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Post by mwalimu on Oct 19, 2014 7:33:48 GMT -8
In the long run I try to make such stoves legal, by getting approval as a Kachelofen / Grundofen / masory heater. But for the experimenting, it has to be done undercover... BTW, a batch heater seems better comparable to a masonry heater than a j-feed mass heater with drum.Not really. A J is using the same channel system. Both styles are masonry heaters. The materials used and shapes throw people off. With a batch heater you can install a door for the feed chamber (even allowing enough air to pass in), looking then like a normal mason heater. A j-style heater has an "open" fire, the hot metal drum and the possibility of back-smoking / burning if too much ashes are left in the burn chamber. Looks somehow dangerous and not really fool proof...
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Post by Deleted on Oct 19, 2014 7:40:25 GMT -8
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Post by Daryl on Oct 19, 2014 8:13:28 GMT -8
Not really. A J is using the same channel system. Both styles are masonry heaters. The materials used and shapes throw people off. With a batch heater you can install a door for the feed chamber (even allowing enough air to pass in), looking then like a normal mason heater. A j-style heater has an "open" fire, the hot metal drum and the possibility of back-smoking / burning if too much ashes are left in the burn chamber. Looks somehow dangerous and not really fool proof...To simplify the J, it is a feed tube/burn chamber with a long channel. The metal drum can always be switched out or covered. The drum is a form of channel/bell. The reason most J's smoke is the draw isn't correct. The J uses the same gas flow science as masonry stoves. I know when people first see the J they think, "What the heck?". It really isn't that complicated.
Anyway, that is how I look at it. Good luck with your build.
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Post by mwalimu on Oct 19, 2014 11:04:46 GMT -8
1. We have a lot of Waldbauern / Forest Farmers here around, dealing with wood chips. The driest you can get have about 25-30% moisture. And the heaters are designed to work with that moisture. Wikipedia quotes: woodchip systems are typically designed to cleanly and efficiently burn "green chips" with very high moisture content of 43–47% (wet basis) 2. Thank you for the capillary advice! An idea starts to grow in my brain...
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Post by mwalimu on Oct 19, 2014 11:39:46 GMT -8
Hi again,
Thank you all for your input. So my plans have slightly changed: -in upper floor Peterberg batch box 6" or equivalent, riser direct into first bell -for the experiment a 150mm steel pipe as heat riser, later replaced with a ceramic (schamotte / fire clay) pipe -No experiments with a russian stove crevice -walls of the bell with upright bricks laid with adobe Mortar. -1st bell 2m high 1m long, inside 20 cm wide -2nd bell a bench about 1m long, 60 cm high -one metal duct uninsulated down to the ground floor for further cooling -checking draft/blast and temperature - if temperatures are above 60°C, a 3rd bell out of bricks will be added . - if below 60°C, the 3rd bell will be a plastic tank with about 10 cm of water on the floor. Wet stripes of fabric will hang down from the top of the Tank / Bell into the water to cool down the gasses further, to condense the vapor, and to clean the gasses from micro particles. - There will be an overflow at 10 cm above the floor to drain the excess of water into the sewage plumbing. - If necessary, a fan with speed control to suck out the gasses. But I hope the cooling gasses will sink down by own weight. - If necessary, a radiator will be connected for cooling down the water further. But I hope the 1000 liter water tank will have a surface big enough to radiate the heat away, coming down to 30°C.
Further remarks are welcome!
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Post by peterberg on Oct 19, 2014 11:55:41 GMT -8
You need a fan to do that, almost certainly. Batch boxes and all rocket heaters for that matter, are heavily depending on gas velocity. When this gas speed slows down the afterburn flame will stop and the combustion will become very dirty.
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Post by mwalimu on Oct 19, 2014 12:55:07 GMT -8
You need a fan to do that, almost certainly. Batch boxes and all rocket heaters for that matter, are heavily depending on gas velocity. When this gas speed slows down the afterburn flame will stop and the combustion will become very dirty. Hmm, I was lured to that idea through some comments from permies.com, claiming that the cooling of the drum will create a pull and the gasses can be exhausted horizontally, and that the heat lifting the gasses is not needed. Now I found out, that its not really true. Still I have a small hope that gasses will sink down when they are cooled. As I see, nobody has tried this yet to cool down the gasses this much.
Tanks for commenting.
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Post by satamax on Oct 19, 2014 13:45:44 GMT -8
It's been tried, there's a thread at permies, and a video on youtube. Thought, it's proven to be very unreliable.
