Ralf
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Post by Ralf on Nov 7, 2016 1:58:36 GMT -8
Tanks Peter for your reply !
Do you think a J-tube will service less ISA than a batch box ?
If I calculate the planned ISA without the ytong I´m at 3,75 sqm, the bench is 4 meters long and will be 35 cm high on the inside of the bell.
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Ralf
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Post by Ralf on Nov 6, 2016 22:42:34 GMT -8
Hello to the experts,
I´m about to construct my thermal battery for my rocket mass heater with an already finished combustion unit on wheels (6-incher). Since it´s situated in a rented workshop I want to be able to dismantle it if necessary, so I planned it as a hollow bell bench built directly on the concrete floor slab and made of concrete steps (as front side) and multi-layered flagstones (as top), with tiles on the surfaces, all mortared with cob.
Concerning this build I have two questions:
1) The slabs I will use are exposed aggregate concrete / washed conrete so I thought to put this on the inside to have a bigger heat exchange surface. With this bigger "rough" surface of half-embedded gravel, do I have to change the calcuation of my maximum ISA for heat exchange ?
2) The bench sits along a wall that doesn´t need to be heated, so I thought of making the backside of the bench with blocks of insulating air-entrained concrete (Ytong). Does an insulated internal surface still count in a calculation of max. ISA ?
And if you think any of those ideas might cause problems please let me know.
Thanks, I´m very grateful for all the great Information and generosity on this board !
All the best, Ralf
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Ralf
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Posts: 42
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Post by Ralf on Apr 10, 2016 4:13:25 GMT -8
Hi everybody, here´s a small video clip of my first almost finished build, a 6" J tube combustion unit which is mounted on wheels. I tend to think that at this point it doesn´t make much sense to go into details since the unit is not time-tested. It was only an experimental run, not hooked up to a thermal battery, and since summer is approaching the real testing will be not before next winter. It´s just for the joy of watching fire buring upside down This is the third test run, the first two had no vertical chimney stack but only a horizontal run of 1m attached. With a half-closed feed opening this worked acceptable, but nothing compared to 2 m of uninsulated tube going up. Perfect rocketieness and much more heat generated. Enjoy & feel free to ask questions. Ralf
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Ralf
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Post by Ralf on Mar 30, 2016 23:17:23 GMT -8
Hi Terry,
thanks for describing the burn tunnel geometry ! Another idea for your "octagon batch box": If you manage to cut the angles of the "wedges" so they fit tight you can also put a few band clamps around on the outside, maybe shape grooves for them in the hebel blocks so they won´t slip. If you cosse a light gauge they will have enough flex to expand and contract along with the burn cycle while holding everything together and won't crush the hebel blocks.
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Ralf
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Posts: 42
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Post by Ralf on Mar 29, 2016 22:23:04 GMT -8
Hi Terry,
thanks for the nice and explanatory pictures ! Just to clarify your flame path: After the letterbox / port, you have a horizontal tunnel with a 90-degree bend to the left and shortly after that anoter 90-degree bend upwards to the heat riser ? Does the tunnel have a wider csa than the letterbox port ? I tend to think that this horizontal bend in the burn tunnel replaces the "rams horn" in terms of mixing the gases nicely, though it might induce a little more drag.
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Ralf
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Posts: 42
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Post by Ralf on Feb 19, 2016 11:53:38 GMT -8
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Ralf
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Posts: 42
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Post by Ralf on Jan 31, 2016 1:11:35 GMT -8
Hi, these ceramic tubes also come in 2.3 " / 6 cm outer diameter, I'm afraid the inner csa of these are a bit short of 3.14 sq in anyway. Good to see that your solutions work perfectly for you, just wanted the information to be up here in case somebody wants to try.
