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Post by peterberg on Sept 29, 2023 4:18:08 GMT -8
With the heavier core (firebricks instead of perlite) we need to re-inforce the L-profile support structure today. Just two steel legs that are resting on the bell floor under the support structure would do it. Are you aware of the fact that the walls of the bell are to be built all around the firebox? Of course with 12 mm superwool between bell wall and box, bottom excluded. |
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Post by firerob on Sept 29, 2023 4:49:25 GMT -8
With the heavier core (firebricks instead of perlite) we need to re-inforce the L-profile support structure today. Just two steel legs that are resting on the bell floor under the support structure would do it. Are you aware of the fact that the walls of the bell are to be built all around the firebox? Of course with 12 mm superwool between bell wall and box, bottom excluded.
Ehm...I hope I understand you correct: the bell walls you see on the picture will be build up to ca. 1,7m high and then comes another 40cm double skin bell (with cfb in between). The core out of firebricks will be wrapped in 13mm cfb (including under the core). But I wanna build the core first and then continue the bell walls (or maybe build them parallel).
Is that what you were trying to make me aware of? (Thanks for this by the way; every hint is appreciated)
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Post by firerob on Sept 29, 2023 9:26:48 GMT -8
Re-inforced the core support. Ready to insulate and put down floor of core.   |
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Post by peterberg on Sept 29, 2023 12:19:39 GMT -8
It looks the right way, according to the pictures. In one picture there's a piece of superwool visable. Build the core first, the walls and deck of the firebox flush with the outside of the bell. Then a generous strip of that superwool around the firebox, right in the place where the bricks of the bell's wall would meet the sides of the firebox. THis way, there's a flexible medium between bricks and firebricks, to provide an expansion and slip joint for the expansion of the core.
Is this clear now?
The metal frame is a good solution, it'll ensure the exhaust gases are freely flowing into the exit opening to the chimney.
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Post by firerob on Sept 29, 2023 22:36:38 GMT -8
[..] Build the core first, the walls and deck of the firebox flush with the outside of the bell. Then a generous strip of that superwool around the firebox, right in the place where the bricks of the bell's wall would meet the sides of the firebox. THis way, there's a flexible medium between bricks and firebricks, to provide an expansion and slip joint for the expansion of the core. Is this clear now? [..] No, I'm sorry, I still don't understand. [..] flush with the outside of the bell. [..] Do you mean after the core is up, build the bell up to be flush with the top of the firebox (before insulating)? [..] where the bricks of the bell's wall would meet the sides of the firebox. THis way, there's a flexible medium between bricks and firebricks, to provide an expansion and slip joint for the expansion of the core. [..] The bell and the firebox meet only in the front (door). On all the other sides there are 13-15cm of air space between core and bell.
Very sorry if I'm obtuse. Please clarify! Maybe this helps: Next I wanna put down a layer of cfb, on top of that the floor bricks of the whole core, then build the firebox walls and lower part of riser on top of the floor bricks, then insulate with cfb all around. Like on this picture from hof's build: What I don't know yet is, how does the cfb stick to the walls of the core?
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Post by peterberg on Sept 30, 2023 3:22:54 GMT -8
Look at the picture you posted yourself. The firebricks of the firebox are a bit back from the outer surface area of the bell. What I meant was: keep these in the same vertical plane, so the ends of the firebricks are flush with the outside of the bell.
The strips of superwool (the white fluffy stuff) which are at the sides of the firebox provides an expansion joint as well as a slip joint between the firebricks and the normal bricks of the bell's walls. This is done because of the expansion of the firebox when it gets very hot, it will expand in horizontal and vertical direction quite a bit.
The easiest way to attach the rest of the superwool (the white etc.) around the firebox and riser is using some of the same refractory mortar you are using for the firebox itself.
Just look at the picture: it's nearly exactly what I meant.
Still not clear? I give up.