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Post by mwalimu on Oct 19, 2014 14:32:37 GMT -8
You need a fan to do that, almost certainly. Batch boxes and all rocket heaters for that matter, are heavily depending on gas velocity. When this gas speed slows down the afterburn flame will stop and the combustion will become very dirty. There is theory and practice; before I try something out I will try to understand the theory, then I will try out, if it s working. So we agree: We need a draft in the system to get a certain velocity and a clean combustion. The question is: Can a stove create a draft though cooling gasses? In an normal stove, the hot gasses rise, and they are escaping in an exhaust, which is somehow higher than the fire chamber. They go even down sometimes, and then up again, provided there is enough draft through rising heat at the end of the system. But the draft needed is not much. Now the other question is: Can this system be reversed? Means: gas is cooled down and is sinking down, preferably to an even lower outlet. Let's check it from my project: The gas is pushed up trough the riser, getting a certain velocity. The highest point and the hottest temperature is at the end of the riser or on the top of the bell. From now on, the heat is decreasing, The colder gasses are sinking down and are trying to move to the lowest part of the system. In the upper floor the bell is about two metres high above the bottom. The cooling gasses are sinking down. Luckily, the bells are connected on the bottom so no rise is needed for the gasses. In the second bell, the gasses are cooling down further, either getting less resistance or even creating a slight vacuum. Then down the metal pipe 3 metres and again cooled, because there is no insulation around it. Falling down and decreasing in volume, creating a draft. Then passing vertically through one or two bells on the bottom, still decreasing in volume. (Getting down in the sewage system would add again 2 metres difference in height plus again cooling down to soil temperatures of about 8°C.) For me it seems to be possible that thus a draft is created, at least enough to avoid a resistance against the blast of the riser. I even think it will be a quite good draft. When the system will be installed in one story, then even the difference between the first bell and the outlet at the End of the last bell should be enough. Why it seems impossible for practitioners that the downdraft is working? 1. No one has cooled the gasses down this far. 2. No one has built a stove with always sinking flu. So far the theory. Any logical or physical flaws?
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Post by mwalimu on Oct 19, 2014 14:39:41 GMT -8
It's been tried, there's a thread at permies, and a video on youtube. Thought, it's proven to be very unreliable. The video claiming this I know. But isn't there always a slight rise at the end of the exhaust, lets, say about five feet above ground? And there is a thread where Erica Wisner is telling lots of advantages for both vertical and horizontal outlets. But is there als a thread or video of the exhaust getting out straight on ground level?
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Post by Donkey on Oct 19, 2014 20:23:14 GMT -8
Why it seems impossible for practitioners that the downdraft is working? 1. No one has cooled the gasses down this far. 2. No one has built a stove with always sinking flu. So far the theory. Any logical or physical flaws? Welcome to the boards, mwalimu. I have built a stove that works on the sinking flue principle. It built it as an experiment in my yard. It worked well enough under the conditions in which I did the experiment. The MAJOR problem is that it will ONLY work on hot days, when you don't need the stove. You have to GUARANTEE that the exhaust will ALWAYS be colder than the outside air. Try that trick in a northern climate (Germany?), with 4 feet of snow and 20 below zero F.. The cold chimney can NOT be guaranteed, and when you need it most, it is least likely to work.
