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Post by Vortex on Nov 29, 2021 7:10:11 GMT -8
I used CF blanket to insulate the bottom part of my chimney that's inside the stove. I used aluminum foil to wrap it and taped it up with silver foil heating duct tape. The calcium silicate boards were a lot cheaper than CFB, so I used them for the insulation around the firebox. They react a bit with the steel though, so I might try wrapping them as well next time I have them out.
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tferr
Junior Member
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Post by tferr on Nov 29, 2021 7:23:42 GMT -8
I wish I could get Satanite in Canada. Iwould coat it with that.
Oh yeah I realized i didnt pour the roof section yet also realized once I factored in the angled pieces I am going to need another bag of the cast plus
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Post by Vortex on Nov 29, 2021 10:54:24 GMT -8
Anything that soaks into the fibres is going to lose you some of the insulation value as it's the air pockets that are the main insulator.
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Post by marcios on Nov 29, 2021 11:02:51 GMT -8
No way to make it in one piece, you'd need to cut it. If you cast it in one piece it will almost certainly crack down the middle, so best to make it in 2 halves. A 4 inch hand grinder will cut it with a masonry disk. If you don't have access to one then you can take the slab to a masons shop and they'll cut it on a wet saw for you.  That drawing was for a 6" /150mm system. The pieces sat on top of the side and back walls which were 2" / 50mm thick. You'd have to adapt it to your needs but it gives you the basic idea. 
The details of the firebox roof were timely, I was also going to ask about it. Are these measures considering the sloped front and rear sides of the port? I was referring to the "shelf" (afterburner roof) in a single 40 or 50mm piece, if it would be feasible to change the top chamber exit to avoid the sunken in front of it. |
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Post by Vortex on Nov 29, 2021 11:24:39 GMT -8
Those details were from a few years ago so don't include the sloped port on them yet. You'd have to add an inch / 25mm on the top of the inside of the front of the port. You can see I've cut a small wedge shaped piece of firebrick and stick it into mine. The rear is just a small piece the same sat on top of the firebox back wall.  The afterburner shelf can just be done in one piece, but the shape and proportions of the top chamber are very important. The surface area to volume ratio creates just the right amount of back pressure to maintain the vortex in the afterburner. The sunken area and exit might not be important, I am limited within the shape of my stove, so cant test it to find out. I think you should be able to tune it by watching the vortex at the peak of the burn, if the flames stream around the shelf up into the top chamber, increase the surface area to volume ratio (make the top chamber wider and shallower but maintain the 1 CSA) until the flames stay in the afterburner. |
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tferr
Junior Member
Posts: 69
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Post by tferr on Nov 29, 2021 15:44:32 GMT -8
Trev do you have a good CSA tutorial thread
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Post by marcios on Nov 30, 2021 3:46:52 GMT -8
Those details were from a few years ago so don't include the sloped port on them yet. You'd have to add an inch / 25mm on the top of the inside of the front of the port. You can see I've cut a small wedge shaped piece of firebrick and stick it into mine. The rear is just a small piece the same sat on top of the firebox back wall. The afterburner shelf can just be done in one piece, but the shape and proportions of the top chamber are very important. The surface area to volume ratio creates just the right amount of back pressure to maintain the vortex in the afterburner. The sunken area and exit might not be important, I am limited within the shape of my stove, so cant test it to find out. I think you should be able to tune it by watching the vortex at the peak of the burn, if the flames stream around the shelf up into the top chamber, increase the surface area to volume ratio (make the top chamber wider and shallower but maintain the 1 CSA) until the flames stay in the afterburner.
