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Mr. Lee M-S November 30, 2001 21:05

How to solve this problem about radiation?
Hi! everyone.

I'm studying about temperature & velocity in the cylidrical heater(ID:0.1m, Length:0.7m).

Inlet Velocity:0.5m/s Heater Temp : 1000K

But radiation condition makes me craze.. Heater tempeature is about 1000K, so radiation effect can't be neglect. So I have to choose the radiation model. But I don't have any idea how to choose that. From the guide, optical thickness can be good guide line to choose that. I know optical thickness is aL, but I don't know how to calculate a, absorption coefficient. I tested a lot of case varying absorption coefficient now . so I know absorption coefficient effect temperature result significantly.

And why static temperature and total temperature is different in my result. what is problem?

Please make me free from this dilema.

Josť Carlos December 20, 2001 06:33

Re: How to solve this problem about radiation?
Hi Mr Lee Absortion coeficient is a property of the fluid. For example, for the air , absortion coeficient is pracically 0, then optical thickness is near to zero and Rosseland or P1 models are not valid, you must use DTRM or DO model. I prefer DO model, you can use 2 for theta and phi coeficients or 4 for both coeficients. If the fluid is water (incompresible fluid) the properties change,... Seek absortion coeficient for your simulation... Remember, P1 and Rosseland is for optical thickness near to 1 and 3, and for others cases DTRM (with 4 or 8 rays) and DO (with 2 or 4 theta and phi). I hope that you have understood me... Excuse my English language, please... Regards Josť Carlos PD: If you give me more details of the simulation, I can help you anymore... PPD: Search information of radiation models in

Erwin December 20, 2001 13:02

Re: How to solve this problem about radiation?
Using the Weighted Sum of Gray Gases (domain based) is a good way to have Fluent calculate the absorption coefficient, since its value depends on local H2O and CO2 concentration, and local temperature. The WSGG method includes those effects.

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