dvawolk
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DSR2 125mm open system (actual project)
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Post by dvawolk on Apr 4, 2013 0:10:44 GMT -8
Ok, then.
It all looks that i can not help with thermal conductivity coefficients of materials when trying to estimate ISA with different materials?
But how can i then estimate the difference in ISA if i use brick, concrete or some insulative material?
For now i only know the factor between ISA of metal sheet and ISA of brick wall.
And firebricks come in different options: some can have 0.6 W/mK and others can have 1.2W/mK. I think there must be some influence on having different ISAs with these different firebricks. Or is the difference insignificantly small?
But if you compare thin metal drum and 10-times thicker metal drum, my guess is that the last one would extract much more heat from gases? Based on that guess i was thinking that ISA factor is more closely related to thermal conductivity coefficients of materials...
Peter. that stove in Netherlads... I am VERY interested in details: measures, photos, videos of burning, smoking (?!?)
This exhaust temperature is very similar to mine at the begining (with lousy chimney and slight bottleneck): two bells, 6.9 sq.meters.
When i shortened the second bell so the system ISA was 4.9 sq. meters, the exhaust temperature got over 50°C. (still with lousy chimney and slight bottleneck).
Based on previous conversation my exhaust temperature should be even lower (having a stove outside, air temperature 5°C, very high humidity and higher efficiency of double bells and larger ISA).
Is the exhaust temperature in the mentioned stove reached as maximum at full firings?
What about smoking? Is it extensively present?
What kind of wood is used for firing?
It is maid of unfired bricks? That is like dried only water+clay+sand combination?
Is there anything put over the bricks, like some kind of plaster? Thickness?
What should be understood like that "this stove is doing quite nice at the moment"?
Sorry for a list of question but this IMO this is very comparable project and i would really like to compare the details...
Klemen
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Post by Deleted on Apr 4, 2013 1:30:13 GMT -8
It all looks that i can not help with thermal conductivity coefficients of materials when trying to estimate ISA with different materials? To calkulate the amount of heat that can be transfered you need values in W/m2 K by Fourier's law and the heat transfer coefficient. You need at least three values: 1.) the value for flue gas to material, as value for forced convection. 2.) the value for the material by Fourier's law 3.) the value for the material to air. If the material ( wall )has more than one layer you need values for each layer and for each layer to the next. Based on those values , the thermal power of the fire and the specific heat capacity of the mass you can calculate the area. Due to the transition from gaseous media to solid media and then from solid media to gaseous media the differences between solid medias will be less significant as one may expect. Thicker medias will lead to an enlarged outer surface. Once I had to use a slide for such calcultions. Much simpler with computers and calculators One can move the double heat amount of the other. The value of the bricks depends on the mix and porosity. For firebricks its usualy the amount of alumina and the porosity, which have the most influence. The more alumina the higher the more porosity the lesser. Because of the contact resistances between medias, there is a light temperature drop at each transition surface. www.kxcad.net/SolidWorks/COSMOSWorks_online_help/analysisbackground/thermalanalysis/thermal_contact_resistance.htmLarger particles in material mixes are conducting better than a lot of smaller ones. |
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Post by peterberg on Apr 5, 2013 1:48:28 GMT -8
that stove in Netherlands... I am VERY interested in details: measures, photos, videos of burning, smoking (?!?) Klemen, This a commercial build, I can't possibly comment on the construction unless the builder gives his blessing. I don't know the internal surface area exactly, the builder has agreed to send that to me so you have to wait for that. See the two videos in this thread for burning. Photos are published earlier, see this link.We've been on the roof while it was at full bore, a 1 m (3') plume of water vapor smelling vaguely like wet charcoal was the end result. Exhaust temperature reached 50 C, (122 F.) during the course of a 2 hour run. We used about 6.5 kilograms of mixed soft wood and oak, moist all of it less than 14%. The loam bricks consist of clay and sand, made in a machine applying about two tons of pressure to form the brick. Over the bricks there's a layer of cob and short hemp straw, about 12 mm (1/2 ") thick, another layer of 1/4" (6 mm) incorporating a mesh