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Post by luddite on Apr 4, 2014 17:15:45 GMT -8
Hello. My first post! Thanks to all for your experimentation and even more for the discipline to share and explain your findings! I have been reading this forum a lot but i seem to be missing a few points regarding bells. Correct me if I am wrong but as I understand it a 6 inch j-tube should have less then 4 sq meters (43 sq ft) ISA (internal surface area) while a 6 inch batch box could have up to 6 sq meters (65 sq ft) for a single bell system. So by my math that would give an 8 inch j-tube about 7 sq meters (77 sq ft) ISA and an 8 inch batch box around 10.75 sq meters ( or 116 sq ft). All math done long hand so??? Extra bells would subtract 15% ISA per bell. Measurements of ISA do not include floor of bell. So here I get to the questions. 1-how horizontal can a bell be made? that is to what extent can a bell be made wide and deep while minimizing height? 2-what effect would be caused by building part of bell with insulating materials? would the "effective" ISA be decreased? 3-is there a minimum volume of bell? I seem to recall something about 4xCSA but not sure it applies or how to apply
my thought is to build a greenhouse bench/table as large as possible. I like the idea of using a bell for this because it would distribute heat more evenly across surface. seems to me there must be a minimum height to allow stratification of gasses. also i believe peterburg mentioned the floor of bell not counting as ISA unless the gasses exited bell downwards? Again thanks to all.
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Post by satamax on Apr 4, 2014 23:50:41 GMT -8
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Post by peterberg on Apr 5, 2014 1:42:22 GMT -8
1-how horizontal can a bell be made? that is to what extent can a bell be made wide and deep while minimizing height? 2-what effect would be caused by building part of bell with insulating materials? would the "effective" ISA be decreased? 3-is there a minimum volume of bell? I seem to recall something about 4xCSA but not sure it applies or how to apply. Luddite, welcome to the boards. As for answers: 1/ Imagine a bench with a height of 16", 12" internal. The inlet and exit could be for instance 4" high and 8" wide, both openings at floor level. Which means above the opening is 8" left. That bench will be getting hot, no doubt about that. Even a difference of 6" or 5" will work. 1a/ In order to provide enough room for the gases to stream in and out the length of the stream profile should be at least the same as the circle which is representing the system size. The side which is effectively the floor not counting would mean the length of the profile is 16 inch, divided by 3.14 = 5 inch diameter. So even with a 6" system this openings should be larger than 4"high and 8"wide. Don't try to be clever and make the opening 4"wide and 8" high, in effect the top half of the opening will be used primarily while the bottom half is not used for a large part. This is a much overlooked effect, very important. 2/ Yes, the effective ISA will be decreased and will not take up any heat to speak of when part of the bell's inner wall is of insulative materials. 3/ Try to imagine this as a wall with hole in it. The hole is the stream opening, the wall is the volume immediatly after the opening. So, that wall has to have a csa of at least 4 times the opening csa. In reality, it is a pipe of a certain csa which opens into a pipe with a csa which is at least 4 times larger. A 6" pipe would therefore need a transition to a 12" duct or equivalent in order to achieve the desired effect.
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Post by luddite on Apr 6, 2014 5:23:33 GMT -8
Thanks for the response Peter. Very helpful. I will be building a mold for a 8.5 inch J today! Am very excited about providing efficient greenhouse heat. I will start a new post for project but don't know if it will be innovative enough to be of much value. As a mason I have repaired and rebuilt many historic fireplaces and ovens hoping to gain insights from their long dead builders. Knowing how much knowledge, gained by trial and error has been lost leaves me overwhelmed with gratitude for all your efforts.
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Post by daniel on Oct 4, 2015 23:43:57 GMT -8
Hi,
If the part of the bell if made of insulative material would be at the lower part of the bell would that help with the draft since the cooler gases which descend will hit the insulated part?
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Post by peterberg on Oct 5, 2015 12:21:53 GMT -8
Whichever part of the bell is insulated will help the draft because there's less ISA to extract heat. THat part could be evrywhere, the hotter places are more effective of course.
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Post by daniel on Oct 5, 2015 21:45:21 GMT -8
Thank you Peter,
In other words if I will build the lower part of the bell where the cool gases are with bricks with holes to help the draft and the upper part of the bell with heat retaining materials would be in fact better than building the whole bell out of heat retaining materials?
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Post by shilo on Oct 6, 2015 0:38:47 GMT -8
this way, you get less heat from the gas and you let more energy to escape your home. it could be good thing or bad thing.
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Post by daniel on Oct 6, 2015 4:12:18 GMT -8
Actually I thought if using insulating brick in the lower part where the cool gases stay and heat absorbing materials in the upper part where the hot gases go it will help the draft and allow the same amount of thermal energy to be stored in the upper part, furthermore if the lower part of the bells will not draw energy from the upper part which is hoter. I don't see why this is not so. Please correct me if I am wrong.
