[Howdoo]

Hi, I am performing a simple analysis in ANSYS NLT (non-CFD) prior to setting up a more complex scenario. The model is a surface-to-surface radiation problem; an infinitely large plate, set to a temperature, radiating to a cylinder separated by an air medium at 60% humidity. The cylinder is 5m in diameter and offset 8m from the plate. For the following question please assume the model is set up correctly i.e. correct surface emissivity's, radiation set as surface-to-surface in an Open enclosure.

In short, the temperature results I am getting on the cylinder appear to be particularly high for my expectations. What I would like to know is, as this version of ANSYS is incapable of calculating transmission losses through a gas i.e. absorption/scattering and the results are based on a view factor method only; would the difference be that much different in a CFD package to warrant further investigation?

Please note that I am only concerned with air as the transmitting medium. From research I know absorption is not that much of a factor in air. I am however not to sure on the importance of scattering over a distance of 8m, nor if the relative humidity would have a large impact.

Any help would be much appreciated.

[Rami]

Hi Howdoo,

You may get a reasonable solution by the surface-to-surface solver if the volume between the surfaces is vacuum or a transparent medium (e.g., dry air). However, when the medium is semitransparent (as in your case) the radiation is absorbed and scattered. For example the car headlights intensity reaching a certain distant object on a foggy day is far lower than on a clear day. This is due to the above, mainly scattering in this case.

Therefore, to get a closer agreement, you'll need to have a solver that allows for radiative transfer through semitransparent media.