Vortex Stove

[martyn]

I did see your post but my original design (by pure coincidence) offered a similar setting as shown in my first video and as I had not found any better settings, I thought it was worth going back to the start but with a slightly bigger exit.
I have big issues getting wood at the moment but we will moving out of lockdown next week so hopefully I will be able to get on with experimenting and actually finishing the exterior of the stove!
I have enough wood for one more fire tomorrow,I intend to close down the exit to around 80% and also place a baffle to deflect the flow upwards ....

[lums]

Hello,

I have been following peter's various posts for a long time and your posts (thanks to a translator)
thank you to you and to the speakers it is really captivating.

I'm not sure I understood your last modification, you removed the trebucheur and reduced the height across the width from 280mm to 63mm by 200mm in depth, and the remaining 110mm in depth is still 75mm in height with a 117mmx118mm output port?

[Vortex]

Hi lums, Sorry, I should have explained that better. This was the previous best configuration:

www.vftshop.com/images/others/Stove/topchamber21-20-1.jpg (Stumbler 230mm x 42mm, End port 120mm x 117mm.)

This is the new 'top chamber' setup I used yesterday and the day before, 63mm high x 275mm wide (just under 1 CSA). The exit was 120mm x 145mm (just under 1 CSA):



The results were:





Today I reduced the width a little, so it was 63mm x 255mm. These were the results:

[martyn]

This mornings fire was good if a little tame, I decided to open up the exit and the whole top chamber to a full 100% and then back track (when i get more wood) I am sure it was a clean burn but the vortex was visually not so vivid or impressive as yesterdays 90% settings .
One thing i did notice was the stove worked very nicely with the door wide open, the flame was just occasionally lapping over the shelf and the hot plate temp went up to 290c.
I lifted the hot plate and took a reading on the glass and that was around 470c .
With the next fire I will keep the top box at 235 x 60mm and reduce the exit to 90% csa.
Oh and i forgot to say the glass i put on the floor of the afterburner did not last as several cracks appeared but the glass under the shelf Is still going strong.

[Vortex]

Today I setup the top chamber so every surface except the roof was wrinkly vermiculite board, even lined both sides of the exit with it. The exit port ended up a little over 1 CSA. Results were quite similar to the last 3 runs, but the sub 100ppm CO. was even longer this time. The high surface area to volume ratio seems to create very stable long steady burns. The vortex on mine was also not as visually vivid or impressive as usual, something I noticed in the last few, but it was more obvious in this one with the slightly larger exit. I think I'll try reducing it a bit tomorrow as well.

[Vortex]

Same setup as yesterday but top chamber end port reduced to 90% CSA. Startup a bit quicker and vortex a bit more pronounced but CO. was a bit higher and not so much sub 100 ppm CO.

[martyn]

One more fire this morning so top chamber at 100% exit at 90%
No problems with start up as I left the bypass open for the first 10 minutes.
No smoke on glass but again a slightly disappointing vortex display for the first half hour but it really did perk up for the next half hour and then we were at the coaling stage.
Cor so many variables to try.....

I was wondering about trying 100% 100% top box and exit and reducing the afterburner chamber to get a tighter vortex?

My main issue so far was getting a smoky glass with the smaller exit so I will try extending the shelf towards the window and maybe a 45* glass ramp at the bottom of the widow?
I did make a deflection plate after the exit, not a restriction but a gentle curve upwards, this has worked as i am nw getting a vey even 280c all over the hot plate.

[Vortex]

I worked out the afterburner chamber size from a load of experiments on my initial outside setup, I picked the size that produced the best looking vortex. That setup had no mass or contraflow system though, just a short straight up chimney from the back end under the hotplate. No idea if the results would be the same on a different setup, but if I had to guess I would think they would be. Pushing the shelf closer to the glass will shorten the life of the glass, you'll get etching of the surface happening.

I tried a 100% top chamber and exit today. While setting it up, I noticed that the gap between the top layer of vermiculite board and the inside edge of the frame the hotplate sits in was about 0.95% CSA, so I enlarged that to 100% as well. I had to remove some of the wrinkly side pieces to get the extra space. Startup was excellent then about 18 minutes in the O2 dropped below 7.5% and it overfuelled badly for about 10 minutes. CO. went up to 5000ppm then dropped straight back to 100ppm and it ran happily for the rest of the burn. Highest exhaust temps I think I've ever had. Core felt too loose, not enough resistance to avoid the overfueling. I think I might try reducing them all to 95% next.

[martyn]

I made a few small mods but they were all irrelevant as my new wood stock that was delivered this morning is rubbish and next to useless being damp!
What a difference damp wood makes, it was really difficult to get it going and then the glass stayed black for the total burn and there was a fountain of steam (maybe some smoke too) pouring out the chimney.
Not much I can do at the moment as we have at least one more week of lockdown....

[Vortex]

That's disappointing, Martyn. There's no tradition of seasoning wood in Ireland either, so it often arrives with green leaves still on it. Luckily I have my own firewood supply and have about 4 years stored seasoning. The main problem I have is not enough straight wood, as the strong coastal winds make it grow all twisted and knotty. That's tricky for laying top lit fires and hard to find enough that will split for kindling. Next season I'm going to downsize my core to a 5", as I'm living with the house door open most of the time, that way I'll need a lot less wood and can be more picky about it.

