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Post by woodburner on Mar 24, 2012 12:57:20 GMT -8
Ah, but in a rocket stove, you get gas movement out of heat differential. The difference in temp (and density) between the heat riser and the barrel allows flow without a chimney. Anyhow, there will be plenty of heat left over to drive a chimney attached to the bottom. I think it might be difficult to get much of a differential with this particular stove as it is small. With the bigger barreled stove the differential would be larger. I think with this stove a chimney would help. |
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Post by thewongs on Mar 27, 2012 7:18:55 GMT -8
Sorry for the delayed response, but work got the better of me for the last few days. Anyway... I ran the rocket as a barbeque last Saturday at my wife's birthday bash and it performed very well indeed. The only thing I could say needs attention is the feed box. It's 4" box and the rest of the system is 3" tube, so it feels lke it's too big. Sometimes, if there was a lot of wood piled in, it would tend to start burning before getting low down in the box. Whenever possible, I blanked of about half of the top and it became sweet again. So... As the grille, it's cool. Now to get the heater part working. I think the plan I'm going for is to cut out about half of the bottom. This will hopefully allow the exhaust to escape while allowing me some access to insulate the burn tube and riser. There will not be a lot of insulation on these, but I think some is better than none? Any suggestions on what to use? I was going to find some larger diameter pipe then fill with vermiculite, but if there was something I could wrap around, it would be a lot easier? I imagine it would have to put up with some serious heat! When it comes to heating a bench, I will sit him on it and then the reduction of diameter can happen somewhere in there. I was hoping to make the bench light and moveable, so thought of doing a simple box with the 3" pipe running inside, heating the air inside. Does this sound like the sort of thing that could work? I was hoping to make a horseshoe shaped bench and have him sitting in the middle, but that may open the door to more problems with him feeding both sides at once? I guess it's going to be a "suck it and see" approach.  |
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Post by Donkey on Mar 27, 2012 7:52:21 GMT -8
Sorry for the delayed response, but work got the better of me for the last few days. Anyway... I ran the rocket as a barbeque last Saturday at my wife's birthday bash and it performed very well indeed. The only thing I could say needs attention is the feed box. It's 4" box and the rest of the system is 3" tube, so it feels lke it's too big. Sometimes, if there was a lot of wood piled in, it would tend to start burning before getting low down in the box. Whenever possible, I blanked of about half of the top and it became sweet again. So... As the grille, it's cool. Now to get the heater part working. Yeah, feed boxes that are larger than system size tend to cause problems.. I learned this the hard way too. I like to reach my arm inside the burn tunnel for cleaning, it's easier that way, so (at first) I tried making the boxes a little extra long. 'Course, the thing(s) would smoke back unless I covered the feed. They work a little better when narrowed slightly to make up for the extra length. Even so, you can't get away with too much, when the feed is extra long, even when narrowed to "system size" it can cause problems. I've learned how much I can get away with.. Just enough to get my elbow 'round the bend and no more.. (this is mostly with 8 inch systems, it ain't an issue with 4 inchers. ) You could get some kaowool. The stuff is amazing. Looks like un-backed fiberglass, handles the temperatures. Just wrap it around the pipe and maybe twist some wire around to keep it on. Interesting idea.. If the box is all metal and you make a duct in it to carry input to floor level, you will have a little bell stove. It could be pretty much any shape (as long as it's a bell, no ducting) and if you put a stove gasket at the connection, it might seal well enough to just set on.. Removable. A metal box will be too hot by itself to want to sit on (I think) so you might want to cover it in something non-flammable for that.. |
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Post by thewongs on Mar 27, 2012 13:33:06 GMT -8
Thanks Donkey. Your advice is always welcome (and helpful). For some reason kaowool seems to be difficult to find here in the North West of England, but I did find this stuff: www.bathpotters.co.uk/products/13mm-superwool-607-max-blanket/3986/And: shop.vitcas.com/ceramic-fibre-blanket-25mm-vitcas-ceramic-insulation-197-p.aspI imagine it would be the equivalent, or at least good enough for the job? I'm going to a major change to the feed box. After reading what you said about cleaning, it makes sense to make the box the correct size to work well, regardless of how hard access is. Then, hinge the whole thing so it can be emptied and also allow access to the fire tunnel at the same time (I hope my description is understandable?). I was originally going to hinge the bottom for emptying the ash, but this seems to make better sense (to my crazy mind anyway). The bench will be a long way down the line, but it doesn't stop me thinking about it. In fact, I seem to spend more time thinking about how to do that than anything else. I was thinking about a metal box directly below the stove, to handle the main heat (this could also be the point to reduce back to system exhaust size??), then doing the circular bench part as a ply or fibreglass box with the metal ducting suspended down the centre. Hopefully, the heat from the ducting will be enough to just warm the air inside, resulting in a warm surface to sit on... I HOPE! It gets a little confusing when I think about it as a horseshoe shape. Because it's in the middle, it would need to send heat down both sides. So, do I make the ducting half the system size on each side? 1 1/2" ducting sounds very small??? Or do I use 3" on each side and hope for the best? |
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Post by Donkey on Mar 27, 2012 19:32:00 GMT -8
Well.. If it's a metal box, or a series of metal boxes (or even brick (or adobe) boxes), you either wouldn't need ducting at all or just enough to connect the boxes (at the bottoms, as close to floor level as possible).
I wrote above "ducting" to connect the heater with the bench(es), if you think "channel" instead of "duct", you can paint a different kind of picture...
I like the hinge idea. Kinda makes sense at that size.
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Post by Donkey on Mar 27, 2012 19:47:36 GMT -8
OK... Imagine this: 3 metal boxes connected by channels or openings between, set low in the boxes but much larger than "system size". The middle box would need to be more wedge shaped, rather than square to get the horseshoe look. The stove would set on top of (and key into) the middle box and there would be a channel to guide heat down to the bottom of that box. Now, if you make a single horseshoe shaped box, entirely open inside, heat distribution would be VERY evenly distributed throughout the box and the chimney could be almost anywhere as long as it's attached to the bottom, at floor level. If you use multiple boxes, the heat distribution would still be quite good, but it would be hotter in a fairly direct line between the stove and the chimney.. Like this.. If the heater is on the center box and the chimney is on the box to the left, the center chamber and the one to the left would be hottest. If the chimney were on the center box as well, the center would be hot and both sides would be cooler though probably evenly. I imagine that a bit more heat would escape out the chimney, might be a good thing as I've no idea how much heat would be left. If you place the heater at one end (of three boxes) and the chimney a the other, you will get progressively cooler boxes.. And so on. I may be over complicating things here... Anyway, it's fun to think about.  |
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Post by thewongs on Mar 28, 2012 6:48:23 GMT -8
Yes. You are getting the picture inside my head now. As you say, it's an unknown as to how hot this bench will get. I like the idea of not needing 3" tube and going for the "bell" approach. It is fun to think about, but takes up too much of my brain time at the moment. With every step there is more and more ideas! Just picked up some more steel today, so will get the new feed box made and take some pictures soon. |
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