Next Core Iteration (Walker Core / DSR / Vortex / Aryan +)

[DCish]

Jan 26, 2019 10:58:20 GMT -8 Vortex said:

Your double vortex looks a little 'scissor handled'. 9 inch wide seems to be the ideal size, but of course it's awkward to make the afterburner wider if you don't have any larger bricks or slabs for the roof.

I'm going to try another burn tonight. I'll see if I can scoot the bricks out a bit more on each side and see what it does.

The rams horn in your second video is being perturbed a bit by the secondary air. Try it with the pipe so the open end is down in the embers. I find I get just as good secondary combustion that way and it doesn't disturb the double vortex.

I think I had the secondary air tube plugged at that point. I think the pattern might be caused by the burn rate getting high enough that the gasses start filling back toward the glass instead of just flowing away from it. I'm planning on flipping the "L" brick that forms the port so that the port is right up against the glass, and see if that changes it. I kind of like that the flame isn't up against the glass all the time in the current configuration, though, on the rationale that it might extend the life of the glass.

[Vortex]

Could be it backing up, if so a slight increase in the size of the transition from your primary to secondary afterburner chamber aught to solve it..

Keeping the flame off the glass is a good idea, it should at least slow down the etching of the surface if not stop it. When you cleaned the fly ash ram's horn pattern off of your piece of top glass, did you happen to notice if there was any sign of surface damage yet?

[DCish]

Two burns last night.

Burn 1
- Widened afterburner box to 8.75", the most I could get and still reliably stack the bricks.
- 7" slot moved to front of firebox by the glass

Burn was reliable and stable, but still frequently lopsided toward the right, the direction in which the gases exit the primary afterburner.


Faster / higher burns were often pretty even, but still frequently weighted a bit to the right.



Burn 2
- All else the same, but decided it might be interesting to add a restriction immediately after the initial vortex.

Insulating firebrick scraps are cut to 3/4" thickness and attached with stainless steal wood screws for this test. Internal dimensions are roughly 7.5" x 3" (22.5 sq in).


The idea was that if the vortex is getting lopsided because it is being drawn toward one side, a smaller transition might create a bit of back-pressure, allowing the vortex to form and stabilize without being drawn to the side.

The idea seemed to work, though I will have to try it again to know for sure, since I slapped this together while a burn was in progress, modified it while the firebox was still full of coals, and the only video I have is of this after refueling, which tends to behave differently than an burn from scratch. Here is the first vortex formation - it seemed to be more balanced, and variations appeared more based on how fuel was placed. Here the initial re-loaded fuel is quite close to the port, and the vortex is fuller on the left.


Here is a shot of a higher burn moment.

I didn't expect it to go like this, but I did find the "nested" vortices quite interesting. In hindsight it is quite logical that the vortex, trapped between the gasses streaming up through the slot, across the top, and down the sides would be already shaped into a smaller, tighter vortex, and that this vortex would continue in spiral shape through the box. I rather like the effect, which is more pronounced in person than in the video.

[wiscojames]

Are you looking for the ultimate in efficiency, compact design, or just really beautiful flame patterns?

I'd like a core with that view in my future domestic heater.

[DCish]

Jan 27, 2019 16:34:03 GMT -8 wiscojames said:

Are you looking for the ultimate in efficiency, compact design, or just really beautiful flame patterns?

I'd like a core with that view in my future domestic heater.

Kind of all of the above, really. I have specific space constraints, a desire to maximize the aesthetics, and I am a sucker for high efficiency. I've done a bunch of iterating toward this, and this feels pretty close. I was really hoping to be able to objectively test it to ensure that the layout and aesthetic elements aren't wrecking the efficiency, but it looks like that's not in the cards (no response to my idea about a crowd-funded flue gas analyzer, and I can't afford one myself right now). I may end up just building it now and hopefully test it later. It would be really nice to get a baseline test of the current commercial box stove I have before swapping it out, though. I'd love to have a baseline of how efficient it is without the mass behind it, then run a load with bypass flipped to run things through the mass, then test this vortex batch box on that same mass and see how the two stack up together under real-life circumstances.

[DCish]

Did one more quick run this evening from cold. Ran beautifully! A real shame that I didn't clean yesterday's ash off the window first, though. The whole thing was cold (40F), and a bunch of moisture condensed on the window when I first lit it, then a bunch more ash stuck to it and it made for a really murky view. Still, I really like how it ran. The constrictor box did seem to keep the vortex in the slot area for longer, there was little flow-out and dispersion of the flame front. For much of the burn almost no flame entered the secondary portion of the afterburner until I deliberately pushed it by throwing five 2" x 2" splits of oak on an already strong fire. Even then, by damping down the air a bit I could keep most of the flame inside the vortex box. This video shows one of the interesting characteristics of this setup - the higher the burn, the more the vortex fills from the outside toward the center. Filming this there was some really intense heat coming off the glass even from filming distance, so it had to be quite hot in there.

