Anybody seen this type of rocket stove?

I saw this:  [youtube]https://www.youtube.com/watch?v=HR0JXjV8_sc,[/youtube]  it looks like it has two chimneys.

This video: https://www.youtube.com/watch?v=TM3cMLSh0Gs, explains when you have two chimneys, air flows down one, and air goes up the longer one, but the point I saw is that over one candle, the flame is dead calm, over the other candle, the flame is turbulent.  When you join two chimneys in the k-type rocket stove, it somehow mixes dead calm and turbulence in one.  Thought I would share it.

This one is a similar rocket stove but appears to draw better: https://www.youtube.com/watch?v=B6trSpA_YJs, here the second "chimney" meets the main chimney right at the diagonal, instead of the second chimney being higher in other k-types.

These two stoves don't intentionally have two chimneys, but due to poor design they could work that way if the wood got too hot. That's why they need to have doors on the feed opening. One essential for a rocket stove or combustion core is that the fire have a clear direction of draw, which means making the chimney/riser considerably taller than the feed tube (generally at least three times taller, for a non-horizontal feed).

I notice that the wood slides smoothly down the slanted feed on these brand new stoves; I wonder how it slides when the internal surfaces get roughened from use and corrosion and possible char buildup. (If they get used regularly with hot fires to get good combustion, the internal steel surfaces will corrode.)

The candle experiment shows one flame-chimney side establishing a stronger draft than the other. The one that established the exhaust path burns steadily because air is going smoothly up, while the other is flickering because air is being drawn down the chimney and colliding with the flame trying to rise. The flicker is effect, not cause.