DIY wind screen thingy. Probably safe.

[simon t]

https://imgur.com/gallery/EqB1sBX

DIY wind screen thingy.

Seems to burn nice and blue.  Think it’s getting enough air flow but I’d like a second opinion as the big brains tend to hang out here.  Cannister seemed safe from overheating.

Titanium, cut with scissors, corrugated by using a ruler and sharpie to daw lines, Ti bent over ruler and held on with a silicone band.  14g (3g band, 11g screen).

Idea was to give wind protection and maybe a minor efficiency boost by chaneling the hot air/ flame up the side of the pot.

Works better to leave it attached and slide it up and down than to disconnect/reconnect.  This makes it a tight fit for my cozy so I’ll need to make a slightly bigger one.

I ran my cannister empty doing tests last night.  I have another one somewhere… if I locate it I could do some pics of her in use and maybe conduct a wee efficiency test.

 

 

[Jon Fong / Flat Cat Gear]

Looks great to me!  It would be great to see some ful efficiency/wind test results, but the basic concept looks spot on.  See if you can keep your fingers on top of the canister (possible up to about 145 F) as that will give you an idea if it is overheating.  My 2 cents.

[Jerry Adams]

Nice looking windscreen. That’s similar to one I’ve made.

Does the silicone band get too hot?

I have not found that it gets the canister hot.  It’s about the same as any stove/windscreen.  The heat radiates more to the top of the canister, but that’s not where the fuel is.  Touch the canister down where the fuel is and if that’s warm, then that’s a problem.

I’ve measured about 10% efficiency improvement.  It would be interesting to see data from yours.

 

[simon t]

Thanks Jon and Jerry.

Quick and dirty test.  No regulator so just eyeballing to get the same position on the stove handle.  Measured water temperature with probe suspended so it didnt touch the ti pot and stopped at 99c.

Still (inside, no wind)

Without screen;

300ml boiled in 3:22. 5g fuel used

With screen;

300 ml boiled in 3:23 6g of fuel used.

Ran the stove a bit faster than I normally would just because it corresponding to a 66.7 degree turn that was easy for me to line up and replicate.

Silicone was fine.  Fingers were definitely hotter with screen down but cannister didn’t feel dangerously hot.

I think I have a fan somewhere…

[Jerry Adams]

funny that the windscreen makes it worse

was the amount of water precisely measured?  Like, you could measure the weight which is more accurate.

what was the difference in temperature between start and end for each case

if you did 4 test runs – without screen, with, with, without, then you’d start to get an idea what the random variation is.  Like, if the two withouts were 5g and the two withs were 6g, then maybe you’re actually determining what the real difference is.

If you’re looking for an improvement that might be 10%, then you really need to measure in tenths of a gram.

[simon t]

Jerry.  Just a single pass for fun.

https://imgur.com/gallery/yJsSZsg

When I went to take the starting weight of the cannister for the next experiment it was 1g lower which would make the fuel use the same.  Just cheap digital kitchen scales.

Water was weighed and starting water temp was within 1C. I allowed the setup to cool between tests.

 

The “wind test” is a bit more telling.  I have a USB poweeed silent cabinet dual fan. With 3 settings.  I used High, which I would describe a a pretty gentle breeze.

No screen;

Water temperature stalled at 90C and I stopped the test at 10 minutes when it became clear that I wasn’t getting to 99c and I was just wasting fuel. 10g fuel used.

With screen;

300ml boiled in 4:07

Fuel used 6g.

I won’t be going full scientific method but this quick and dirty experiment showed that in zero wind conditions, there isn’t any noticeable efficiency improvement (possibly a tiny decrease in efficiency) and in wind the efficiency improvement is significant.

Combustion appeared complete with the screen and the canister didn’t explode :)

[Brian C]

I did something similar and had things set too low or surrounded too much.  Managed to melt the plastic valve inside the canister.  Weirdly, that caused part of it to block the intake on the stove cutting the stove off entirely.  Of course removing the canister from the stove caused fuel to start spewing everywhere.  It was exciting.

[Jerry Adams]

Yeah, one does not have to analyze everything scientifically :)

In my experience, that works really good, I think you have a good design.

Mine is shorter so it fits inside my pot but it isn’t quite as good in the wind

[Jon Fong / Flat Cat Gear]

For DIY testing, your results are great.  Slight wind no windscreen fails , with a windscreen it passed.  If you want more resolution, you will need to measure the wind speed.  As a quick reference, a BIC lighter tends to work up to about 2 mph.  If you want better resolution, you need a scale that will measure to 0.1 g.  But I think that your results are good enough for your cookset, great job.

