Half a croissant, on a plate, with a sign in front of it saying '50c'
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ooh, my gut tells me that this idea that popped into my head today might be a good'er
  [vote for,

Rising heat can be made to tornado if given a little nudge.
This has led to conjecture that it might be possible to use this phenomenon to create chimneys out of thin air without the need for a huge towering stack for solar updraft towers.
I think that is a stellar idea, but... again the heat is just thrown away after it exits the turbine chamber.

What if, instead of building a solid chimney, one were to construct a scaffold-like tower which is open to the air with only enough support to safely suspend a hemispherical cap, (round end up), designed to match the diameter that the tornado will be at that height.
The center of the hemisphere is cut away and above this is a parabolic funnel shape with the turbine blades ringing it.

In this case the heated air entering the bottom of the hemisphere is directed at ninety degrees to its former direction of flow in order to escape and turns the blades of the turbine in passing. The air then flows radially outwards in all directions but the negative pressure beneath the hemisphere created by the uprising tornado causes this radially directed hot air to bend downwards due to the Coanda effect and is eventually dragged back into the swirling vortex at its base following a path of least resistance and conserving almost every bit of the excess heat which would normally have been tossed away.

Basically it would be wrapping a tornado back on itself, or making a spinning vortex ring comprised of spinning vortex rings.

I think I might try welding a small model and see if I can get a camp-fire tornado to wrap back on itself.
It would look just like a magnetic field made of flaming swirls.

...and I'll probably also toss in a few handfuls of metallic salts at some point. You know, for science.

: ]

Desktop Fire Tornado https://www.youtube...watch?v=1BxQd6AGYiI
[bigsleep, Feb 03 2018]

Coanda tornado 1 https://imgur.com/Ha3IPOv
pencil sketch [2 fries shy of a happy meal, Feb 05 2018]

Coanda tornado 2 https://imgur.com/RK4Mzkk
marker sketch with some weird ghosting thing going on beneath it I didn't draw. [2 fries shy of a happy meal, Feb 05 2018]


       Wait a minute. I thought a convection current needed cooler fluid crowding in at the bottom to sustain it. If you return the hot fluid from the top to the bottom (by coanda) without dumping its heat on the way, won't you somehow undermine the convection process?
pertinax, Feb 01 2018

       I don't know. This just popped in full-blown.
I see the camp-fire tornado being fed by cold air drawn in at the base of the fire, and the Coanda effect curling the fire streams downwards and re-entering the maelstrom above the level of the burning fuel. Since the turbine would be located at the uppermost point in the system the heated air would be trapped and pass through the turbine again and again until the heat energy dissipates.

       You'd get a convection current with a cold air intake 'and' a conservation of heat loss from vortex-ing the vortex... I think.   

       I could be wrong, but the visual I got was totally awesome and I want to play with it either way.   

       What about birdstrike?
Ian Tindale, Feb 01 2018

       //What about birdstrike?// yum.   

       Scaffold might be the limiter. Poking a subtle dynamic system is hard to engineer finitely. Not saying it's not possible though.
wjt, Feb 01 2018

I think that the airflow from the vortex would deter birds and insects almost like an elliptical, hmmm or maybe egg shaped, force field of extremely hot air leaving secondary vortices in its wake.

       //Scaffold might be the limiter.//
Good point. I figure as long as all of the inward facing surfaces are curved to follow the swirling of the air then the inner tornado will be effectively channelled while allowing the... Coandized air to re-enter the initial tornado wherever it feels comfortable doing so along its way to the ground.
Since convection begins above the heat source, the majority of the waste heat should be sucked in right nice and close to the base if the geometry fits the BTU's

       On a side note; did you know that the proper decomposition of wood chips gives off the same BTU's as combusting the wood but over a longer time? ...and when it's done giving off its heat it becomes topsoil instead of released carbon.   

       Cool eh?   

       So you're doing sort of fire sculpture? Like that idea. Any chance of uploading a rough sketch? I think I get it but a sketch would be cool.   

       If it's what I think it is it's a neat idea.
doctorremulac3, Feb 02 2018

       I wonder if you start with a small stack like the fire tornado in [link], the tornado will then extend the height ?   

bigsleep, Feb 03 2018

       That link is great. That was certainly what I had in mind for the campfire version.   

       Ok I did a quick felt marker sketch. My wife and I sold our house and we're kinda currently living in a camper for the winter until we find our next place, so I'll have to sweet talk her into scanning it at work come Monday.   

       ps. it's not the greatest sketch.   

       This sounds very much like a crossover between a plug nozzle rocket motor and a vortex cannon, both of which are Baked and WKTE.
8th of 7, Feb 03 2018

       Maybe, but I don't think so. Nothing leaves any sort of launcher, the vortex just sort of sits there twisting and swirling back on itself over and over turning a fan until all of the heat of the fire or the compost heap dissipates.   

       Heat is heat after all. Fire is just the most easy to visualise airflow.   

       [2 fries] What device are you posting this on?
wjt, Feb 03 2018

       My wifes' laptop.   

       Obviously then , not fitted with a webcam nor do you possess a camera or cellphone in this period of pixel transportation.   

       Oh, As an absolute last resort there's Paint.
wjt, Feb 05 2018

       I now have an image of [2 fries] sitting around a campfire, slightly misty-eyed, with a can of Kokanee in his hand singing Oh Coanda.
AusCan531, Feb 05 2018

       Funny, we are waiting for an offer on a campground/rv park to be accepted so your vision might be clearer than you think... except about the Kokanee bit. Watered down piss-water that, but in a pinch, and if they're cold enough I can be tempted.   

       Yeah I guess worse comes to worse I could always snap a phone pic and upload that next time. Scanned the sketches and I just need to put them in photobucket. Give me a second or eight.   

       Ok, a little bit later... photobucket doesn't like that I've used their free image hosting for years without paying anything and I just get bounced from there now, so... Imgur it is for now.   

       [couple of links]
The pencil sketch is too light and the marker sketch shows no detail but between the two it should make sense.

       ...also with the color sketch the flaming streamers would twist around the outer diameter of the... I don't know the word... fire-backwash I guess, and not be entirely vertical but more of an undulating sheet sort of like a roiling plasma with little fire tornados spinning off at random, but I couldn't draw what I see in my head.   

       My gut feeling is that the Coanda loopback stream will be be unstable a) because the system is open to environmental conditions (look at the structure in the video to just do the tornado) and b) the flow has to deal with being a fraction flowing back down, spread out over a sphere around the upmoving tornado.   

       Maybe an initial push or fanning can set up the right conditions to get that second level that will loop the tornado all the way around. Experimenting with a tornado flame, with your structures, next to a constant downdraft may indicate plausibility.
wjt, Feb 05 2018

       Yeah, all I've got to do is play with heights and diameters and curves of the geometry. I'll show you... just give me a bit of time.   

       <side note> I learned two new things today. Almost had a melt-down. The stimulus has been overwhelming.
I'm gonna go lie down for a bit.


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