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Post by mwalimu on Oct 20, 2014 2:01:49 GMT -8
I have built a stove that works on the sinking flue principle. It built it as an experiment in my yard. It worked well enough under the conditions in which I did the experiment. The MAJOR problem is that it will ONLY work on hot days, when you don't need the stove. You have to GUARANTEE that the exhaust will ALWAYS be colder than the outside air. Try that trick in a northern climate (Germany?), with 4 feet of snow and 20 below zero F.. The cold chimney can NOT be guaranteed, and when you need it most, it is least likely to work. Thank you for your response and insight. My theory was: Gasses which are cooling down try to sink to the coolest pace, thereby creating a draft towards a lower output / exhaust The theory coming from your experiment is: The exhaust gasses have to be lower than the ambient air to create a draft downwards. So the question is: What matters - inside or outside temperatures? Your experiment was outside in the yard. Did you really cool down the gasses below the ambient temperatures? Went the exhaust pipe at the end downwards, upwards or straight horizontally? Lets think about a hot day, 30°C / 85°F. So your exhaust temperatures reached let's say 25°C / 75°F? Did you measure that? How were you able to cool it down this much? However, having a cool thermal mass from the night will guarantee the cooling, but only until the system has it's equilibrium, and then the thermal mass is above ambient temperature. It seems that outside temperature has something to do with the draft of your system, but I have not yet figured out what. So back to the physical principles of my proposed system:
-The height difference is about 15 feet from the highest / hottest point (1st bell) to the outlet. -The gasses are cooling down and because they are getting heavier, they are sinking down to what... In a bell the heavier gasses go down to the bottom of the bell. If the outlet is sightly lower than the inlet, they will tend to go there. Again, they are shrinking and creating something like a slight vacuum. But there is also resistance: The gas mass in the exhaust after that point is standing still and has to be pushed to get into move. And there is again friction to the walls of the flu (or how do we call it?) system. -The gasses get heavier, like to sink and shrink, thereby creating space for the following gasses, which are pushed from the riser's thermodynamic. At this time the gasses do not know anything about outside temperature. At the end of the exhaust the gasses are standing still and the temperature in the exhaust and the ambient air are the same - or even a bit less, when the horizontal exhaust is ending with the slightly cooler wall. -In each bell the gasses are cooling down, sinking down, are shrinking, as well in the uninsulated connecting pipe down into the ground floor. And they are causing the gasses moving to the exhaust. The velocity will increase according to the height difference and the cooling rate. -In the last bell with about 30°C / 85°F the vapor in the gas will condensate, giving even more space /creating a little vacuum. -Now the moving gasses, cooled down to about 30°C/85°F will reach the end of the exhaust. And there we meet there the grueling outside temps of 20 below (-30°C). What will happen? 1.The exhaust is exactly horizontal, so the gasses will move up, because there is a heat difference of 60°C and more than 100°F. (well, we are talking about extremes). But even if they are moving up, nothing special will happen. 2. If the exhaust pipe goes bends down further into the cold ambient air, we get a problem, because the gasses, now warmer than the air, like to move uprwards - back into the exhaust - thereby slowing down the gasses inside the system. 3. If the exhaust pipe is going up, then the now rising gasses will even accelerate the gas speed. 4. If we put a tee pipe there, one end moving up, one down, the gasses can choose to move up or down, according to their temperature related to the ambient, possibly adding some draft to the system. 5. Now if we connect the exhaust to the sewage system, the gasses will move down into the cold ground (about 8°C / 46°F) and are cooled down further, and sinking down further - provided no poop or heavy flushing will block the system... One thing to add: At this point the volume of the gas will be very little, as it is cooled down and the water vapor is extracted - less than the incoming air. If I'm not wrong, the proposed system seems to work. Of course, there are still some hindrances during practical work, but the physical principles are clear to me now. I like to add that I'm very thankful to discuss this here and to receive all your doubts and experiences. For me the whole thing was not really clear. But now I went through the process of deeper thinking and I'm starting to see some points a bit clearer. So thanks again!
BTW, the answer to the question above what matters seems to be: Not the total difference between outside and inside temperatures matters, but the difference of temperatures on a certain point of the system and the difference of the weight of the gasses at this point. And if that weight can be converted into gas movement and is able to overcome the resistance in the system.Another rule out of this could be concluded:To improve draft, as long as the gasses are sinking and shrinking, the flue should go down. As long as they are heating up and expanding, the flu should go upwards (e.g. in the riser) and the space for the expanding gasses should be added. On a spot where gasses are warmer/more lightweight than the surrounding, the flu should go upwards (e.g. end of the exhaust).So far my outpourings...
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Post by pinhead on Oct 20, 2014 9:40:03 GMT -8
Warm and cold are relative terms - you have to define what you are comparing to in order to ascertain whether the air/exhaust/gas will rise or fall.
At the top of the chimney, you must have a temperature differential between the exhaust and the outside air, otherwise the chimney won't draw air through the system. If the air inside the chimney is colder than the outside air, you won't get enough draft to get the stove started and in fact, the draft will likely reverse when the heat is added to the inlet of the stove.
The reverse is also true if you want your exhaust to 'sink' out of the system - your exhaust gasses must be cooler than the air into which it is being drawn (outside air).
With no external chimney, the heat riser is doing all of the "pumping" of the exhaust; the heat riser is hotter than the inlet of the stove. Likewise, the exit of the heat riser is a bit hotter than the air inside the primary heat exchanger (the barrel), thus allowing for convection to "draw" the hotter air out of the riser. This is why an insulated heat riser is so drastically important - especially on systems with a poor (or no) chimney. This temperature differential (between the riser and the inlet, and the riser and the barrel) pressurizes everything aft of the heat riser, pushing exhaust out of the system.
