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Post by erikweaver on Aug 19, 2015 18:53:29 GMT -8
Eri[k], regarding caulking the seams, one technique i have been having success with is mixing sodium silicate with fine sand and enough water to make a medium-thick paste. This can be smeared on by hand with surgical gloves or the like. I've heard Karl mention that so si can start to denature around 900c and potassium silicate closer to 1000c (if i recall correctly). And i cannot say i have subjected my risers to much more than those temps. But so far it has proven to be simple and strong. Thanks Patamos, I appreciate the suggestion. I have not yet worked with sodium silicate. For right now, I suspect it will remain in the same category for me as the poured refractory solutions, meaning I expect I'll wait to experiment with that until a later date, not wishing to divide my time too thin this season. I have ordered some refractory cement, which I believe is rated for 3,000 F. I'll read the directions on the package when I get it, but I am half guessing I'll simply apply it thinly, similar to thin-setting fireclay, which worked well for me last year. When I built my prototype stove I mixed the fireclay to a pudding-like thickness and then simply smeared it on the edges of the (soaked) fire brick, then rubbed the brick I was setting onto the previous brick until I felt the brick-to-brick contact, so it was a pretty thin "mortar" joint. When researching the construction of masonry heaters, I have previous read that 3mm was the recommended maximum joint, with many suggesting 1mm, and a fair number of masons indicated they like to "feel" the brick-to--brick contact, and I liked that idea, so that's what I did. Given the fire brick is so uniform in dimensions, I felt that would work well, and I believe it did, at least through last winter.
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Post by peterberg on Aug 20, 2015 0:43:56 GMT -8
OK Patamos, as far as I am aware of, only Adiel and Shilo in israel used a straight piece of rectangle steel duct as floor channel. They did that on my request combined with a p-channel and the results were very encouraging. No hard numbers of course. Recently, during the workshop in Warsaw due to time limitations installation of the p-channel was skipped and I used a floor channel on its own. The results were quite good with both systems, again.
My own mass heater is on its way albeit slowly, the plan is now to use a floor channel as the sole secundary air intake. Testing will be very easy because the heater will be in our living room. Test results will be available before Christmas I'd think.
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Post by patamos on Aug 22, 2015 3:54:57 GMT -8
Thanks Peter.
Somehow i had gotten the impression that Matt let go of the vertical section of his 'pre-port secondary air tube' when he switched to the side exit into the half riser. Maybe i got mixed up after viewing Shilo and Adiel's videos… Anyway, this bottom feed air technique appears to hold much promise - for more than just L-feeds. It gets me to thinking how to evoke the most ideal turbulence for various port exit set ups. In particular a top rear exit vortex i am experimenting with… more on that elsewhere.
Apologies Eric for drifting on your thread topic.
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Post by erikweaver on Aug 23, 2015 6:38:36 GMT -8
Don't apologise, Patamos! I like the drift But I may say that because I frequently tend to drift around the main topic myself In fact, I'm tempted to do exactly that right now, drifting back into the topic of bell ISA. lol I agree that longer, detailed discussion of alternate designs for the secondary air in-take most likely should be in an appropriately titled thread so we can find it later. I am very interested in the up-coming developments and discussion! Construction sounds easier to implement, if a little more challenging to maintain (keeping clear of ash). But maybe the clean up would be as simple as using a bellows to gently blow the ash out of the far end of the secondary air in-take? Sadly, I'm basically lazy and if maintenance is a chore, it would be put off until it became an issue. But I think I would lightly blow a bellows into the opening of my secondary air in-take before stoking the heater.
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Post by patamos on Aug 23, 2015 9:57:22 GMT -8
Ya i've been further pondering the pros and cons as well.
As Peter mentioned, the possible draw back of a metal plate set on splits to create the air intake below is its potential for warping.
Aside from that there are a few possible benefits. For cleaning the plate can be easily removed to clear the ash. And/but it is best to do this before each firing. I have been wondering about making a depression below the grate (where the air joins the combustion process). This might allow for less frequent cleaning, but might also affect the desired venturi-like turbulence in a good or bad way…
For the grate (which keeps the coals suspended), i have been using little chunks of rebar ala Flip and Jonh's approach, set loosely into the side ledges. But i find they tend to want to hop out of their nacelles and bust up the masonry around them. I've taken to welding them together with a spine underneath which works fine, but the less welding i have to do the better. So have taken to cutting pieces of heavy gauge 3/8" to 1/2" mesh and applying them more sacrificially.
Another possible advantage of the simple deck plate is that all the air can come through the one bottom port. To adjust primary vs. secondary the plate can be moved slightly forward or back from the front door. I wonder (and i think Matt touched on this in his 'pre-port secondary air' thread) if having the port @25% CSA and leaving a gap for half of that to make its way up into primary air intake would allow the system to manage itself. Cutting the total back to 12% could be done through the one port and the direction it goes from there could be decided by the fire (?).
Another thought. Creating the air port with a 1.25" tall split and making it overly wide will make for more air to hot metal contact on its way through. the CSA of the port entry and channel can be adjusted with little shims (chunks of tile etc…) . Perhaps there would be an advantage to having the port grow in CSA further along to help accommodate expansion pressures. Here again, we have questions about optimal rate shape and trajectory of the air flow... I am looking forward to hearing about Peter's experiments on the mater.
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Post by davidludt on Aug 26, 2015 11:19:14 GMT -8
Hi everyone, Im preparing for an 8" diameter batch box build and I noticed something I wanted to follow up on... and this thread seemed like a good place to try to do so....