The wedge-shaped piece looks above floor level, wouldn't it be better lower down (with an angle anchor), or do you think that might not make a difference? |
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Post by Vortex on Nov 30, 2021 3:52:55 GMT -8
Trev do you have a good CSA tutorial thread CSA = Cross Sectional Area. This refers to the area of a cross section of the main chimney pipe the stove is designed to run on. Example: On a 6" / 150mm (chimney pipe size) system: The radius (half the diameter) 75mm x 75mm x Pi (π 3.142) = CSA: 17673mm² 6" / 150mm: 75 x 75 x 3.142 = CSA 17673 5" / 125mm: 62.5 x 62.5 x 3.142 = CSA 12273 4" / 100mm: 50 x 50 x 3.142 = CSA 7855 The CSA should be maintained as the minimum size though the whole system, except for any intentional restriction like the port or air supply etc. Hope that's clear, later I will try and explain the Surface Area to Volume Ratio. |
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Post by Vortex on Nov 30, 2021 4:26:56 GMT -8
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tferr
Junior Member
Posts: 69
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Post by tferr on Nov 30, 2021 4:45:41 GMT -8
Trev do you have a good CSA tutorial thread CSA = Cross Sectional Area. This refers to the area of a cross section of the main chimney pipe the stove is designed to run on. Example: On a 6" / 150mm (chimney pipe size) system: The radius (half the diameter) 75mm x 75mm x Pi (π 3.142) = CSA: 17673mm² 6" / 150mm: 75 x 75 x 3.142 = CSA 17673 5" / 125mm: 62.5 x 62.5 x 3.142 = CSA 12273 4" / 100mm: 50 x 50 x 3.142 = CSA 7855 The CSA should be maintained as the minimum size though the whole system, except for any intentional restriction like the port or air supply etc. Hope that's clear, later I will try and explain the Surface Area to Volume Ratio. Perfect that is what I thought. I wasnt sure if volume was a factor...ie length of chimney. So my 7" system CSA would be 89 x 89 x 3.142 = 24887 So where the "exhaust" exits the top chamber into a bell do I want to maintain 1 CSA there or can I make it smaller and will that increase velocity. I am guessing it is where it enters my bell is where the ISA and volume ratio become important |
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tferr
Junior Member
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Post by tferr on Nov 30, 2021 4:52:39 GMT -8
Thanks Dan
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Post by Jura on Nov 30, 2021 6:19:08 GMT -8
The Sketchup file has very kindly been updated by dan (Upstate NY, USA) @woolf1004 Neither of the links work for me. It opens empty page. |
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Post by Vortex on Nov 30, 2021 6:45:04 GMT -8
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tferr
Junior Member
Posts: 69
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Post by tferr on Nov 30, 2021 9:06:12 GMT -8
works for me
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Post by Vortex on Nov 30, 2021 14:06:08 GMT -8
Surface Area to Volume Ratio: en.wikipedia.org/wiki/Surface-area-to-volume_ratioThe top chamber has roughly the same Cross Sectional Area (CSA) and volume as a 6" / 150mm pipe of the same length, but they have quite different internal surface areas (ISA): A 1 CSA pipe (150mm) circumference 471.3mm x the length 470mm = 221511 mm2 ISA. A 1 CSA chamber (272 x 65) perimeter 674mm x the length 470mm = 316780 mm2 ISA. 316780 divide 221511 = 1.43 Surface Area to Volume Ratio (SA:V) = 1.43 (Thats a simplified version, as the chamber is slightly wider but contains the small triangular piece, so I averaged the width out to 272. Also the chamber includes the rear wall but not the exit in the left-hand wall, but the exit and rear wall both have the same area so cancel each other out.) Why is the top chamber surface area to volume ratio important? Over the last 3 seasons I have been mostly experimenting with different size, shapes and configurations of the top chamber, stumbler and exit port. When I built the first experimental model in my garden in summer 2018, I discovered that a restriction made it more stable and less prone to overfueling. Originally this was the gap between the front of the afterburner shelf and the inside of the glass, but was later moved into the top chamber as the glass was getting burnt. A restriction only works so far though, as over a certain level the bottleneck starts to slow down the gas flow too much, which itself makes the stove overfuel from lack of air. In December last year I noticed that making the top chamber exit squarer, somehow made it work better. It turned out that in the process of changing it around to fit in the square port, I'd unintentionally increased the surface area of the top chamber, and that was what was causing the effect. I experimented with various ways of trying to make use of this discovery, but it wasn't until late last winter that I realised that I could just do away with the restrictions of the stumbler and exit port altogether and use the resistance of the increased surface area instead. Earlier this season I experimented with increasing the SA:V to the maximum possible level to see what that would do, it created a very stable burn, but also slowed the gas stream down too much. By increasing the primary air and gradually reducing the top chamber surface area, I managed to find a perfect balance that holds the vortex nicely in the afterburner and resists overfueling and thermal runaway. |
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