Ralf
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Post by Ralf on Jan 4, 2017 1:37:46 GMT -8
Hi Brian, I´m amazed because I recently had the exact same idea of shaping channels in insulative firebricks located at the port to provide the secondary air. The only possible flaw I can suspect at your design is that when you feed the air to the 45° upward channels from the bottom only the 2 lower ones will have access to the supply channel. From my understanding most of the crucial mixing sould take place in the upper part of the port. Maybe you can carve an additional vertical supply channel that stops at the highest diagonal supply channel at the rear part of the firebricks .
Just my 2 cents.
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Ralf
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Post by Ralf on Dec 28, 2016 1:12:44 GMT -8
.... Maybe its time to start thinking about a cushion that can take the heat from the bench... Hi, I´m also thinking about what to put on my bench as a cushion, I will try cherry pit cushions or grape seed cushions since they are used to store and release heat when you put them in an oven.
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Ralf
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Post by Ralf on Dec 27, 2016 4:44:49 GMT -8
Hi Michel,
I did a bell bench made of concrete pavers that is 50 cms wide and 35 cms high on the inside and it works now (after shortening it form an initial 4.2 m down to 2 m length ). It is supplied with a 15 cm /6 inch j-tube that has considerably less btu output than a similar-sized Batch Box. It gets up to 40 °C at the hottest spot after a few hours of firing. I suspect that 30 cms inner height will also work fine if you build a "flat funnel" for the cooled gases towards the chimney close to the floor, which I did.
After a double layer of pavers & cob mortar I arrive at 46 cms outer height, which will be too high for sitting comfort if there´s a vented wooden bench on top. You could build a raised step around the bench to compensate for that. My bench will get a final coat of tiles that add another 2 cms to the height. I will install a wooden floor around it that will bring the actual sitting height down to comfortably low.
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Ralf
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Post by Ralf on Dec 14, 2016 4:16:18 GMT -8
I agree with pinhead here, I fired my fully installed RMH with bell bench for the first time yesterday and without bypass it would have surely been a mess, I´m so glad I did install it. Highly recommended. Also useful for fine-tunig the draw of the stove and stack temperature later in the burn.
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Ralf
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Post by Ralf on Dec 6, 2016 13:32:10 GMT -8
Hi Folks,
does anybody of you know how vaccum-formed ceramic fibre tubes are made ? I happen to have a vacuum pump and could do some experiments if it´s doable with home equipment.
I suspect it's not done by using some sort of liquid ridgidizer, for that you won´t need a vacuum, right ?
Best wishes Ralf
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Ralf
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Post by Ralf on Nov 29, 2016 22:24:35 GMT -8
Dear Peter,
just read this and love the idea of using adobe bricks inside a bell to store heat. But: How does that effect the ISA ?
One could easily make a mould for bricks that are rounded so they run snug along the perimeter of the outer metal bell. I was also thinking if it makes sense to put grooves or ripples on the brick surfaces pointing inwards to increase the heat extraction surface.
best wishes, Ralf
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Ralf
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Post by Ralf on Nov 23, 2016 6:12:57 GMT -8
Great, thanks very much for the well reasoned reply ! I´m pretty sure the Testo won´t ly.
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Ralf
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Post by Ralf on Nov 23, 2016 5:09:00 GMT -8
Hi, I´ve got a few questions concerning the specific pre-port secondary air supply in Peter van den Berg´s newest design shown here.It´s a floor channel with a vertical pre-port tube opening half way up the port. Peter states that this configuration produces the best results when fired "upside down", starting the fire at the top of the fuel close to the back. I read many times that it´s crucial to preheat the secondary air well before injection in the burn path. How does this happen here if the fire starts at the top, heat will rise but the bottom air supply channel is well shielded under the fuel pile ? I´m just asking about the start of the burn until all the fuel is on fire. And how long does it take until the fuel is completely lit with this lighting method ? Could this channel better be heated right from the start by flipping it upside down and feeding it from a tube running through the ceiling (as the p-channel does) ? I´m aware that this design makes the build and exchange of the pre-port super-easy, and that my proposal would re-complicate it. Would the possible benefit be worth it ? Thanks for clarifying ! All the best, Ralf PS: I also discovered this "upside down" firing method in an advice link given by a local oven builder for best practice in a "standard" woodstove (here the fire´s lit close to the front as opposed to the batch box). Audio is in German with funny Swiss words mixed in, but when you watch you´ll get the idea. Light at the top, keep air supply fully open throughout and you have a smokeless burn (possibly unburnt hydrocarbons not adressed).
