Walker Core Variation

[DCish]

Inspired originally by the vortex stove but wanting a batch box like Peter's with a compact, insulated afterburner, I was immediately inspired by Walker's compact, riser-less core. Here is my first stab at a variation that would fit my space and aesthetic requirements. It is intended to replace the standard wood stove I have feeding the bench I built last winter.



Here is the Sketchup file (in 2014 for those who need that): (https://www.dropbox.com/s/60j5ioq1miqc1mu/DCishWalkerCoreVariation_v2014.skp?dl=0)

Secondary air is a slight variation on the Walker version with the injector tube nearly flush with the side wall, accomplished by beveling the wall bricks. The injector juts back into the burn box a bit to help keep wood out of the port and facilitate good airflow).

The secondary burn area (afterburner) is behind glass to the left. The white liner behind the glass is half-inch superwool. I could only get a full roll, so I have plenty. I figure that keeping space relatively tight immediately after the secondary air injection will help keep heat confined and temps up while at lower burn stages, while stepping quickly up to full CSA will allow for lots of mixing and expansion, hopefully keeping temps high until burn is complete. 

Any and all feedback is welcome!!!

[DCish]

Seeing no cautionary responses, I picked up some fire brick in preparation for the build. I have some other things going on for the next two months, but hopefully I'll be able to cobble together an outdoor mockup before the summer is out. Will post updates as available.

[patamos]

Ha,
i was waiting to hear what anyone else might say…

But i do wonder what might be gained or lost in not having a second port between the two half risers.  
I look forward to the feedback from your mockup experiment...

[DCish]

Thanks Pat! I think that is a valid concern. I see two potential issues. The first is that with a relatively short afterburner and only one end of the burn area being confined, there will be rapid heat loss in the direction of the window. The second is that while my hope is that the stepped wall of the burn chamber will promote mixing, I suspect it is equally likely that it will act as a cone and expand relatively smoothly. Will enough mixing occur as a result of the right angle turn and stepped walls? Will enough heat be contained for long enough to sustain the burn? We'll see how effective it ends up being in the end. Hopefully I can figure out a way to get the core tested once built... Anybody with a testo coming the DC way later this summer or fall?

[patamos]

Ya DC,

I think you will be losing turbulence for mixing, but maybe you don't need it. Could be you will gain flow rate which could make up for it somewhat. I wonder how much Matt played with these variables before settling on his riser less core design. Shilo and Adiel sure seem to be tweaking it in a hotter direction...

The nice part is that if your top deck is removable, you can always play with the shapes by adding in port-like features. Even just a couple of firebricks stacked loose on end along the side walls, and one or two on edge atop of them… might create something of a second half-riser

Any which way, the visuals through the window should be fun

[DCish]

Long hiatus, returning now for a bit more effort on this. Set up a brick perimeter to contain some sand to start the outdoor mock-up. Realized that I can't really start cutting brick until I confirm my ability to get the secondary air injector done up. Did some brainstorming and figured I'd try some steel pipe, which in the DC area results in something cheaper than starting a conversation with the local weld shop. I was planning to use 2" pipe, but the elbows are prohibitively gigantic to fit, so I went with 1.5" ID. These elbows fit the 2.5" thickness of the bricks with about 3/16" of play to allow for expansion under higher temps. Being cheap threaded steel pipe, any part that burns out should be easy to replace.



The idea is to cut the vertical piece to length once assembly progresses to that point, then cut the air supply slit. The feed tube is intentionally long to allow me to play with door options when the time comes. I plan to cut short slits into the threaded part under the cap to allow for air regulation, should that be needed, the cap allowing full closure to try to cut flow through the stove when the burn is done. All for now...

[pinhead]

I just downloaded your .skp file - nice work on the model!

I see one glaring problem, though, IMO. The area post-port is too "wide open" to create any mixing of the gasses - you wont' get the desired "double rams horn" that is so effective at mixing the hot gasses. Further, the wide-open area behind the window will allow the gasses to rapidly expand which will reduce the heat density, further reducing combustion efficiency.

