Austin Shackles wrote:Just to add I'm trying to create a distinction between "batch" and "burn". The way I see it, when you fill up the firebox with fuel and light it that is a batch, and that's what distinguishes a batch-rocket (stove) from something like a J-tube where you feed it little and often.
A "burn" is composed of 1 or more batches and is the time during which the stove is alight until you decide not to feed it any more. This, I think, conforms to the idea of a "burn" in a J-tube. And if it doesn't, I'd like it to. So for example you could do a 1½-hr burn in a batch stove which used 3 or 4 batches, and after that the stove and bench would all be nice and hot for the rest of the day/night.
Yeah, that's how I interpreted what you wrote earlier. Yup, I could see how with too many batches in a burn, the chimney temps keep rising, and it's lowering system efficiency. I suppose that also means that having the stove sized well to the space is helpful for efficiency, too.
I think bypasses makes this interesting, too. As chimney temps rise in one "mode" it can be bypassed to a new mode for more heat exchange potential. I suppose with a water exchanger there is another aspect, too. There can be a "heat dump" hot water system, such as a hot bath. Then, the new cold water will strip heat faster from the gases, keeping the chimney temps lower. Well, at least in theory.
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I'm so focused on this stove project. I forgot yesterday was my day off. A friend reminded me and I took the afternoon off. I still managed to put in a decent morning session.
The wet stacking is way fun. That said, I've run into a couple challenges. The cleanout I have it partially warped and has a tiny lip. I didn't quite fit it perfect, and I accommodated for the bulging in a way that kept the plug happy. It seems to work pretty well as is without the mortar cured, so I think it will be pretty solid in a couple days.
I'm realizing with all my different brick sizes, and my prioritizing the inside channels being consistent, I'm going to have a pretty jagged outside face. It's also going to be like 6 shades of red. I think I'll just continue and try to keep it close, within 1/4in. Maybe ill consider a finish on the outside tile or plaster that smooths out the irregularities.
I lay the first couple courses and I'm about halfway through the third course. At this point, I'm looking to embed the copper coil in the downdraft chamber and figure out the bypass plate. I have pipe bender for 3/4in pipe. I started to use it to bend the copper... Not so easy. Much more difficult of a job than I anticipated. Its stiff and has a tendency to mini-kink at sharper bends(6 in radius). Also, its hard to fix in both planes while shaping, and the other 20ft of pipe is sort of flopping around, in the way. I thought with a proper pipe bender, it would be easy to shape. I was wrong. I called it early and I'll have to re assess how to shape it before proceeding. I think I'll have to get a proper table setup and involve in a clamp on the actual pipe bender and use open cupped palms and moderate force to shape, a few inches at a time. I'm not trying to get it perfect, but it does need to be a general shape and size without restrictions. Maybe filling the pipe with sand and using gentle heat will smooth it out and make it easier? I may try this, tomorrow. I have 4 ft of 1.25in straight copper that I can use if I mess up part of this coil moreso than I have.
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I've heard back from Matt Walker about my proposed downdraft mods. Its not his recommendation, and he's unsure if it will function as I'm hoping, but would not rule it out as possible. I would say he's not discouraging my mods, so that is enough of a green light for me to gamboool on my proposed design. Worst case, it will be a fail, information for the community + require a difficult retrofit. I'm hoping for a best case, fluid dynamics work in my favor(!?) and gases do the stuff that I'm wanting them to do, I get my goals met in terms of performance, stove footprint, and y'alls get a successful innovation.
His main concern is that the downdraft chamber will behave bell-like and gases will spread and stratify In the top of the chamber when the oven/masonry route is opened. They would prefer to do that, rather than get pulled through the oven/bench passageways. To be fair, I didn't even consider this initially, although it makes sense. I think very likely he is correct. The chamber is essentially an open bell with a much larger CSA than my system csa, and the draft is looking to pull the gases a fair distance through the system.
I have been considering options. I've landed on a couple adjustments which I hope(basically just guessing at fluid dynamics, here) will allow for a good function in all 3 modes(start up, water heating, masonry). My plan is to keep the downdraft entry to oven entry passage short, insulated, and partially defined path. I will do this by lining the inner front left wall with kiln brick, and recessing that kiln brick inwards, slightly.
In addition, I plan to put a divider brick at the top of the downdraft chamber entry, on top of the top coil pass. The intention is to discourage gases from entering and expanding in the top rear of the chamber.
I'll also be looking to improve overall system draft, which I suspect will help overall, and also help to reduce stratification relative to flow path "suggestions". I will use less 6in stove pipe, only a short double wall transition, and more chimney pipe, and may have to go a bit higher with the chimney. Continuing chamfering inside corners at corners of passageways, and making the chimney pillar to stove pipe transition gradual and smooth(not sure how, yet).
How will this play out in practice? Dunno. Complicated and too many unknown variables, plus my lack of skill in laying brick and fabricating aren't helping. I'm hoping my conceptual knowledge and luck will produce good results
. In a not so favorable outcome, I'll need to design a sliding plate baffle to create more seperation within the chamber. I have a hard time imagining the gases preferring stratification if most of the passage is closed off relative to the shorter oven path. I hope this is not what will be needed in practice, as it involves more fabbing and additional operational controls/complexity.
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I tested the sharp silica sand and fireclay joint on kiln brick. I dried it, then fired it in my woodstove. It was about 1/8in-3/16in thick, a bit more than my planned joints. It fired well, no cracks. It's got enough compressive strength, me standing on it with my heel was fine. It held bond. I could hold one brick sideways or from the top and let the other hang. Sideways, gentle finger taps were okay. As soon as I tried to pull it apart with gravity assisting, the bond broke.
This tells me high compressive strength, low shear strength. I need to re-enforce the firebox area. Fuel entering the firebox that could bump a brick could easily break a bond.
I'll test my black sand kiln brick joint tomorrow. It's closer to 1/16 - 1/8in. I expect it seperate on the hanging gentle finger tap test. I have a thick blob on top to assess cracking.
I'm using my native clay to make a weak clayslip for use as my "water" for the mortar mix. Im using less fireclay, closer to 3.5-4:1 sand:fireclay. I like this strategy, as I can bypass screening my native clay, and still get benefits. Im also using a bit of black sand with the silica sand, in the mix, currently. As far as performance goes, I've had a few bonds break from pretty heavy swings with a mallet when fitting other bricks, adjacently... but they generally seem to be bonding pretty strong light taps don't break bonds. I plan to use less clayslip and less black sand, as I approach the core. I think for the core, I'll screed ash for the mix.
Id like to try and complete layers instead of mortar batches when possible.. the bond breaking situations are happening when I restart work on a partially finished layer and start tapping adjacent bricks to get level/flush.
Also, I would like to note that on the bricks I popped loose, I've simply painted / sealed the joints with mortar. I imagine this is not ideal for bond strength, but probably okay if it's only in a few places.
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