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What are those helical things on large chimneys?

They are vents. They let the smoke out whilst keeping rain and squirrels out.

You will all so see them on roofs, to exhaust heat. I've seen some painted with swirls and stuff..real pyschadelic, man.
 
Those are there to add strength to the chimney structure without adding too much weight or raw materials. That's my guess anyway.
 
Originally posted by: Nohr
Christmas lights.
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FTW! 😀

Never seen those before either. The "for strength" suggestion sounds feasible enough, but I've seen taller chimneys w/o those wrapped around them. So...😕

 
Originally posted by: giantpinkbunnyhead
That looks like some sort of tower with somethin wrapped around it... I've never seen that before. Is that common in your area?
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I've seen them a number of times - they're not very common, but they seem to be on large industrial chimneys (usually for incinerators or power plants).

I just happened to come across the picture (linked above) and I relised I didn't know what they were.

My first thought was that it was some kind of rain deflector - but that would be pointless.
 
Originally posted by: Mark R
Originally posted by: giantpinkbunnyhead
That looks like some sort of tower with somethin wrapped around it... I've never seen that before. Is that common in your area?
Click to expand...

I've seen them a number of times - they're not very common, but they seem to be on large industrial chimneys (usually for incinerators or power plants).

I just happened to come across the picture (linked above) and I relised I didn't know what they were.

My first thought was that it was some kind of rain deflector - but that would be pointless.
Click to expand...

I just noticed that you are in the UK. The only photos I found online were from chimneys in the UK.
 
Originally posted by: MichaelD
Originally posted by: Nohr
Christmas lights.
Click to expand...

FTW! 😀

Never seen those before either. The "for strength" suggestion sounds feasible enough, but I've seen taller chimneys w/o those wrapped around them. So...😕
Click to expand...

Look closely at the taller chimney's and you'll see horizontal bands instead. If it's built in place then they wrap the horizontal bands and tighten them. If they are smaller and can be assembled and shipped then they can use other fancier options like the one in your picture. All of this is assuming that it's a thiner metal structure and not a massive reinforced concrete structure.
 
It seems to me that if they were for strength, they would extend to the bottom of the tower. The bottom is supporting the most weight. Also, I think a helical shape like that is inherently flexible, which isn't good for a brick structure. On the other hand, there's the straight thing that goes up the side closest to the camera, if it cross links the two strands of the helix, you can get some strength that way. But I'm basing my opinion on molecular biology, not civil engineering, so I might be way off.

Can anyone find more pictures, particularly closer up?
 
So I looked it up. I was wrong. The helical "strakes" are there to reduce vortex shedding...less turbulance from wind.
 
Originally posted by: Savij
So I looked it up. I was wrong. The helical "strakes" are there to reduce vortex shedding...less turbulance from wind.
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ahhhhh, thanks for looking that up.

Now I'm even more curious. 🙂
 
Originally posted by: Savij
So I looked it up. I was wrong. The helical "strakes" are there to reduce vortex shedding...less turbulance from wind.
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Cool. Learn something new every day.
 
I think in that picture it's a stairway so people can go up and inspect the chimney and take samples of the gas coming out of it. Some chimneys also have pollution control devices inside of them that need maintenance.
 
Originally posted by: Demon-Xanth
I think in that picture it's a stairway so people can go up and inspect the chimney and take samples of the gas coming out of it.
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You volunteering?

P.S. That's a picture of a nuke plant

Oh, and thanks to Savij for looking it up - strakes. Cool word.
 
i had a job where i had to help setup test equipment to sample the exhaust of tall stacks, climbed up a few of them. ~150 ft or so

we would run a hose up the side of the stack and attach a probe, basically a metal tube and tie it up so that it was sticking out into the middle of the top of the stack
 
When air blows past a stack like this, there are vorticies which are shed around it (picture a flag flapping in high wind). If the frequencies of the vorticies match the natural resonate frequency of the stack, then the wind can destroy it.

They usually just build the stack strong enough for the wind load.
 
Originally posted by: 5to1baby1in5
When air blows past a stack like this, there are vorticies which are shed around it (picture a flag flapping in high wind). If the frequencies of the vorticies match the natural resonate frequency of the stack, then the wind can destroy it.

They usually just build the stack strong enough for the wind load.
Click to expand...

Exactly. Many non retractable car antennas have this now. Basically, it changes the airflow for structural reasons (and in the case of a car antenna, to stop it from whistling in the wind 😀)
 
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