Capillary Hoop Stove discussion
First of all my apologies to "donthaveoneyet" for hijacking his "Cat Can Stove - Questions" thread here: http://whiteblaze.net/forum/showthre...tove-Questions
This is new thread to continue the discussion of the CHS (Capillary Hoop Stove) and constructions techniques
Quote:
Originally Posted by
BirdBrain
It is all about balance. I explained the math elsewhere. If I can find it, I will copy and paste it here. The short of it is that as the cross-sectional area of the ribs increases, the pressure in the hoop increases. This causes what TetKoba calls "bubble bomb" (things get lost in the translation). Vaporized fuel is forced out the bottom. The hot vapors cause increased thermal feedback. If you are seeing any bubbles in the bowl of your stove, you have too great a cross-sectional area in your ribs. This is where things get ugly. One might think that if you increase the number of ribs, you will also increase the amount of cross-sectional area of the ribs. It is actually the opposite. I will not belabor this point. I will revisit it if I can find my diagrams that illustrate this.
The reason it is important to "squash" the walls (as TetKoba would say) is to ensure uniform ribs and predictable cross-sectional areas of the ribs. If you do not detail the ribs, you will end up with a crap shoot of pressure in each rib.
The secondary hoop is a JSB thing. It provides a secondary buffer against the "bubble bomb" and allows for faster initial priming.
The slanted ribs provide for smoother wicking. Contrary to the name, this is not a capillary stove. It is a metal wick. Think about the effort it takes to lift a heavy object straight up. Then imagine having a slant to push it up instead.
These things are very marginal. I do not expect builders to follow my obsessive nature. It is not reasonable. I have built many of these things and tested for every variable many times. I sought to build a balanced stove that would have as little thermal feedback as possible. I have only succeeded 3 times. I have used one of those successes hundreds of times. It shows no change in performance. That one is the one shown in the video of the stove in my hand. I figure between that one I am using now and the 2 spares, I have a life time of stoves on hand. I stopped building months ago.
On a related note, I sent OMO a less than perfect stove. He did not get one of my 3. I have mailed so many of these things out, I have lost track. One that I was fairly happy with is now in Australia.
Now I am off to see if I can find my cross-sectional area illustrations.
BB, thanks for your description. I am definitely seeing "bubble bomb" and excess thermal feedback in my stove, hence it gets too hot to hold. I followed your reasoning about reducing the capillary area with more channels, and think it makes sense. I will try to clean up, tighten my channels and see if that helps.
As for the JSB secondary hoop, I could see how such a feature would help ensure more uniform pressures in each of the channels/wicks/tubes, however it is not clear to me where and how to integrate this feature into the stove. Is it just formed in the space between the bent tabs (making an inner ring) from the collet and the bottom/outer bowl? Its some sort of azimuthal additional ring to balance channel pressures, but where is it and how is it made?