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.

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 José Carlos PD: If you give me more details of the simulation, I can help you anymore... PPD: Search information of radiation models in Fluentusers.com

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.