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Post by pyrophile on Mar 8, 2015 2:25:14 GMT -8
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Post by pyrophile on Mar 8, 2015 2:46:16 GMT -8
In Russia there are many books on stove design and construction, for masons or for engineers. Bell system is exposed and sometimes critisized. What happens in bells is explained (pressure, velocity, etc.). But everything in russian! Very very frustrating!! On warmfires.ru, bell system is critisized and the author condiders that bell system acts as a channeled system. Google translation is very poor, so frustrating! If you copy this on google and ask the translation for the Warmfires.ru site you will have many things on stoves and on bells (cavities!) : Here is the table of contents of only a section of the site, the fifth section, very interesting, not translated by google : www.warmfires.ru/page-1022.htmlTo translate, copy this : 5. Климатический (отопительный) модуль - Печи и камины and submit it to google and ask for translation (check it is warmfires.ru) Or : www.warmfires.ru/study-1040-1.html and the pages aoound bell subject On the russian site gornilo.ru, you find these pdf of those great books dedicated to mass wood stoves, unfortunately in russian : gornilo.ru/08art-im/fHosh_2013/G2_84-137-2.7mb.pdfAnd following pages : gornilo.ru/08art-im/fHosh_2013/G3_138-167_1.2mb.pdfThen : gornilo.ru/08art-im/fHosh_2013/G4_168-205-1.7mb.pdfThe articles of warmfires seem to come from this book. Any tranlator?
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Post by pyrophile on Mar 8, 2015 7:07:16 GMT -8
Bells seen on those Chernov images contain columns of bricks as did romans in their hypocausts and as it was done before them in Corea, China, etc. Russians use these comumns for a long time. Kuznetsov, and maybe everybody there, lets 13 cm of free space beetween bell's walls and columns and around each column. With time, I am considering that these 13cm are too much and I am narrowing this space to about 5-7cm in my last current stove (7" -18cm- batch box stove). I hope it helps the bell's effect. I have the impression that bell's effect is stronger in narrow exchangers (like on Chenov's one shown here) and maybe in cylinders than in square or rectangular bells with more depht.
Has somebody any idea about that?
Benoit
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Post by Deleted on Mar 8, 2015 10:40:09 GMT -8
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Post by Robert on Mar 9, 2015 9:09:16 GMT -8
Hey Pyrophile.
Karl is right. The more column you put inside the bigger heat loss. In russia they used columns, so they could cap the bell with bricks. When i build the bells i try to avoid columns... Then i use big boards to cap the bell and thats it.
I just had some nice email exchange with Alex Chernov. It is very interesting that the bell system is not only much more efficient but also it produces cleaner burns. Much less PM...
Anyway my email exchange was about the fireboxes. I remember when you said that you do not trust much Kuznetsov firebox. Alex also. He did lot of test and stopped using a dry joint... But that is another topic.
Pyrophile i am very interested what kind of fireboxes you are buulding, and also wheter you was testing them.
