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Post by fasardi on Apr 30, 2019 8:08:34 GMT -8
Is there some room for a little change in the section? Really don't know which measures are standard here. I guess than making it smaller wouldn't be a smart choice, but maybe a little bigger if I couldn't get the right section? I reckon every dimension would allow a tolerance of 10% in the plus without problems. If at all possible, try to aim for 2 mm wall thickness of the parts. Especially in the stub more material means cooling isn't as effective. I checked out the dimensions in my town and for a 250 mm system i can make a floor channel horizontal part from three 40x40mm tubes (sorry, don´t know if i can name square tubes with that word... tube). That way the CSA will be 4332 mm2 (all tubes have 2 mm wall thickness, so CSA is really 38x38x3). This is a little bigger and really close to the 8,25 % of the riser CSA. I don´t know if i can get out with it, but if i could use a 50x100 tube i´ll have less welding to do, but the CSA will be 16% bigger than needed. For the vertical part, a 60x60mm will be 27% bigger than needed, but if i go down one measure, to 50x50mm, will be 14% smaller. So here are the questions! 1) If i go with the 60x60 tube, and maybe obstruct the upper end to have the CSA needed, will it work? 2) The opening in the top of the tube have to be 5.4% of the riser CSA, right? or just the bottom part of the tube have to have that CSA and the top part needs to have the same size as a P channel? 4) regarding the threshold, i was planning on doing it 9 cm in the box, and with a 9 cm height, because i extrapolate it from a post about that than i saw, am i right? 5) About the primary air opening, in the chart says it has to be 20% of the riser CSA, but i saw another post where Peterberg said than could be 25% but when the riser is hot should be diminished to 2/3 of that. Is that ok? 6 (and last, sorry!) The air inlet has to be in the bottom of the door, but since the Floor channel is in the middle, can the primary air come from a side of the door? i guess it will be better if it comes from both sides but i don´t really know. Thanks in advance!
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Post by peterberg on May 1, 2019 1:34:10 GMT -8
Fasardy, I started to recalculate your numbers and found some inconsistencies. Where's that 8.25% coming from? I seem to have stressed before the feed part should preferably be twice the stub part. So if the stub's csa is 5.4% of riser csa, the feed should be about 10.8%. Don't overthink it, I'm aiming for simple rules, not complicated formulas. Larger csa is preferred above smaller. The stub part's top opening, as drawn, is a bit smaller than it's own duct anyway because it's a triangle. I know that, but it has been tested like that and it works. Threshold is OK. Total air openings are about 25% of riser's csa, that's one. Using a p-channel the proportions are 20% primary and 5% secondary. Using a floor channel proportions are somewhat obscure since both primary and secondary air are fed through the same opening in or under the door. To start, I'll always open the inlet fully and the door a crack. When coming up to temperature, I'll close the door. When really hot, for example while burning two loads back to back, I'll deminish the air inlet somewhat. Air inlet isn't just a case of opening, it's a combination of opening and air velocity. The higher the velocity, the smaller the opening. Sounds logical, isn't it? As I said above, the best placement for the floor channel is behind the door. During the burn, emphasis is shifting from primary to secondary, exactly like what one would want in a dynamic combustion process like wood burning. Air inlet preferably over the full width of the door, at the same or lower level of the floor channel's feed. Distance between door opening and channel feed 50 mm or something like that.
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Post by peterberg on May 1, 2019 7:15:22 GMT -8
A couple of minutes ago I added another picture and downloadable file, according to the latest findings. The air flow is optimized in such a way that the top half of the port recieves the majority of the secondary air stream. Please see batchrocket.eu/en/designs#floorchannel.
