Cramer
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Post by Cramer on Dec 22, 2013 10:09:49 GMT -8
Another option would be to cut the smaller barrel down so the effective ISA (internal surface area) comes closer to the ISA consensus for a 6 inch J tube. That might work also correct Peter? And then insulate the long run of exhaust piping to the chimney.
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Cramer
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Post by Cramer on Dec 22, 2013 10:03:49 GMT -8
Ah ha! I knew someone would ask this question for me!
Thoughts? It seems to me that one MIGHT be better than the other but it also seems to me that there may be no difference (operationally) whatsoever.
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Cramer
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Post by Cramer on Dec 22, 2013 7:47:42 GMT -8
I almost dread posting this and possibly showing my ignorance but if I am off base I am sure that one who knows much more than I will be quick to chime in and correct me so here goes... It seems to me that if you have a cold plug now with a six inch all the way through your system (more or less) then you will likely really smoke yourself out if you try to put an 8 in combustion system on a six inch system/chimney stack. In the picture you posted of the heat riser section, I wonder... how much does one of those bricks weigh? They look to me like dense firebrick which may be absorbing the heat from secondary combustion. They will well withstand the heat in the riser but are not the best thing to use as a riser stack. Maybe it is just me but I think once everything is dried out (which may well take a very long time but over time I think it will happen) I think you may well be able to store a fair amount of heat in your ground. I don't think though that without some above ground storage and dissipation that you will be able to maintain the temperatures you seek. From one who lives here (see picture)... I very much like your greenhouse!
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Cramer
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Post by Cramer on Dec 22, 2013 6:29:40 GMT -8
That is exactly the kind of information I was seeking! Once again Peter, my thanks to you sir! You have been playing with fire for a long time so I think I can "take that figure to the bank!" (I am rife with colloquialisms ).
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Cramer
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Posts: 129
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Post by Cramer on Dec 22, 2013 6:16:33 GMT -8
The drawing was intended as a tool for further understanding of the concept, I would not see actually doing such a thing would have any real practical purpose. except maybe for shrinking a bell to achieve a smaller footprint while still maintaining a single mass of stratified gasses. I did not locate an exhaust outlet because in this case it did not matter where it was... and yes, the round bit was intended to represent the inlet side of things . Actually, I believe you are understanding them quite well as you have provided the answers I was seeking! Thank you sir!
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Cramer
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Posts: 129
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Post by Cramer on Dec 21, 2013 18:24:56 GMT -8
So, now you have a single tall bell and a bench for the cat. You have a good draw, that is good. How did this affect the temperature at the chimney and did it work in giving you more heat into the area where you are working?
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Cramer
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Posts: 129
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Post by Cramer on Dec 21, 2013 15:36:30 GMT -8
Now this is useful information! I hope others have measurements to share also. Thanks much!
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Cramer
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Posts: 129
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Post by Cramer on Dec 21, 2013 14:28:09 GMT -8
I have heard a few maximum temperatures bandied about in regards to rocket burners. I am guessing that the larger 8 inch or larger risers produce the highest temperatures but I really have seen no test results indicating what the maximum temperatures that need to be withstood in feed chamber/burn tunnel/heat riser for different sizes of rocket burners. A chart or info-graphic of tested temperatures for different sized burners burning at maximum would be a great help in material selection for different parts of the burner assembly.
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Cramer
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Post by Cramer on Dec 21, 2013 6:00:45 GMT -8
Excellent! I believe my single bell 6 inch combination just became a double (or maybe triple) bell 8 inch! Since temperatures are successively lower from bell 1, to bell 2 and then finally to bell three there will be variances in the surface temperatures which I can put to use in my application! Is a three bell combination for an 8 inch burner feasible or would a double bell be the limit for a J Tube? If a J tube will only support a double bell then using previously learned parameters I would assume a batch box would easily support a triple bell. To further understand the concept of ISA, if (as in the attached) there was a freestanding wall open at the top instead of at the bottom so that the gasses could stratify around the mass, would both sides of this wall figure in to the ISA calculation? freestanding wall.skp (16.47 KB) Previously it was mentioned that a double bell was approximately 15% more efficient than a single bell. This sort of bolsters my thought that ISA is connected to adsorption (a surface phenomenon) rather than absorption (which would concern the entire mass of a material). If that is indeed the case then it would simplify things greatly. The 15% increase in efficiency would then translate to the surface area of one side of the dividing wall between the two bells, which would be the side facing the chamber where the hot gasses originate but in the case of something like the attached drawing BOTH sides would be considered in the calculation of the total ISA.