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Post by pyrophile on Mar 12, 2015 13:10:44 GMT -8
Yes, I totally agree. But I think that all the story is not said! In the principle of bells, it is supposed that there is no need of columns or baffles. The internal surface, if it is big enough, should capture the calories of the gases because gase expand in all the bell. If you have not enough surface you add columns or baffles. But I find that if gases actually occupy the entire space in the bell, they do it in a certain way, independently of the free gas movement. That is this difference beetween what we expect and what really happens that I would like to recall. I think that hot gases occupy the top of the bell in a rather uniform pattern only in a static approach. That's what must happen when a bell is warmed with electricity. But a fire needs draft, which changes many things and adds complexity. Velocity produced by the fire and by draft "force" gases to take different route than one should expect. Then, gases are not ONLY subject anymore to gravitation (or convection). They occupy all the bell but the concentration in hot gases varies and is not only at the top. The lesser concentration in hot gases is not only in corners. That's why we add columns and baffles, not only to rise internal surface or to facilitate capping of the bell, which is true too, of course. Those columns and baffles seem to isolate the flow of gases from the forces of the draft and maybe other forces due to the fire, like jet effect for example. They force gases to rebuild the stratification, in front of each column. IN MY POINT OF VIEW, of course! I suppose that it is the reason why we see for the first time Chernov using columns...Because bells don't totally act as they should And the exchange surface does not totally determinate the quantity of exchange... And that's also why he uses a narrow exchanger whereas, in theory, any shape should work. Even the narrow shape, which actually works better, works best baffles or columns. In my opinion! A second important aspect for me is that it is probably interesting to mix different types of exchangers. Indeed one can consider that the first bell is not exactly a bell, as it was already said here. With this kind of exchanger with hot gases coming from above, russian stoves use another way to capture heat where bricks are not laid vertically but horizontally : That is also what we see in the famous stove of Grum-Grzimailo which combines horizontal and vertical exchanger (as the image above). In its cylindrical stove, the bricks are in a star shape to oppose a vertical and an horizontal obstacle to hot gases and capture their heat : As the bricks don't touch in the star, they capture heat not only to hot gases going down throw the bricks but they also capture heat to gases going horizontally -owing to their temperature that determinates their situation in the bell. Stratification is there also possible, more or less of course because there is not so much place for all these phenomenoms! In this stove, the gase leaving the firebox were measured at 900°-1000 °C (in 1926 or 1927) and were leaving the stove at 150° C, which seems very good for such a narrow stove! All this does not mean that bells are not interesting! I use them for ten years and I still use them in each stove I build. But I find that they are not so easy to use as I thought, as I hoped a few years ago...Maybe to mix with other system ...Owing to me, of course! Any comment? Benoit
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Post by Deleted on Mar 12, 2015 13:43:15 GMT -8
If you have time you should learn to use a CFD simulator, which may help to get your desired answers faster than with real experiments.
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Post by grizbach on Mar 14, 2015 10:20:19 GMT -8
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Post by pyrophile on Mar 14, 2015 11:08:03 GMT -8
I am not able to know if these simulators say everything. Maybe they do, maybe not! To decide you must be able to compare what you experiment with what the simulator says. Are there stovemasons among us who have this knowledge with bells and simulators ? I have little confidence because I don't know the subject and because I find with time that bells are more complex in the reality than what the theory says. Once again, I don't know the subject of simulators but I feel that I know a bit the subject of bells after more than 30 stoves with bell accumulators. I can change my mind because I prefer truth to my own pride but as it is my job I can not trust a simulator that I am not able to evaluate and that maybe does not work with bells heated with wood. For example, you must introduce , I suppose, the speed of your gases leaving the heatriser but also their volume or the temperature of the internal walls of the bells, etc etc. Few people know bells well by experiment. Maybe it is not necessary for simulation. I am not able to decide! But I don't say you are wrong!
Benoit
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Post by Deleted on Mar 15, 2015 3:36:23 GMT -8
Energy2d is to simple. There are very sophisticated free scientific 3D CFD simulators, including even a combustion simulator, which can be feed with CAD data. Such a simulator computes the resulting speed of fluid itself. Due to their complexity it would take some time to master. Commercial 3D CFD simulators are more convinient to use, but extremely expensive.
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Post by pyrophile on Mar 15, 2015 3:45:16 GMT -8
I forgot to say that I am not friend with computers...
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Post by Deleted on Mar 16, 2015 4:16:18 GMT -8
The next best thing to a computer would be to build a test bell mostly of glass, with moveable inner parts. The radiation of the flue gas could be checked from the outside. Small amounts of chemicals producing smoke of different colors could be used to watch the gas and see what will happen.
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Post by patamos on Mar 16, 2015 20:05:14 GMT -8
This introduction of colour to perceive movement reminds me of how studies are done in fluvial geomorphology, involving the relationship between the flow of rivers/streams and the land that contains them. Although the dynamics of water-earth and gas-heat-earth are not exactly the same they might be similar enough. For example, vast or deep chambers allow the fluid/gas to slow down and pool. The more they can be stilled the better they stratify (drop sediment/heat), but the closer and/or more direct a line from entrance to the downstream exit the more likely a create a central current/short cut will manifest. There will be some eddies and pools along the sides, but a current through the middle... So the buoyancy of the hotter gasses must be stronger than the downward pull of the exiting current. The shape and width of the exit and where it goes/turns shortly after will determine the spread/shape of its pull from the pond. The stronger the stack effect the stronger the vacuum, the more central the pull. Curves always create eddies just after the inside turn. The current at the outside of the curve accelerates and tends to spiral into a cyclone. I could go on and on drawing comparisons. But sitting by a river or stream above the plains can explain so much more.