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Post by firerob on Sept 30, 2023 3:35:20 GMT -8
Look at the picture you posted yourself. The firebricks of the firebox are a bit back from the outer surface area of the bell. What I meant was: keep these in the same vertical plane, so the ends of the firebricks are flush with the outside of the bell. The strips of superwool (the white fluffy stuff) which are at the sides of the firebox provides an expansion joint as well as a slip joint between the firebricks and the normal bricks of the bell's walls. This is done because of the expansion of the firebox when it gets very hot, it will expand in horizontal and vertical direction quite a bit. The easiest way to attach the rest of the superwool (the white etc.) around the firebox and riser is using some of the same refractory mortar you are using for the firebox itself. Just look at the picture: it's nearly exactly what I meant. Still not clear? I give up. Yes! It's clear now! Ok, I understand. Thanks for your patience.
Here's a mockup of the firebox, how I plan to build it. And I guess, it is the way you recommend: flush with the outside of the bell bricks. I'll put cfb (the white fluffy stuff) around the firebox where it touches the bell and around the door where it touches the firebox.
By the way, the primary air inlet is 12cm x 4,2cm (=50.4cm²). Not the 7,1cm x 7,1cm - is this ok? Note: this is just a mockup: the riser will closed in the back and the back wall bricks will be cut to size, etc... |
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Post by peterberg on Sept 30, 2023 7:05:19 GMT -8
Here's a mockup of the firebox, how I plan to build it. And I guess, it is the way you recommend: flush with the outside of the bell bricks. Now shift the firebricks of the firebox walls forward, so they are flush with the outside of the bell bricks as well. I'll put cfb (the white fluffy stuff) around the firebox where it touches the bell and around the door where it touches the firebox. CFB is short for Ceramic Fibre Board, it's white but not fluffy. The fluffy stuff is Morgan Thermal Ceramics Superwool. The rest is correct bar one small detail: don't put superwool under the firebox. For one, it isn't necessary but it'll create a flexible base for the firebox so the walls will get wobbly during the build while the wool is gradually more compressed. By the way, the primary air inlet is 12cm x 4,2cm (=50.4cm²). Not the 7,1cm x 7,1cm - is this ok? Depends on what you want, a floor channel/ primary inlet combined would need 63.6cm². With the secondary air channel (p-channel or floor channel) separated from the main inlet it would be OK. The retangular shape of the inlet is OK as well. Note: this is just a mockup: the riser will closed in the back and the back wall bricks will be cut to size, etc... It looks like you are going to build this firebox with split firebricks, the thin ones. It can be done, but stability is less and you have to be very careful with loading of the firebox, please don't throw fuel in, this will dislocate the rear wall bricks in next to no time. |
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Post by firerob on Sept 30, 2023 10:31:05 GMT -8
CFB is short for Ceramic Fibre Board, it's white but not fluffy. The fluffy stuff is Morgan Thermal Ceramics Superwool. Oops, sorry. I thought CFB stands for Ceramic Fibre Blanket. I'll call it superwool from now on. The rest is correct bar one small detail: don't put superwool under the firebox. For one, it isn't necessary but it'll create a flexible base for the firebox so the walls will get wobbly during the build while the wool is gradually more compressed. Ok, I won't. I am suprised though, I have to admit. I thought in the core it's about little mass and lots of insulation and now I'm building the core with lots of mass and no insulation (at least under the floor). By the way, the primary air inlet is 12cm x 4,2cm (=50.4cm²). Not the 7,1cm x 7,1cm - is this ok? Depends on what you want, a floor channel/ primary inlet combined would need 63.6cm². With the secondary air channel (p-channel or floor channel) separated from the main inlet it would be OK. The retangular shape of the inlet is OK as well. Ok, sweet. We have a p-channel in the making, so we are good. Thank you!