of hemp fabric. Your stove ISA is restricted to 4.9 m2 at the moment, I would think that would be the maximum because it do consist of two bells which are estimated as being 30% better at storing heat as compared to a single bell. As I've mentioned before, it's not completely dried out yet. But performance looks good, sound is as it should be. There's one important point to make, the recommended primary air inlet proved to be too small. The chimney stack do consist of an insulated 15 cm (6") diameter stainless steel duct. My experimental model is using a 3 m (9.8 ') bare pipe, half of that horizontal, to lead to the chimney. My chimney itself do consist of a square 18 cm (7.09") brick uninsulated vertical channel, about 9 m (29.5') long. Yesterday, it became obvious my chimney do produce a stronger draw compared to the 15 cm duct. As a result, the air velocity was at a lower rate and the fire couldn't get enough air. We opened the door slightly until the burning picked up as it should. The total primary air intake is hard to guess, but is estimated at 35 to 40 cm2 (5.43 to 6.2 sq. in.). My sincere apologies to all, especially to those good men who built a stove based on my recommendations. I've unwillingly misled you into thinking a 6" system being one to one comparable to mine. |
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Post by pinhead on Apr 5, 2013 6:01:06 GMT -8
There's one important point to make, the recommended primary air inlet proved to be too small. The chimney stack do consist of an insulated 15 cm (6") diameter stainless steel duct. My experimental model is using a 3 m (9.8 ') bare pipe, half of that horizontal, to lead to the chimney. My chimney itself do consist of a square 18 cm (7.09") brick uninsulated vertical channel, about 9 m (29.5') long. Yesterday, it became obvious my chimney do produce a stronger draw compared to the 15 cm duct. As a result, the air velocity was at a lower rate and the fire couldn't get enough air. We opened the door slightly until the burning picked up as it should. The total primary air intake is hard to guess, but is estimated at 35 to 40 cm2 (5.43 to 6.2 sq. in.). My sincere apologies to all, especially to those good men who built a stove based on my recommendations. I've unwillingly misled you into thinking a 6" system being one to one comparable to mine. I'm somewhat confused as to what you're implying, here. Are you saying a 6-inch chimney doesn't produce enough draft to efficiently run a 6-inch Peterberg stove? That would somewhat correlate to my experience with my homebuilt 6-inch Peterberg stove; my stove doesn't have nearly as much airflow as your videos show. My first chimney consisted of about 6 feet of vertical (uninsulated) 7-inch pipe, then to a 6-inch reducer and an elbow, horizontally through the wall (about 3 feet) and then another 4-feet of double-wall 6-inch pipe. Total height from the floor to the top of the chimney is approximately 15 feet. While this worked, there was a lot of condensation and I had to keep the primary air inlet pretty small to keep smoke from spilling out the front of the stove. I later replaced the 6 feet of 7-inch pipe with well-insulated 6-inch pipe (6-inch pipe with 8-inch pipe around it, with vermiculite between the two). This was quite an improvement, though I still don't have nearly as much draft your stove has demonstrated. I had assumed that my double-bell bench was simply pulling more heat out of the exhaust stream than your large single bell barrel configuration, thus reducing the chimney temperature when compared to your stove. Are you saying that a simple 6-inch chimney doesn't produce enough draft to fully utilize the efficacy of the Peterberg batch stove? |
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Post by peterberg on Apr 5, 2013 6:58:48 GMT -8
Are you saying a 6-inch chimney doesn't produce enough draft to efficiently run a 6-inch Peterberg stove? What I meant to say was: the primary inlet should be larger than my recommended 4 sq. inch in order to run properly. The upgrading of your chimney resulted in a much better draw, that should be expected. Still, your stove and bench represent a triple bell system IMHO, and such a configuration is bound to generate more friction in the smoke path. All in all, we are back to the inlet size at 25% of the riser csa, like Donkey and Canyon found out at first. The stove I've seen yesterday do consist of one single bell, although the inside is rather complicated, the bench is part of that bell as well. Nevertheless, the thing is capable of burning as clean as it should, despite the 6" insulated stack being smaller than my chimney. |
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Post by matthewwalker on Apr 5, 2013 9:02:40 GMT -8
Peter, I've found the same in my builds. Not that I have any way to accurately measure, but I know I need more air when it starts smoking upon closing the door completely. Thank you for confirming this.