IMO This wouldn't be much more efficient than a standard "box" stove. The port and secondary air supply will help, but the mixing won't occur as it does in a true Peterberg Batch Box.

[DCish]

Thanks for taking a look Pinhead, it's been a good experience getting to know how to work with sketchup. Regarding the mixing problem, I had a similar take-away from the comments Patamos made. I have continued to run into barriers to starting the physical work. Maybe that's a good thing -- it prompted me to sit down earlier this week and make some revisions to the afterburner. Basically I gave it just a single interior skin of half-inch insulation and added a second port out of ceramic glass just before the riser to create a semi-isolated afterburner chamber. I'll get some pics of that up soon for review. Thanks again for taking a look, I appreciate the constructive criticism! Shuffling electrons on a screen is quicker to get to than making physical mods later on.

[DCish]

Ok, a couple of views of the modifications. Thoughts?

[EDIT 2/2/2020: Original images lost. Reconstructed image below.]

[oxbowfarm]

Is there a reason you want to use glass for the second port versus brick or a casting? To me it seems like the wrong material for that purpose.

[DCish]

Solely for fire viewing purposes. Seeing what Shilo and Adiel have been able to do with glass in their setups emboldens me to give it a try. Not thermally ideal, but I'm hoping it will help create something of a contained afterburner with additional turbulence at the exit.

[oxbowfarm]

I have not ever worked with ceramic glass, but I've worked a lot with soda glass in stained glass. My gut says there isn't a way to make a single piece with a rectangular hole in it the way the drawing looks. Does that show a single piece or does the dotted line at the top of the port indicate a separation between three different glass elements? It probably IS possible to cut a hole out of a sheet of glass like that with a great deal of caution and care, but the square corners are going to concentrate all the stresses at those two points. My guess is a solid piece will crack on the first firing, or even before just getting knocked around building the stove. But I could be totally off base never having cut or worked with ceramic glass before.

If you make it three pieces with the top piece set lintel fashion over the port sides, you still have the issue of balancing a big piece of glass on edge over two narrow pieces. I think your design would be better off having a big sheet of ceramic glass on top for fire viewing vs the glass port. More likely to hold up to thermal shock and way easier to build. JMO.

Edit:  If I were going to try and cut that hole in soda glass I would drill oversize holes at the corners first, then grind the cut on at least one of the long sides, preferably both.  Very carefully with the glass fully supported below and held really securely.  Once both the long sides were cut from the edge to the holes, I'd try and score and snap the top port.  The round holes at the corners would slightly reduce stress concentration.  But I still think its gonna crack, probably while you are trying to make the cuts.  

[DCish]

I would never have thought to even give it a try if I hadn't seen some of the punishment others have put it through. That said, the precautions you mention seem like a good idea for cutting the port. From the little I've done so far, it seems to behave a lot like ceramic tile. I thought I'd use my buddy's wet saw for the straight cuts. Figured I'd cover the whole thing in a couple of layers of tape to provide a degree of protection while working with it.

[keithturtle]

I wanted a window in the front of my propane tank stove, so I bought several of these Pyrex lids. www.pyrexware.com/glass-casserole-1.5-qt-lid/5307233.html#sz=12&start=27

I felt the knob would be a safety hazard, lest someone grabs it to open the door, so I cut it off.

I used a diamond sawzall blade jigged into the metal lathe so it would slowly wear its way thru the glass below the knob. With water slowly dripping on the cut, it turned at 150 rpm and only took 7 hours to wear thru to the point where it snapped off.  Not very efficient use of electricity.

I got real disappointed when I later discovered the glass is only rated for 350*F, with short exposure to 400*F.  My last temp reading on that door when burning hot was 600*F.

I guess we shall see what happens when I mount that glass door and fire it up.

That's my experience with cutting glass

Turtle

[Vortex]

Keith, I used Pyrex dish lids as my stove door window for about 5 years. The really old ones seem to last longest but I had to replace it once or twice a year, usually when a piece of burning wood fell against it. I read online they are rated at 500*C.