Smoke stack design
Smoke stack design
(OP)
Just thinking about a subject that I've been wondering about for some time. At times when I'm driving past a refinery or a heating plant, I've noticed that some of the smoke stacks have a helical fluting or strakes along the exterior of the stack, usually near the top. Does anyone know the purpose of this? I have read a paper that suggests that this is for modifying the airflow around the stack to control the dynamic forces of the wind, but that doesn't explain why one stack has the helical strakes and one right next to it may not, as shown in the following photo:
http://www.ucar.edu/communications/quarterly/summer98/smoke.stack.gif
I was thinking that there might be a thermodynamic reason for this.
It's nothing that I'm working on, but it is something that I think about and say "hmm, I should know that..."
Thanks,
Poor Rod
http://www.ucar.edu/communications/quarterly/summer98/smoke.stack.gif
I was thinking that there might be a thermodynamic reason for this.
It's nothing that I'm working on, but it is something that I think about and say "hmm, I should know that..."
Thanks,
Poor Rod





RE: Smoke stack design
saxon
RE: Smoke stack design
These strips can be used to give the exhausting medium extra bouyancy or lift by channeling the wind (picture what happens when the passing wind is directed up these strips!). Hot gases generally rise without any problem, but other types may tend to linger around the stack, or worse, may drop to ground level and deposit any nasties they contain.
Hence some have them, some don't! You'll see them mainly in built up areas and on stacks that aren't very high.
Cheers
GT
RE: Smoke stack design
The strakes are fitted to shed turbulence caused by other obstructions but they are only required on free standing stacks.
The jury is out on how effective they are.
RE: Smoke stack design
RE: Smoke stack design
It looks like the first chimney is seamless pipe while the other one is a spiral weld.
209larry
RE: Smoke stack design
That photo was just one that I found on the internet. The chimneys that originally sparked my interest are along a route I bike ride along every weekend. If I remember to take a digital camera one day, I'll try to take a photo and post it though now I understand the purpose of the strakes.
Rod
RE: Smoke stack design
RE: Smoke stack design
* The stack installation is devided by 4:
1. Self supported
2. Guy wire
3. Derrick structure
4. Combination guy wire and derrick structure.
Usually the self supported stack (with variety in diameter) install with wind braker, but not with another.
RE: Smoke stack design
You can also consult API 573 (Inspection of fired boilers and heaters).
RE: Smoke stack design
Experts in stack construction recommend that self-supporting steel stacks be made less sensitive to wind-induced vibration, by reducing the diameter towards the top in at least two steps. In this way the stack becomes more elastic and the excitations have different frequencies.