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Ralf
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Post by Ralf on Nov 16, 2016 21:24:30 GMT -8
Hi jeanlou, I don't know how may pieces they got in the bourry box kiln at one bake, I´ve never been there but I imagine it would be fun to help them firing one day. I also heard of a wood-fired Raku kiln that`s made of a metal garbage bin lined with ceramic fibre insualtion. It´s got an opening for loading the kindling-sized wood fuel at the bottom and is an updraft kiln with a short chimney mounted to the lid of the bin. Pictures can be seen here, the text is in German though. I met some potters who said that they reach 1350 °C / 2460 °F with this thing easily. The soft fibre sheet is fixed with ceramic knobs on the inside that are sewn through to the bin wall with Kanthal wire. By the way, this would be exactly the method that I would use construct my future heat risers for rocket heaters. I´m courious how your build will perform, it looks promising. Good luck ! Ralf
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Ralf
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Post by Ralf on Nov 16, 2016 21:02:01 GMT -8
Hi Matt,
thanks for that interesting video. Just for my understanding, is the 45 angled ceramic fibre sheet that forms the "walker tube" at the left of the firebox with the slot visible towards the middle ? And the mixing zone around the back corner to the right ?
This also perfectly explains why the firebox on these should be well insulated.
I like your "zero CO" goal, if I had built a batch box I wouldn´t settle for anything less.
Cheers, Ralf
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Ralf
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Post by Ralf on Nov 14, 2016 15:34:56 GMT -8
Hi Folks, I think I got my last question answered over at PermiesChimney dampers in RMH´s are almost as doomed as metal. For good reason. Cheers Ralf
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Ralf
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Post by Ralf on Nov 10, 2016 4:13:33 GMT -8
As I read many times most experts strongly advise against usage of a chimney damper with a RMH. If the system is air tight it should be enough to cover the feed tube completely once the fire´s done to stop heat loss through the chimney, or am I missing something ? Since I have a sturdy T tubing to install the bypass shutoff valve I could easily install an additional valve towards the chimney, question is whether this makes sense. It would surely require strict operation rules, f.i. only close it once the fire´s completely out, but how you determine that ? No glowing coals ?
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Ralf
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Post by Ralf on Nov 9, 2016 1:50:56 GMT -8
Hi Yasintoda,
thanks for your reply & encouragement, I was looking for typical duct lengths of 6 inch systems in Erica & Ernies Book yesterday just to get a feeling what might be right, and the bell system has less friction, so plus the estimates of Peter I´m pretty sure I´m on the safe side. Chimney will be insulated, it´s originally an old square brick chimney and I´m going to put a stainless chimney duct inside and backfill that with loose Perlite.
All the best, Ralf
PS: Calculated that the bench will weigh about 2 tons, pretty curious how log it will stay warm.
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Ralf
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Post by Ralf on Nov 7, 2016 6:34:42 GMT -8
Hi Guys,
this is neither exactly a Raku nor a rocket kiln, but it´s got interesting similarities to rocket stove technology, since the fire burns downwards and there is no smoke even in a reduction atmosphere. The firebox is called Bourry Box style. I also like the hinge mechanism of the insulated firebox cover.
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Ralf
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Post by Ralf on Nov 7, 2016 2:56:21 GMT -8
Ok, I like experiments ! As for the rest of the dimensions: My combustion unit is a 6-inch / 15 cm-System on wheels, j-tube is made of insulative firebrick lined with thin (1 cm) cordierite plates on the inside of the burn tube. Heat riser is just short of 1 meter made of cast very light insulative refractory I mixed myself, giving more of a 1:2:4 ratio of the j-tube proportions. The manifold area is constructed as an intersection of the vertical 40 cm "barrel" tube and the 15 cm horizontal tube, creating lots of space for a smooth direction change of the exhaust gases. The unit functions very well in standalone mode as can be seen here (back then the interns were still humid and now it had a summer to dry out completely) donkey32.proboards.com/thread/1994/combustion-unitThis mobile unit will be coupled to the bench that sits in an adjacent room. The exhaust gases will be delivered to the middle of the bell by the delivery duct. Bell internal will be 4 m length x 35 cm hight x approx 50 cm width. The walls will be 15 cm thick on the front and approx 20 cm thick on the top, ytong at the back is 10 cms. I will also install a shortcut valve for cold starts, chimney runs inside an old brick one and will be 13 cm diameter stainless pipe backfilled with perlite and about 3,5 ms high, opening 60 cms above an almost flat roof. I hope the information is now complete. I´m documenting everything by photographing and filming, but I will only publish it after at least one season of operation, so as not to claim that it works before it´s proven. ;-)
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