Understanding Radiation
 

Hi All! I am working on a CFD simulation with radiation implementation. The model I used mostly is the DO model with high angular discretization (say, 25 titah and 25 phi) and fine pixels too (say, 9 x 9). (3D problem with semi-transparent walls)

It took awhile to figure out how to properly set up a radiation problem but I believe I have understood and mastered that :cool:.

Now, my question is to do with the results. In the simulation result, one of the result I have access to is: Incident Radiation with units (W/m2).

http://www.sharcnet.ca/Software/Flue...ug/node984.htm
(31.4-21)

My question is:
Why are the units for Incident Radiation (W/m2) when the equation in the link is clearly just W.

Can I hand calculate the Incident Radiation so I can compare theorectical background with Fluent results? (I have made quite a few tries but none successful :()

Thx for reading.

Although your query is specific to Fluent (and better be posted in the Fluent forum), the Eq. (31.4-21) you cite is the explanation: The intensity I integrated over the whole solid angle w results in W/m^2 as the units of the incident radiation, G.

Thanks for your reply. I will try to move this discussion over to the appropriate forum as soon as I figure that out. Thanks. Back to the query.

I am unsure of what Fluent considers intensity, I as. From my understanding of intensity; it is defined as power per steradian (solid angle) and doesn't change with distance from source/antenna. Therefore, it should have units of (W/sr) and after integrating with a range of solid angles, should result in simply (W).

I am aware however, there is fragmentation in definitions of intensity in the world of "optics" so I looked up Wikipedia to gain a better understanding.

http://en.wikipedia.org/wiki/Radiation_intensity
http://en.wikipedia.org/wiki/Power_density
http://en.wikipedia.org/wiki/Solid_angle

According to Wikipedia, radiation intensity is the power density per solid angle. This confuses me even more because if so, the units will be (W/m^3) * (m^2) = (W/m??)

I know I am not an expert in this topic so please be patient with me :( Thanks for any help and feedback.

The intensity, I, is defined (see e.g., Modest or Siegel and Howell or Sparrow books) as the power per area normal to rays per steradian, and its units are therefore W / (m^2 * sr).