[graham]

Can you try measuring the wood weight, and the amount of heat being thrown off as a rough measure of efficiency?

[peterberg]

DCish, to me it looks like the vortex is clearer every couple of seconds analogue to a slow pulse. This usually means there's a restriction down the line which could be well the one you built in.
In order to produce a symmetrical double vortex it's important to have the port exactly placed in the middle in a a symmetrical system. I am unsure what the effect would be in an a-symmetrical system like yours, whether the vortex would be stronger on the wider or the narrower side. I seem to have solved that same kind of problem some years ago but can't remember which side it was shifted to get it even.

Is your experimental model still leaking like a sieve? In that case, you would do best to seal it up completely. In my experience small leaks everywhere is changing the behaviour of a test system enormously.

Overall efficiency is the product of combustion efficiency and heat extraction efficiency. Heat extraction can be tuned by temperature of the exhaust gases, relatively easy. Tuning combustion by eye, nose and ear is simply impossible. Seven or eight times out of ten my gas analizer didn't agree with me during experimentation. Spectacular fire behaviour isn't the same as clean burning, far from that.

[Vortex]

Your double vortex looks nicely proportioned now

The lopsidedness should be solved by just a small piece added to the end of the right side wall of your afterburner. I did this in my first vortex stove top box to stop it drawing from one side of the throat. The little kick in on the left of this cast solved it completely: PIC

I think what you're referring to as 'nested' vortexes, I called conical. It's really annoying that it doesn't come out on video as it's a beautiful 3 dimensional effect. It seems to happen with a very specific mix of conditions, but I found the 2 small secondary air inlets at the front inside edges of the port on my test model really helped accentuate it. The introduction of the denser gasses pushed the front into a cone shape, and the burning gasses it fed produced nice color contrasts and defined spirals.

Any dampness in your wood or firebox will cause condensation to form on the glass at startup. I even found throwing a used tissue in when lighting it caused it! I leave my wood and kindling behind the stove to dry for a few days before use which seems to stop it happening.

[DCish]

Jan 27, 2019 22:09:38 GMT -8 graham said:

Can you try measuring the wood weight, and the amount of heat being thrown off as a rough measure of efficiency?

That would certainly be one way to get some sort of number. I think it would be hard to compare to the likes of the numbers that Peter gets, though.

[DCish]

Jan 28, 2019 2:06:46 GMT -8 peterberg said:

DCish, to me it looks like the vortex is clearer every couple of seconds analogue to a slow pulse. This usually means there's a restriction down the line which could be well the one you built in.

Good point. Is a restriction-induced slow pulse at the very top of the burn associated with any other negative things in particular that I should be concerned about? Could be something to observe / tweak.

Is your experimental model still leaking like a sieve? In that case, you would do best to seal it up completely. In my experience small leaks everywhere is changing the behaviour of a test system enormously.

Yes, I've been focusing on flame path ideas for the most part up until now. I think I have a flame path that will fit my footprint / viewing goals well, so I've likely hit the limit of what my leaky dry stacked test unit can be helpful with. Looks like it's time to take build quality up a notch.

Overall efficiency is the product of combustion efficiency and heat extraction efficiency. Heat extraction can be tuned by temperature of the exhaust gases, relatively easy. Tuning combustion by eye, nose and ear is simply impossible. Seven or eight times out of ten my gas analizer didn't agree with me during experimentation. Spectacular fire behaviour isn't the same as clean burning, far from that.

Yes, I'm still not sure how, but I do want to figure out a way to do some real testing. So next steps are non-leaky build, then figure out how to get it tested, and hopefully tweak it into something with acceptable combustion efficiency.

[DCish]

Jan 28, 2019 4:34:50 GMT -8 Vortex said:

The lopsidedness should be solved by just a small piece added to the end of the right side wall of your afterburner.

Cool!

I think what you're referring to as 'nested' vortexes, I called conical. It's really annoying that it doesn't come out on video as it's a beautiful 3 dimensional effect.

Totally agree!

It seems to happen with a very specific mix of conditions, but I found the 2 small secondary air inlets at the front inside edges of the port on my test model really helped accentuate it. The introduction of the denser gasses pushed the front into a cone shape, and the burning gasses it fed produced nice color contrasts and defined spirals.

The added 3/4" constriction box took this effect from intermittent to being present through a fairly wide range of burn levels. The 3/4" box may be too much constriction, but it was the thinnest I thought I could shave the insulating firebrick down to for this rough test without messing it up when screwing it together.

