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Post by esbjornaneer on Apr 27, 2019 1:28:59 GMT -8
The other detail that looks different to me is that there is a difference in the floor height in the actual port and the rear 160mm of the heat riser stub. It may just be a drawing issue but the floor in Peter's drawing is the same height from the back of the heat riser stub through the whole of the port. Looking forward to more posts. And thank you Peter for the clarifications here.
Also: the end port in the afterburner/top box is not the full width.
2.9.1.0
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Post by peterberg on Apr 28, 2019 2:01:20 GMT -8
The ISA of the Bell is approx 7 m² and the distance between exhaust and top of the bell 30 cm. I seem to have missed this, that 7 m² is too small for a 200 mm system, my (checked) dimension table says 9.4 m². Anything smaller will result in higher exhaust temperatures. Your projected ISA is about 74.5% of the recommended value. You could do one of two things: make the system size smaller or the bell larger. In case that bell is a fixed size but you need the larger system because of the depth of the firebox? An alternative is to use a smaller system with an extended firebox depth. Up to 25% is no problem at all, this has been checked a number of instances. System size would be 175 or 180 mm in order to match the 7 m² ISA.
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Post by stefanvh on Apr 29, 2019 8:47:47 GMT -8
Looks much better now. Remarks: shortest distance from the port's corner to the side of the channel stub is 49 mm in your drawing. This distance should be half of the port's width, in this case 35 mm. I moved around a bit with parts: the forward corner of the channel stub should be 14 mm away from the rear wall's face as a consequence. I'll do a picture to clarify. I think I kept the distance parallel to the floor channel to 35 mm (i.e. the horizontal part ends 35mm before the port). Thanks for pointing this out. The idea is to add a heat exchanger (steel pipe probably) to the back wall of the bell (inside of the bell). I figured that this would greatly increase the heat transfer so I intentionally kept the ISA smaller than recommended. Higher exhaust temperatures will decrease the efficiency, but I think that would be less of a problem than an exhaust temperature which is too low. The other option is to use a heat exchanger at the outside of the bell, but I am not sure if the temperature (and thus heat transfer) is high enough to heat water to the appropriate temperature (~60 C). I expect that the outside temperature of the bricks will drop fast when I extract heat with water (and as a result, the water won't get to the right temperature). I also couldn't really find any builds with a similar setup as they all seem to heat water directly with the fire/exhaust gas.
About the pile of bricks: I basically just drew a bunch of them such that the firebox is at the right height. A steel frame is probably a better option if I am 100% sure what the dimensions will be. For the top: you're right, haven't thought about warping yet. It's probably even impossible to get it airtight because the warping will open any seems . I'll probably use the firebricks on the insulated steel angles if I don't come up with a better idea. Ideally I'd build a system that I can tinker with later, but unfortunately bricks and mortar aren't really flexible.
The other detail that looks different to me is that there is a difference in the floor height in the actual port and the rear 160mm of the heat riser stub. It may just be a drawing issue but the floor in Peter's drawing is the same height from the back of the heat riser stub through the whole of the port. Looking forward to more posts. And thank you Peter for the clarifications here. Also: the end port in the afterburner/top box is not the full width.
2.9.1.0 You're right, there should be an extra brick in the floor underneath the port. The port height was measured from the floor, but I forgot to draw the extra brick underneath the port. I'm not sure what you mean with the last sentence? I kept the size of the end port relative to Peter's reference drawing.
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Post by esbjornaneer on Apr 30, 2019 4:01:05 GMT -8
Peter's end port is the full width of the top box. You can still make it the same area by making it the recommended(=wider) width but not as deep (from front to back). Saying it with numbers: Your end port, out of the core, seem to be 206mm wide & 80mm deep (=16480mm^2). Full width of top box 292mm as width of end port would give a depth of ~56.4mm to the end port while retaining close to the same area opening (=16468.8mm^2).
