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Post by fiedia on Oct 2, 2023 5:56:17 GMT -8
Ok, thanks for the scaled down chart, but I am still confused about the missing plateau: The chart shows that after 12 minutes the temperature in the HR reaches 900°C, this still makes sense but then 24 minutes into the burn the temp drops to 700. Shouldn't 12kg of wood give a strong burn for more than 24 minutes, which means that the HR temp should stay up instead of dropping down 200°? I am not trying to be difficult, I just have the feeling that there's something I have not understood yet about the dynamics. I did not weight the wood load. It might have been less than 12kg but it is close to that.
You may get a plateau depending on BBR dimensions and wood load I guess.
Furthermore, you have a 3 bell system, right? If the temp in bell 1 never goes beyond 250°C measured 44cm below the bell ceiling, then how warm can the gases be that enter your bell 2?
Do you have numbers for bell 1 exit temperature? It is a 2 bell system. There is a detailed analysis on the 125mm BBR here: results-chaining-batch-box-bells. I decided from this analysis to chain the 200mm BBR bells on top and bottom as proposed by Peterberg in this post. The results are not as good as I expected. I am still working on it. |
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Post by firerob on Oct 2, 2023 9:09:59 GMT -8
Most people make the mistake that the brick square where the chimney is resting on should have the same cross setion area as the chimney itself. Yes, the brick hole is 180mm square. When a piece of pipe is placed over the hole you will see that the circle is partly blocked by the 4 sides of the square. A way to get around this problem: a steel plate of, say, 1mm thickness with a hole cut in it that's 10mm smaller all around. Then, use a set of not-too-small pliers to bend a flange all around this hole so the male end of the pipe will fit in. Take your time, do it step by step with the pliers until the angle of the flange reach 45 degrees. The rest of the bending could be done by hammering the flange further. In several rounds, until the pipe fits. If it's too wide, you will be able to hammer it back to obtain a tight fit. I like your idea. I would even have the materials for it. But to save time I'm thinking about using three pieces of re-bar (see picture) under the last layer of bricks to create three evenly spaced points to rest the flue on. Then fill the gap between round flue and square bricks with clay/cob.  Progress today  There's just one thing I didn't pay attention: the primary air inlet hole is 4,5cm x 11,3cm (=50,85cm²) on the outside, but the opening on the firebox side is only 4,5cm x 11,1cm (=49,95cm²). Problem? I could somehow file it open once hardened. |
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Post by firerob on Oct 2, 2023 9:34:20 GMT -8
It is a 2 bell system. There is a detailed analysis on the 125mm BBR here: results-chaining-batch-box-bells. I decided from this analysis to chain the 200mm BBR bells on top and bottom as proposed by Peterberg in this post. The results are not as good as I expected. I am still working on it. Ok, wow, it gets very complex very fast, I guess. There's not much I can say to that, I'm just not there (yet).
All I can do is hope that our single bell BBR will be enough to heat our 36m² (105m³) house. If not, then I don't know...
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Post by peterberg on Oct 2, 2023 12:21:16 GMT -8
I like your idea. I would even have the materials for it. But to save time I'm thinking about using three pieces of re-bar (see picture) under the last layer of bricks to create three evenly spaced points to rest the flue on. Then fill the gap between round flue and square bricks with clay/cob. Saving time now, more work in future. The cob will crack in due time because of expansion and contracting of the pipe. Keep a bucket with wet cob at hand to repair if and when necessary. There's just one thing I didn't pay attention: the primary air inlet hole is 4,5cm x 11,3cm (=50,85cm²) on the outside, but the opening on the firebox side is only 4,5cm x 11,1cm (=49,95cm²). Problem? The difference is minor, don't worry about it. Maybe you have to keep the door open a crack a little bit longer until the core is heated up. Normal startup procedure, nothing fancy. |
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Post by firerob on Oct 3, 2023 7:41:54 GMT -8
 What is the latest knowledge regarding that chamfer at the bottom back of the riser (I think I saw it called "sweep" before?)? Is this recommended or is it considered obsolete? It looks like it wasn't put in on the video of the Mallorca build.
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Post by peterberg on Oct 3, 2023 11:34:21 GMT -8
No back sweep in these risers anymore. In practise, there will form an ash slope in the course of a few weeks. In a month or three this ash will turn into clinker, it won't grow anymore since all surplus ash is blown away. Save yourself the hassle of fitting the right amount of slope. It will form naturally anyway, perfectly adapted to your heater and chimney draw.
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Post by firerob on Oct 4, 2023 9:41:32 GMT -8
(Note: p-channel in the front)  |
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Post by firerob on Oct 5, 2023 8:22:04 GMT -8
Riser still needs one more layer. Peter, took your advice once again  (from a washing machine side panel)    |
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Post by martyn on Oct 5, 2023 10:53:39 GMT -8
Looks nice and tidy, it will be a powerful stove!
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Post by peterberg on Oct 5, 2023 12:18:57 GMT -8
I fail to see the cut-back at the riser facing end of the p-channel. Are you aware of that?
