RFC: Upright Canister Windscreen Design

[Daniel Fish]

…

[Paul Mason]

I have a Brunton Raptor and was able to take an piece of aluminum and attach it to the stove supports – 3 -with small holes. The aluminum only hags down from the supports by about 2.5"* or so and my pot was not as wide as where the aluminum was attached. I didn't go all around – maybe 2/3.

It looks like you may be able to do the same.

*I'm not at home so I can't measure it. I'm going from memory.

I now use the Soto OD1r with its wind screen.

[Paul Mason]

Be cautious about how low you go. You don't want thermal feedback to heat up the canister.

My guess is that you only need the wind screen to be just below the stove head.

[Jan S]

Some turbulence coming from the lower and upper edge of the screen might hit the flame. So a longer windscreen would help.

Google gave me this stunning image that should give an idea of what I mean:

(from: http://www.tekura.school.nz/departments/horticulture/ht110_p5.html)

I doubt this actually is what happens, but those things on the right side of the wall should be there in some form or another.

I've always wondered what would happen if you put a disc with lots of holes in it directly below the pot stands. Kind of like the Trangia windscreen has to keep the burner up.

In theory that should break any turbulences further up and either give you a more laminar airflow or make lots of small turbulences that don't reach the flame. And it should reflect some heat up and keep the canister from getting hot and produce better efficiency.

[Jan S]

One more thing if you're worried about heat getting to the canister: Roger seems to recommend a simple foil heat reflector on top of the canister. Look in the middle of this article for an example. Something like this should be extremely easy to make and shouldn't have any impact on air supply. Not sure if that is necessary with your setup and just here as an idea.

[steven franchuk]

"And best of all, the flame wasn't affected by the wind and no little whippy sounds of turbulance like before."

Wind affects two areas of the stove.
1. Wind blows the flame to one side of the burner.
2. Wind disturbs the flow fuel in the jet and airflow around the jet.

I did some time ago and found that blowing air on the burner itself would blow the flame to one side but it would not blow out the stove or affect the sound. However when I blowed air on the jet itself the stove would go out. I found the jet to be very sensitive to air flow. low winds can cause the "little Whippy sounds" and stronger winds on the jet can blow out the stove.

After that I wrapped a thine metal strip loosly around the stove jet. That eliminated the sound variability. But that little jet shield didn't appear to improve stove efficiency. Stove efficiency appears to be mostly related to the effect the wind has on the burner, not the jet.

"Roger seems to recommend a simple foil heat reflector on top of the canister"

In my testing I have found that most of the heat that gets to the can gets there by conduction instead of radiation. The hot burner transfers its heat to the tube and then down to the stove valve and eventually to the can. I have measured the valve at 80C (hot to the touch) but the canister was only warm and could safely be handled. I
don't believe a radiation shield will have any significant impact on the canister temperature.

[Roger Caffin]

I experimented with all those designs, but they were all too complex. These days I use some Al shim sitting on the ground, going half way up the side of the pot, and wrapping 3/4 – 7/8 of the way around the pot. Clearance to the pot about 20 mm but not real fussy. It works fine, and is so much simpler! KISS.

Cheers
PS: the radiation shield was discarded ages ago.

[Michael Schwartz]

Roger, Would you please explain a bit more: "Clearance to the pot about 20 mm but not real fussy."

Mike

[Paul Mason]

Daniel,

Check out this thread and the cup designs there
– Jerry Adams'.
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=58105&skip_to_post=495031#495031

[Paul Mason]

Daniel,
If you have some aluminum remaining you might want to try the Soto type wind screen.

http://www.traildesigns.com/micro-windscreen-od1r-stove

It would be smaller, lighter and easier to use.

Or you could use your current design but bend the bottom flanges inward.

Post a photo if you do it.

[Jerry Adams]

That one is so passe

I like this one better http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=68713

[Roger Caffin]

> Would you please explain a bit more: "Clearance to the pot about 20 mm but not real fussy."

Have a look at the first pic in http://www.backpackinglight.com/cgi-bin/backpackinglight/essential_stove_maintenance.html#.UWI4VTdVZwM
or the first or third pics in http://www.backpackinglight.com/cgi-bin/backpackinglight/2013_developments_canister_stoves.html#.UWI4lDdVZwO

The 20 mm is the clearance between the pot and the windshield. As you can see from at least one of these, my clearance can be quite high! But do NOT wrap the windshield aropund the pot too tightly: that may generate lots of CO.