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Post by shilo on Oct 6, 2015 5:19:49 GMT -8
there is a given amount of energy. you need do decide the ratio between the energy you give to the mass and the energy you loose throe the chimney. there is no magic.
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Post by daniel on Oct 6, 2015 12:05:17 GMT -8
Hi,
I got to the point to where I need to insulate/build the heat riser. I have used refractory sleeves with ID of 200mm and OD 230mm, (these sleeves are used in chimneys) and now I have to figure out how to insulate the heat riser without. I could make a form around the sleeves and fill it with perlite and clay but I am worried about how the clay-perlite will behave inside the bell in the long run if it will hold without some exterior sleeve around it ?
Second question is if it is better to wrap chimney type rockwool or ceramic blanket to reduce that space needed for insulaiton which would allow me to replace the sleeves if the ever need replacing. I cant't find such a big sleeve around the insulation so the only option would be to make a brick sleeve layed flat which will take a whole lot of space. ..........
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Post by mkrepel on Oct 8, 2015 15:43:57 GMT -8
What if you use ceramic wool and find some way to attach it to the outside of your liner and leave it at that? Perhaps some stainless steel bands around the insulation just tight enough to hold it in place. I believe others have built a risers in a similar manner. There shouldn't be anything particularly destructive happening on the outside of the riser; just a smooth flow of very warm gases downward. If your liners are clay, however, they may not hold up in the riser. That particular item gets very hot very quickly and the clay cannot keep up. I have read that clay cracks fairly easily when the heat stresses go up.
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Post by daniel on Oct 8, 2015 22:08:37 GMT -8
Thanks, my liner are refractory made for chimneys to withstand creosote and chimney fires, I am worried about the fibers from the ceramic wool and I read that its thermal insulation properties decrease when the heat goes up compared to perlite which has an R value of 2.7 or 2.4 per inch. Also I am thinking that the ceramic fibers should be somehow contained in there perhaps wrapping some stainless as you said around and put some clay slurry over. Do you think if I cast clay perlite in a form made of sheet metal and stamp it in place will hold after demolding?
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Post by daniel on Oct 11, 2015 2:56:44 GMT -8
1-how horizontal can a bell be made? that is to what extent can a bell be made wide and deep while minimizing height? 2-what effect would be caused by building part of bell with insulating materials? would the "effective" ISA be decreased? 3-is there a minimum volume of bell? I seem to recall something about 4xCSA but not sure it applies or how to apply. Luddite, welcome to the boards. As for answers: 1/ Imagine a bench with a height of 16", 12" internal. The inlet and exit could be for instance 4" high and 8" wide, both openings at floor level. Which means above the opening is 8" left. That bench will be getting hot, no doubt about that. Even a difference of 6" or 5" will work. 1a/ In order to provide enough room for the gases to stream in and out the length of the stream profile should be at least the same as the circle which is representing the system size. The side which is effectively the floor not counting would mean the length of the profile is 16 inch, divided by 3.14 = 5 inch diameter. So even with a 6" system this openings should be larger than 4"high and 8"wide. Don't try to be clever and make the opening 4"wide and 8" high, in effect the top half of the opening will be used primarily while the bottom half is not used for a large part. This is a much overlooked effect, very important. 2/ Yes, the effective ISA will be decreased and will not take up any heat to speak of when part of the bell's inner wall is of insulative materials. 3/ Try to imagine this as a wall with hole in it. The hole is the stream opening, the wall is the volume immediatly after the opening. So, that wall has to have a csa of at least 4 times the opening csa. In reality, it is a pipe of a certain csa which opens into a pipe with a csa which is at least 4 times larger. A 6" pipe would therefore need a transition to a 12" duct or equivalent in order to achieve the desired effect. Peter, what is the stream profile, can you explain this thing please.
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Post by peterberg on Oct 11, 2015 17:13:25 GMT -8
A stream profile is an imaginairy thing, formed by the outline of the opening plus the width of the space right in front of it. Mentioned already, when the bottom side of the opening is at floor level that side doesn't count. The size which is mentioned above is 8" wide and 4" high. So that's two sides of 4" plus one side of 8" which will make 16" together.
Multiplied by the space right in front of the opening, which could also be the distance between the riser and the barrel. When the resulting figure is less than the csa of the riser opening you'll have a problem on your hands. In my opinion, the resulting figure need to be at least 50% larger than the riser csa in order not to form a restriction. The gases need to go around a bend of 90 degrees so it need a lot more space.
Personally, I like to have a number which is 200% of riser csa in order to make sure it will be smooth in all circumstances.
I hope this is clear.
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