Vortex Stove

[Vortex]

Excellently built stove and very informative videos. Thank you, Pat.

The front of these stoves get very hot. I've seen videos of people with batch boxes just lifting the glass off the front with bare hands - no way you'd be doing that with these. Having the port at the front above the fire draws the heat forwards, which is why the secondary air passing between the door and frame works as well as it does.

[patamos]

Thanks Trev

Throwing so much heat forward was a very good thing in this application where we wanted much of it to radiate into a large room.
I've cast the top slab of big masonry fireboxes in the 3 to 4" thick range without trouble. But thinner than that has cracked. So, i think so long as that front lintel is thick enough there should be no problem

I'm getting ready to build another 2 of these at least.  The next one i build i think i will place a ceramic glass on top to get a better sense of turbulence patterns in the throat.  As mentioned in the second video, the additional gap for secondary air above the door frame does not seem useful.  Maybe there is a way to shape the door and frame metal to tweak secondary combustion for the better…  
I wonder what it would take to induce a double rams horn..

[Vortex]

Hi Pat, The thing that's always put me off of J-tubes and batch-boxes is having the fire at the end of a long tunnel moving away from me. I like to have a really good view of the fire, so for me if it's a case of sacrificing a little efficiency for the aesthetics, I'd go that way, other people have different priorities.

The front lintel on my stove cracked the first time it was fired, but it has a piece of re-bar in it so it's never moved. The rest of my castings are all still perfect and on their 8th season. They're all made of castable refractory, most are at least 3 inches thick except the top of the firebox which is a 2 inch slab with chicken wire in it.

The simplest secondary air would be to put a pipe through the right-hand side wall of the stove so it came in along the inside edge of the throat/port. Alternatively, the door could be made of box section steel so you could heat the air inside it and deliver it at the top just infront of the throat/port.

I sometimes notice a rams-horn pattern in the front of the fire just behind the primary air. You could try the idea I mentioned here for a horizontal 'riser', or even add a heat-riser above the present throat/port - just to the left or right so it would be 'L' shaped. Should give a good rams-horn. Would make it very high but that's always the trade off in these designs.

[patamos]

Hi Trev,

Yes i agree that the viewing aesthetic is worth small compromises in efficiency. And then, when one considers the relatively slow absorptivity of earthen mass, the slow gassification mode of your design likely compensates by increasing harvesting efficiency. Over sizing the bells and adjusting the bypass gas flow as the system warms up can enhance the harvesting even further.

I wonder if the rebar in the lintel cast was a contributing factor to the cracking?

Yes box section sounds like a great idea Simple enough.

The idea in your lower drawing was what i planned to do in this build, but opted to stick with what i knew would work.
Even if the throat/riser were extended only half the distance that might be enough to significantly affect the secondary combustion. It would also send the hotter surface of the griddle further back which could be a nice safety feature for toddlers with curious hands...

[Vortex]

Hi Pat, Hadn't occurred to me that the re-bar might have caused the crack, but of course you're right, the higher expansion rate of the steel could easily have caused it. I've got so used to putting chicken-wire into castings without any problems that I just presumed it would be OK as well.

I look forward to seeing the results of your innovations in the throat/riser, keep us posted.

[patamos]

One thing i noticed in my filmed visit after 12 or so firings that i did not mention in the video is minor crack in the cob finish plaster where the top right (facing it) corner of the fire box meets the shelf and soft return towards the wall. I placed two layers of 1/4" felt back to back outside the fire box, and 4 odd inches of medium density clay perlite between that and the red clay brick side walls.
Across the front lintel i used one layer at varying depths in the build up, but not with complete coverage. That whole package is tied in pretty tight so i did some humble checking in with my gut and kept my eye on the anticipated temperatures all round.

At this point i'd say i've asked too much of the fiber glass to send the box stretching to the left. Could be gas fried already.
Anyway, this is a good way to assess the tensile strength of fairly fibrous cob.
Holgar Laerad, my good friend and mentor, and his mentor Eckhardt Bruehl (sp?) figures cracks are part of the picture. so long as they find a smoke see equilibrium…
I mention their names here because i feel than Eckhardt deserves a mention for all the old old multi-purpose hearths he dis-assembled, studied and restored in the Weimar.
I only met him once and/but get the sense that he'd rather just get on with building all kinds of clay things than spend any time in a broader arena.

So we'll see on this one. Might need some felt buffer surgery. Might not...
And offered here as a heads up for self and all to see


btw, one of the kind fellows who took a look at it when i had some pressing questions - John West of Black Jack chimney services and WETT certifying wood stove installer… graciously offered his time while slightly under the weather. He mentioned one thing that is worthy of consideration in any (BC box fireplace) code modification/interpretation: Drywall ought to b considered a combustible due to the paper coatings. Upon further reflection i'd say much less so than wood in that the volatile wood resins are absent. But still, food for thought...

[Vortex]

My stove has a small crack in the top left that opens slightly every time it's fired and closes as it cools. It doesn't leak anything out so I've always just ignored it. I think it's caused by a combination of the door frame and stove top frame expanding from the heat and lifting the bricks slightly. Note how much the steel angle of the cooktop is bowing from the heat:

[dustylfc]

Love this stove best I've seen if am honest
Well done

[Vortex]

Thank you, Dusty

Pat, regarding the secondary air that we talked about above. Seeing the experiments being done by Peter, Shilo and Adiel, using some exhaust gases in the secondary air. Gave me an idea - would be interesting to try some experiments with channels from the top of the left-hand bell through the side of the firebox into the top of the throat/riser. Could even run a small pipe right through from the both sides with lots of small holes or a long slit, so you'd have air coming in from the right and recycled exhaust gases from the left.