The draft produced by this configuration (no chimney) can be enough to keep the stove going under certain circumstances, though there will be smoke-back at times depending on the relative temperatures throughout the system.
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Post by mwalimu on Oct 20, 2014 11:36:35 GMT -8
Warm and cold are relative terms - you have to define what you are comparing to in order to ascertain whether the air/exhaust/gas will rise or fall. >>>>Yes, I studied again the theory of chimney stacking, and in a simple stove/chimney combination is every thing clear. At the top of the chimney, you must have a temperature differential between the exhaust and the outside air, otherwise the chimney won't draw air through the system. If the air inside the chimney is colder than the outside air, you won't get enough draft to get the stove started and in fact, the draft will likely reverse when the heat is added to the inlet of the stove. >>>>> I have a stove/chimney combination in another house, which behaves like you describe. Very often the gasses a cooling down in the chimney and the smoke come out of the stove.. The reverse is also true if you want your exhaust to 'sink' out of the system - your exhaust gasses must be cooler than the air into which it is being drawn (outside air). With no external chimney, the heat riser is doing all of the "pumping" of the exhaust; the heat riser is hotter than the inlet of the stove. Likewise, the exit of the heat riser is a bit hotter than the air inside the primary heat exchanger (the barrel), thus allowing for convection to "draw" the hotter air out of the riser. This is why an insulated heat riser is so drastically important - especially on systems with a poor (or no) chimney. This temperature differential (between the riser and the inlet, and the riser and the barrel) pressurizes everything aft of the heat riser, pushing exhaust out of the system. The draft produced by this configuration (no chimney) can be enough to keep the stove going under certain circumstances, though there will be smoke-back at times depending on the relative temperatures throughout the system. Okay, now I have learned again something: To increase the "pumping" effect, I have to work on the riser: -increasing the length, -increasing the temperature. -better insulation -increasing the distance between the end of the riser and the top of the bell. But are there no other effects? What about -cooling down gasses at the surface of the drum - causing them to sink down (this was often remarked at permies and the youtube videos) -in a bell there are different hot gasses, some are sinking down - do the add to the acceleration of the exhaust gasses? -the shrinking of the gasses during cooling in a pipe with constant diameter do they add some kind of vacuum or not? and the condensing action, removing again volume? -the move downwards of the gasses constantly cooled down, does this affect nothing? (I am really asking - I don't know) Yes I have a strong radial fan, I just could add it, and there would be no problem - or possibly too much draft. But somehow this is not the way a rocket heater should be run... And now I have another idea: Could there be something like a negative riser (or a "sinker") having the same pushing effect downwards as a riser? By means of using the cold sinking gasses? Which means there are somewhere two different hot gasses and the colder ones are accelerating downwards? The question is: Does everything depend on the temperature between the out-coming gasses and the ambient temperature? Or can there something reversal happen inside the system like the riser did? It has not only to do with the temperature or the weight of the gasses, but also with pressure. The rise is building up internal pressure, could there be something which reduces the pressure, thereby creating a "sucking" action or at least reducing the resistance? Here the idea of a negative riser: in a bell there is a pipe or barrel vertically attached to a cool wall. The gasses inside cool down, are sinking and runnnig towards a kind of funnel connected to the outlet of the bell, pushing the gasses out. Or: A vertical pipe leads the incoming warm gas towards the center of the bell, where the gasses are rising towards the ceiling, getting cooled down on the walls, and are pushing towards a funnel-shaped bottom with an exit in the center. And still I think this will happen automatically, even when only the outlet of the bell is a bit lower than the inlet.I found already: a big plastic tank for the last (condensing) bell, a big metal hood with about 4,5 m² for one bell, and another 200 liter drum. As this project should run quickly, there will not so much mass be included. The heat storage will be left over for one bench and the already existing brick walls nearby. And I found out that the batch rocket is not so easy to handle, so I will start with a J-Style burner / riser.So far for today.
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Post by Donkey on Oct 20, 2014 12:32:38 GMT -8
My main, number one design criteria, the BIGGEST question that I always ask myself when designing something is this: Does this solution here, this solution that I'm now considering, solve more problems than it creates or does it create more problems than it solves? I always use the balance-beam of this question to answer the fundamental question: Is this worth it or not?
On one hand, I REALLY like the direction your inquiry is going, I think that it is a worth-while line for experimentation. On the other hand, in my opinion, it is HIGHLY unlikely that solutions along these lines will be practical enough to satisfy my base criteria..
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