Hope this is clear enough without being annoying. I never know if I give too much info or too little :/
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Post by stefanvh on May 1, 2019 6:36:05 GMT -8
Peter's end port is the full width of the top box. You can still make it the same area by making it the recommended(=wider) width but not as deep (from front to back). Saying it with numbers: Your end port, out of the core, seem to be 206mm wide & 80mm deep (=16480mm^2). Full width of top box 292mm as width of end port would give a depth of ~56.4mm to the end port while retaining close to the same area opening (=16468.8mm^2). Hope this is clear enough without being annoying. I never know if I give too much info or too little :/ I see. I noticed that the end port was 50mm smaller than (half) outside width. I didn't realize that this is actually just the size of the outer wall .
You're never annoying as long as you're right . And even if, feedback is always helpful.
Thanks, I'll change the end port to be full width.
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Post by stefanvh on May 2, 2019 1:57:04 GMT -8
I made a change to the bell design, also incorporating the wall to which it will be build:
Instead of a heat exchanger inside the bell, the idea is to extract the heat from the back wall instead. I left a small open space in which a heat exchanger can be placed. I might not reach the desired temperature, but it should at least somewhat work for low-temperature floor (central) heating and there is no chance of leaks or explosions. The ISA of this Bell is ~9.3 m².
I noticed that Peter made an update to the floor channel on his site. I'll have a look at it and update it later.
Edit: And an update of the core:
I made some slight modifications and scaled Peter's new floor channel to the correct dimensions.
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Post by esbjornaneer on May 4, 2019 1:14:17 GMT -8
Hello Stefan, I realised after the last post that I should have let you know that Peter just made some more clarifications in his thread. I am quoting it below as it is suggesting other modifications to your core: Peter is there any advantage of the 'stumbling block'/'hanging brick' being a full brick thickness rather than a split? I know it may affect combustion compared to your tested results... and should a split in that case be placed 1) 250mm from the back wall of the afterburner like the full brick, 2) central in full size brick, or 3) at the trailing end of the full size brick? Only asking as you said it is very important to get the location right for it. And thinking that it may be good to have less mass? Oops... I am not sure what you mean so I'll give you the dimensions I used. The stumbling block as it is now has been done in two sizes: 25 mm high and 63 mm wide seen in stream direction, and second 25 mm high and 54 mm wide in stream direction. The second was done in hard firebrick since my last insulating firebrick broke up in half a dozen pieces. Results seemed unchanged so the width is still within critical limits I'd say. There's a marked difference between a block or a trip wire though. The block version is the stable one of the two. Location of the different parts: the stumbling block is centered in the depth of the top box, so center of box and block are at the same location. The end port is centered in the front half, it has been different now and then but I think this is the best location. I'd say the block need to have a certain minimum width in order to work as intended. A block with dimensions 25 mm high and 25 mm wide isn't advisable in that case. Something tells me that's what you meant, yes? To answer your last question, I don't think mass is an issue in this case. Part of the rear half ceiling is hard firebrick now and nothing has been changed results-wise. I'm gearing up for building the hard refractory reference design, within a month (or maybe two) we'll know whether mass in the core makes a large difference or not at all. Or something in between.
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Post by stefanvh on May 4, 2019 8:07:53 GMT -8
Thanks for letting me know. I actually didn't pay much attention to the stumbling block yet as I thought it wouldn't be that critical, but I'm probably wrong about that. But since my design is not 100% following Peter's design due to the larger size and different firebricks, I'll probably have to do some testing myself. I expect that it will probably bring along some complications as Peter has often encountered during his testing, but I'm pretty sure that it will perform better than the wood stove that we currently have.
Edit: Drawing for the door + frame:
Edit2: I actually made a miscalculation on the air inlet. Fixed it:
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Post by peterberg on May 4, 2019 10:55:00 GMT -8
The stumbling block is a critical part, yes it is. Your "design" is upscaled and might be built of different materials but it's still mine. I am very sure what it will do without one or more of the finer details. And I am very curious how you want to do "some testing" yourself. Buying a Testo and get aquainted with it perhaps?
Let's put it straight: I can't advise you anymore when you want to do your own thing with it. Please go ahead.
