Vortex Stove

[Vortex]

Hi Peter, I've intentionally not changed anything on the stove, so I'll have a good comparison. The CO. cell was working OK, I borrowed a friends to compare the two at the same time, and mine was reading CO. just 15ppm higher. I started getting a message on the testo the last week I was using it saying that the sensors had passed their replacement date - or time used - or something like that. The O2 sensor was reading the O2 content of the air perfect, and the pump was working fine, the only problem I was having with it was the thermocouple dropping out, the same as yours was. We'll see when I get it back.

[peterberg]

Sounds positive, hope for the best then.

[Lucian]

Jul 20, 2021 5:04:13 GMT -8 Vortex said:

This year I decided to try adapting the design to make a dedicated 4" cookstove. We often get people coming to the forum asking for small cooking stove designs for the 3rd world, and I've been wondering how well this would work.

To adapt it to a dedicated cookstove I wanted the hotplate above the port, as the main difficulty I see with getting heat into hotplates is the problem of laminar flow, where a layer of air separates the flame from the metal plate.

I removed the top chamber and cut some small pieces of vermiculite board to make the side and back walls of the afterburner. The top is now the hotplate and the exit of the afterburner is to the right and left sides (65mm wide x 75mm high). The chimney was the same as previous.





The increased resistance of the double exit channels seemed to have the same effect I observed on my 6" stove when I increased the surface area to volume ratio for the top chamber (Page 56).

Hi Trev,

This version looks really great, reduced height and increased surface-to-volume effect. I decided to build it, already ordered the vermiculite board, could only find 30mm thickness but I think it is OK if not better than 25mm.

Could you please be so kind to confirm or correct my understanding of the afterburner/top chamber sizes:

1) Height is still 75mm, but not sure about the length of the afterburner walls, are they still 208 mm (280 total depth minus 72 mm distance from glass to shelf front - as it were in the "summer of 2020 original version" drawing at page 45)?

2) Afterburner width is still 153 mm?

3) Total width between firebricks left and right of exit channels is 65+25+153+25+65= 333mm ? (65mm channel width, 25mm vermiculite board thickness, 153mm afterburner internal width), should be 343mm in my case with 30mm thick vermiculite walls

Thank you for your excellent work and openness to share!

[Vortex]

Hi Lucian,

I went out and checked the dimensions for you, here's a quick diagram with them on. IIRC the afterburner width was 6" / 153mm, the vermiculite board pieces seem to have pulled in a little at the bottom so they're now 150mm:



I couldn't find a 4" pipe so ran it with a short 5" piece of single skin stainless, which is why it says 125mm and not 100mm, but most of the other dimensions are scaled down to the 4" size (.666 x the 6" sizes).

Trev

*EDIT: Corrected the port width from 39 to 33mm.

Link to original 4" Cookstove post: donkey32.proboards.com/post/36456/thread

[Lucian]

Thank you Trev, highly appreciated! Will post picture as soon as it's up and running (still waiting for the vermiculite board delivery).

[holmix]

Hey Trev,

Thanks a lot for the excellent work so far and to all others for the helpful contributions. I'm planning to build a stove for heating very similar to the original vortex stove on the first site of this threat, I think it's just perfect in size and also very beautiful. I'm just wondering, if I follow your exact plans for the combustion and afterburner chamber, will it be able to fit the new EU-Ecodesign 2022 requirements? Or do I need to modify anything to make It more efficient, since there has been a lot of development on this since 2013. I didnt find anything on the emissions-requirements in this forum so far, so I figured I´d just ask here.

Thanks and best regards from Germany!

Sam 

[Vortex]

Hi Sam,

Thanks for your comments. I read through the new 2022 regs a couple of years ago when they first came out, I don't remember the exact details now, but I do remember it was well within them then and it's improved since.

The plans on the first page are well overdue for an update, basically the top chamber seems to work best at 1 CSA with a high surface area to volume ratio (instead of a stumbler and exit port). I'm experimenting with different ways to implement that at the moment, so just make your top chamber accessible so you can easily update it and tune it to your mass. As an example here was today's test version.







Trev

[holmix]

Hey,
thanks a lot for the quick answer! I was actually referring to this stove, that you build with your friend: www.vftshop.com/images/others/Stove/Vortex%20Stove.pdf does it work in the same way or would you recommend sticking to the newer vortex stove design with the top chamber?
Greetings,
Sam

[Vortex]

Hey Sam,

That was the Mk1. I wouldn't recommend building it that way now as those huge complicated casts are difficult and expensive to make. The Mk2 firebox worked in the same way but was easier and cheaper to make. Discussion of it starts on page 20, or if you're only interested in the firebox construction, on page 23. Its not as clean or efficient as the Mk3 (present stove) but the Mk2 tertiary air and insulated secondary burn chamber were a great improvement on the Mk1. I didn't have a testo back then but I burn about a third less wood in the present stove and the yearly cleanout now seems almost a waste of time for the tiny amount of sooty ash that comes out of the channels, barely covered the bottom of a bucket this year.

If I was building a Mk2 for someone now the only things I would do differently is to forget that complicated grate cast and just cut up a slab to make a V-shaped grate, like I'm using on the present stove (I have a scan of the plan for how to cut it if you want me to upload it). I would also use vermiculite board instead of ceramic fibre board in the secondary burn chamber, that's about it.