[simon t]

Jon and Jerry, thanks again for your input. And encouragement.

I had moved to an system like a Caldera Cone (UK/EU Vesuv) with alcohol stove but the Cairgorms National Park is cannisters only (no fires, no alcohol stoves) and only 40 miles from my house.

This does fit inside the Bot 700ml with the canister and the corrugated pattern wedges it to stop the cannister moving.  I found I prefer it attached to the outside and sliding it up and down for storage/use.  For now I prefer to keep it on the outside and to make a larger cozy.  The corrugated pattern and larger cozy will give a bigger air gap and hopefully insulate better for rehydrating meals as I rehydrate in the pot as I don’t like boiling water and plastic meeting.

Brian C, that was my fear.  The stove and cannister were hotter in the still air test.  I think I’m good as long as I don’t overextend the screen over the stove in still conditions.

 

Brian C, do you think the damage was done by the trapped heat conducting through the stove or the top of the cannister overheating?

If I was to make another, I’d consider bigger ridges for more free flow air area (these ridges are made of 2x 1 cm panels).

I would also consider losing the pot handles and going a full 360 combined with a wider silicone band that can be used to handle the pot.

The screen could also be shorter as the flue channeling doesn’t initially appear to add a  noticiable efficiency improvement.  It just needs to be long enough to be effective as a windscreen.

 

[Brian C]

My guess is the stove itself but that’s completely a guess and only based off of the o-ring also looking a little… sad?

[Jerry Adams]

nice how you pack it together

I tried corrugations that were twice as wide, and it didn’t matter, but not scientific

If you do 360 degrees, it can block the valve on the stove making it harder to turn on and off

[Jon Fong / Flat Cat Gear]

OK, I think that your set up if fine for most backpacking trip.  However; if you are going to Cairgorms National Park, that isn’t the stove that I would take. The last place that I would like to be in the wind is with a BRS 3000t.  The Cairgorms can be one of the windiest places in the world and much of it is above tree line.  I would highly recommend that you switch to a Soto WindMaster.    My 2 cents.

[simon t]

Thanks Brian.

Jerry, interesting about the larger corrugations.  With a 360, if it covers the valve handle, it would be too low… but a cut out for easier access would be good.

Jon,  I’ve had the brs out in cairngorms last week and I did have to build a windbreak out of my stuff which is why I finally got around to building a screen.  I might get a more suitable stove in the future but I think the BRS with the screen or an improved version will do just fine.

 

[Jerry Adams]

Recent reports showed a brs doesn’t work by itself in the wind, but with windscreen it’s okay

[Adrian Griffin]

An ingenious deign. The crinkle-cut titanium and the silicone band solves the problems of supporting the windshield, providing a path for the exhaust gas, and giving some heat conduction from the hot exhaust gas to the pot.

The lower efficiency in still air isn’t a complete surprise. Your windshield is working as a heat exchanger and may be conducting heat away from the pot rather like cylinder fins on an air-cooled engine. The Gear Skeptic found that windshields sometimes lowered efficiency in still air.

But what matters is real-world outdoor conditions. I think a more realistic baseline is a 2 mph (0.9 m/s) wind. That’s not even a breeze—it’s a light air on the Beaufort scale. At that wind speed, your windshield is saving fuel.

Fuel rate has a dramatic effect on efficiency. In a light breeze with a windshield, the flame needs to be turned down more than you think. Fuel rate should be 0.8–1.2 g/min. Take a look at the graphs in my March 2024 posts in the thread Canister Topped Stove Performance in the Wind. You were doing 1.5–1.8 g/min.

The other takeaway from these tests is that with a windshield, the burner-to-pot distance doesn’t matter much. I found that with a windshield enclosing the flame area, the Hornet II did slightly better than the Pocket Rocket 2. Jon’s and other people’s tests showed that without a windshield, the Hornet II is less efficient than most other stoves.

[Roger Caffin]

The blue flames look pretty good to me.

Loss of heat to the titanium windshield – it’s a poor conductor of heat, so I would not expect it to suck much heat off. Mind you, if the pot is also titanium – dunno.

I have to agree with the suggestion that a resolution of 0.1 gram is needed, and that several runs are needed to look at variability. Yeah – the fuel bill. I made an adapter for my V7 stoves to go on the ‘fly spray’ butane canisters – $5 for a pack of 6 at 220 g each.

