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Post by hanuman108ian on Mar 22, 2019 7:25:46 GMT -8
Hi new to the forum could not find this topic. I just finished a 6in batch rocket with a cob bell in a greenhouse. The draw was not great so I starter to problem solve and I think the floor channel size is off. We used the demensions for the batch and riser from batchrocket.eu but they are for a p-channel and we did not modify it for the floor channel I am wondering if there is a modification that I can do without ripping everything apart. Ie shorten the vertical shaft of the floor channel or increasing the hieght of the port or both. Thx ian
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Post by gadget on Mar 22, 2019 7:37:13 GMT -8
I would run it and dry it out first. Wet cold new heaters usually don't work as good till they dry out. Mine took a week to fully dry out.
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Post by peterberg on Mar 22, 2019 13:32:38 GMT -8
Hi new to the forum could not find this topic. I just finished a 6in batch rocket with a cob bell in a greenhouse. The draw was not great so I starter to problem solve and I think the floor channel size is off. We used the demensions for the batch and riser from batchrocket.eu but they are for a p-channel and we did not modify it for the floor channel I am wondering if there is a modification that I can do without ripping everything apart. Ie shorten the vertical shaft of the floor channel or increasing the hieght of the port or both. Hi Ian, welcome to the boards. The p-channel is another animal, the floor channel works on different principals. In general: the horizontal feed duct of the floor channel is as far as I am aware of, in several drawings specified as twice as large as the vertical part, cross section area speaking. Which means the vertical part works as a temporarily restriction where the gas speed should increase. In other words, it is a venturi. Extending this vertical part there's a fat chance it won't work as intended or not at all. Increasing the height of the port won't help either, you'll wreck the tested configuration by doing that, which could end in worse results quite easily. And I'll second Gadget, all the water in the heater is the main problem now. You didn't mention the size of the channel, please specify. Is the cob bell's csa conform specifications?
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Post by Orange on Mar 23, 2019 0:54:18 GMT -8
p-channel is easier to make. So the floor channel has significantly better performance than the p-channel?
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Post by peterberg on Mar 23, 2019 1:34:06 GMT -8
p-channel is easier to make. So the floor channel has significantly better performance than the p-channel? Yes, performance of the floor channel is better in the sense there's a stronger tendency to keep the hottest zone low in the riser. Using a p-channel it goes up and down the riser, accompanied by the possibility of exiting the riser. Which is coupled to spikes of CO and also smoke. And on top of that: the floor channel is easy to replace while the p-channel isn't.
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Post by hanuman108ian on Mar 23, 2019 10:00:33 GMT -8
So I pulled the floor channel out completely and fired the rocket and I could see a better vortex and draw. The cob is still wet but drying fast with the firings. The floor channel was reducing the opening of the port in the back of the batch significantly thus slowing the draw. I have pics but having issues posting them here. The top of the floor channel was 2cm below the top of the port almost. As I said the dimensions of the batch don’t account for the floor channel sitting at the bottom so I loose 1.5 in of port. This floor channel was not my design.
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Post by hanuman108ian on Mar 23, 2019 10:02:58 GMT -8
The cob bell was made to the suggested surface.
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Post by wiscojames on Mar 23, 2019 10:39:17 GMT -8
Hanuman - you'll need to host the pictures elsewhere and link to them.
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Post by drooster on Mar 23, 2019 13:14:56 GMT -8
The floor channel was reducing the opening of the port in the back of the batch significantly thus slowing the draw. <iframe width="17.56000000000006" height="4.199999999999989" style="position: absolute; width: 17.56000000000006px; height: 4.199999999999989px; z-index: -9999; border-style: none;left: 15px; top: -5px;" id="MoatPxIOPT0_67299040" scrolling="no"></iframe> <iframe width="17.56000000000006" height="4.199999999999989" style="position: absolute; width: 17.56px; height: 4.2px; z-index: -9999; border-style: none; left: 824px; top: -5px;" id="MoatPxIOPT0_77041618" scrolling="no"></iframe> <iframe width="17.56000000000006" height="4.199999999999989" style="position: absolute; width: 17.56px; height: 4.2px; z-index: -9999; border-style: none; left: 15px; top: 85px;" id="MoatPxIOPT0_81836220" scrolling="no"></iframe> <iframe width="17.56000000000006" height="4.199999999999989" style="position: absolute; width: 17.56px; height: 4.2px; z-index: -9999; border-style: none; left: 824px; top: 85px;" id="MoatPxIOPT0_91440241" scrolling="no"></iframe> Is your floor-channel outlet too close to the port?
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Post by fasardi on Apr 24, 2019 16:00:02 GMT -8
Hi Ian, welcome to the boards. The p-channel is another animal, the floor channel works on different principals. In general: the horizontal feed duct of the floor channel is as far as I am aware of, in several drawings specified as twice as large as the vertical part, cross section area speaking. Which means the vertical part works as a temporarily restriction where the gas speed should increase. In other words, it is a venturi. Extending this vertical part there's a fat chance it won't work as intended or not at all. Increasing the height of the port won't help either, you'll wreck the tested configuration by doing that, which could end in worse results quite easily. And I'll second Gadget, all the water in the heater is the main problem now. You didn't mention the size of the channel, please specify. Is the cob bell's csa conform specifications? I think there's a general need of specifications on how to do a floor channel. For Ian and me at least...
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Post by peterberg on Apr 24, 2019 23:49:58 GMT -8
Drawing of a floor channel is available on the batchrocket website, as part of the second cast core. For the downloadable drawing see the end of the article, please read all the information thoroughly. I'll give it some thought to include a separate drawing.
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Post by fasardi on Apr 25, 2019 1:05:57 GMT -8
Thank you, Peterberg. I saw it, just don't really know how to extrapolate it to different sizes of cores. Is distance between the portal and the channel fixed? The height of the vertical part is? I guess the section of the vertical part is proportional to the size of the channel at the outside. Making the first drawings of my future core i run with this problems and went for a p-channel instead, but in this thread you said than a floor channel is better... Again , thanks for your help! I wouldn't be even thinking about making a stove if this forum didn't exist
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Post by peterberg on Apr 25, 2019 2:56:15 GMT -8
It's quite simple, really. Let's see what your questions are and I'll try to answer them.
#1 The distance between the channel and the port are fixed. In the sense that left and right of the channel (between corner of the port and side of the vertical part) there should be as much space as half of the width of the port. Sounds logical to me, this way there won't be any extra restriction.
#2 The height of the vertical part without that "cap" on it, is half of the port height.
#3 The section of the inside of the vertical part is proportional to the size of the horizontal channel at the inside. This is logical, since wall thickness of the respective parts could be different.
Scaling of the respective parts is actually simple: when scaling up from 6" to 8" for example means every linear measurement is going up 33.33%. This holds true for virtually every figure, one notable exception being the depth of the port.
Another rule of thumb: the horizontal channel's (known as "feed") internal csa should be twice as large as the internal csa of the vertical part (known as "stub").
Dimensioning is done like that so that the secondary air is fed into the upper half of the port. The difference in csa of both channel parts means air velocity in the stub is much higher than in the feed. Thus creating another venturi, and due to the higher velocity cooling of that steel part is much better than using the same csa throughout.
It's possible dimensioning of the drawn channel is different. The above laid out rules are according to latest findings.
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Post by fasardi on Apr 25, 2019 3:23:45 GMT -8
Thanks for taking the time for such a elaborated answer, really clear for me, hope it helps other people in my situation. 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?
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Post by peterberg on Apr 25, 2019 6:12:32 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.
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