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Post by sailbad on Jan 2, 2012 11:04:41 GMT -8
I've spent the last 3 days reading everything I can find on the rocket stoves. I think I finally found what I was looking for in a post by Donkey back in Sept of 2007. I want to build a stove out doors. The purpose is to heat the ground under my 28ft 5th wheel trailer. I don't need the barrel to transfer heat. I need to heat the exhaust and transfer that heat to the surrounding ground. But as I write this, I wonder if I need the barrel to complete the combustion. The freeze line is about 24". I can use either 6" or 8" pipe.
Thoughts.....Sugestions?
Dave
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Post by ytksgmt on Jan 4, 2012 12:01:57 GMT -8
Just an idea, no empirical construction, no reliability based on experiences.
How about directly discarding heat to upward exhaust flue at the end of exhaust piping?
At normal RMH system, rising flows and corresponding downward flows construct push-power to (on?) the exhaust gas underground at the starting point, and terminal vertical pipe creates pull-power to the exhaust gas underground at the end point. This push&pull system's main engine is a push-power not a pull-power. To construct the push-power, certain rate of heat energy must be discarded through barrel surface. TANSTAAFL. But, some lunch can be cheaper than others. The Insulated Barrel type RMH shown in the picture beneath will have a pull-power as it's main engine, whose power will be created by the chimney effect at the vertical exhaust end. This system might be more efficient than normal RMH for ground heating, I guess.
I also guess that this insulated barrel type model may/must have some drawbacks. First, ignition might not be easy. Warming air in the flue pipe by heat conduction through metal surface takes time. You may have to set primer somewhere along the vertical exhaust pipe. Second, the air tightness of underground pipes must be guaranteed. In the insulated barrel system, pull-power is dominant, which means that at the majority parts of the underground pipes, pressure will be negative. Cracks or holes on the pipes cause the draft power to cease. Through holes, outer air (or water) will flow into the pipes. This drawback is the reverse of an advantage. At the negative pressure area, you are relieved from the fear of spouting of CO gas. (In the insulated barrel system, the riser is not indispensable. The non-riser system will be driven by the pull-power solely. This means that at almost all parts of the underground pipes, negative pressure will be maintained. This system will be safer than normal RMH in case set for heating ground of a green house.)
You can grasp the image of the system from the picture attached. My idea is simple. Avoid throwing heat away through barrel surface to air by convection or to space by radiation. In return, discard heat to exhaust flue gas at the end position. I have no data for deciding the proportions of parts in detail. Probably there is no experts of this type of stove. If you try and gain the data, you are the expert.
Well, because of my poor English literacy, I can't understand the size of the system sailbad needs. "28ft 5th"? "freeze line"? If the length of the pipe underground is in a range of normal RMH's max power, selecting the normal style would be better or wiser choice. At least, there are examples/samples to follow.
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Post by sailbad on Jan 5, 2012 19:34:26 GMT -8
Thanks for the reply and picture. However what I have in mind is much close to a standard RMH. The fire box would be on the surface feeding an exhaust that would be down at least 24" to the top of the pipe underground. The temperature under the ground is approximately 50* which I think would assist the draw. I would use 2 45* elbows to reduce friction in the pipe. I have 2 questions. First what happens if you insulate part of the barrel? Second can I get away with 6" pipe or should I plan on 8" from the start.
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Post by canyon on Jan 6, 2012 11:17:12 GMT -8
Be sure and put cleanouts for every run of pipe even if it means having a dugout access pit. 8" systems are the way to go but you can split it into two parallel 6" runs if it makes sense for available materials etc. I don't think 50 degree soil temp is going to help with draft. you definitely will need a primer fire at the exit stack end to get it going. Insulating the barrel justs allows more heat to go into storage directly, as long as the materials can handle the higher temps, no problem. Please share how things work out for you as the common pool of experience is valuable to many.
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Post by mintcake on Jan 6, 2012 11:20:49 GMT -8
Silly idea... What happens if you have: a) An extractor fan at the end of your heat pipe. b) No a heat riser, just your 2 45degree bends. c) A well insulated and longer than normal burn tunnel (taking the place of the heat riser)
Start the fan to get the air flowing well, and you should have sufficient airflow, turn it off when the fire's out. Then hopefully your combustion is over before the burn tunnel ends and you might get rocket-stove efficiency without the riser. You'll probably want something to make some turbulance though, so maybe you *should* have a nice sharp corner in the burn tube.
But... Why do you want to heat up all that soil? Are you trying to do underfloor heating, or just keep your toes from getting so cold? If the latter, then surely replacing the top 2 -4 inches of soil with some insulating material (e.g. extruded polystyrene panels, or even hay) would give you the same benefit. If it is for real heating, then I'd suggest you surround your heated soil with lots of insulation anyway.
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