I have happened onto this discussion just as i am pondering whether and if so where to put baffles in a double bell i am building. But with much less experience than Benoit, i have turned to the study of water and land for insights. So i am very interested in hearing ideas on how my comparing might be flawed Robert, about that other topic: when you speak of dry joints do you mean ceramic felt between the metal door frame and brick work?
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Post by pyrophile on Mar 20, 2015 13:00:13 GMT -8
Russians seem to have experimented many things about movements of gases in bells and other systems. In the articles listed above, they speak about that, but in russian...water flow, gas flow, etc : api.viglink.com/api/click?format=go&jsonp=vglnk_14268824533288&key=bbb516d91daee20498798694a42dd559&libId=i7hzzjlt010004m6000DL3pfh83w&loc=http%3A%2F%2Fdonkey32.proboards.com%2Fthread%2F1593%2Fbell-theory&v=1&out=http%3A%2F%2Fgornilo.ru%2F08art-im%2FfHosh_2013%2FG2_84-137-2.7mb.pdf&ref=http%3A%2F%2Fdonkey32.proboards.com%2Flogin%2FgmLoFGOBLgANPhZNkNBm%2F1611&title=Bell%20theory%20%7C%20Rocket%20Stoves..%20Experimenters%20corner..%20Answers%20questioned!&txt=gornilo.ru%2F08art-im%2FfHosh_2013%2FG2_84-137-2.7mb.pdf Unhappily, my theorical knowledge is rather poor and it would be interesting if we could , together, understand better what happens in a bell. In my opinion, there are dfferent forces which act on gases in a bell : - A one end of the bell, there is the jet effect (like a jet of water) which ejects gases with a direction and a speed, in a vetical or horizontal motion (owing to the kind of firebox). In our batch box stoves, it is of course a vertical direction and a rather high speed. - At the other end, draft attracts gases to the bottom of the bell. - In the middle of the bell, gravitation acts on heavy gases and hotter gases rise. The nearest from the exit of the bell, the most influenced by draft. The farthest, the more influenced by bell effect and also by jet effect. I suppose that it explains the inteerest of columns and baffles : it takes away draft effect and its attraction to the low part of the bell and favors bell effect and its vertical and upward motion. Does it seem correct? I am wondering also on columns: Do you think that gases arriving in front of a column divide in two equal parts or do they favor rather one side ? I am always wondering about that and for each stove I finally decide to make baffles! This time I made both comumns and baffles! What is your opinion on this? In his book on bell effect, Groum Grzimailo, in the beginning of the 20th century, "proved" "mathematically" that cooling gases must go in a downward direction if one wants that they divide in equal flows. Is this still accepted? Maybe that is the reason why we can see sometimes this kind of russian exchanger that looks like a downdraft brick kiln :
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Post by pyrophile on Mar 20, 2015 13:14:01 GMT -8
If I may answer to a question asked to Robert, a dry joint was added by Igor Kuznetsov in order to give bell's effect in fireboxes. It is a thin slot 2 or 3 cm wide but so high that it rises to the summit of the firebox (or below for Alex Chernov). It is supposed to help colder gases like ballast gases (nitrogen, excess air and so on) to leave the firebox before they cool it and let them go to the bell exchanger. They are supposed to leave the firebox at an height depending of their temperature.
Alex Chernov said for years that it was extraordinary, so extraordinary that he stopped using it, as I did some time ago too... It's maybe a bit a pitty that he did not say so loudly that it didn't work as he said loudly that it was a great firebox...On MHA News as on his website, he spoke a lot of the great qualities of this kind of firebox. I would find fair from him to say on the MHA site that it was not such a good idea and why. Everybody could learn...
About small particules that are less with the bell's exchanger tested in Austria (see first post above), I think that they are not measured because they falled in the bottom of the bell! They were actually created by the firebox but not sent in the atmosphere. IMHO
Benoit
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