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Post by Karl L on Dec 19, 2017 10:22:09 GMT -8
Thanks, Joseph, but I was looking for sources in the UK :-)
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Post by Karl L on Dec 17, 2017 11:42:01 GMT -8
I can answer two of those. Yes, they are safe. Mortar should be clay/sand. Thanks, Matthew. How do I get hold of, or make, clay/sand mortar?
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Post by Karl L on Dec 17, 2017 0:27:03 GMT -8
I have some questions about materials used in the construction of the batch rocket or double shoebox stoves.
What specifications or brands of ceramic fibre board would be best? (For use in situations where high temperature, low strength, some rigidity, and insulation are required.)
Are these boards relatively 'safe' - i.e. non-carcinogenic (e.g. like Superwool: non-bio-persistent).
Also, another question:
When constructing from heavy or from insulating fire brick, what is the best mortar to use?
Is this different for a bell and a firebox?
Who are the best suppliers of these materials in the UK?
Thanks!
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Post by Karl L on Oct 25, 2017 23:44:44 GMT -8
Thanks - and sorry for not noticing!
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Post by Karl L on Oct 25, 2017 14:15:16 GMT -8
Hi Peter,
Can you post the Sketchup file for that, so I can understand the details of the secondary air arrangement?
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Post by Karl L on Jan 24, 2016 9:47:28 GMT -8
Description:
This is partly an experimental stove, to test ideas. It is designed to be taken apart easily, to modify the design as experiments progress.
The batch box is constructed from steel, lined with 25mm fire brick or Vermiculite board. The batch box port is on the left hand side at the back, with a short tunnel leading to the port and riser, so that the 'riser' sits inside the brick bell.
(The 'riser' is very short, relying mostly on chimney draft - the experiments I've done show that when combustion is complete, all the burning gets done in a very small volume.)
There is a Walker-style secondary air pipe in the short tunnel. This is a simple - made from 50mm square ERW steel tube.
The port itself has a sloping top surface - to try to direct the jet of flames downwards into the 'riser'.
The brick bell is constructed so that it has a large radiation surface facing out into the room. In the top of the bell is a stove-glass window, so I can see the combustion in the riser.
There is a vermiculite board 'gate valve' (inside the top of the batch box) that can redirect the exhaust from the riser back into the top of the steel batch box, or can divide the exhaust between the steel bell and the brick bell.
The exhaust from the brick bell exits from the bottom of the bell, under the 'riser' and into the bottom of the batch box shell, where it goes up to the flue exit. This path might be insulated so as not to lose more heat.
The chimney/flue connection is an existing small old fireplace built into the wall. The chimney will be lined with a 150mm stainless steel liner, with vermiculite insulation. It is ~10m high.
I've not shown the steel bell - I forgot to include it in the drawing I uploaded. This would sit on top of the main batch box, instead of the flat top shown.
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Post by Karl L on Jan 24, 2016 1:04:07 GMT -8
OK, thanks - I've done that - edited original post.
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Post by Karl L on Jan 24, 2016 0:30:29 GMT -8
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Post by Karl L on Jan 23, 2016 11:24:33 GMT -8
Thanks for that, Karl! -- I didn't see your post because I was so busy doing calculations. Your link above shows that HTC varies a bit with temperature, but my estimate wasn't too far out Karl L
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Post by Karl L on Jan 23, 2016 10:54:05 GMT -8
I've done some calculations of convected and radiated heat from a bell.
For a surface at temperature T, convected heat is: Hc = h A DT
Hc = Convected heat h = Heat Transfer Coefficient A = Surface area DT = temperature difference between hot surface and air.
For a vertical plane surface, h is about 4-6 W/m2 K (I calculated this from a ~2Kw domestic radiator, guessing the effective surface area, but there are similar values listed on line).
Radiated power is:
Hr = S E (Th^4 - Ta^4)
Hr = Radiated Heat. S = Stefan-Boltzmann constant = 5.6×10-8 W/m2K^4 E = emissivity (This is about 0.75 for fire brick and for 'oxidised steel'.) Th = temperature of the hot surface Ta = the ambient temperature. '^4' means Raised to the forth power (I.e. squared, then squared again).
I made a simple spreadsheet to calculate convected and radiated heat for different temperatures, etc, assuming that the convecting surface area and the radiating surface area are the same, which would be true for a barrel or a bell, but is not true for a finned domestic 'radiator'.
The results are shown below for a Surface area of 1.0 m2, Heat Transfer Coefficient of 5, emissivity of 0.75, ambient temperature of 20C: T(C) C(kW) R(kW) R/C 50 0.15 0.15 1.0 100 0.4 0.5 1.3 150 0.7 1.0 1.6 200 0.9 1.8 2.0 250 1.2 2.8 2.5 300 1.4 4.2 3.0 350 1.7 6.0 3.6 400 1.9 8.3 4.4 450 2.2 11.2 5.2 500 2.4 14.7 6.1
The R/C column compares radiated power to convected power. As you would expect, radiation increases much faster with temperature than convection because it depends on T^4, not just T.
The front of my current (non-rocket) stove is usually at ~350C, so this area is radiating ~4 times as much as it is convecting. But all of the stove surface is hotter than 50C, so radiation is everywhere the dominant heat transfer mechanism.
Let me know if you want a copy of the spreadsheet.
Karl
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Post by Karl L on Jan 23, 2016 8:51:30 GMT -8
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Post by Karl L on Jan 22, 2016 10:00:51 GMT -8
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Post by Karl L on Jan 18, 2016 15:39:09 GMT -8
I've been thinking about why Peter's vertical batch box slot, combined with the 'S-portal' or the 'Walker port' might work well.
These arrange the burning wood gas and the secondary air as three flat sheets or layers. These layers have a large area of contact with each other, which gives more opportunity for the air and wood gas to make contact and react (burn). The turbulence in the double vortex is then even more effective, because the layering has already done a lot of the mixing.
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Post by Karl L on Jan 18, 2016 15:19:10 GMT -8
Thanks everyone, This discussion is very useful. I have been struggling to think about all of those factors, and it's useful to know that it's not easy!
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Post by Karl L on Jan 17, 2016 9:00:18 GMT -8
Thanks :-) 34C sounds like a very low temperature, and 15-24C is below typical room temperature! I was expecting people to be answering 100C at least!
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