Trev

[holmix]

Thank you so much! I'm going to get the material and start building it whenever I find time during the winter. Amazing design! I just wonder if you have tried bigger channels for the secondary / tertiary air? do you think the amount of air flow would mess with or maybe improve the burning of the leftover gases?

Sam

[Vortex]

It would have benefited from a larger secondary air supply, I had to start it with the door slightly open to make up for it. The primary and tertiary were OK. Bottom air was also very effective at burning up the coals at the end. In this old video you can see the jets of flame from the bottom air coming up and tertiary air coming down: gasburn.mp4

[patamos]

Hi Trev,

Great to see this thread humming along.
I've been out of the loop for a long while (too many projects on the go...) but am now getting ready to do some sort of tiny heater in a friends cabin, so thought i'd check in.
And 'voila' here you have the specs for a 4" system.

A couple of questions though: Around here people are not interested in chopping their firewood shorter than 16", so i wonder what effect a longer firebox (say 42cm) would have on the overall dynamic? Would you perhaps recommend a longer narrower firebox ceiling port? Or maybe set it forward a little?

Also, many stove operators are not as interested in fine-tuning their air supplies mid burn, so my thought is to make the sloping firebox floor as you have, with 1/2" gap down the centre, but also notch in a bunch of small air ducts along the outer/upper sides of those sloping floor slabs... and then have all of that be the primary air supply. I am sure the constant bottom air supply is going to increase the potential for over-fuelling, but with operator error and/or disinterest an inescapable factor... I am inclined to make things as simple and stable as possible. Maybe implore them to lay a big wedge shaped piece of wood into the bottom of that V will help.

I look forward to hearing your (and everyone's) thoughts on this.


On another note, the other Pat from BC was asking about refractory suppliers in our area. Once upon a time Clayburn based in Abbotsford offered world class HHD and MHD fire-bricks, but they were bought out by a big TExas corporation a number of years back and no longer produce locally. Truth be known, their 110 year old factory/quarry site was subsumed by urban sprawl, and they may have been running out of raw materials anyway.

Dave at Improheat in Vancouver is a helpful fellow. And there is another fellow, Heinz Weiduwit at 'Alliance Refractories' who knows his stuff. All three of those companies are importing materials from US, Chech, and China.
IMHO, the best people to deal with are 'Alphatherm' back in Ontario. A fellow there named Elvis is super switched on and happy to scurry up anything you may need at a reasonable price. I get all of my MHD firebrick (Alseys from mid west US), 12"x24"x2.5" AL-43 slabs, calcium silicate board, and various other stuff from them. All of the masonry heater builders I know recommend him highly as well.

And one more note (seeing as it has been so long): On the matter of how much mass to have in the firebox walls, one advantage of thicker (up to 2.5" say) is that once the fire is out you can pre-load the next day's fuel and the residual warmth will thoroughly dry it out overnight. Makes a huge difference on startup efficiency.

thoughts for now

[Vortex]

Hi Pat, Welcome back again .

The most efficient clean burn is had when the fuel isn't too far from the port, so making a 16" long thin firebox probably wouldn't be the best in that regard. No idea what a longer narrower or more centrally located port would do. Correct air control seems less of an issue on the 4" than on the 6", and so long as it's got enough air then it wont soot the glass up, too much will just make the vortex into a palm tree shape, soot is always too little.

Are you planning to do the cooktop version, if not just make the top chamber 1 CSA but with a wide shallow channel, the increased surface area will give you the back pressure to keep the vortex in the afterburner, that seems to work better than a stumbler and exit port. Constant bottom air will lead to overfueling. You could make the cuts in the top edges of the V shaped floor and feed the secondary air down underneath the sides and up through the cuts, so they'd come up the sides of the firebox walls, that should be OK.

The downsides of thick walls are slow startups, and if you are not reloading the fire can crash after the peak of the burn, as the walls are still sucking the heat up. Ideal Vortex stove wall thickness seems to be about 2" for a 6" stove, 1.6" for a 5" and 1.3" for a 4".

I look forward to seeing what you come up with.

Trev

[patamos]

Thanks Trev

Think I'll try that coin biscuit technique to use 1.25 HHD splits in the fire box.
I've seen metal pins in pretty high heat areas of flue runs so could be in safe range. The key will be having a contingency plan if it doesn't work...

Might move the throat forward by however much i lengthen the box from your specs. That way fuel at front isn't too far away.
Will keep you posted.

Also, this will be a cook top version with quite a bit of heated bench downstream.  So my back pressure equation will have to be adaptable.

[patamos]

Hi Folks,

I'm well into a variation of Trev's 4" cookstove. This may be more like a 5"  The fire box is changing shape with standard brick size differences, and it is longer cuz folks around here just don't wanna cut their firewood shorter than 16"

vftshop.com/Video/IMG_3184.MOV

Towards the end of the video (after I've done waving my hands around about having to beef up the firebox cuz its gonna get abused...) I pose the question of what other builders would do with the heated backrest we are squeezing into a 2' wide footprint (very small cabin...)

Please chirp in and let me know what ya recon?

And thanks again Trev for uploading the imagery