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Post by fasardi on May 3, 2019 4:00:03 GMT -8
Fasardy, I started to recalculate your numbers and found some inconsistencies. Where's that 8.25% coming from? I seem to have stressed before the feed part should preferably be twice the stub part. So if the stub's csa is 5.4% of riser csa, the feed should be about 10.8%. Don't overthink it, I'm aiming for simple rules, not complicated formulas. Larger csa is preferred above smaller. The stub part's top opening, as drawn, is a bit smaller than it's own duct anyway because it's a triangle. I know that, but it has been tested like that and it works. Threshold is OK. Total air openings are about 25% of riser's csa, that's one. Using a p-channel the proportions are 20% primary and 5% secondary. Using a floor channel proportions are somewhat obscure since both primary and secondary air are fed through the same opening in or under the door. To start, I'll always open the inlet fully and the door a crack. When coming up to temperature, I'll close the door. When really hot, for example while burning two loads back to back, I'll deminish the air inlet somewhat. Air inlet isn't just a case of opening, it's a combination of opening and air velocity. The higher the velocity, the smaller the opening. Sounds logical, isn't it? As I said above, the best placement for the floor channel is behind the door. During the burn, emphasis is shifting from primary to secondary, exactly like what one would want in a dynamic combustion process like wood burning. Air inlet preferably over the full width of the door, at the same or lower level of the floor channel's feed. Distance between door opening and channel feed 50 mm or something like that. Thanks for your help Peterberg! "Using the steel ducts as drawn, the vertical part is 5.4% of the riser CSA and the horizontal part 8.25%. " It`s in the paragraph than starts with "The burns during winter of 2015/2016..."
Don`t know if I miss something in the calculations or your design changed. The total air openings are now clear to me! Thanks! One last doubt (for now, i won`t cheat myself). The angles of the cuts in the top of the vertical part are 45 degrees both?
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Post by peterberg on May 3, 2019 23:57:29 GMT -8
The 8.25% it`s coming from batchrocket.eu/en/designs#floorchannel "Using the steel ducts as drawn, the vertical part is 5.4% of the riser CSA and the horizontal part 8.25%. " It`s in the paragraph than starts with "The burns during winter of 2015/2016..." Don`t know if I miss something in the calculations or your design changed.The total air openings are now clear to me! Thanks! One last doubt (for now, i won`t cheat myself). The angles of the cuts in the top of the vertical part are 45 degrees both? You are right, this is the configuration that's on the website. About 1 1/2 year ago I switched to other proportions and forgot about it. To remedy this omission I made a new drawing and updated the website accordingly. All angles of the cuts in the top of the stub are 45 degrees, that's correct.
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Post by martinm on Sept 9, 2019 5:47:56 GMT -8
Helllo , on secondary air floor channel : considering the chance of the top , vertical part of the feed tube to deteriorate, also thinking of the option to change the geometry of this part by replacing it : I will try to make it in such way : the floor channel will have a hole with size a mm or more larger than the profile of the vertical part. in the refractory plate which is the bottom of the fire box there will be a square opening to receive the vertical part of the sec. air tube to go through . the two parts will not be welded , instead - the horizontal tube is "buried underneath the floor of the firebox and the vertical will be inserted in both the square hole in the refractory floor and the horizontal tube. A steel"sleeve"around the lower part of the vertical tube will be welded , so the part will "stay "on top of the refractory floor and thus will be easier to be replaced. Any one tried something similar ? Here the square hole in the floor of the fire box is seen : a cardboard dummy in place , beveled walls of port , so air supply could be closer to Heat riser while keeping the air flow of the sides of the ,metal tube going through the same area as above. : drawing explaining the "sleeve"
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Post by peterberg on Sept 9, 2019 6:26:46 GMT -8
I did spot a major hiccup in this layout: the beveled sides of the port. Several builders tried that before and every time the result was smoke from the chimney. Those beveled sides somehow seem to disrupt/change the aerodynamic properties of the core. In at least two instances the builders were able to change it back to 90 degree edges and everything was working as expected after that.
Having the feed part of the floor channel buried under the firebox' floor is OK. Has been done before and as far as I know there weren't unwanted effects. A channel through the brick construction could be one of the options, the feed doesn't need to be steel. Remember though, the feed need to be twice as wide as the vertical stub.
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Post by martinm on Sept 9, 2019 6:56:31 GMT -8
Thank you peterberg for the timely input ! I already mortared the first layer of bricks and fortunately took a short break before advancing further. So somehow the flow pattern on both sides of the secondary air duct gets disrupted being directed by the beveled corners - interesting . For sure I will continue building with the bricks straight to avoid this terrible effect. Hopefully soon will try to make a dry fit model and test this situation.
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