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Ralf
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Post by Ralf on Jan 29, 2016 23:58:50 GMT -8
Hi Matt & John,
did you think of or try using kiln shelf support columns from pottery supply for the Walker port ? They´re made of dense and hard "Cordierite" material which is able to withstand pottery firings up to 1300 °C / 2370 °F that last for hours or days while supporting the shelves for pots to be fired. Here in Germany they´re pretty cheap ( under 10 bucks a piece). Most useful: They´re hollow and a vertical slot for the secondary air release could be easily cut in the wall with an angle grinder or a tile saw. Standard dimensions here are: 43mm / 1,7" outer Diameter, 0.7" or 1" inner diameter, thinner-walled versions available, lenghts up to 300 mm / 11.8" . If you mount those in a connector at your bottom air supply tube degradation should be fixed. Only thing in question would be how they handle thermal shock, but since Coriderite has a very low expansion coefficient I think it´s worth a try. I bought some of these myself, but committed to be well-behaved and finish my first-build standard j-tube first before starting wild experiments ;-)
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Ralf
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Posts: 42
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Post by Ralf on Jan 13, 2016 9:01:13 GMT -8
If I add a bypass before the bench and start the stove until the chimney gets warmed up I can avoid to run the bell under pressure, right ? Pinhead, I just read through some of your threads, which solved another worry about my heat riser: I´ll probably also use a heat riser mix like yours with furnace cement and Vermiculite. Thanks again, I´ll present my work in detail when it´s running :-)
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Ralf
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Posts: 42
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Post by Ralf on Jan 13, 2016 8:22:00 GMT -8
Thanks so much for the detailed answer, all of that sounds very reasonable to me. One thing that I like about this kind of bell bench is that it can be easily shortened / expanded by removing or adding a barrel half at the dead end, so I will be able to tune the system to my local conditions. Where do you have the cleanouts for your bell bench ? My guess would be to punch a hole and fit a cap at the vertical wall of the dead end.
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Ralf
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Posts: 42
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Post by Ralf on Jan 12, 2016 21:11:17 GMT -8
A hearty hello,
after becoming a RMH addict and absorbing tons of information I found here and at permies.com, I started to build. My plan was to avoid asking a lot of questions and use all the good advice, but I have to make one exception:
My build is a standard 6-inch J-tube system according to „the book“, P-channel and trip wire included, only high quality and insulative refractory material in the flame path, metal (all stainless) beginning only on the outside of the heat riser.
I´ts located in a one-story brick shack with two rooms, each 12 sqm / 130 sqft, combustion unit will be in one and thermal battery in the other room.
For the thermal battery I plan a straight low bench which could be up to approx 4 m / 13 ft long or shorter, depending on calculated flue run or max. ISA of a bell. Connection to a 3.5 m / 11 ft chimney will be on the same end as the input.
I like the idea of a low friction but almost complete heat extraction, hence the questions:
* For the setting described, would you recommend a) traditional flue in system size, running back and forth with a u-turn, b) an analogue but shorter run with an increased pipe diameter (8 inch, Matt Walkers bench comes to mind) c) a half barrel bench (inspired by Kirk Moberts recent retrofit, I can get stainless barrels of 60 cm /23 in diameter) ?
* Is the recommended maxium bell ISA the same for batch boxes and J-tubes ?
* If a half barrel bench is an option, how to seal it securely from gas leakage, is it enough to cob it in ?
* Best spot and method for installing inspection access(es) ?
* How to drain eventual condensation from a long half barrel bell if it sits on a floor slab ? I was thinking of a sealed and angled internal floor with a drip line at the lowest spot. I´ve got plenty of big concrete paving slabs for construction.
* Best positions for feed and exhaust when they have to be located at the same side of this dead end - low ceiling bell ?
I could also try and put in the half barrels in with the cut face up to ease condensation collection and drainage, build the bench so that the load is not on the half barrels and rest them in perlite insulation underneath. Good idea ?
Thanks for your valuable time answering these questions. I´m documenting my build with a lot of filming and photographing, when it will be up and running I will return some of the brilliant input I got here !
Cheers Ralf
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Ralf
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Posts: 42
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Post by Ralf on Dec 27, 2015 5:50:39 GMT -8
Hearty Hello to manuel and the forum !
It´s my first post (after a year of becoming a total RMH-addict and reading everything about it) since I´m happy to see that you incorporated a feature I´m also going to do in my first build, which is under consruction these weeks. It´s the crossing and intersecting pipes at the manifold area. My question is: Did you measure the opening by eyeball or did you use a formula ? I figured out a formula for a template that´s glued on the surface of one of the tubes for cutting the opening with a jigsaw (since I don´t have a plasma cutter or other "easy-go" equipment). The shape it produces looks reasonable for different amounts of penetration of the tubes, but I want to be sure if I got it right, also plan to check it with some cardboard tubes first.
I also like your built-in Walker channel, I found that "flat-liner" CO diagram in his thread very intriguing.
Cheers Ralf
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