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Post by twohorsepower on Jun 9, 2013 13:09:06 GMT -8
Looking for a point in the right direction re a suitable system size based on the materials we have available. I have had a quick scan at the ianto evans book and haven't yet got a firm idea of what we can do with the obtianium to hand.
We have 2 very heavy duty cylindrical compressor tanks made of perhaps 3 or 4mm (1/8"- 1/6") sheet steel which we are hoping to use to make a RMH which also heats water to pump into radiators. the RMH will heat a workshop directly, and indirectly the water will be used to heat a few rads in small workspaces further away from the RMH.
The smaller tank is 450mm diam X 1500mm high (18" D X 60" H), and the larger tank is 760mm diam X 1500mm high (30" D X 60" H). Both tanks have a domed top.
My very limited knowledge tells me that most RMHs use a system size (internal burn tunnel,riser, and exit flue diameter) of either 6" or 8" and a 55 gallon oil barrel to surround the riser. Would I be right in assuming that neither of these tanks would be useful as a riser, but that one of them may be good as a heavy duty barrel? And if the smaller is no use as a riser, would a riser cast using a mix of fondu cement (high alumina), sand and vermiculite be suitable (I believe this mix is suitable for 1000c (1800F ish))?
For the water heating, would it be reasonable to consider a copper coil wrapped on the outside of the barrel and then well insulated, and in this way protect the copper from the very high flue gas temps, or even perhaps set the copper coil in sand outside the barrel and then a layer of insulation around this?
Any pointers gratefully received.
Rgds
2HP
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Post by satamax on Jun 9, 2013 14:10:07 GMT -8
Both tanks sound good. But if you haven't built a rocket before. If i were you, i'd avoid the water heating part. Where are you located?
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Post by twohorsepower on Jun 10, 2013 14:46:25 GMT -8
we are in ireland. we are well versed in handling/plumbing hot water having worked with solar hot water systems of various kinds, albeit with solar as the heat source normally at <100c, the 1000c temps of a RMH is something quite different. but at least we know what needs to be done to avoid steam explosions.
the hot water aspect of this RMH is fairly central to the requirements so it is not something we can ignore at this stage. we are certainly not going to fit water pipe between the barrel and the riser. would welcome suggestions for where the best place would be to fix/ bury / embed the water pipework. the water loop will be pumped, but will have all the necessary built-in venting required to avoid a build up of pressure in the event that the pump fails. we don't need a buffer tank, and we probably need to circulate water at no more than 60c around the rads. we could use a lladomat,esbe or similar thermic valve to ensure the coil grabbing the heat stays above a minimum temperature and does not overcool whatever section of the RHM we extract heat from.
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Deleted
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Post by Deleted on Jun 11, 2013 3:22:18 GMT -8
You may consider using a heat chamber.
A heat chamber works like a heat pipe.
The tubing inside the heat chamber would have no direct contact
to the fire or hot and aggressive flue gas.
There would be very small temperature differences inside and outside of the heat chamber at any point.
You could use tubes made of other materials than copper.
Fin tubes would be the best.
Making a heat chamber is pretty simple and there are virtually no limitations to the size.
Just weld a chamber from eg. stainless steel and let only a small hole open.
Through the hole fill in a small amount of water,
just slightly more as needed mo make the whole inner surface wet,
including the surface of the tubing, and to fill the volume with steam.
Then heat the chamber until steam is escaping from the hole and close the hole by welding,
while the water inside is boiling.
The water in the chamber will then start to boil at 0°C.
The heat chamber will reach normal pressure at the temperature it has had at the moment the hole was closed.
Depending on the volume and the amount of extracted heat it may never reach a high pressure.
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Post by peterberg on Jun 11, 2013 5:48:34 GMT -8
We have 2 very heavy duty cylindrical compressor tanks made of perhaps 3 or 4mm (1/8"- 1/6") sheet steel which we are hoping to use to make a RMH which also heats water to pump into radiators. the RMH will heat a workshop directly, and indirectly the water will be used to heat a few rads in small workspaces further away from the RMH. The smaller tank is 450mm diam X 1500mm high (18" D X 60" H), and the larger tank is 760mm diam X 1500mm high (30" D X 60" H). Both tanks have a domed top. What do you think of this: since both tanks are of the same length but different diameters, you could think it over to weld the smaller one inside the other. Or maybe partly, the point here is the creation of a stove which would heat water in a reliable way. Since you are knowledgeble enough to use a laddomat valve this could be done. The space between the outer and inner tank would be filled with water, the pump would take care of the necessary circulation. The riser could be built from refractory cement and vermiculite, yes. Mind the gap around the riser, that's very important. Another way to do it is wrapping the coil around the barrel and insulate around it. Has been done before, it will work but at a low temperature. The coil inside the barrel is highly dangerous because of steam lock or other mishaps. |
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Post by twohorsepower on Jun 11, 2013 12:25:20 GMT -8
Karl - I've never heard of a heat chamber before but from your description it uses the same method of energy transfer as the heat pipes used with evacuated solar panels. i wonder, instead of sealing the chamber with weld, would it be better to tap a thread into the wall and fit a 'ball and sping' type pressure relief valve? And If the chamber wall is made from SS/inox, is there a reason why the internal pipework and fins could not be copper?
Peterberg - Re your idea of welding the two tanks concentrically to make a single tank, would this be to create a water jacketed barrel to surround the riser, i.e., keeping the two domes on the tanks? Or remove the two domes and essentially make a water tank with a single vertical fire tube, which we could set above the riser, similar to the water boiler concept used at milkwood farm (http://milkwood.net/2011/08/03/our-rocket-stove-water-heater-2-5-years-on/)?
Thanks to both of you - These ideas have got me thinking.
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Deleted
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Post by Deleted on Jun 11, 2013 23:29:03 GMT -8
i wonder, instead of sealing the chamber with weld, would it be better to tap a thread into the wall and fit a 'ball and sping' type pressure relief valve? You need to get all the air out of the chamber and fill it with steam at normal pressure and seal it. Then later about 500°C would be needed to get 1 bar over pressure. (1/373*773) As you can see there is no pressure relief valve needed. If the chamber is cold there will be a -1 bar vacuum. The chamber walls needs to be rather thick enough to resist the vacuum than the over pressure. Of course the pipework and fins could be copper. Electro erosion doesn't happen with purified water or steam. But as there is virtually no size limitation to the (insulated) chamber its possible to use cheaper materials with a lower heat conduction. The steam will distribute the heat quite evenly over the whole volume. |
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Post by peterberg on Jun 12, 2013 2:13:48 GMT -8
Re your idea of welding the two tanks concentrically to make a single tank, would this be to create a water jacketed barrel to surround the riser, i.e., keeping the two domes on the tanks? Yes, that's the general idea. |
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Post by melkijat on Mar 21, 2022 5:12:39 GMT -8
Re your idea of welding the two tanks concentrically to make a single tank, would this be to create a water jacketed barrel to surround the riser, i.e., keeping the two domes on the tanks? Yes, that's the general idea. Hi Peter, I hope I can revitalize an old thread... Do you have idea what ISA would be for such water jacket? I guess it is not so straight forward as for ISA for ordinary bell? But at the other hand, it was concluded that ISA needed for steel drum or brick bell is practically the same. |
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