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Post by peterberg on Sept 30, 2023 11:56:52 GMT -8
I thought in the core it's about little mass and lots of insulation and now I'm building the core with lots of mass and no insulation (at least under the floor). As usual, it isn't an on-off situation. Please bear with me and read the following explanation. This is how I see it, everybody is entitled to have their own opinion. In the case of a J-tube rocket mass heater, the small core is (largely) outside the barrel and the bench. Logically, the core need to be insulated so it would heat up quick, being on working temperature early in the process. A batchrocket mass heater is slightly different in this respect, the complete core is inside the main bell. The core is also a lot bigger than the J-tube's core. Normally, while the thingy is fired up every day, the bell and core won't cool off, not at all. The function of the insulation around the core is to slow down heat extraction by the core's outside. In short, initially the core won't take up heat from the outside of it. But after a while the temperature of the bell will rise so the heat will go through it, due to the higher temperature difference. And the core will be heated from the inside as well, of course. |
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Post by firerob on Sept 30, 2023 23:32:46 GMT -8
The function of the insulation around the core is to slow down heat extraction by the core's outside. In short, initially the core won't take up heat from the outside of it. But after a while the temperature of the bell will rise so the heat will go through it, due to the higher temperature difference. And the core will be heated from the inside as well, of course. I see. And that is why the outside of the core is not calculated into the ISA, I guess. And this is also why the 5-minute riser is so successful, I assume. Because there's no heat extraction happening in the riser. So, in your opinion, would it be worth the effort to insulate (at least) the lower 40cm of our riser from the inside with superwool? (riser build from split bricks with outside superwool) Would this make a noticable difference in the start-up/general behaviour? |
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Post by peterberg on Oct 1, 2023 9:13:27 GMT -8
So, in your opinion, would it be worth the effort to insulate (at least) the lower 40cm of our riser from the inside with superwool? (riser build from split bricks with outside superwool) Would this make a noticable difference in the start-up/general behaviour? In my opinion, it would make a difference when started cold. For an inhabited living space, that would be just once per season. Frankly, I fail to see how you would build that, the riser needs to be a straight tube. Place the bricks wider apart in the first 40cm, superwool 1" inside (the 1/2" isn't sturdy enough) and the rest of the riser bricks won't fit on top of the base. Just a thought: most people with superwool risers have a barrel as bell. They are able to lift the barrel when maintenance is required. In order to reach the riser the brick bell need to be demolished partly in your case. Please keep to the tried and tested... |
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Post by firerob on Oct 1, 2023 22:47:33 GMT -8
Ok. We'll stick to the tried and tested. Bedankt. This is where the flue will sit on (there will be one more layer of bricks)  The core floor mortared in place (without superwool under)  |
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Post by peterberg on Oct 2, 2023 5:07:42 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. This is utterly untrue, in order to have the same capacity to transfer gas through, aerodynamically speaking, the sides of the square should be the same size as the diameter of the circular chimney pipe. The hot, fast streaming core is always more or less round in a vertical channel, the corners of the square impose more drag despite it's larger cross section.
I sincerely hope that opening you have there is 180 mm square for a 180 mm system, not smaller. It might be that you already got that, in that case the following is not directed to you.
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.
Place the plate between layers of bricks to hold it in place, of course in such a way there's no obstruction at all. In order to avoid deforming the plate while bending and hammering: use the bottom of an old barrel, while it's still in place. Once the hole is right, use a grinder to cut it out to the right size. I did that a couple of times, (first for the Mallorca build) and it worked flawlessly every time.
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Post by fiedia on Oct 2, 2023 5:32:15 GMT -8
Hello firerob, Regarding temperatures inside the bell, I did some measurements inside my 200mm BBR. Here is a typical run :
You can see that the brick ceiling above the HR will be too hot for normal bricks. You would better use refractory material. In contrary, the temperature decreases very rapidly underneath the ceiling. One row of refractory bricks under the bell ceiling should be enough.
Just to be real clear on your chart, does "-22cm" and "-44cm" mean these temps were taken on the inner bell wall at 22cm and 44cm below the ceiling? Someone is using concrete as their bell wall material in another post and I always read that was a no-no. But if the temp drops that low just 22cm below the bell ceiling... I'm tempted to use concrete at least at the base of the bell. Maybe even halfway up before transitioning to red brick (then fire brick above the riser of course.) |
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