The firebox dimensions we used at the wildacres build in april are wider than what is specified on our dimension spreadsheet.
The 8" specs from our reference library: 11" 8/16 wide 17"4/16 height 23" 1/16 deep
our wildacres buildout: 13" 8/16 wide 18" height 20" deep
now I know that some dimensions are more important, more fixed than others
-and-
I will confess to wanting a wider firebox: (door selection gets easier) (bigger uglier firewood will fit better)
following the rest of the 8" measurements, how wide can i go?
thanks
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Post by peterberg on Aug 26, 2015 11:53:39 GMT -8
Hi David, Yes, the Wildacres build happened to be a little bit different, although I ain't sure about the difference of 2" in the width of the firebox. I altered the thing in order to cater for the use of whole firebricks. But the full firebricks we used were 230x115x64 mm, so this can't be right. At this moment I can't have a look at the design, but the inside of should be very close to 460 mm deep and 460 mm high. In inches, that should be close to 18.1" deep and 18.1 high. Depth isn't really important, this was tailored what I was told the fuel length would be. Don't know about width, what I compromised there.
It all boils down to how much fuel can be burning at any given time which is why the measurements are quite tight. As for the door, you could try to make large 45 degrees chamfers left and right, that will make it easier to choose a door. Or of course, you opt for building an even bigger batch box.
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Post by johndepew on Aug 30, 2015 12:18:43 GMT -8
About your barrel gap: Do you have 5.5 inches all the way around? My barrel is pushed almost all the way up to the riser on the back side, giving more space in front, and I think (from poor memory) that the gap in front is something like 6 inches, tapering down around the sides to about zero on the back. Somewhere on here there's a formula for calculating the air spaces you need inside the barrel. I did that before putting mine together, and it fit within the parameters, seems to work fine. I think I've got about 18-20 inches of free space over the riser. Don't quote me on any of this, but it seems to be working fine the way I've done it.
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Post by tallgrass on Sept 16, 2015 15:36:53 GMT -8
Like David, I am hoping to use a wider fire door... (Htt426 from northstone heat) for the 6" system which would give me an additional inch on either side of the riser, 2" overall adjustment to the horizontal dimensions. If cheating the horizontal dimension out 2" can be related to overall volume, could I compensate by increasing the depth of the firebox by an appropriate ratio? If not I will use the chamfer solution... If I cut a brick chamfer to accommodate will it compromise the strength of the firebrick? I am meaning to drill into the brick to hang the door. I have a rotary hammer drill but I am worried about the hammer function shaking apart the mortared masonry joints, or driving apart a brick that was already subject to the damage of sawing. How do I go about hanging the hardware? Cut the chamfer and pre-drill holes on a mocked up version before mortaring? How much smaller should my pre-drilled hole be than the diameter of my hardware?
-Another drifting question while we are here... at wildacres this year we also mortared the firebox together with pure fire-clay. Is that standard and will it hold up to the loading and unloading and heat differentials over time or should I use a refractory cement for the mortar?
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Post by daniel on Nov 13, 2015 23:24:23 GMT -8
I wanted to ask if a rectangular steel floor channel would come out at the port through the middle of the firebox and if so if it should have the same dimensions as the P-channel.
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Post by peterberg on Nov 14, 2015 2:11:22 GMT -8
At the moment I am conducting some tests to determine which configuration would be best for a floor channel in my situation. Uptil now, best appears to be a straight piece of rectangle duct of the same size as the p-channel, 60 x 20 x 2 mm. Sunk in the middle of the floor , forming the only horizontal area between the slanted sides of the firebox. It ends just before the port, the floor of the riser is at the same height as the underside of the channel. In practise, without the channel the firebox floor is at the same level as the riser. The metal duct will burn out eventually but it's easily to replace since it's a single straight piece. This is done in a 6" version with rigidized superwool riser by the way.
Beind the door is a lower part where the floor channel entrance is, with a steel treshhold of 40 mm high directly above it. The main inlet is in the door, situated as low as possible. The incoming air is icy cold compared to the inside of the firebox so will be at the bottom first, creating a preference to stream into the channel very willingly. The result is a comparatively slow view of the flames with a raging hot riser in the background. Tests are good but not excellent as far as the lowest oxygen and carbonmonoxide numbers are taken into account. But there are no high peaks and unstable burns and the average numbers are really, really good.
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Post by daniel on Nov 14, 2015 12:32:18 GMT -8
Thanks Peter, I left the lower part of the door unfinished just to be able to tryout different things with it. Preheating the primary air through baffles located in the door would be my next try, did you experiment with preheated primary air?
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Post by peterberg on Nov 15, 2015 1:08:28 GMT -8
Thought about heating primary air. But didn't try it bacause the pyrolysis in the firebox would be accelerated again. This is contrary to the situation described above where the primary burn is slowed down intentionally. Risk of overfuelling is lower with a slower burn, as long as the afterburning in the riser is kept going all the time. Mind you, this situation in my heater is achived with a very low exhaust temperature. A cold start is going upto 80 C (176 F) and a warm start not more than 110 C (230 F) at the end of the burn measured in the heart of the vertical stove pipe, about 1.5 m (5 ft) high from the floor. Understandably, the efficiency is high, around 95% LHV average in most cases.
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Nov 15, 2015 2:05:21 GMT -8
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Post by peterberg on Nov 15, 2015 5:10:24 GMT -8
I'm sorry Morti, but I bought the things through Joris Pouls in Belgium. He's buying those by a refractory firm who made the mold at his request and uses a vacuum process to form it. The specs mention 1400 C as the maximum temperature load.
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