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Post by Deleted on Apr 5, 2013 9:38:34 GMT -8
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Post by pinhead on Apr 5, 2013 10:56:33 GMT -8
Thank you very much for the clarification, Peter.
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dvawolk
Full Member
DSR2 125mm open system (actual project)
Posts: 273
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Post by dvawolk on Apr 5, 2013 11:56:16 GMT -8
Karl: looks like there is no simple equation... I was thiking that since i know (from experimental info) how much the temperature of gases can drop after passing certain amount of ISA with firebrick material, then i can somehow conclude the required ISA of other materials based on the same tempearture drop...?!?
Peter: Oh, this photomaterial is precious to me! I can see why this is only one bell. Just yesterday this option for connecting first bell to bench: almost the same ISA but only one bell. I will take out a brick on the upper part of my bench and horizontally connect it to the first bell. Then i will check the temperatures again. This will be a nice comparison!
Those bricks used in the reported stove are probably 25x12.5x6cm or something like that?
Correct me if i am wrong, but if the bench is connected like that (forming only one bell) that means that it can be less than 4times SystemCSA, Right?
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I would like to know how right is my guess regarding chimney draft. Below is the order of different chimneys from the least draft to the most draft.
A: 4 meters high 18x18cm square
B: 4 meters high 18 cm diameter
E: 4 meters high 20 cm diameter
C: 8 meters high 18 cm diameter
D: 6 meters high 20 cm diameter
Also is the statement: "if the chimney is narrowing (linearly) to the top of it then the draft is enhanched"?
Best regards,
Klemen
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Post by Deleted on Apr 5, 2013 13:08:21 GMT -8
Karl: looks like there is no simple equation... I was thiking that since i know (from experimental info) how much the temperature of gases can drop after passing certain amount of ISA with firebrick material, then i can somehow conclude the required ISA of other materials based on the same tempearture drop...?!? Calculating heat transfer is no simple task, even in rather statical cases like transfer through house walls. Fourier's Law allows to calculate heat transfer through materials. Here are some links to online calculators. donkey32.proboards.com/index.cgi?board=reflib&action=display&thread=780Above I have gave a link to a simulationssoftware. A 30 days demo is available. No chain can be stronger than its weakest element. Analogously, no higher amount of heat can me moved than the weakest transition allows. Gas is usually much more lousy as conductor than solids. |
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Post by grizbach on Apr 5, 2013 16:13:10 GMT -8
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Post by peterberg on Apr 6, 2013 0:46:15 GMT -8
Yes, I have found extra restriction to have a huge impact on primary air. Griz, I think you are right, I'd move that thread to the reference library. |
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Post by peterberg on Apr 7, 2013 0:22:52 GMT -8
Those bricks used in the reported stove are probably 25x12.5x6cm or something like that? You are about right, many other sizes do exist of course. The bench in this configuration will get warm, provided the exit to the chimney is at the lowest point. In this case, this exit is lower than the floor of the bell. Correct me if i am wrong, but if the bench is connected like that (forming only one bell) that means that it can be less than 4times SystemCSA, Right? Theoretically, yes. But you are getting a very tiny bench by that, only suitable to small children... More height will mean a warmer place to sit on in this case. I would like to know how right is my guess regarding chimney draft. Below is the order of different chimneys from the least draft to the most draft. Errhmm... A and B will generate the same draft, C and D are on a par I would think. Also is the statement: "if the chimney is narrowing (linearly) to the top of it then the draft is enhanched"? That's true only for high chimney temperatures. Such a stack would be a great risk using a stove that sports low end temps. |
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dvawolk
Full Member
DSR2 125mm open system (actual project)
Posts: 273
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Post by dvawolk on Apr 9, 2013 2:57:33 GMT -8
So, i did some more tests with shortening/lengthening the bench. Below are some data that seem to me the most useful...
All tests have a plastic tube for chimney, 4.3meters high with diameter of 19cm. Outside temperatures were similar, about 2 to 5°C. Of course, my wood is bit over 20% of humidity, beech wood.