[patamos]

Ya Trev,

Been thinking much the same thing.
Wondering how to shape a port from the downdraft chamber that is conducive to pulling from the otherwise strong current in the down draft. I understand that the throat will likely have a stronger negative pressure, but if the behaviour of wind and water are any indication, a fast-ish rate of downdraft current will also have a stronger negative pressure.   So we want to create some kind of eddy out.

The feed into the port could be via a metal tube with a slit much like the vertical section of Matt's secondary port on his split riser design.  But in this case aligned horizontally through the throat.

The tube could also be shaped to evoke a trip wire or some such feature that optimizes flame pattern.  Might be worth a look at the re-burn set ups on some of the newer air tight metal bodied stoves.  Then factor in a way hotter environment and higher flow rates.  We could work with a basic firebox design and interchange the air ports to see what effect they have.

With fresh secondary air feed from the right the ratios can be tweak able.  But how best to preheat this air?  Maybe it comes up a channel between the right side door and frame.

A testo is making its way up my wish list...

 

[Vortex]

Yeah, a Testo would be really nice. At the moment I'm working on creating a space in my workshop where I can built and experiment with stoves.

On the right-hand inside of my firebox, I can often see a couple of little jets of white hot flame from air leaking in at one or two firebrick joints. The air has to travel between the hot sheet metal skin and firebrick, before going through a small gap in the clay mortar, so it's well heated by the time it gets inside. Maybe this could be a way to do it intentionally?

I don't have the down draught channel at the side of the firebox (like in the one you just built), so for me it would be connecting into the top of the mini-bell. It's easy enough for me to see if it would flow in the right direction, all I need to do is drill a small hole through the clay mortar, just below the throat/riser and watch the flame pattern there. On a stove that has the down draught right next to the firebox, maybe an elbow on the end of the pipe that's inside the down draught channel facing upwards, so the natural flow would tend to go into the pipe. It could block up with fly ash though...

[patamos]

Ya, drawing from one of you mini-bells ought to work well.
And the plenum between hot bricks and sheet metal makes sense too.

I wonder what effect simply letting the EGR jet in from the sides would have without a tube across the throat?

For the stove with a downdraught next to the fire box, maybe a sloping ledge would be enough to coax some of the gasses out of the general trajectory

[patamos]

Hi Trev,

I'm getting ready for two more stove builds this winter-spring. One in my 400sq.ft workshop. The other in a 100sq.ft sauna with 200sq.ft. living space above and the need to heat water for an outdoor bath.

There are so many cool things about this vortex design that i am going to keep working with it. The fact that it throws a lot of heat forward is an asset in both applications. Also the way the griddle top can heat up quickly.

For the sauna i see the front half of the deck as a griddle for splashing and the back half encasing a vertically oriented vented water tank with copper coils inside.

One thought is that the existing volume and power output might be a bit much for these applications. So the thought of scaling it down becomes more serious. I wonder how best to go about this. Seeing that Peter's batch boxes scale up and down fairly well is a good sign. 

I think the firebox, door and general design of the vortex is very sound. And who knows, you/we may already have optimized the combustion efficiency without knowing it.  But with future testo analysis in mind, and possible desire to tweak things, i have been thinking of how to have the layer of mass above the throat (or upper throat if you will) be interchangeable. Perhaps just the front half of that layer. In doing this we can experiment with various 'heat riser' shapes without having to do major tear downs. And once one approach is decided as the ideal, heaters we build in the interim can be retro-fitted.


thoughts for now…

[Vortex]

Hi Pat, I look forward to seeing those builds come together. I have the same kind of idea to create a test bed version in my workshop, something that can be easily modified. Will be great to have somewhere to experiment with these things properly.

I tried a hole just below the throat/riser through into the top of the mini-bell. I'm not seeing any flame jet there, and no sign of flame being drawn into it either. There isn't such a high velocity in this setup as you'd get in the riser port of a batchbox, so the pressure difference probably isn't enough to pull it through. A tube full of holes right across the throat into the bell would have a lot more draw than just this one small hole. Time will tell.

I'm sure the Vortex stove will scale up or down OK within the same kind of 5" to 8" range as the Batchbox.

For a higher cooktop (or sauna steamer) temperature make the gap under the top plate very shallow and wide, so you increase the surface area the flame path comes into contact with. When I was in my 'open fire' phase, I raised the top gap to reduce the drag and stop the occasional smoke-back when it was windy and the stove was running open. That lessened the efficiency of the cook top. So no need to make them with such a high top gap now as the gasifying mode and large glass window means there's always a nice view for fire gazing.

[patamos]

Hi Trev,

Could also be the EGR port didn't draw because there is a path of lesser resistance around the door perimeter. Maybe plugging that up (if only temporarily) will change the flow.

Thanks for the suggestion re wider flame path.
On the build mentioned above i used the extra top gap space to shape curves and trip wires into the top of the throat.
I might keep the height so as to play with the modular insert at the top of the throat (should we call it a vortex port or 'V-port'?) .
Further thoughts on that aspect. Shape the front lintel sand side bricks/castings above the throat with a 1" set back to create a three sided ledge for the cast V-port to sit on. Line the front and side perimeter of it with ceramic felt so that it really heats up without transferring too much of that heat into the surrounding masonry .

I haven't wrapped my head around the exact scale down of the box, but it will likely be to fit standard firebrick sizes, and maybe a 5" pipe and 25" CSA.

thoughts for now…