As the O-rings are probably Viton, which is good to 250 C, getting the stove hot may not matter. And a hot stove simply pumps heat down into the canister, which is all to the good. I don’t know what the valve seat inside the Lindal valve is made of: could be Viton or could be nitrile. Nitrile comes in a range of formulations, w temp range 120 C to 165 C. I recommend the Touch Test for safety, which limits things to ~40 C.

Just a thought: how would larger ripples in the Ti shim go? Fewer points of contact, and maybe better air flow up the side.

Cheers

[Adrian Griffin]

Yes, get adapters so you can refill your expensive propane-isobutane canisters from cheap A4 spray paint/fly-spray butane canisters. Many are available from Amazon or AliExpress. Two pieces are needed. One is the adapter that clips to the top of the A4 canister and turns it into a Lindal valve. The second is a double-female Lindal with a valve that allows you to drain the A4 into your chilled propane-isobutane canister.

As for weighing things, Amazon, AliExpress, and Temu have many low-cost electronic scales. I got one from Amazon for about USD12. The calibration weights cost more than the scales! And for wind speed, you can get an anenometer from Temu for not very much money. Then you’re all set to be a testing lab.

[simon t]

Thanks, Roger, Adrian and Jerry.

I’ve doodled out a v2 and ordered more titanium, i’ll grab a scale with better resolution too.

Adrian, the info in your linked thread was very useful.

Roger, if I get a bit of spare time I’ll try and figure out the optimal flue area and coresponding corrugation.

 

 

[Jerry Adams]

“Yes, get adapters so you can refill your expensive propane-isobutane canisters from cheap A4 spray paint/fly-spray butane canisters.”

There is another rat hole to get lost down

adapter – search for “butane refill adaptor” – each time I look the product I saw before isn’t available anymore.

Buy 8 ounce cartridges from Korean grocer for $2 each.  This doesn’t work very good below 32F or so, without fiddling which is pretty easy.  I use it down to 20F.

If you search for “gold scale” on amazon there are scales < $10

Don’t set sucked into weighing down to put into baffles of garments you make – bigger rathole

[Adrian Griffin]

These are the adapters I use. The double Lindal on the right can also be used to top up partly-used canisters from another canister.

[Jerry Adams]

I think the windscreen absorbs heat from the exhaust gas and conducts it to the pot

Heat is not conducted from the pot to the windscreen

Based on the fact when the water is boiling, there are bubbles coming from inside the pot opposite where the windscreen touches it

And based on the fact that when I’ve measured efficiency, the winscreen adds 10% efficiency

And, logically, the pot is touching the water so won’t be much more than boiling temp.  The windscreen is in the exhaust gas so will be much hotter

My pot is titanium, windscreen is aluminum.  But I don’t think it matters.

I painted the inside of the windscreen to better absorb heat and radiate it back to the pot.  The outside of the windscreen is aluminum which radiates less heat to the atmosphere.  It feels like this is cheating on the laws of thermodynamics :)

[Roger Caffin]

when the water is boiling, there are bubbles coming from inside the pot opposite where the windscreen touches it
Not theory, not speculation, but observation.

It feels like this is cheating on the laws of thermodynamics :)
Ha!

Cheers

[Adrian Griffin]

Yes, Jerry’s right. A windshield, crinkled or not, won’t transfer heat outward from the pot. The exhaust gases are hotter than the water in the pot. That said, a windshield might conduct and radiate some heat from the hot exhaust gases outward to the surrounding air.

So why did Simon and the Gear Skeptic find that a windshield slightly lowers efficiency in still air? Could be what I just mentioned, or could be less-complete combustion because the windshield partially obstructs the flow of exhaust gases. In small boils, it could be the need to heat the thermal mass of the metal windshield.

But in the slightest breeze, these effects are outweighed the savings occurring as the windshield traps the heat from the burner flame.

[Jon Fong / Flat Cat Gear]

Well, I think that I know a fair amount about windscreens. I have found that controlling the airflow is crucial to maintaining good fuel efficiency. Too tight, and you starve the stove. Too loose and you don’t add enough protection from the wind.

With respect to GearSkeptic, I did not see anything in his Backpacking Stove Efficiency, Part 3: Windscreens that implied that fuel efficiency was reduced with a windscreen. The caveat being this is a known phenomenon with the Ocelot MAX for large pots. The MAX was designed to work with large pots and has by design a tortuous path for the exhaust air. We even recommend not using the MAX in light breezes. The Ocelot Mini (or other Ocelots for that matter) exhibits the same fuel efficiency in calm conditions as a bare stove.

With respect to Simon’s data, having an accurate scale could shed more light on the situation. From looking at his pictures, I cannot see how his windscreen would reduce the fuel efficiency over a bare stove. My 2 cents.

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