Today's test run was done with the top chamber set to 95% CSA right through from the glass to the exit. The vortex was nicely defined and lasted right from the start until the afterburner went out. Also I broke my all time low CO. level with 11ppm CO. it stayed under 14ppm for 20 minutes, and was under 100ppm for 1 hour 15 minutes. I will do another test run with this configuration tomorrow to see if it's a one off or not.

[lums]

Soon the stove which consumes more CO than it produces

Is it complicated to add the CO averages of O² in order to better take into account?

when I calculate the csa of the post combustion I do (23x11.4x2) / (23 + 11.4) = 15.244186047.
15.244186047 / 2 = 7.622093023.
7.622093023x7.622093023x3.14 = 182.42 for the csa.
its good?

you say 95% of csa but the shape is also important right?

Looks like you've gone back to something like 275x63 and 120x145 and near the glass always 230x110 ?
is the striated vermiculite the only difference with one of the previous tests at these dimensions?

it looks like the start-up went better than before, if it happens again tomorrow it becomes even more fun

[Vortex]

Mean (totals): Stack temp 94.6C. CO2 7.86%. O2 12.9%. CO ppm 150. Eff. 91.0%.

I cant understand your math, but it's not my strong point, so please correct me if I'm wrong:

The CSA of a 150mm chimney is 17673mm2. (3.142x75x75=17673mm2)

The gap between the inside of the glass and the edge of the vermiculite shelf is still 110mm, but the shelf is now 3 layers of 20mm vermiculite board, so the gap between the top front edge of the shelf and the metal frame inside above the glass is 73mm x 230m = 16790mm2 / 17673 = 0.95 (95%).

The top chamber is now 360mm from the front edge of the shelf to the rear wall.
265mm wide. 63mm/64mm high. (63.3x265=16774.5/17673= 0.95)

The sunken area in the rear corner in front the exit is 140mm x 115mm x 40mm deep. (140+115=265)
Exit is 120mm x 140mm. (120x140=16800/17673=0.95)

No idea if the shape is also important at this point.

Hope that is clearer. If it turns out to be a good setup I'll make more pictures.

[lums]

Thanks for the averages, I find it more telling when these numbers accompany the charts.
co 150 ppm seems really excellent
your calculation is obviously good but I do not understand where you find the csa 150 base on your stove.
i started with peter's batch rocket calculations.
I consider that the riser is the post combustion which has a rectangular section of 114x230.
to have the equivalent of a round chimney starting from a ractangle I had found an empirical calculation, always in the texts of peter which allow the conversion from one to the other. (23 + 11.4) = 15.244186047, which makes an equivalent round internal chimney of 152.44mm and after calculation gives an exact csa of 18251.49mm2.
this being said the figures are close and maybe my calculation is useless. I'm just trying to understand all the parameters as well as possible.
thank you for the measurements, it's pretty clear, yes except for the 73x230 measurement that I can't quite locate and The top chamber is now 360mm from the front edge of the shelf to the rear wall, because 360+ 110 = 470mm and the combustion chamber is 420mm deep.
so either the combustion chamber is now deeper or the post combustion has become deeper?
for the moment the tests which I made of the vortex stove are outside with the means at hand.
very difficult to start but once on the way wow, it's really nice, I love to see the vortex which in addition gives a lot of indications on the combustion.
in general the vermiculite in the post combustion still holds?
I have the possibility of buying vermiculite in 30mm thickness of relatively insulating density 600kg / m3 or 1200kg / m3 less insulating but more resistant. No streaks. What do you think?
I am thinking of making the fireplace in cast refractory concrete, what thickness do you think is ideal 30mm, 40mm? The thicker it is, the more resistant it is?
Does the fireplace need insulation or is it counterproductive, too much temperature causes too much degassing?

[Vortex]

That is the difference between a metric and imperial pipe, 6 inch and 150mm are very close but the actual difference is:

150mm = 5.905511811 inches. So the CSA = 17673.75mm2
6" = 152.4 mm. so the CSA = 18243.83448mm2

I'm using a metric chimney pipe with an internal dimension of 150mm, so CSA = 17673.75mm2.

The top chamber has always been deeper on the new stove, it was the same on the old original when first built but was shortened at some point not long after if I remember correctly. The vermiculite board pieces in the top chamber (post combustion) is mostly bits I used on the original test model in my garden years ago. The 2 pieces at the sides behind the glass have been there for 3 seasons and are still perfect. The large piece that forms the roof of the afterburner is new this season and has some very fine hairline cracks on the surface but still has a ring to it when tapped. I would expect it to last at least 1 season probably longer. Only time vermiculite board has actually broken on me while in use was outside on a damp test setup.

My vermiculite board comes from here: www.dineensales.com/Dinboard.aspx
I've never used vermiculite board from anywhere else, so dont know if yours is the same quality, you can compare the data sheets though.

My core has 50mm thick cast walls and 25mm insulation behind. I've never run the stove with thinner walls and thicker insulation, so dont know if that would lead to more thermal off-gassing or not. Any overfuelling normally only happens during the startup phase though, when the casts are still at a lower temperature than the fire.

[martyn]

My stove is built with 30mm cast walls and has two inches of insulating CF so quite different to Trevor’s!

So I was up early this morning to use up my basket of wood that has been in the airing cupboard for two days sitting on the boiler.

95% 95% and yes is was a good burn, there was very little wind and that might of played a part too but a better vortex and very hot burn.
I also noticed the chimney temp has risen to around 75c however I am still not quite happy with theses new setting as it was a fast burn going from match to coals in one hour.
I will try again with less air next time.