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Post by Daryl on Feb 28, 2014 3:28:42 GMT -8
We were discussing this very topic over at the UK Rocketstove forum. In the future, there will be more hybrids. Many commercial stoves use some sort of core. Even the Kimberly was using vermiculite panels the last time I checked.
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Post by ronyon on Feb 28, 2014 10:40:42 GMT -8
Hey, could you post the address for that Forum?
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Post by satamax on Mar 1, 2014 9:15:59 GMT -8
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Post by sparks on Mar 4, 2014 8:32:17 GMT -8
this very clearly makes your point. I completely "get it" now. I am going to start over with a casting as shown in the video above. Perhaps the heat riser configuration here will be satisfactory. Thanks.
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Post by photoman290 on Mar 4, 2014 15:40:19 GMT -8
looking at the video of the firebricks i couldn't see why rob bothered to dado the ends of the bricks? as there are in a metal cage wouldn't it have been just as easy to put full size bricks in? i suppose they may be a bit more secure but they are not going anywhere inside that cage anyway. i do like the design though. there is product called ceraboard here in the UK that would work very well. i have used it of a coal fired range and a woodburner. seems to hold up pretty well, even with coal and wood being thrown in it. it is quite expensive though. here is a link. www.sigtechnicalinsulation.co.uk/show_prod.asp?ProdID=1131&CatID=45&SubCatID=103
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Post by satamax on Mar 4, 2014 22:04:20 GMT -8
Photoman, it's dead simple why he didn't use full bricks, mass! The more mass in the heat riser, the longer it takes to heat up to working temps.
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Post by mintcake on Mar 5, 2014 3:51:54 GMT -8
Could you tell us if you used the 100 (1200°C) or 115 (1400°C)? Also, what thickness of it? A list of proven refractories and the different situations would probably be good for the reference library. e.g. Unobtaniboard: 6mm, highly insulating, survived 5 years in heat riser, and also able to hold up a tank, cost $0.1 / m2. (anyone know a supplier???)
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Post by sparks on Aug 18, 2014 18:17:34 GMT -8
Sparks, I'll take a quick shot at the metal/masonry part of your question. I posted this elsewhere, and it's been said by others before as well. If it's metal and it's holding up, it's not working properly. If it's performance is starting to approach that of a simple masonry J rocket burner, it won't last but a few hours. In your example above, your bare metal burn tunnel can both absorb and then reradiate heat from the combustion out to the space. This is directly at odds with the basic principle of rocket burners. Focus the heat of combustion back on the combustibles until everything that can be burned, is. Then, and only then, do we harvest the heat of combustion. Whether stored in mass, radiated to the room via a metal radiator, stored in water, etc. All of that should happen downstream of the riser. So, if you were to take your design, and modify it to achieve those goals by effectively insulating the metal burn tunnel, as it approached working temperatures the metal would quickly fail. Woodstoves last because they can radiate the heat to the space before it becomes fatal to the material. As for designs, there are a million and one ways to utilize the heat of combustion from one of these burners. One of the downfalls of a little heater like Zero's, and most of the metal shop rockets, is that they fail to utilize the one of the best parts of the design. Namely, the fact that we can harvest a much larger percentage of heat of combustion than is possible with most traditional burners. So, Zero's might be an okay starting point, but without subsequent radiators or mass storage, I think a little modern box stove would heat better with less fuel. He's got the front end, but is sorely lacking in storage/radiator in my opinion. These things move a LOT of air through them, so if you aren't storing the heat as best you can you have made a wicked wood fired hair dryer. Heating the air from your space and blowing it outdoors at a high rate. If you are going to run this much CFM through a heater, you really need to get that exhaust temp down as low as possible. A single radiator just doesn't do that effectively enough, in my opinion. All that said, I'm not as dismissive as Max. I think playing with fire, metal, and ideas is reason enough to build innovative metal heaters. I just do not think they are in the same league as even a simple masonry J, and that is where a lot of folks get off track. They spend endless effort trying to optimize metal heaters when they aren't even close to the starting line with respect to a simple masonry J. That's my opinion, anyway. An almost free contraption made of cast found clay/perlite, or stacked bricks, and a few barrels in series can provide exceptional efficiency and useable heat to a space. From there, the sky is the limit with regards to materials and configurations, which is one of the enchanting things about these heaters in my eyes. Edit: Oh, ha! I see 2Trance posted my casting video while I was writing this. That's my preferred method for creating the combustion unit. Matthew, It has been a while since I posted this thread and got to see your magnificent plans for the cast process rocket stove. After reading the posts here, I immediately abandoned further research in the use of metal. You guys convinced me of that. Last autumn, I was talking to a guy (Paul) who is the construction supervisor for a project here and he liked the rocket stove idea so much that he went home and showed it to his wife who immediately "became a convert". After not seeing him all winter, I ran into him this week and he came to me and told me about this great idea where he can create a rocket stove by casting it with plywood forms using fireclay and perlite. I told him it was designed by you and he said, "how did you know that?" I said, "cause 2Transform posted Matt's video on a thread I wrote about my rocket heater project." I told him where to look and the next week he came to me with Ianto Evan's book and said he was ready to start a project with your design. That having been said I am going to work with him on that because he wants to build one for his friend's "hoghouse" (man cave with a bar) and then for himself...(at the advice of his wife) and one for me, too! So now we are looking at a project of 3 of these...(takes me a while to "get to the point".) I would like to know your opinion on the idea of casting the riser tube with the same build as the plans you show here so that it is all one unit? That seems a bit more efficient with respect to assembly issues etc. This will make the outer plywood box you show now become an L shape, vs. a rectangular cubic shape.