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Cramer
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Post by Cramer on Dec 20, 2013 15:18:11 GMT -8
Does the surface of the divider between the 1st and 2nd bell contribute to the ISA then or only the exterior walls?
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Cramer
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Posts: 129
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Post by Cramer on Dec 20, 2013 4:00:10 GMT -8
Well, I answered one of my own questions. The question about how to quote snippets of a post has been discovered!
That being behind me now I have a proposition for thought. Since the above is true, maybe the relation of surface area inside a bell has naught to do with absorption but everything to do with adsorption of the gas molecules upon the solid. Since adsorption is a surface phenomenon whereas absorption involves the action of the entire mass then the gas molecules must be adsorbing onto the surface of the material, being brick, glass, steel et. al. then being absorbed into the material and conducting through it like water being sucked into a paper towel.
To test the hypothesis one could create a smaller than optimum bell and "corduroy" the inside of it producing a greater surface area inside the bell effectively increasing the surface area for adsorption of the hot gasses and measure the output temperature of the flue gasses?
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Cramer
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Posts: 129
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Post by Cramer on Dec 19, 2013 18:26:27 GMT -8
Hey, I just thought of this! If I put two tea kettles on top of a double bell stove, when the water boiled, I would have "bells and whistles"...
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Cramer
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Post by Cramer on Dec 19, 2013 18:13:44 GMT -8
Peter said: Interesting stuff isn't it? My Reply: It most assuredly is! This one quick question is a bit off topic but how do you quote the small snippets and reply to those individually? Edit: Never mind, I figured it out.
So, if the metal were as "thick as a brick" then the conduction rate would be marginally similar to that of the conduction rate of the brick bell wall? One may store heat a bit better than the other but they would store a similar amount? I think that is what I gleaned from the answer above but please correct me if I am in error.
Then the ISA would be pretty similar whichever substance is used for the walls of the bell. In a two bell system then the dividing wall between the two bells would allow one to use a smaller footprint than a single bell because that extra surface area, though it conducts heat but does not for the most part transmit it's heat through radiation (except from the warmer side to the cooler side before equilibrium is reached) does figure in to the ISA calculation. Correct?
I think I see why a batch box can use a larger ISA. More heat is dumped at once (uninterrupted by refueling) into the bell?
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Cramer
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Posts: 129
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Post by Cramer on Dec 19, 2013 4:03:38 GMT -8
Thanks satamax, useful information. I will check back this evening for other answers, should any be forthcoming. I feel rather honored to have the conversation moved with the colloquialism in the title
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Cramer
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Posts: 129
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Post by Cramer on Dec 18, 2013 15:49:37 GMT -8
Okay, that completely clears up the question, except I do not recall after reading the thread a recommended ISA of a 6 inch system. I was thinking before the question was cleared up that the cubic footage was the determining factor but now I see that if I increase the ISA I can use a larger (maybe 8 inch) system with more output and that if the cube shape is not used but rather a longer more narrow shape with a greater internal surface area (ISA) is used then the 6 inch system would likely stall?
So the question then becomes what is a rule of thumb on the ISA of a 6 inch system and is the ISA linear in regards to proportion when up-sizing? Another question comes to mind here that is inextricably linked to this question. What would be the effect of insulating the exterior of the bell as in providing a double walled bell with an insulating air space between the interior bell that gasses pass through and an exterior "shell" that the gasses would not pass through? I ask this only as a hypothetical, not that I would plan to do such a thing. But for fine tuning a belled system it seems to me that if the bell is made with too large an ISA thus causing the system to stall because the chimney will not draw then insulating one wall would have the same affect as decreasing the ISA because thermal energy would not be expended as rapidly as it would through a non insulated wall. Is this assumption on the mark or off base?
Which, alas brings me to another question, does the material of the bell affect the calculation of ISA? If dense fire brick is used with more heat adsorption capability would the ISA calculation then be smaller than, for example using red brick for the bell? And if a steel "lid" is used for the bell which gives up heat readily then should the ISA be reduced by some margin?
Peter, "armchairing"... just an attempt to impart a little information to you (very little) in return for your tireless efforts to all of us. I am glad you enjoyed it.
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