KISS
Cheers

[Michael Schwartz]

@ Roger. Thanks for the reply. After I posted, I actually found some of your pics that illustrate your points. The ones you mention in your last post are helpful too.

What are your thoughts on the design Jerry mentions above? This one:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=68713

It looks very good to me, and I am thinking of making one.

M

[Roger Caffin]

Hi Michael

Hum, yes, well … complex, ennit?

I wonder how it works? I suspect that it is working (if it does work) in a very different way from what was hoped. I think the bottom edge of the concertina projects downwards below the pot bottom far enough that it is capturing the hot air flow and bringing it up the side of the pot a bit closer to the pot wall than you would get with no windscreen present. I don't think the amount of contact between the pot wall and the folds on the concertina are good enough to transfer much heat by themselves.

If this is correct, then you could achieve the same result by having a very conventional windscreen sitting just 10 mm away from the pot. Much simpler to make, much simpler to use. And being simpler, much more reliable too.

Fwiiw, that is roughly what I do when i am concerned to save a gram or two of fuel. And I have a lid on the pot and the flame turned down too.

Any photos showing my pot with the lid missing are like that to show off the stew in the pot, because I do not cook without a lid. Hey – stew makes for a more interesting photo!

Cheers

[James Marco]

Yeah, I agree with Roger. I doubt that the contact is all that effective. Though I am sure it accounts for *some* heat transfer. The very thin line described by the sharp fold would not have enough surface area to transfer any significant quantity of heat.

For short burns, a relativly tight fitting wind screen would do well with trapping heat next to the sides of the pot. Hanging down over the edge of the pot, typically a larger heat loss area due to mixing with cooler air/turbulence, the folded screen would channel hotter air up into the windscrren where it could do usefull work, heating the pot sides.

Of course, you have to be carfull you don't overheat the canister with "toppers. Such stoves were never really designed for such use. (Not that that ever stopped any of us.)

Again, I agree with Roger that a remote stove is best for using tight fitting windscreens. The popular Caldera Cone is, perhaps, not the best design for the wind screen, however. The tapered design, while quite stable, allows edge turbulence right where you want to eliminate it. The thermal feedback is highly amplified in such a screen, though. Heating the stove entirely. This can be mitigated by allowing air intakes at the critical parts, the fuel tube connection(unless lenghened,) the valve and seat which can distort inder a couple hundred degree's of heat, and the removal of any plastic parts, obviosly.

[Jerry Adams]

Roger and James are skeptics : )

first – do no harm – I observed flame and it's blue and spreads out nicely over bottom of pot – I think I'm getting enough air flow – I've tried a number of configurations with bigger/smaller holes that resulted in not enough/too much air flow – obviously haven't measured CO

exhaust gas is directed up the side of the pot so some heat is transferred there

some heat is absorbed by the aluminum and transferred, even via the small area of contact

I have noticed that food sticks to the sides where exhaust/contact is so there is some heat transfer going on, but that's subjective

I have measured that 15% less fuel is required to heat the same amount amount of water the same amount of temperature difference, but that measurement is tricky. There is about 15% variation from test to test with the same configuration, so the best run with old windscreen is as good as the worst run with the new windscreen.

I have used the new windscreen on a number of trips. Maybe 30 nights. I have noticed that I now use a little less than 1 ounce per day where I used to use a little more than 1 ounce per day.

Make one yourself and measure it : ) I could make one and send it to you but it takes just an hour and depends on pot size.

[Jerry Adams]

Nice

Shakespeare? : )

How does your pot fit into it? How much space is between the edge of the pot and the windscreen?

[Roger Caffin]

> Roger wins a 5lb rucksack from the 80s.
How …. nice. Thank you.

Trouble is, I use a wide Ti pot that sticks out beyond the ends of the pot supports. More efficient heat transfer that way.

Otherwise – pretty simple.

Cheers

[Paul Mason]

I suggest hanging the screen from the pot supports and I get …

I'm hurt

[Jerry Adams]

"I suggest hanging the screen from the pot supports and I get …

I'm hurt"

She probably gave me credit because Roger and James were beating up on me : )

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