Vortex Stove

[martyn]

Yeah I am enjoying the trip!
Even with the ceramic top at 530 the edges are still only 90c so for me the glass is not going to work, I have the insulating bricks just below the glass and I thought the heat would travel over the brick tops and heat the glass to the edge but not so far anyway.
I can increase the main air aperture a little more ...
One thing I did not anticipate was the paint burning off my stove pipe bypass, it is coved in titanium wrap but smoking through that and stinking out my room with toxic fumes, I guess the insulation has caused the pipe to go beyond the paints integrity .
Yes only off cuts and a single log.
I will give a full load tomorrow.....
I would love to get on with finishing the fire but after 10 month of being Covid free the virus is back in our island and we are in total lock down so I can’t get any materials for the time being.
just a question though, when you load it up with logs, how far from the top and where do you set in alight ?

[Vortex]

I didn't know that about the ceramic cooktops, but I haven't played around with them yet. You wont have that problem with steel, but make sure it's a good thick steel cooktop at least half an inch thick though, otherwise you can have problems with it warping. Mine is 15mm, a 10mm slab with a slightly larger 5mm piece welded on top, so it sits in the whole and gives an overlap surface to form the seal.
You can load the firebox right up to the top with just enough room below the port to light the kindling:

[martyn]

Well I loaded her up with seasoned but not especially dry logs, I was surprised just how long it lasted ..... over three hours before the flames died right back!
The vortex was not visible for the first 25 minutes although I am sure it was working i just could not see it through the sooty glass, once the glass was clear the vortex was very active and lapping over the shelf again.
I had already opened up the main air vent to 135 x 37mm so I opened the door a crack but if anything it was getting more furious and lively !
I tried shutting down the air a bit at a time but the main fire started to stall ... anyway I sat back and watched the display however it just went on and on.

The vortex was furious for about 45 minutes and then it settled back under the shelf and ran like that for another hour so I had a good visible vortex for one hour forty five minutes .
It was then flicking back and fourth for another fifteen minutes or so but, the stove was still kicking out heat for over six hours.!

However I see did not see any particularly high temperatures, the hot spot on the glass peaked around 470c and the steel plate around 200c, the barrel just above the mass was only 75-90 c and the actual concrete was barely warm.
I might try enlarging the exit tomorrow and see what happens...

[Vortex]

Soot on the afterburner glass at startup is because it's running too rich - not enough air, or too fast - not enough resistance.

What size is the top chamber exit, and do you have a stumbler in it? They create a maximum speed limit, which stops it from burning the fuel faster than the air supply can support, so it doesn't overfuel or thermal runaway. Not having that restriction would mean you'd need a larger air supply, if you have the 20% primary and 10% secondary then you should be able to solve the overfuelling by sorting out the top chamber exit port/stumbler. Your primary should be 1" x 4" and secondary 1" X 2" or equivalent. Note, if it's through a piped preheating system then the pipe needs to be larger to compensate for the resistance from surface friction.

The top chamber exit port and stumbler also have an effect on the spin of the vortex in the afterburner, which my present experiments are an attempt to understand, so if you notice adding more restriction causes a change in the vortex that's why. This is the best configuration I have found to date, it adds the necessary resistance without negatively affecting the vortex:

5"/125mm system: Stumbler = 192mm x 35mm, 75mm in from front edge of shelf. Top Chamber exit port = 107mm x 107mm.

[martyn]

My system is based on 136mm due to the bypass valves fitted onto the chimney.... my port is 155 x 47 stumbler port 200 x 37 exit 150 x 78.
However they were not that size yesterday as i did not have a stumbler piece and the exit was 150 x 68.
So todays results are very different from yesterdays .... no soot, vortex formed within a few minutes, however the vortex lasted one hour compared to yesterdays one hour forty five and the fire was turned to coals in one hour thirty minutes compared to three hours .

So very different results for small changes, the glass top was quite consistent at around 450-470c however the outer edges went up to around 120 and the steel plate was up to 220c
Bottom of barrel wet up to 120.and inside my potential oven, was 180c
There was even some gentle warmth in the mass.

One thing i noticed was the vortex was nothing like as active as yesterday, remaining under the shelf but a bit placid perhaps?
So tomorrow I think i will make a few adjustments to see if i can find a compromise.
There were some issues with the wind today as we have 50mph wind that was making my dragon spinner go mad !

I spent many months over several years of tinkering and developing with my previous stove to get it singing ....I am quite happy messing around with this one too....

My last stove would send the steel top, immediately above the riser, red hot at around 590-610c although it took a good hour to do so and the mass would get up to 120c of course i could nor see any flame and it had to be fed every 15 minutes with full air. Very different stoves for sure .
I wonder what the temperature would be if i replaced the glass with steel ... ?

[Jura]

Jan 31, 2021 7:10:14 GMT -8 martyn said:

Even with the ceramic top at 530 the edges are still only 90c

hmmmm... I was pondering about it while using an induction stove at friends' place. but I came to conclusion that the ceramic may be manufactured to behave as steatite and while heated from beneath I would distribute heat evenly

In fact I have been looking for a ceramic glass cooktop for a wile (one may occasionally find it for free in here at a junkyard) but now I start to hesitate.

I wanted the cook top of my future vortex stove to be a source of immediate heat at my allotment garden.
BUt now I wonder if it wise to expect the stove to expend enough heat in a short time through such a small CSA of the 4 "cooking places" of the ceramic glass cookplate.