Temperatures measured were:
- after the gasses reached approximately 1.3 sq. meters of ISA
- exhaust from stove to the chimney
All the burns were quite clean (with an exception of first 5 or so minutes). After that water vapours with aromatic gases. There were some exceptions of very short periods (less than half a minute) of more pronounced smoke. I do not recall any of those exception smokes in the second test...
------First test-----------
DOUBLE BELL SYSTEM with ISA of 5.95 sq.meters (should be similar to 7 sq. meters of a single bell system)
i slightly warmed the stove with two or three handfuls of tiny pieces of wood. When the coal phase started i added
full batch of wood. Temperatures at that time: 63°C/22°C.
Maximal temperature achieved is 353°C and 54°C (not at the same time)
The first temperature stayed above 300°C for 15 minutes.
After 13 minutes of burning exhaust temperature passed 40°C.
------Second test-----------
SINGLE BELL SYSTEM with ISA 5.7 sq.meters, a bench is similarly connected to first part of a stove as in the "netherland's stove" mentioned in previous posts...
First i slightly warmed it (similarly than before).
Maximal temperature achieved is 388°C and 96°C (not at the same time)
The first temperature stayed above 300°C for 25 minutes.
After 5 minutes of burning exhaust temperature passed 49°C.
------Third test-----------
SINGLE BELL SYSTEM with ISA 6.5 sq.meters, a bench is similarly connected to first part of a stove as in the "netherland's stove" mentioned in previous posts...
First i slightly warmed it (similarly than before, but this one was less warmed than previous two. Also this day was the coldest of those three. Humidity was 50%).
At the time of filling it to the top with wood, the exhaust temperature was 6°C..
Maximal temperature achieved is 346°C and 60°C (not at the same time)
The first temperature stayed above 300°C for 22 minutes.
After 15 minutes of burning exhaust temperature passed 40°C.
I think i am getting a feel of how large ISA this stove can have at my place. Based on the previous tests, a bullet proof option will be the second option, single BELL with 5.7 ISA. When built inside, the temperature of the stove can not drop below 18°C or so in normal living situations and the chimney is more than twice as high as in the test and the diameter is 20cm. The chimney is built in the middle of the house, so this is another plus. It is chamote flue.
But the best option, i think, lies somewhere between second and third test... And probably somewhere close to 6.5 square meters.
Do you think it is a safe conclusion to expect exhaust gases of the third option to reach over 100°C - based on the faster draft, and higher starting temperatures (and drier wood), warmer intake. It seems that anything that i can think of is better when the stove will be built inside.
Later in the week i will post the image of temperature graph for the third test.. It might tell you some more useful info...
One more thing. When i build it inside: if i make a thicker plaster around the bricks (it will be a clay plaster), the heat would dissipate slower to the room, right? I concluded this because the heat travels faster in firebricks versus dry clay.
I look forward to your opinions,
Klemen
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Post by peterberg on Apr 9, 2013 9:24:19 GMT -8
Do you think it is a safe conclusion to expect exhaust gases of the third option to reach over 100°C - based on the faster draft, and higher starting temperatures (and drier wood), warmer intake. It seems that anything that i can think of is better when the stove will be built inside. Your results look very very good. Although it's a single bell, it is built in a quite complicated shape. So it would be a good thing to define a difference between simple shapes and complicated ones. Still, I would think the simple masonry bell could be 7 m2 ISA, especially coupled to a chimney stack similar to that one inside your house. Maybe you could build it with an option to lengthen the bench. But for now, as complicated as your stove shape is, it seems a reduction of say, 7.5 % would be enough to compensate. So 6.5 m2 looks like a viable possibility. Mark however, the exhaust temp doesn't need to rise much above 60 C., that is enough to avoid condensation. One more thing. When i build it inside: if i make a thicker plaster around the bricks (it will be a clay plaster), the heat would dissipate slower to the room, right? I concluded this because the heat travels faster in firebricks versus dry clay. The plaster is less dense, that is one reason. But indeed, the more thickness of masonry material, the slower the heat will come through. Spreading the stored heat over a longer period in time. |
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