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Post by DCish on Jan 21, 2017 17:28:41 GMT -8
Hey Peter,
Yeah, I think wider and not as tall would be better. I just re-arranged things a bit today but didn't have a chance to light it off yet. Instead of 4.5" by 4.5" slot I now have 4.5" long by 3" tall flowing into a roughly 4.5" wide by 7" tall "riser" ("burn tunnel"?) running back toward the front of the stove. Can't wait to light it off and see if I get a proper double ram's horn. Oh, and to answer your question, it's a 6" core.
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Post by DCish on Jan 22, 2017 18:42:11 GMT -8
Ah, feeling "dead chuffed" as Satamax would say! Today's run was exactly what I would have hoped for. I ran a 3" high by 4.5" long port at the top, left, rear corner of a 6" batch box, porting into a 4.5" wide by 7" tall channel that ran directly back toward the front of the stove. As you can see by the pics and videos below, it was, by my accounting, a complete success. This is especially significant given that my conditions are less than ideal - it was raining outside tonight and the entire things was damp when I lit it, and it's a hodge-podge of dry-stacked brick and some superwool to plug some of the worst leaks. I had glass on top of the burn tunnel as well as on the front looking toward the port. Still shot from the front at moderate burn:  Video at moderate burn: https://plus.google.com/107386714429613343642/posts/529NXajxbkkVideo at high burn: https://plus.google.com/107386714429613343642/posts/ha9sE58we46Video from top at high burn: https://plus.google.com/107386714429613343642/posts/Y6FR9sGnpfJ |
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Post by matthewwalker on Jan 22, 2017 19:49:49 GMT -8
That top view of the helix is awesome!
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Post by peterberg on Jan 23, 2017 2:14:51 GMT -8
Brian, you did it! By turning the port on its side and creating a horizontal riser/tunnel the whole turbulence pattern changed 90 degrees direction! This is a very uniform and fast spinning twin vortex, no doubt about. While looking at it it's hard to believe the video is taken from the front instead of the top. Congratulations!
Now, the size of the mockup is 6", what is the length of the tunnel and what do you placed on top of the tunnel exit to enhance the draft? A couple of pictures of the setup would be very helpful. This opens a lot of possibilities, a simple setup and let the laws of physics do the hard work. Maybe the tunnel would be even better when the height/width proportions are 1:1, like a riser. Not sure of that one, just guessing.
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Post by DCish on Jan 23, 2017 4:44:17 GMT -8
That top view of the helix is awesome! Thanks, Matthew! I almost didn't put the top glass on, but I'm so glad I did. |
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Post by DCish on Jan 23, 2017 5:16:47 GMT -8
Brian, you did it! By turning the port on its side and creating a horizontal riser/tunnel the whole turbulence pattern changed 90 degrees direction! This is a very uniform and fast spinning twin vortex, no doubt about. While looking at it it's hard to believe the video is taken from the front instead of the top. Congratulations! Now, the size of the mockup is 6", what is the length of the tunnel and what do you placed on top of the tunnel exit to enhance the draft? A couple of pictures of the setup would be very helpful. This opens a lot of possibilities, a simple setup and let the laws of physics do the hard work. Maybe the tunnel would be even better when the height/width proportions are 1:1, like a riser. Not sure of that one, just guessing. Thanks Peter! I'm totally with you, I want to find some plain 6" pipe to cut a slot in and see how the flame looks. I definitely think it doesn't need any extra size. Who knows, tighter might even work. I have some 4" dryer duct I could try, that might be a fun little experiment to do between now and when I can scare up some 6" pipe scraps. By the way, what dimensions did you use for your 50% port? I'm thinking the standard 2" wide seems pretty ideal for a 6" riser test, dividing the diameter neatly into thirds. The 3" slot I used was just a convenience dimension based on scraps I already had lying around. I'll try to get a pic of the outside posted here in a minute. It's basically just a 6" sized batch box with the port out the top left side. The flame path then returns to the front of the stove (about ~23" total stove length), venting straight up into a 3' insulated chimney flue section for draft. The entire thing is completely uninsulated hard fire brick in this configuration, so it likes to be fired pretty hard in order to get a smokeless burn. It's probably akin to what you call thermal runaway at times, with clearish red flame spurting out the top of the chimney stack. After that it's good and warmed up and behaves better when throttled back. |
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Post by DCish on Jan 23, 2017 5:23:48 GMT -8
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Post by peterberg on Jan 23, 2017 7:52:58 GMT -8
Since the twin vortex is so easily turned on its side, I'm inclined to think the whole of the aerodynamics is very much like a straight version. From my experiments in 2012 I learned a round riser giving the best results. Second best an octagon, third a square. I also tried, started with that in fact, a rectangle riser in two orientations. Those were clearly inferior to even the square one in terms of time to burning clean after being lit.
