Current experiment from my other blog,
www.mycanoebuild.blogspot.com
Love solar stuff! Here's a cheap and I bet very effective solar kiln idea for small amounts of bamboo or other wood, or make it big as one wants...
It kind of even looks like bamboo haha! Ok what I imagine is sections of the black metal woodstove flue pipe from the hardware store, however long one wants, assembled with wooden rings added as spacers on the outside and simply covered with greenhouse plastic. Caps, maybe wooden plugs on the ends or maybe foam with a vent hole or two, have to experiment and figure that out. But I guarantee this will get hot enough just sitting out in the sun. Fill it with stalks and just open an end to check on them periodically.
Want it hotter? Make a V shaped trough for it to sit in that's been lined with reflective aluminum foil and align it East/West. Easier even would be a split piece of larger pipe with reflective lining, sort of a solar parabolic trough though not a true parabola. Sufficient enough for our purposes I bet.
What's this got to do with boatbuilding? Well I read we have to cure bamboo by some method. Open air seems to be too long and kiln drying seems to be my personal best option but I don't need a whole big room for it.
I'm not sure, but knocking out the center culms with a long metal bar would seem the thing to do, to allow air flow and lessen splits. Will try some knocked out and some not.
Update same day: Did some price checks. One 3ft length, 6" diameter section of black stove pipe is $8 at my local hardware store. Not everywhere is going to have this stuff and it's more expensive than I thought originally. Got a different, better idea. Corrugated metal roofing sheets! Easy to roll up into a cylinder shape and rivet edges together. New is $15 for 10ft locally. Can spray paint the finished tube flat black. Just happen to have two slightly used sections with a few screw holes but should work ok. Stay tuned for updates to this post.
Update later same day: Did I say easy to roll up into a cylinder? Anything but. Two or better yet three people would not have any trouble throwing one of these together. A lone fabricator must improvise. Started out with riveting both sheets together but could not roll it by myself. Ended up removing the rivets and rolling one at a time.
If you get it this far you almost got it whipped but not quite...
Getting to that point took borrowing a length of 6" diameter PVC pipe from the water dept., used as a form to roll the material around and hold the edge with duct tape. The pipe also serves as backing when drilling for the aluminum rivets. Kept feeding the pipe in a bit and drilled close to where the edge was located inside...
All riveted, 19' 4"...
Overlapped 8" and double riveted all the way around and about every linear foot. Nice and snug, very lightweight right now. Will be cutting out the plywood rings to fit over for attaching the plastic cover and painting the cylinder flat black. Thinking maybe R-Board foam caps for the ends. Wore me smooth out for today so check back later. :)
Update 6/16/12
Trip to bamboo forest. All I can say is wow! It's a huge thing, almost impossible to get to and worse trying to walk out with just a few pieces. Sorry for the cruddy cell pic...
It doesn't look so big in this pic but it's the biggest I've ever personally seen. The grove is badly overgrown and would benefit alot by some sound management for bigger and better quality culms. Came away with five nice pieces at 16ft to try in the kiln...
Update 6/19/12
Kiln is complete and loaded with green bamboo culms. Pretty hot in there, 120F in just a few minutes so we'll see how hot it gets and how well it dries/cures the fresh cut culms...
Update 6/21/12
Three days in. Afternoon temps in the kiln are running about 140F. There's alot of moisture laden heat coming out of the end vent tubes, enough to make my palm feel wet. The fresh green culms are changing color, to be expected...
Condensate on the plastic cover about midway of the unit...
Just like my Dad's old solar vegetable dehydrator perhaps. When there is no more condensate, they will be dry. I'm not sure they should be bone dry, probably not. I'll wait till there is just a bit of condensate showing and call them done. :)
Update 6/22/12
Just wanted to add a drawing to explain the addition of a reflective trough that a unit such as this could set into and way increase the solar efficiency for heating the cylinder. Here is an end view concept...
Simple enough. A wooden frame with legs would be easy enough to add for desired height and the trough surface be covered with or made of a reflective material. Even cheap aluminum foil would greatly increase heating. The arrows simply show how more light energy would be directed onto the cylinder.
I estimate since the current temps now are getting up to about 140F, a reflective trough of foil would add perhaps 50 or so more degrees of heat to the unit. A more efficient reflective surface, such as mylar or standard reflective vinyl would likely put it over 200F on a good sunny day if the trough is aligned well. The trough would need a pivot point on both ends if set North/South to catch the sun all day or set East/West would heat good from about 9am to 6pm summertime with no pivot.
If we want to spend a little to get alot, we can do something like this deluxe model haha...
Make the ends of the trough enclosed with just a hole for the cylinder ends. Cover the top of the trough with glass or "maybe" some quality UV resistant clear plastic but it would have to stand some heat, well, alot of heat, 200F+ I bet. Put a small solar powered fan on one end to slightly move the air through the cylinder, might need a damper to control the air flow, or not. Might not even need a fan with convection carrying moisture out of the cylinder ends...maybe caps for the cylinder ends also with dampering ability at the top edges of the caps? This version would hold alot of heat in during the dark hours, especially with double pane glass.
Update 6/26/12
It's been a full week since placing the culms in the solar kiln. I decided to remove them to see the progress. Not nearly the condensate as earlier. They are much lighter in weight and change of color...
Wiped the wax off some sections with a towel and they shine really good! Almost like a glassy finish...
Interesting difference in the pieces I used for end vent plugs where the hot air passed through...
Other than that one plug splitting, I don't notice any splitting of any of the culms, yet, and they seem to be as straight as they were when started. Broke my heart though and I never gave it a thought, the rivets badly scratched my two best pieces meant for a sail mast. I suppose they could be wrapped with cord to hide the scratches and nobody but me would know. Any more pieces put into this unit will be wrapped with something. I'm considering scrapping the whole thing and starting over, now, knowing of the issues with this unit will make the next one alot better.