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Post by satamax on Aug 18, 2014 22:18:23 GMT -8
Esteban, 1 inch firebricks are good enough. Exept that they are hard to hold to make a heat riser or firebox. Here is how i tend to build donkey32.proboards.com/post/11503/threadTho, that is if you can find the parts. If you have access to a diamond grinding wheel, you can make a little ledge onto two sides of two firebricks, so you can assemble four of thoses in a square tube shape, held by wire. I will try to draw that for you. For the firebox, 2 inches thick firebricks, laid on their edge will do the trick. With 1 inch ones across for the top. 4 inch insulation all around is good. Even the firebox.
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Post by peterberg on Aug 19, 2014 1:47:59 GMT -8
Esteban, It's best to build the firebox and riser assembly from refractory materials. Since you want to use it for one season only rockwool to insulate the riser would be sufficient. Just a thought: depending on what you think is a safe height to stack, you could make a bell out of about 1.5 larger oil drums. The firebox and riser could be built inside the drum, while the firebox is protruding out of one side. Much like the 15 cm system I've built about a year ago, using three barrels. Along these lines, you could use two barrels, the firebox mounted half in the lower and half in the upper drum. This will avoid the work of making a barrel-in-barrel construction in order to achieve enough heat dissipation. For good measure: the bell should have its exhaust opening nearly but not entirely at floor level. Here's the way I have done this.Some time ago I've tried to calculate the internal surface area for a larger brick bell containing a 20 cm batch box system. This is still speculation, but I've used the csa of the riser to calculate this. Riser of a 15 cm system is 177 cm2, a 20 cm system would end up 314 cm2. The larger one is 1.77 times as large as the smaller one. I used this proportion to calculate the internal surface area 10.6 m2 as compared to 6 m2 for the smaller system. A single bell built entirely from barrels in a 15 cm system would still work with an internal surface area of just short of 5 m2. To calculate for a 4"/100 mm system using the same method that would be 177 cm2 divided by 78 cm2 equals 2.26. So a 6"/15 cm system is 2.26 larger than the 4"/10 cm system. This boils down to a metal bell of about 2 m2. So, This could be a single 55 gallon/208 liter drum or maybe two smaller ones when you calculate the circumference and the top. Not the bottom, that one won't get hot.
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Post by Deleted on Aug 19, 2014 4:17:47 GMT -8
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Post by peterberg on Aug 19, 2014 6:22:59 GMT -8
Yes, that's true. But... those properties are achieved by firing the clay/sawdust mix in order to burn the sawdust out. Which leaves small empty spaces inside the fired clay and that will in turn cause the insulating properties. When the clay isn't fired at all, but only dried is this mixture as insulative as the fired clay/sawdust? Unless the firebox in its entirety is built from this mix and fired by the burning inside the stove? Made like this, it could be something along the lines of Donkey's mud batch box.
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Post by Deleted on Aug 19, 2014 7:52:40 GMT -8
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Post by peterberg on Aug 19, 2014 12:50:33 GMT -8
About 240°C are enough to reduce the sawdust. Organic fibers or things made of them like paper have about 0.05 W/(m.K), thus the thermal conductivity will be significantly lowered, even in parts never becoming hot enough to reduce the sawdust. One can use more than 30%. OK then, temperature in the firebox under the coals can easily reach 900°C. Esteban, you said something about having access to good pottery clay, so here is your window of opportunity to make an insulating firebox and riser. Donkey did something like that in the Mud batch box threadBest to make a box of plywood the measurements of the firebox' outside and another the measurements of the firebox inside. Making the clay/sawdust mix as dry as possible and ramming it between those boxes. The top of the firebox could be made out of firebricks. Some time ago I tried to figure out the size of a single bell that would fit a 20cm/8" system. The bell size for a 15cm/6" system is already done, that is 6 m2 inside surface area in a brick bell. An all steel bell made of oil drums is fine at just short of 5 m2. It's all speculation at this point but I've used the cross section area of the riser to calculate the larger one. The 15 cm system has a csa of 177 cm2, the 20 cm system 314 cm2. The larger one is 1.77 times as large as the smaller one. So I reasoned the internal area should also be 1.77 times as large, 10.6 m2 for a brick bell. Now for a single steel bell of a 10 cm/4" system. The csa of the riser as compared to a 15 cm system is 2.26 times. Thus, the bell for a 10 cm system could be about 2 m2, not counting the bottom of the bell, that won't get hot. A single 55 gallon/208 liter barrel could be enough if you are able to build the firebox and riser inside this bell. Exhaust at floor level, but not quite, just a bit above the floor. Of course you could use two smaller drums, something like I have done about a year ago. This way, it isn't necessary to make a complicated heat exchanger.
