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Post by foxtatic on Oct 31, 2024 10:38:08 GMT -8
peterberg I'm finally laying out materials to cut and decided to check my math since it has been so long since I did the calculations. One factor stands out: the percentage of system CSA in the top box negative space (space in the top box excluding the afterburner tube.) Originally you said a minimum of 150%. I think that changed to 160% And for some completely unknown reason I used 185% in my calculations, which feels like a big mistake! Can you recall the recommended percentage for this?
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Post by peterberg on Oct 31, 2024 13:44:51 GMT -8
peterberg I'm finally laying out materials to cut and decided to check my math since it has been so long since I did the calculations. One factor stands out: the percentage of system CSA in the top box negative space (space in the top box excluding the afterburner tube.) Originally you said a minimum of 150%. I think that changed to 160% And for some completely unknown reason I used 185% in my calculations, which feels like a big mistake! Can you recall the recommended percentage for this? The cross section area of the space around the afterburner tube should be 150 to 160% while the end port is system csa again. I didn't try 185%, but it feels quite large. |
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Post by foxtatic on Nov 11, 2024 5:45:15 GMT -8
I’m willing to experiment with this square tube variant. Worst case scenario for me if it didn’t work: I’d simply cut the box back down to the original planned height and buy the round CFB tube to stick in it instead. foxtatic - have you been able to do any experimentation? Would be great if a square tube worked. I built the thing and did a test burn last night! Please see a short slide-show video here. The last 10 seconds are video of the afterburner "square-tube." peterberg theorized this could work if I did a 6 inch square. www.youtube.com/shorts/_ZTP3gz1ns0Build notes: Vermiculite board outer construction. Fire box lined with fire brick. Top box lined with 1/2" ceramic fiber board. Square tube is also 1/2 inch ceramic fiber board held together with ceramic pins. Door slab (not currently attached, just propped) has the 4 slits that equal 50% CSA. Sizing: top box negative space is 185% CSA. Larger than recommended, but if it was any smaller there would be no space between the top of the tube and the ceiling. Test housing is a 55 gallon drum cut to fit around the core. Chimney stub connects directly to the top. 6" insulated flue 36" tall. First test note: It was very slow to start. Lots of smoke back and I could not close the "door" without killing the fire. I theorize that's because I was trying too-small of a test burn. Guessing if I had filled up the firebox and started a top-down burn (kindling on top), it would have pre-heated the afterburner and got things moving faster. I will try another bigger burn this evening to see if that helps. Does the vortex look good enough? I designed this test so that the afterburner tube can be changed relatively easily. Edit: second test burn went much better. Instant vortex and clear exhaust. Just not sure if that double rams horn is strong enough. youtube.com/shorts/by65kJhPm5Y?si=B0iaaIPiz7dVEcWw |
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