Exhaust Plume Radiation Model

[Chem94]

Hi,
I am doing some research for a company and I am looking into a thermal radiation model for exhaust plumes on gas turbines (model to be implemented for off-shore and onshore oil platforms and more of an engineering model rather than CFD e.t.c). I am looking for a calculation method which takes account of variables such as temperature, exhaust flow, wind and nozzle type. Hopefully then yielding plume deflection and thermal radiation. I would be grateful if someone could point me in the right direction for finding research papers on this topic or even point me to some good papers. I am currently attempting to sift through Google scholar, a lot of it seems to be on rocket exhaust plumes and I am unsure of the relevance of that. Thank you.

 

[MikeClay]

If there is no exposed flame, then there is no radiation. That's why enclosed flares are used in congested areas. However, if you are interested in plume temperatures, I would suggest using CFD models. This is especially true if you are looking for small temperature differences for helicopter or crane operations. The standard dispersion models can be used to infer temperatures using surrogate compounds, but these models have some drawbacks:
- Many do not perform cross wind or jetting the flow into the wind.
- Obstacles are not handled easily.

I hope I've been of some help.

--Mike--

 

[Chem94]

Thank you for the information Mike, I am interested in modelling the temperature on the surrounding environment by these plumes. Similar to a thermal radiation model for a flare stack but as you said obviously there is no flame. Correct me if I am wrong as I am sure you have lots more knowledge on the subject; so I am looking at the idea that an exhaust gas is emitted through a nozzle as an exhaust plume and being hot surely it gives out thermal radiation to the surrounding environment which is what we wish to model. Do you know where I can find some information on the standard dispersion model you mentioned and the CFD method, papers e.t.c
Thanks

 

[21121956]

Hello everybody:

As a good source of knowledge, take a look to "Fundamentals of Stack Gas Dispersión", 4th Edition, Milton R. Beychok, Irvine, California, 1994.

El que no puede andar, se sienta.

 

[Chem94]

Awesome, this is exactly the kind of thing I am looking for. Very helpful, I shall look into it.

 

[racookpe1978]

Mike: I'm going to disagree with your assumption that there will be no radiation form an GT exhaust plume if there is no flame.

The exhaust of a one-through GT will be 1200-1400 degrees F, and will be moving at several hundreds of ft/sec. Assume 10-15 feet in diameter for big GT, maybe 4-8 feet for a small one. That 1200 deg F air mass will only cool after it leaves the stack area and begins mixing with the surrounding air.

So your thermal radiation source needs to at least start with a 4-8 foot diameter hot gas cylinder extending vertically 100-150 feet up before it begins mixing with the cooler surrounding air ... then cooling and expanding into a large cone that ends up at only 200-300 degrees after maybe 400 feet. once you get that assumption made, go look at a few flumes with an IR camera, make your first measurements in still air, and start thinking about wind directions.

 

[Compositepro]

Gases do not behave as black body radiators. Each gas has its own IR absorption versus frequency curve. Gases can only emit radiation at frequencies where they absorb. Yellow flames contain glowing soot particles which makes them radiant and far more effective for heating purposes.

 

[davefitz]

I think this problem was covered in the 1960's - 1970's by researchers supported by the US air force- the issue is related to heat-seeking missiles and metods to avoid leaving a significant IR signature. As I recall, injection of MgO magnesium oxide will alter the complex index of refraction sufficiently to confuse the IR sensors.

"Nobody expects the Spanish Inquisition! "

 

[macmet]

CompositePro,

Can you please clarify this statement,

"Gases can only emit radiation at frequencies where they absorb."

I'm having trouble grasping what you meant there.

Cheers

 

[MisterE2]

I wouldn't bother, with perfect blackbody radiation vs convection and conduction, you will never reach dominance over convection or conduction until you end up at around 1000*F by an order of magnitude.

If you do want to bother, first the power law, if you still want to bother, I wouldn't do much research, in excel or matlab just do 1D simulation with emmisivity, absorbitivity, (reflectivity irrelevant obviously) molecular size and a simple for loop or a few hundred...thousand cells, and look at the radiation from the outside, to T(ambient) to 1 ft out to 2 ft out to 3 ft out. While the initial effects of radiation may be a bit chaotic with greybody radiation and resonant frequencies, follow the power law modified a bit for a longer area.

 

[PaulV7427]

Macmet,

If you want to learn more about radiation heat transfer from gases you can also try Fundamentals of Heat and Mass Transfer 6th edition by Icropera, DeWitt, Bergman, and Lavine. Chapter 13 discuses radiation heat transfer and Section 13.4 goes into some detailed equations regarding radiation from gases.

 

[davefitz]

I would suggest as texts "radiative heat transfer" by Mike Modest and also Nasa's "thermal radiation heat transfer" by Siegel and Howell.

"Nobody expects the Spanish Inquisition! "