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Post by satamax on Aug 19, 2014 22:20:47 GMT -8
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Post by Esteban Campestre Abejil on Aug 20, 2014 5:47:26 GMT -8
I am impressed with your good will. I love that you look for ways to help my little project. It's the beauty of such groups. After reading your interesting answers, tips and experiences, I think that -as Peter insinuates- there is a good chance of achieving this project with a lower cost than I was beginning to imagine. Efficient use of space is an important factor in my little (or saturated by stuff) home. We have a little girl of 1 year and 4 months who need the largest possible interior space during the rainy winter. OIL DRUMS.I find particularly interesting the idea of building the stove using an oil drum basic unit. Using oil drum as heatsink and include in it the batchbox is much more efficient in terms of space. I imagine that could also include the exhaust inside the oil drum. This would imply that in the drum 2 flue gas streams would take place, one descending (going from the top of the heat riser) and one ascending, it would be the exhaust but with another shape. Each of these hot gas streams may be separated from the other by an ascending air flow, which capture heat. This would increase the heat spreading surface. I think this would not be difficult to build using oil drums of different sizes or even metallic sheets. I have to figure out a simple way to clean it. I will do a drawing. I think that something like this can be super!! But, maybe with less distance in the bottom. The space under the batchox is wonderful to capture the gases and direct them to the exhaust pipe. I'll have to think through how to immobilize the batchbox at height (earthquakes !!), but I guess it will not be a big problem if I draw it on a simple metal frame. I think there will be enough space for the heat riser with only 1 oil drum over the batchbox. According to the calculator, for a system with 4 inches, the heat riser should measure 28.80 inches (73.15 cm). I imagine that this measurement is from the base. I like it. CLAY + SAW DUST ... and insulation.Donkey's experience with his batchbox 4 inch is exactly what I need! It's cheap, it's fun and it works great. For mixing I think I could get clay for pottery, chamotte (cooked milled bricks, not refractory), sawdust (is better soft as pine or hard as oak woods?), Wood ashes (I have doubts about it!). What else would I need? How thick should the walls be batchbox? What about the heat riser? Would it still be necessary to isolate the heat riser? How much? --- Satamax, if I finally built it with firebricks, I think it would be very convenient to use that form to fit the bricks in the heat riser. I would have to make those grooves on the edges of the bricks by cutting with a cutting disc for concrete. Right? Fortunately, I have the necessary tools to do so. Thanx guys!
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Post by Deleted on Aug 20, 2014 6:08:39 GMT -8
Better soft as pine. CLAY + SAW DUST = insulation.
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Post by Esteban Campestre Abejil on Aug 20, 2014 8:10:09 GMT -8
How thin should be the sawdust? Does the sawdust should be thick (as sawmill) or thinner?
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Post by Deleted on Aug 20, 2014 9:10:04 GMT -8
sawdust not sawings serrín no virutas el polvo no fichas
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Post by peterberg on Aug 20, 2014 9:38:40 GMT -8
I imagine that could also include the exhaust inside the oil drum. This would imply that in the drum 2 flue gas streams would take place, one descending (going from the top of the heat riser) and one ascending, it would be the exhaust but with another shape. Each of these hot gas streams may be separated from the other by an ascending air flow, which capture heat. This would increase the heat spreading surface. I think this would not be difficult to build using oil drums of different sizes or even metallic sheets. Esteban, there should be literally NOTHING in the barrel except the batch box and riser. So, no flue gas streams to direct by sheet metal or whatever. The inside of the drum or drums are meant to be completely empty. The gas stream, helped by gravity, will take care of the separation and heat dissipation to the room outside the drum. This is what we call a bell, the inside of this metal surrounding is what counts in my internal surface calculation of about 2 sq m. The only thing which is paramount is the very low positioning of the exhaust. In order to grasp what is going on, please study the picture and see how the gas stream goes.
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Post by Esteban Campestre Abejil on Aug 20, 2014 13:29:17 GMT -8
Karl... Thanks for your translation. It is difficult to clarify the terms when you try to communicate in a foreign language. Now I understand what you mean exactly. This is anecdotal. My question about the size of the particles of sawdust arises because once I built a boat, which was to make a paste with sawdust and epoxy resin. The manual (in English) saying only "sawdust", but I found almost by trial and error that sawdust sawmill was huge, thick for the job. What I needed was sieved wood dust. But apparently the term "sawdust" in English including all kinds of mini-particle wood from the saw cut. Of course, "sawdust" means that literally. Things that happen when a language plays with one (and not vice versa) Peter. I've always understood how a bell works. My idea of putting the exhaust into the bell comes from my need to optimize space. If I leave the exhaust as in your bell, I must dedicate at least 20 cm for it. However, if I achieve push out the exhaust from the top of the bell, I could make that space instead of losing. But it's just an idea, perhaps overly complicated. Sometimes one must resign that things can not be otherwise. Maybe for a second test.
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Post by satamax on Aug 20, 2014 13:51:51 GMT -8
Two words, plunger tube!
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Post by Esteban Campestre Abejil on Aug 20, 2014 17:58:26 GMT -8
o.O
Tarzan no understand
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