Air intake- exhaust ratio of a cone

[DAN-Y]

I switched from paper clips to stainless steel Drapery Pin Hook. I modified them by bending to suit my needs.

[James Marco]

Roger,

Yes, I figured, roughly, all that stuff. The higher heat also increases the speed at which it exits, increasing the output side volume roughly 4-5 times over the intakes. Most of the air, 4/5 of it anyway, will be the same as it comes in, just heated. Much of the heat will be absorbed by the pot/water (or liquids) in the pot (this is the goal of cooking.)  Around 30-40% of the heat, or around there, running small flames (as with alky stoves) will be absorbed. I often test my burns by placing my hand over the pot & exhaust gasses. The gasses are NOT 1000 degrees as they exit a cone, MUCH less. (Or perhaps I am immune to being burned.) You are thinking of the canister flames.

[Gary Dunckel]

Ah, high-intellect dueling engineers–I love when that happens. Please keep your dialogue going, James and Roger, as I have to see what you two come up with here. From my sophomoric standpoint, it seems that having too many holes in the windscreen might diminish the benefit of having one to begin with.

Dan, drapery hooks? Really? Who knew?

And, Roger, don’t overlook the vast amount of squirrel respect you would garner by using pastel paper clips. They love that sort of thing (and so do hummingbirds, if the clips are red). As you might know, I’m all about squirrel respect, after that huge gray one In Glacier Park 5 years ago tried to bite my ankle (he was trying to get even from when I bonked him with a hard pine cone the afternoon before).

Now, please you two, let’s get back to physics.

[Roger Caffin]

Hi james

Good point: the exit air will be a lot cooler than 1000 C. I stand corrected. Even so, I still prefer more exit holes than entry holes. Actually, I like lots of air circulation. Keeps the CO levels down.

Hi Gary

Pink paper clips – nah, boring. Now BLUE paper clips: they would be interesting. Why blue?

I used to keep a dropper bottle of eco-friendly dishwashing liquid and a small sponge in a small bright blue nylon bag for washing up after dinner. Then an Australian Bower Bird pinched the whole bag one night deep in the rain forest. The males collect blue things for their ‘bowers’ or nests, to attract the females. Sometimes they have 20+ blue straws there … I never found it. Grump grump … :-)

Cheers

 

[Gary Dunckel]

So let’s go with pink or maybe green paper clips, Rog. I kinda like blue myself, but since the bower birds do also, we’d best stay with some other color. “Grateful Dead” patina titanium?

Let’s get this wind screen air intake/exhaust portal thing worked out, OK? First that, then we can figure out the bit about the bower birds. And those angry gray squirrels…

[Roger Caffin]

Chuckle.

But that was a beautiful experiment.

Cheers

 

[DAN-Y]

Just doing some research, came across this thread. Interesting video 1st page on air intake ratio of windscreens.

[Roger Caffin]

Hi Dan

I sat and watched that video twice just now. It should be shown to every alky designer.

But I have to disagree just slightly with some of the comments made by others in this thread. I don’t think the flickering of the flame has much to do with the adequacy or otherwise of the air inflow. Rather, I think it is almost entirely due to the air CURRENTS – as you pointed out several times in the video. You need the air coming up from below the flames rather than going down onto the flames.

My reason for commenting is because I have spent a lot of time with my own Winter Stove, watching the behaviour of the flames inside the Ti burner chamber. I varied the position of the air intake holes wrt the central jet, so that the direction of air flow around the gas flow above the jet changed. If I got that wrong the flames were very poor.

Going back to your video: I don’t think you even need the bottom air inlet holes. You just need some modified paper clips (whatever colour!) to stand the windshield up off the ground by 10 mm or so. That will control the direction of the air flow. Trouble is, that might leave the flame susceptible to any significant sideways wind coming in under the windshield.

Can one put a small ‘windshield’ around the stove to control the air flow currents, inside a large windscreen to block the wind? The inner one would be almost a venturi. Much room here for design and experiment.

Cheers

[Mario Caceres]

Roger said… “Can one put a small ‘windshield’ around the stove to control the air flow currents, inside a large windscreen to block the wind? The inner one would be almost a venturi. Much room here for design and experiment.”

I have been playing around a bit with this idea.  I made a conic windscreen with very generous intake holes which are “shielded” with a carbon felt outer ring.  The carbon felt is porous enough to let air in thru those vents, yet blocks any wind from getting into the stove flame.  The carbon felt is about 1″ tall and adds about 0.5oz to my set up, which is not to bad considering I do not have to worry about which direction the wind is coming from, etc.  The carbon felt “shield” also slow things down a little.  i.e Before the “shield” my starlyte regular would bring 2 cups of 60*water to a boil in 7’27”, but with the Carbon felt “shield” that gets bumped to 10’35”.  There is enough air for proper combustion though, as there is no sooth on the bottom of my pot.

This difference in performance is not so bad, when you operate in simmer mode (For that I add disc with smaller opening on top of the starlyte).  When in simmer mode, without the Carbon Felt “shield”, I can get water to boil in 17’05 while with the shield it takes only 1+ minute more (i,e 18’10.)

Here a picture of the aluminum conic windshield, with the bottom holes covered by the carbon felt “shield”.

[Mario Caceres]

This video shows how good of a job the carbon felt does to block wind…

 

[Roger Caffin]

I wonder what would happen if you put a 50 mm high windshield 25 mm outside around a ‘standard’ windshield which had a 10 mm gap at the bottom? Seems to me an experiment worth trying.
Maybe 75 mm high? Dunno.

Cheers

[Author]

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