arisen while I was thinking about design and I want to make sure I have a clear picture.

1. I understand that height from bottom of firebox to port could affect burn, but what would be the influence of depth/width, other than prevent adding to much wood or help with stacking brick on layer above ?
For an outside stove especially it would be nice if it could allow the odd bit of wood in the firebox without much processing.
And maybe also help with less problems with abrasion.
Would a firebox width of 250mm work instead of the standard 203mm for a 4" ?

2. Any riserless core provides less "push", so ISA of mass down wind should be smaller than J tube or "standard" batch rocket ?
For example: you hook up the 6" vortex to the mass of working 6" J tube. Same flue.
Does having a riser (or a taller riser) allow for more mass isa, less problems on startup, but not necessarily better combustion or heat extraction through mass ?

Thanks.