The flange of the washing machine side panel is pointing upwards. Better to have it downwards if you want to avoid leakage of condensation fluid. Of all the pipes, use male ends (crimps) down.
You are doing nice, please go on!
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Post by firerob on Oct 5, 2023 21:39:34 GMT -8
The flange of the washing machine side panel is pointing upwards. Better to have it downwards if you want to avoid leakage of condensation fluid. Of all the pipes, use male ends (crimps) down. I don't have the typical crimped male ends. The flue elements are just slightly conical tubes (tighter end fits into wider end of other) and I needed to avoid sliding too far into each other with 2 M4 screws+bolts per element (on the "male" side which points down, like you suggest also). What I could do is make the metal plate hole a bit wider, flange down and slide the male end in and keep it from sliding through with out-sticking screws. Then the condensation fluid will drip into the stove instead of collecting on top of the metal plate. You are doing nice, please go on! That's good to hear!! Thank you. I fail to see the cut-back at the riser facing end of the p-channel. Are you aware of that? Yes, I still need to take the flex to the p-channel. The thing is, that if I lay the channel directly on top of the firebox lid, then the front end of the channel sits too deep and I would have to flex a piece out of the frame of the door. So, the channel will have to sit a few cm higher (on firebrick off-cuts, maybe), which changes all the flex marks on the port end of the channel. I'm waiting with the flexing until the lid, insulation and
raise support for channel are in place. If the overhang of the channel is 20mm (from top of the port), then how big of a piece should I cut out (for Bernoulli effect)? Is 10mm enough?
How far away from the firebox back wall should the channel come down? Could it be directly close (almost touching) or should I keep a distance for turbulences? By the way, should the channel be insulated? Is it better to put the firebox insulation under or over the channel?
And one more question: the channel is not entirely in 90° angles (see image). I would like to put the long end of the channel straight, so that it sits centered with the door. But then at the short end of the channel the left side is a few mm farther away from the port than the right. I mean, there's nothing I can do now, but do you think this could screw with the Bernoulli effect?
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Post by firerob on Oct 5, 2023 22:06:44 GMT -8
Looks nice and tidy, it will be a powerful stove! Thanks martyn!
I very much hope so!
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Post by peterberg on Oct 6, 2023 2:14:31 GMT -8
What I could do is make the metal plate hole a bit wider, flange down and slide the male end in and keep it from sliding through with out-sticking screws. Then the condensation fluid will drip into the stove instead of collecting on top of the metal plate. That would be the best way to do it, condensation fluid is smelly and is making black stains. So best to avoid it. If the overhang of the channel is 20mm (from top of the port), then how big of a piece should I cut out (for Bernoulli effect)? Is 10mm enough? In general, the overhang should be the same as the thickness of the channel's duct. The rear cut-out should be the same as the overhang, so the back wall of the channel is flush with the top of the port. In your case: overhang 20 mm, cut-out 20 mm. How far away from the firebox back wall should the channel come down? Could it be directly close (almost touching) or should I keep a distance for turbulences? The channel should rest directly against the firebox rear wall. By the way, should the channel be insulated? Is it better to put the firebox insulation under or over the channel? I would say: under the channel. That way, the incoming air through the duct would be cooler. Which in turn would mean a better cooling of the steel. Please refrain from blocking the entrance of the p-channel, the metal will be spalling in short order during every burn. And one more question: the channel is not entirely in 90° angles (see image). I would like to put the long end of the channel straight, so that it sits centered with the door. But then at the short end of the channel the left side is a few mm farther away from the port than the right. I mean, there's nothing I can do now, but do you think this could screw with the Bernoulli effect? It might be that there will be side leakage, yes, which isn't a good thing but not dramaticly so. Maybe you could grind a little bit off the brick that's against it? |
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Post by firerob on Oct 6, 2023 2:50:46 GMT -8
I would say: under the channel. That way, the incoming air through the duct would be cooler. Which in turn would mean a better cooling of the steel. Please refrain from blocking the entrance of the p-channel, the metal will be spalling in short order during every burn. Ok, firebox insulation goes under channel. Additionally I could wrap the channel (just on top of fb) in superwool, if this would further help against spalling. It should, no? It might be that there will be side leakage, yes, which isn't a good thing but not dramaticly so. Maybe you could grind a little bit off the brick that's against it? Or I could press the channel in wet mortar to form a seal for the left side and the top of the cut-out. If there's no veto, I'll probably do this. I could do this even now-ish before I fix the lid on. |
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Post by peterberg on Oct 6, 2023 6:55:08 GMT -8
Additionally I could wrap the channel (just on top of fb) in superwool, if this would further help against spalling. It should, no? No. it won't. Th heat from the top of the firebox will be much more as compared to what is happening in the bell. At some point, the p-channel will start to degrade. Or I could press the channel in wet mortar to form a seal for the left side and the top of the cut-out. If there's no veto, I'll probably do this. I could do this even now-ish before I fix the lid on. Sorry to say, the metal will expand a lot more than the bricks and the mortar so it'll fall off eventually. |
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(from a washing machine side panel)