Any dampness in your wood or firebox will cause condensation to form on the glass at startup. I even found throwing a used tissue in when lighting it caused it! I leave my wood and kindling behind the stove to dry for a few days before use which seems to stop it happening.

Yes, my test bed is outdoors and things have been very damp, so it takes a while for the thing to dry out even if there hasn't been any rain. I don't think I'd have this problem nearly as intensely on an indoor unit (though I do notice moisture in my commercial box stove window at startup sometimes, possibly an indicator that a damp bit of wood found its way in).

[Vortex]

Jan 28, 2019 15:17:54 GMT -8 DCish said:

I think what you're referring to as 'nested' vortexes, I called conical. It's really annoying that it doesn't come out on video as it's a beautiful 3 dimensional effect.

Totally agree!

It seems to happen with a very specific mix of conditions, but I found the 2 small secondary air inlets at the front inside edges of the port on my test model really helped accentuate it. The introduction of the denser gasses pushed the front into a cone shape, and the burning gasses it fed produced nice color contrasts and defined spirals.

The added 3/4" constriction box took this effect from intermittent to being present through a fairly wide range of burn levels. The 3/4" box may be too much constriction, but it was the thinnest I thought I could shave the insulating firebrick down to for this rough test without messing it up when screwing it together.

Yeah, just adding the top gap restriction on my test model helped produce it a lot more often.

You're looking at the double vortex from the opposite end of the telescope to me - so you must be looking down the funnel of spirals, whereas I'm looking at the outside thin end of the funnel coming towards me. Really wish it came out better on camera so I could see what it looks like from your end.

I was thinking to try adding a small step in the sides of the afterburner chamber, a few inches after the end of the port. I couldn't do 3/4" like you have as it would block my view, but 1/8" to a 1/4" would probably be OK.

[DCish]

Jan 29, 2019 3:21:32 GMT -8 Vortex said:

You're looking at the double vortex from the opposite end of the telescope to me - so you must be looking down the funnel of spirals, whereas I'm looking at the outside thin end of the funnel coming towards me.

Cool! Though I hadn't imagined it that way, it sounds about right that it should look conical from the downstream end.

Really wish it came out better on camera so I could see what it looks like from your end.

I was kind of surprised at how poorly the camera captured it. I know the camera I am using picks up some of the infrared range and renders it as a pinkish red. I wonder if that is part of what is muddying things up. I might try another run with clean glass and see if I can't get a better representation.

I was thinking to try adding a small step in the sides of the afterburner chamber, a few inches after the end of the port. I couldn't do 3/4" like you have as it would block my view, but 1/8" to a 1/4" would probably be OK.

Since my post-slot channel is very short and the right turn comes almost immediately, the constriction started barely a half inch after the slot. It might be interesting to play with a variety of locations for it to see what is optimal as the gasses transition from the area with the 2" wide slot to the area immediately after where the 2" wide upward stream of gasses is suddenly absent, leaving more space to fill. I did think of tapering it from thinner upstream to thicker downstream to see what happened.

It also might be interesting to see what happens with just a strip on the bottom. From my upstream view of the vortex, the top seems to be tugged the least in the downstream direction since it has just come through the port. It seems that the vortex begins to be tugged downstream more as it comes across the sides and toward the bottom. It should also be relatively easy to place and shift by just laying a scrap of something in there. It would be really cool to be able to move it while the fire is going to get a live view of how things change as it moves!

As I'm thinking about it, a couple of different ideas come up for possibly playing with:


These will probably remain as just ideas for now for me, though, as I am thinking to transition away from my leaky test bed to an indoor-worthy model. I think my next step is making a sketchup model of it. I'll be interested in your feedback when that step is done, since I'm thinking to take a page out of your book and do a steel frame with sheet metal sides as the container / skin. I found a place locally that says they can get me 1" ceramic fiber board, so I'm thinking of making the innards mostly out of that, so it should be light enough to test outdoors, then bring inside and "plug in" to my existing mass bench. We'll see how long it takes me to get the model sketched up.

[Vortex]

There's a few fairly easy quick ways to make it air tight. If you have enough left, just wrap the sides of the stove in ceramic blanket, otherwise a thin layer of either clay, fireclay or even gypsum plaster over the outside of the bricks will seal it up. It's easy enough to clean off afterwards.

Vermiculite board is good for cutting up into small pieces for experimenting with. It's a lot cheaper than the CFB and easier to cut up than the firebricks, and lasts OK so long as you don't try using large pieces where there's a big temperature differential across it, otherwise it suffers from expansion cracks.

I made a hot-moveable top gap when I was experimenting with different size restrictions. I welded a 6" nail onto the corner of the steel plate I had sat on top of the afterburner. The nail poked out the front side of the glass window, so using the welding gloves I could pull or push the plate to try different gap sizes while it was running.