Sep 28, 2012 at 9:21 am #1294522
MSR has this heat exchanger that is a windscreen for canister stove plus it improves efficiency with this heat exchanger, but it weighs 6 ounces so will never save weight over-all.
I think maybe it was Dave Thomas that mentioned bending aluminum flashing back and forth, accordian style.
Voila – lighter weight version of MSR exchanger:
I made this with light aluminum flashing.
It's two pieces attached together because I didn't have a piece long enough.
I marked lines 1/2 inch apart and folded part way over a straight, sharp edge – piece of plywood. Then folded by hand to make completed shape.
#18 galvanized wire on the outside. Several holes through flashing that I put the wire through.
No channels where the handle is to keep it cool.
Adjusted wire length so there's some "spring" pressure of flashing against pot.
Nests into pot:
Weighs 0.9 ounce.
Compared to my old windscreen:
Old one weighs 0.66 ounce.
I brought water to almost boil. Weighed water. Weighed canister before and after. Took temperature before and after. Calculated oz of fuel to bring 1 pint of water 150 degree F increase of temperature. Repeated twice:
old windscreen = 0.236 oz/pint/150F
new windscreen = 0.189 oz/pint/150F = 15% better
I previously did this with bigger channels – 1 inch between folds, and it didn't make much difference.
So, I use 15% less fuel with new windscreen.
I typically go out for 4 nights. 1.2 ounce of fuel per day, so 4.8 ounces total required. With new windscreen I only need 4.06 ounces so I save 0.74 ounces but the windscreen weighs 0.24 ounces more so I save 0.5 ounces my first day of hiking – too small to make much difference.
On the other hand, for 4 nights I need 4.8 ounces of fuel with the old windscreen. This is too large for the small canisters so I have to take a big one – 13 ounces for canister and fuel to start. With the new windscreen I need 1.01 oz of fuel per day (which includes a bit extra just to be conservative) so I should be able to use a small canister which weighs 7 ounces so I just saved 6 ounces.
Or, if I use big canisters, with my old windscreen I usually used a little more than half a big canister so I need a new canister on every trip. With the new windscreen I should be able to get two 4 night trips per canister.Sep 28, 2012 at 11:29 am #1916423
Very nice work, I may have to try to emulate that. So what's supporting the windscreen in place, the spring-like pressure?Sep 28, 2012 at 11:47 am #1916427
Yes – spring like pressure (friction) keeps it in place.
You have to bend the hook in the wire piece at just the right place.Sep 28, 2012 at 12:18 pm #1916433
Excellent, now I see the two hooks in the wire under the pot handle. Great design, thanks. Going to add it to my winter project list.Sep 28, 2012 at 12:28 pm #1916435
Gary DunckelBPL Member
I like that a lot, Jerry. Good work!Oct 1, 2012 at 10:33 am #1917152
Kevin BeedenBPL Member
The rigidity provided by a simple fold is very useful*, and I started playing with foil BBQ trays, and then developed the idea into the SqueezeBox Stove, which involves some tedious double-folds…
* I made a 6g pan support & windshield whilst playing with the idea, and it supported at least 3.6kg; that's as far as I dared go, since I didn't want to crush the thing.
I don't think such a windshield will provide much in the way of heat exchanger function, since the thin foil cannot be clamped into good thermal contact with the pan. Improvements in efficiency are more likely to be due to simple windshielding, and keeping the hot gas close to the pan. The 'chimneys' provided by the folded sections work well, and avoid the need to exhaust holes. I found that, with an alcohol burner, I couldn't hold the windshield next to the pan, as it reduced the exhaust flow causing poor combustion. With a gas stove that you can throttle back, you may not have this problem (possibly aided by the simpler combustion chemistry of propane/butane).Oct 1, 2012 at 11:11 am #1917158
John DonewarBPL Member
@newtonLocale: Southeastern Texas
I followed the link to the SqueezeBox Stove.
Origami meets the ultralight hiker kitchen! ;-)
Quite seriously though I see a lot of thought, ingenuity and skill involved in those windscreens and stove.
I've been doing some solid fuel stove test / experiments lately and my latest round combination windscreen and pot stand acted similarly to your stove. The flame ever so slightly "licked" out through the double row of 1/4" vent holes and looked very much like a stove without a windscreen.
I admire your "outside the box" thinking. Keep the ideas flowing!
NewtonOct 1, 2012 at 11:25 am #1917161
Very imaginative, Kevin
Main thing is protection against wind which those provide goodOct 1, 2012 at 11:37 am #1917163
How was your old (non-folded) windscreen secured to the pot?Oct 1, 2012 at 12:19 pm #1917171
"How was your old (non-folded) windscreen secured to the pot?"
you have to make it just barely wide enough to fit
make it long, fold one side, put it up to pot and mark a line where it has to fold on the other end, fold.
If it's still a little short, then you can just cut a sliver off the end
If it's too long you can unfold, flatten, re-fold
You might want to get the length right and then punch the holes in case you screw up and have to try again with another pieceOct 1, 2012 at 12:53 pm #1917184
Any issue with the Al getting too hot and melting?
Also, do you think adding more holes would make it closer in efficiency to the folded version?Oct 1, 2012 at 1:21 pm #1917199
I use pocket rocket which the flame goes up onto the bottom of the pot, then sideways into the windscreen
If the flame was directly on aluminum it might melt?
I tried fewer holes, and there wasn't enough airflow, so looking at the burning flame, it wasn't a nice even blue colored flame
If you had too many holes you might lose the effectiveness against wind?
But, the flames get deflected out the holes and away from the pot. With the folded version, the flames go up the outside of the pot between it and the windscreen. The pot gets hot, and the wondscreen gets hot which gets transferred to the pot. When I look at the liquid inside the pot, it bubbles and spits against the sides right at the surface. That's where you get the 15% improved efficiency, as I measured it.Oct 1, 2012 at 1:28 pm #1917202
Thanks Jerry!Oct 3, 2012 at 11:09 am #1917812
Kevin BeedenBPL Member
> Origami meets the ultralight hiker kitchen! ;-)
Newton, glad you liked it. It made it to BPL briefly at the time, but seemed largely to fall down the cracks…
The idea won Alpkit's CoLAB09 competition the next near, which got me a nice sleeping bag and down jacket…
The thing about inspiration is that the ideas do just pop into your head; the three main ones documented in the OM article. But I guess the seeds are sewn over many years of thinking and researching, and playing with other ideas, and it all comes together without too much apparent effort. I later used the folding technique to make a vaned wall for a kelly kettle. As it turned out, Rog Tallbloke had had exactly the same inspiration, entirely independently. I bet we can both trace the way we arrived at the idea, and I bet those paths will be entirely different.
Folding Al foil is a pain. Folding Ti foil is more than a pain, but it has been done; the Cicerone guidebook writer, Paddy Dillon, is a big SBS evangelist, and has made a Ti version which he uses on many of his research trips, including Iceland, Greenland, Tenerife, etc. using a couple of my little Red Bull 'inverted conic' burners.
I confess that I've moved on to clones instead…
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