I'd suggest that the 6" pipe might be best as tunnel, and yes, my 50% slot is 2" wide. Although it's shorter because of it being a smaller system. The length of your 50% port in a 6" system should be 7".
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Post by DCish on Jan 23, 2017 10:14:44 GMT -8
Sweet. So my next test target is a 2x7 slot into a 6" tube.
By the way, what are your thoughts on how high up the wall the slot should be? So far I've done it at the very top out of quick build convenience. The obvious advantage is that it is almost impossible to block with fuel. The disadvantage is that it then requires a taller, more robust fire to get through the port and get secondary combustion engaged, both at the start of the fire and at the end. On the other hand, too low a horizontal port would be easily blocked by fuel and even ash. I'm thinking maybe 2/3 of the way up should be a pretty good compromise, what do you think?
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Post by peterberg on Jan 23, 2017 11:10:08 GMT -8
Yes, looks like a good compromise. The thought about having the slot so high up requiring a stout fire crossed my mind this morning. What you could do: load the firebox beforehand right up to the port, kindling on top, start the fire there and see what happens.
It might help as well if you were able to add the back sweep to the tunnel end, like the riser's back sweep. Not sure of this one, but I have to mention it anyway.
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Post by DCish on Jan 23, 2017 18:19:37 GMT -8
Ah, yes, the back sweep. I'll try to remember to stuff some super wool or something in there to approximate that. And the top light fire sounds like a good way to get things going too. Thanks for the ideas. Fingers crossed that I can find some free time to tinker this weekend.
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Post by drooster on Jan 24, 2017 13:13:28 GMT -8
Brian do you have a diagram of the firebox and port?
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Post by DCish on Jan 24, 2017 15:06:43 GMT -8
Brian do you have a diagram of the firebox and port? Sure. It's dead simple, though, so not much to show. Just a hole in a wall and a channel at 90 degrees back toward the front, covered with ceramic glass top and front (the picture above shows that part). https://plus.google.com/107386714429613343642/posts/1nz6kRgJ1fkThe next step is to cut a 2x7 slot in a 6" tube and nest that in the return channel to test a round burn tunnel shape. |
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Post by DCish on Jan 25, 2017 7:56:41 GMT -8
Random brainwave... someone on a kiln site was suggested using kanthal wire to secure ceramic wool insulation inside a kiln. I have lots of half-inch ceramic wool insulation. What if I use kanthal wire to secure a liner across the top and sides of the fire box, and coat with rigidizer to help bind the fibers together a bit? I'm sure it would still be sacrificial, but the wire is cheap, and I already have the insulation. I considered insulating fire brick, but I don't want to have to tear the whole thing apart to replace the firebox walls if they get abraded over time. A replaceable sacrificial layer inside the firebox, however, would be ideal. I was thinking ceramic fiber board like Matthew Walker uses until I checked the prices (!?!). Thoughts?
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Post by matthewwalker on Jan 25, 2017 8:46:11 GMT -8
DC, a fella over at Permsteading was playing with whole builds of super wool a few years back. Here's a link to the last iteration. If you search that user or BOOH you'll find more ideas for your wool. I think it works fine, but is permeable, so I believe it isn't a great choice on it's own. www.permsteading.com/viewtopic.php?f=6&t=338I suspect you are over estimating the IFB wear. Try it. They work great, and it will take a long time to wear one to the point of being a worry. At which point your other ideas are still valid. |
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