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Post by Deleted on Jan 6, 2018 7:03:43 GMT -8
Trying to get a j-tube to work with a riser that's marginally higher than the feed and a relatively long tunnel is doomed to fail. Also, it might be that the material isn't as insulative and/or dry as one thinks. As I have stated already in this thread : I had no problems with similar dimensioned cook stoves on the Philippines
which were made from less insulating clay, by using similar wood.
Some tropical biomass produces large amounts of ash.
Oversized tunnels help to cope with that.
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Post by esbjornaneer on Jan 6, 2018 7:34:14 GMT -8
If the riser has double the high of the feed and the feed has 900 K how much is required in the riser ? I will show my ignorance of maths and chimney effect! I found a formula onlineI think I am right to calculate draft for heat riser {D(hr)} and draft for feed tube {D(ft)} and as long as D(hr)>D(ft) it draws up the heat riser. So as P, and the factor 0.52 are the same on both sides of the ">" in the equation they can be eliminated. D(hr)>D(ft) H(hr) × ((1/T)-(1/T(hr))) > H(ft) × ((1/T)-(1/T(ft))) as it is H(hr) you ask for: H(hr) > ((1/T)-(1/T(ft))) / ((1/T)-(1/T(hr))) x H(ft) T=absolute atmospheric temperature (I assume = standard atmospheric absolute temperature) = 293.15K T(ft)=900K if T(hr)= T , then your balcony roof is not tall enough as H(hr) reaches infinity. but as the difference between T(hr) and T increases you soon get down to a handleable height of H(hr). So say T(hr)=T+60K=353.15K H(hr) > ((1/293.15)-(1/900)) / ((1/293.15)-(1/353.15)) x H(ft) H(hr) > 3.97 x H(ft) If you can achieve 900K in the feed tunnel without a 60K increase at the other end of the burn tunnel it will be tricky though  I have not kept up with J-tube development since 2015 but I think the advice was for the heat riser part to be 4x feed tunnel height. And will the temp of T(ft) reach 900K instantly? If when establishing the draft direction T(ft) is only 506.15K(=T+233K) at the ignition temperature of paper. At which point you only need a T(hr)=328.15K=T+35K for a H(hr)=4xH(ft) j-tube. It was due to maths I was thrown out of University. So it would not surprise me if I am wrong.  |
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Post by Deleted on Jan 6, 2018 9:29:16 GMT -8
To calculate the tilt point one can ignore the atmospheric pressure.
Only the volume increment respectively the resulting reduction of pressure is of any interest.
Assumed the environment temperature is 300K then the volume increment at 900K is three times and the pressure is reduced to one third.
The feed side has two gas colums of equal hight,
Thus the pressure in the column above the feed is 3/6 and in the feed 1/6 and the combined pressure 4/6.
For the tilt the pressure in the riser exertet by the gas column in the riser needs to be reduced to 4/6 or below,
which can be achived by a volume increasement of minimum 1.5 respectively a temperature increasement to above 450K.
For a 3/1 ratio of feed and riser the tilt pressure is 7/9 and for a 4/1 ratio 10/12 and so on.
But remember at the tilt point the system is extremely instable.
One meter of air exerts at ambient temperatures on sea level only about 1.2 KG per square meter or 0.12g per square centimeter.
Therefore a stable system requires significantly higher temperatures in the riser and an attached high chimney respectively a quite large thermal buffer.
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Post by drooster on Jan 8, 2018 12:09:28 GMT -8
Please make a riser of the same material in order to make the shape at least a working stove shape, and show it working. "Too insulative" is a red-herring. |
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Post by Deleted on Jan 8, 2018 12:41:26 GMT -8
To insulative" is a red-herring. No. Please read my example calculation and the explanation. |
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Post by drooster on Jan 8, 2018 13:57:33 GMT -8
To insulative" is a red-herring. No. Please read my example calculation and the explanation. Forget calculations. Put a riser on it. |
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Post by Deleted on Jan 8, 2018 14:13:57 GMT -8
Forget calculations. Put a riser on it. Makes no sense. |
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Post by coastalrocketeer on Jan 8, 2018 17:29:00 GMT -8
Forget calculations. Put a riser on it. Makes no sense. Of course it makes no sense to a Tesla, but it is the Edisons like me who have to try, try, and try again, to make it work for not being able to intuitively grasp the simple beauty of 3, 6, and 9. (If you don't get that reference, I'll understand, as it is a slightly esoteric attempt at being poetic, and is definitely intended entirely as a compliment) Can I offer a solution that would allow you to put a relatively highly insulated riser on that core to satisfy us Edisons, with a minimum of additional effort on your part? I am able to provide a suitable width of the 1"x48", 8lb, ceramic fiber blanket to line whatever inexpensive piece of round steel ducting, chimney, or exhaust pipe you can cheaply obtain, scavenge, or borrow, using pinhead's ceramic fiber blanket in ducting, "5 minute riser" design. I have purchased enough to make approximately 11 6" diameter risers and only need to make one or two for my own needs. I would be willing to ship this to you at my expense if I can ship it for a cost under $100. The material is excess and already paid for, such that I am happy to donate it, and the shipping cost, to the cause of providing the proof for those who need it. I got it for only $2/sq foot at the quantity I bought, so the blanket it's self is no major expense. If you can find, or make, a suitable diameter ducting two inches wider than your build's inner diameter I will cut off and send you enough of the 48" blanket to be able to trim the width to allow it to be self-supporting on the inside of 4 feet of your chosen duct size. Most of us cannot so easily feel validated about the potential of this material when refractory "super insulation" has been the holy grail goal of achieving extreme combustion efficiency, but is now being blamed as the culprit over accepted suitable dimensions of a j-tube rocket stove... I mean ZERO disrespect to your analysis of it, as I frankly don't interact within the realm of mathematics beyond ratios and measures very proficiently, and tend to get a headache trying to work out an understanding of calculations like that, and then successfully inferring what effect "excessive insulation value" would be on gas temperature and flow within that configuration of passages is a step beyond that It would be a fairly quick and easy way for you to validate this for everyone who is doubting, or on the fence, with minimal effort, and I would be happy to do it to save you some effort and assist you to advance the development and use of this family of refractory geopolymer materials by as many as possible. |