We intend to use the ~7x7" *49 in2 format you describe. He wants to add a small ash pit at the bottom of the magazine like what is seen in Evans' book.
What is your opinion of the addition of the ash pit? I proposed to make it the same depth as one FULL size fire brick and that way the remainder of the stove can sit on a bed of fire bricks to further protect the material under it (assuming that it has a remote possibility of actually burning...)
If there are any "improvements" on the design before we embark on this project, NOW would be a really good time to find out about them so they can be incorporated into our 3 stove project.
Thanks...
Maintain course and speed
Trim sends
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Post by matthewwalker on Aug 19, 2014 17:58:30 GMT -8
Hi Sparks, glad you came back. I'll answer your questions as best I can, but please remember it's just my opinion. I'm pretty good at being wrong!
So, the casting....I wouldn't recommend one piece construction for various reasons, not the least of which is that it is a pain in the ass and you will regret having to cast such a large thing all in one go. Also, it's not that strong so it will probably crack at the joint anyway and you'll have two pieces regardless. Further, if the mix is wet it will just flow down out of the riser section and overflow the lower box. And so on. Just do it in two pieces if at all possible. I think it's important to use the little drum as a "riser canister" if you hope to move it into final position. It helps to hold it all together when lifting and carrying.
I'm not a fan of ash pits, it just delays cleaning and makes it harder to do, in my opinion. Clean the thing weekly and you'll have no problems. For sure you need non combustibles underneath the core, by the way. It will for sure catch anything below it on fire if it's set right on combustibles.
Peter has developed improvements to the standard J shape. You might consider incorporating them into your casting if you desire.
The only caveat, and I try to say it often so folks don't miss it, is that my casting mix is soft and fragile and your wood feed area will wear fairly quickly and need regular maintenance. My mix and the video is my attempt to show folks a simple way to cast a very high performance core with easily sourced materials and simple techniques. It has its compromises, and the durability of the feed is probably the biggest. I always recommend using an off the shelf insulated castable refractory if that is something you can source. That said, I'm about to start my 4th season with my heater, which I built using the technique I show in the video. Actually, it's more fragile as I hadn't started adding the furnace cement at the time I built this one, so mine is just simply clay and perlite. I patch up the feed a few times every heating season, say every two months or so, and I'm happy with it. Everything downstream of the feed is holding up just fine.
Lastly, it is meant to be a true core, or perhaps "liner" is a better word. It will not hold together well enough to use by itself. You have to cob around it to hold it all together. So, expect cracks and little bits to fall off at first. Get it in place and cover it in cob, patch any bits that fell or big cracks using the same mix, and you'll have a really high performance core. Good luck on your build, I'm happy to help any way I can.
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Post by sparks on Aug 23, 2014 5:28:28 GMT -8
Matt, thanks so much for the added guidance. I never "Went away", I only post when I have something to add or a question. One can spend too much time on the computer if not careful. I will incorporate all of your guidance and research Peter's improvements. More when I have something to show/say! Thanks again Sparks
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Post by sparks on Aug 27, 2014 17:19:50 GMT -8
ALCON, My next project is going to be a rocket stove water heater. The core of the stove will be cast and will closely follow Matt's recommendations. The project came to me as a result of the Permaculture Design Institute (Geoff Lawton) which is a group in Australia who among other things are very interested in promoting the rocket stove technology. Erika and Ernie Wisner are among their consultants. (not sure how that part fits in here) But I am also keeping an eye on Permies.com which is a site specifically dedicated to the Permaculture philosophy. Having said all that, I am going to be using a discarded autoclave jacket for the pressure vessel. The autoclave was simply discarded because it was not being used rather than because of material failure of some sort. The tank weighs close to 300 lbs. and is heavy gauge stainless steel. My guess is that it tolerates significant pressures and will work quite well for this purpose. Do any of you have any design recommendations for this project. My intention is to fill the jacket with water through which a copper tubing coil will pass. The cold water will travel through the copper coil and come out hot on the other end. The water in the jacket will obviously build pressure but the tank has several outlets to keep the pressure under control. I have seen this done successfully with a tank that has no where NEAR the strength of sophistication of this one. I am not worried about over pressure because of both the strength of the tank as it was designed but the ability to control the pressure with the multiple openings to allow that pressure to be released.
I just thought I'd mention it here in hope of finding someone who has done something like this before. Thanks in advance Maintain course and speed. Rig for rough seas. Trim sends
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