Neither patamos nor paul mentioned such issue. Can it be your plate case specific ?

[Vortex]

OK so CSA=14529mm2. Your stove dimensions would be x0.9 mine.
136mm system: Stumbler (0.55% CSA) = 207mm x 38mm, 81mm in from front edge of shelf. Top Chamber exit port (0.78% CSA) = 106mm x 106mm.

I've found the amount of surface area of the inside surfaces of the stumbler and exit ports has as much influence as the size of the aperture itself. I haven't been able to find anything better than that triangular stumbler yet, more or less surface area seem to both have a negative effect.

If your primary air is directed towards the roof of the firebox you can get a premature coaling phase. I get the same happen if the threshold is too high. Can also happen sometimes if the wood is packed too tightly at the bottom, needs a few gaps for air to get in.

IIRC the steel cooktop on mine gets up to around 500C. If you want it so the top is as hot as on your previous stove you would have to make it so the top of the afterburner was the steel cooktop, with a channel around each side from the front meeting in a chamber at the rear.

Great to have someone else playing with it, look forward to hearing what you find works best for you.

[martyn]

Lots of little things to try then.....
I have some 1mm stainless sheet that i hope to shape enough to direct the air forward and i will reduce the exit a little.

I dont need 500c 400c is perfect for searing a steak and them moving it to cook on the 200c steel plate!

What i do want is more temperature for longer inside my 10” tube as i want to put a rotisserie through it !
I might have to insulate the top of the barrel, wrap some titanium tape around the top (red would be cool) and maybe load some fire bricks in the bottom of the barrel .....

Like most things i build, it is not until it is built that you realise how you could of done it better!

I would of like two 32mm id pipes running trough the barrel instead of twin 25id and i would of used an opening top window and raised the fire another 100 mm to get a better eye level viewing while seated but we will get it running as best as possible as it is ... for this year anyway!

I have lots of off cuts of ceramic glass so i can used them to adjust the ports and other aspects.

[martyn]

This mornings fire was again very different, I saw the highest temperatures so far at a massive 620c on the glass, 250c on the steel plate and 180 inside my oven!
Unfortunately it was all over in one hour and down to coals, lots of coals too.
I did change quite a few things, I will work out the port percentages later but It was far to hot and fast for my likening anyway, so I will do a few changes again tomorrow.
I will give some more details later......

[martyn]

So my first two burns were done with the same settings ie no stumbler in place fire box port 50% top box 90% exit 65%
Next fire was 50% 52% 78%
Todays fire was 50% 52% 70%
Todays fire was by far the most furious with a distinct orange flame and a bit smoky... I am sure it was not a clean burn!
I will try the 50 90 70 tomorrow .....
I did some other mods today, I lined the afterburner floor with glass and put glass under the top box vermiculite floor, it was all glowing red hot when the fire was raging!

[Vortex]

Thanks for the feedback Martyn. My best configuration is 50 55 77/78, but yours may well be different because of the differences in implementation. With the increased resistance of that config the color of the vortex looks more like a plasma to me than flame. It's surprising how much effect small changes make to it.
Is that ceramic glass your cutting up and using from a recycled cooktop or stove door glass? My local recycling center have said they would save some ceramic hobs for me.

[martyn]

I did use the off cuts but I have lots of bits lying around from the local stove store who re place stove glass, they save their off cuts for me as I am a good customer!
I was sweating in my summer house today, the walls went from 13c to 24c in less than an hour.
I will keep at it until I find a good setting but it is obviously going to do the job one way or another.
I have been keeping lots of notes and taking pictures as I go .....

[martyn]

I was wondering if there is a way to speed up the coaling phase, it is just that for cooking, especially in an oven it would be good to keep the fire going or be able to re load once the fire dies down.

What about a using some sort of elevated grid so the coals fell through or perhaps using a finer grid and feeding or re directing air under the coals once they have formed?

i also wonder why my barrel and mass is not getting that hot, perhaps the ceramic glass is shedding too much heat, I might try placing some insulation over it ....

[Vortex]

You can just add more fuel on top of the coals if you want to carry on cooking..

The reason you're getting a lot of coals is not enough air across them - did you change the direction of your primary air yet?

Also you can vastly speed up the coaling phase by having a tiny bit of bottom air up through the coals. When you rise up your stove for better fire viewing, add an ash-trap at the bottom of the V-shaped floor, with an ashbox underneath with a small air vent into it. Just upto 5% CSA, a round hole about the size of the end of your thumb, with a spinner disc over it you can turn to open. It really helps to lower the CO emissions during the coaling phase by burning it off.

I was using the Austrian method to deal with the coals but the strong winds here mean that even with the best stove door seals you can have, it still manages to suck enough air through to keep them burning slowly. I like to have the fire completely burnt out to fine white ash, then completely close the chimney damper to stop the heat being sucked out of the mass by the wind overnight, so being able to quickly burn off the coals is very useful.

Maybe you could get one of those old hinged Rayburn/Aga hotplate insulators and use it as a door over the afterburner glass when you want more heat in the barrel and mass.

[martyn]

I have just come in for a drink, the fire is still going but I put a steel plate over the glass and Bobs your uncle all the barrel and mass temperatures went up even the steel plate wet up to 500c.
I will give more later ....

PS yes good idea about a hinged lid!