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Post by esbjornaneer on Jan 9, 2018 0:31:09 GMT -8
To calculate the tilt point one can ignore the atmospheric pressure. Only the volume increment respectively the resulting reduction of pressure is of any interest. Assumed the environment temperature is 300K then the volume increment at 900K is three times and the pressure is reduced to one third. The feed side has two gas colums of equal hight, Thus the pressure in the column above the feed is 3/6 and in the feed 1/6 and the combined pressure 4/6. For the tilt the pressure in the riser exertet by the gas column in the riser needs to be reduced to 4/6 or below, which can be achived by a volume increasement of minimum 1.5 respectively a temperature increasement to above 450K. For a 3/1 ratio of feed and riser the tilt pressure is 7/9 and for a 4/1 ratio 10/12 and so on. But remember at the tilt point the system is extremely instable. One meter of air exerts at ambient temperatures on sea level only about 1.2 KG per square meter or 0.12g per square centimeter. Therefore a stable system requires significantly higher temperatures in the riser and an attached high chimney respectively a quite large thermal buffer. From my point of view once the flow has been established in the direction of the riser. Be that by a puff of air, lighting a paper twist far into the burn tunnel, or sending a blow torch flame down the burn tunnel. Ambient temperature air will be drawn into the feed tunnel cooling the feed tunnel down from the 900K while the heat generated moves over towards the heat riser column and then establishing stability even without mass. Due to a cooling of the feed tunnel temperature and a heating of the riser temp. And even just for showing this j-tube base coping with the temps established in it would it not be sufficient to put a length (1 meter) of un-insulated stove pipe on it (the cheapest one can find? Or have you already tried that Karl? |
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Post by Deleted on Jan 9, 2018 8:38:27 GMT -8
As I have already stated elsewhere a sufficiently long riser would come to close to the ceiling of my balcony. In Germany I own only a part of a very large house and thus have no private open ground to experiment with fire. coastalrocketeer try to get a sack of micronized KMI zeolite for your under $100. |
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Post by coastalrocketeer on Jan 9, 2018 12:56:42 GMT -8
Thank you Karl... And, having been raised in the city, I understand the issue of not enough suitable space for such experiments with fire.
I am blessed to live in a rural area now, where that is not an issue.
I was only going to spend that $100 this month on things other than bills and food and gas, if it was going to provide a quick, lower effort way for you to provide a test of the refractory suitability of the zeolite core material)
Since having a 5' tall "fire-pipe" shooting a stream of 2000F+(?) gasses out of the top is not possible where you are, I'll use the blanket to make someone else a stove.
I will look at the micronized zeolite to experiment with in the future, but per your past suggestions elsewhere, am also considering building a ball mill or converting a cement mixer I have, into one. As this will open the possibility of working with free, local rock, and other mineral sources.
I have to say, having seen how well even my crude attempts with not optimum sized binder feed-stock zeolite has hardened and become refractory and moderately well insulative. I am impressed and inspired to broaden my geopolymer experiments, while also building something for right now with the zeolite/bentonite "high water mix" soaking of rockwool tufts, as a 6" Jtube feed and burn tunnel, with a ceramic Fibre riser ala Pinhead's "5-minute riser" design. so that I can be warm enough to enjoy the experimenting.
Or perhaps I can send you that $100 and you can ship me a beautiful core and I can put a "5-minute riser" on top of it and test it through the rest of the heating season for everyone, with the branch fall from my yard ;-)
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Post by chozen on Jun 29, 2020 12:51:14 GMT -8
To calculate the tilt point one can ignore the atmospheric pressure. Only the volume increment respectively the resulting reduction of pressure is of any interest. Assumed the environment temperature is 300K then the volume increment at 900K is three times and the pressure is reduced to one third. The feed side has two gas colums of equal hight, Thus the pressure in the column above the feed is 3/6 and in the feed 1/6 and the combined pressure 4/6. For the tilt the pressure in the riser exertet by the gas column in the riser needs to be reduced to 4/6 or below, which can be achived by a volume increasement of minimum 1.5 respectively a temperature increasement to above 450K. For a 3/1 ratio of feed and riser the tilt pressure is 7/9 and for a 4/1 ratio 10/12 and so on. But remember at the tilt point the system is extremely instable. One meter of air exerts at ambient temperatures on sea level only about 1.2 KG per square meter or 0.12g per square centimeter. Therefore a stable system requires significantly higher temperatures in the riser and an attached high chimney respectively a quite large thermal buffer. From my point of view once the flow has been established in the direction of the riser. Be that by a puff of air, lighting a paper twist far into the burn tunnel, or sending a blow torch flame down the burn tunnel. Ambient temperature air will be drawn into the feed tunnel cooling the feed tunnel down from the 900K while the heat generated moves over towards the heat riser column and then establishing stability even without mass. Due to a cooling of the feed tunnel temperature and a heating of the riser temp. And even just for showing this j-tube base coping with the temps established in it would it not be sufficient to put a length (1 meter) of un-insulated stove pipe on it (the cheapest one can find? Or have you already tried that Karl? I think esbjornaneer may be right. You should be approaching this as a inverted siphon. Once it starts going, it will continue until plugged or emptied (goes out and cools) , in this case, as long as the outlet is above the inlet. |
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