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Post by stefanvh on May 4, 2019 13:00:37 GMT -8
I by no means want to discredit your work Peter. I try to follow your design as strict as possible, but due to the larger scale and different materials it is hard to follow it exactly for 100% and still create something that is easy to build. It is comforting to hear that it will still do without some of the finer details. You're right, there is no real way for me to actually do some testing because I don't have the right equipment (I wish I did). With testing I meant for example to change the location of the stumbling block or place a constriction in the upper box for example (as I believe you did in your early experiments). But when I think of it, this would make no sense because I can't test the CO levels etc. So I would basically have to do an educated guess if something did have an effect....
I often seem to think that some design parameters were picked somewhat arbitrarily, but you really seemed to have tested everything. E.g. the step in the riser seems like a minor detail to the untrained eye, but as you said it is quite important. But this is also where my problem arises: do the changes I made to the finer details to be able to build it more easily with the available materials also have an effect? The engineer in me would like to test it all, but I should probably leave it to the people with the right equipment . If the stove will burn without smoke back or setting the house on fire, I'm happy with the result.
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Post by peterberg on May 4, 2019 13:16:39 GMT -8
It is comforting to hear that it will still do without some of the finer details. That's not what I said, it was:" I am very sure what it will do without one or more of the finer details." Not comforting at all, just a warning that leaving out those details could create a less than desirable heater.
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Post by stefanvh on May 6, 2019 7:03:22 GMT -8
It is comforting to hear that it will still do without some of the finer details. That's not what I said, it was:" I am very sure what it will do without one or more of the finer details." Not comforting at all, just a warning that leaving out those details could create a less than desirable heater. Ouch I misread that but I get what you mean. Leave out the crucial details and it won't work as expected. I now added the stumbling block to the drawing, but as with the rest of the design the location and thickness are slightly different because of the used material.
Thanks for the help so far.
Edit: This is a scaled version of the RC sketch overlayed on my drawing:
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Post by stefanvh on May 17, 2019 6:12:55 GMT -8
I have a question with regard to the riser insulation. Usually the riser seems to be made of (fire)bricks and then wrapped in superwool on the outside. I noticed that Pinhead's 5 minute riser actually has the superwool on the inside. So I'm wondering if the superwool can also be used to insulate the riser on the inside in a DSR/batch rocket? I would think that it would degrade quickly, but if it works in the 5 minute riser, what's the reason no one seems to use it to insulate the bricks on the inside?
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Post by peterberg on May 17, 2019 11:09:38 GMT -8
Funny, I am in the process of rebuilding the thing using hard refractory materials. I created the riser by folding 1" superwool in the rear compartment of the bottom box, on three sides. This core isn't ready yet, so I don't know at the moment what the effect will be. No other insulation materials planned so far.
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Post by stefanvh on May 24, 2019 7:08:09 GMT -8
The door has been constructed, but apparently I didn't make it clear that the air inlet should be able to be fully opened, so it's now somewhat restricted. Here are the dimensions for my design. I tried to stay as close as possible to the dimensions of the DSR/batch rocket design, but due to restrictions in the material it sometimes differs a bit (e.g. to get the exact area for the floor channel would require some non-standard steel ducts). Building starts next week so we'll see how it will perform. In the riser an additional 25mm superwool blanket will be placed similar to Peter's latest build (5 minute riser style).
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| % |
| Riser |
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| Width | 195 |
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| Height | 195 |
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| Area | 38025 |
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| Port |
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| Width | 70 |
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| Height | 330 |
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| Area | 23100 |
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| 60.75 |
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| Exhaust | Width | 314 |
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| Depth | 80 |
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| Area | 25120 |
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| 66.06 |
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| Floor channel | Horizontal |
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| Width | 70 |
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| Height | 45 |
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| Area | 3150 |
| 8.28 |
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| Vertical | Width | 40 |
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| Height | 40 |
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| Area | 1600 |
| 4.21 |
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| Door air inlet |
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| Width | 50 | 160 |
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| Height | 60 | 60 |
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| Area | 3000 | 9600 |
| 7.89 | 25.25 |
www.dropbox.com/s/8bbcn7xl9ryxm6a/DSR%20200-4%20new%281%29.skp?dl=0
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