Hi,

I’m working on a model in which the first step is to validate the heat radiated by black body at 5800K.
I’m not obtaining reasonable values which should be around 64 MW/m2
Looking in detail into the Ccx Manual v.2.19 I can read:

q = emissivity * (θ^4 − θ0^4) (formula 614)

This formula is missing the Stefan–Boltzmann constant ¿isn’t it?.

Thanks

Yea, that doesn’t look right unless you consider flux q to be in some more natural units. But I think CCX still works correctly for an infinite sink (constant θ_0). You have to specify the Stephan Boltzmann constant with the *PHYSICAL CONSTANTS card.

Hello,

I have an analysis that is not responding properly.

There are two concentric spheres where the internal surfaces facing one each other share a *RADIATION condition + CAVITY.

The whole system has an initial temperature as BC of Ti=2000K.

The system is leaking energy constantly somewhere like if some of the emitted radiations were not absorbed. I know it because the temperature is decreasing in both spheres simultaneously.

Could someone confirm that please or if I had made something wrong. The system is constantly cooling, and it should not.

To identify where the leakage is produced (where the view factors could be failing) , I have set up a user element orientation with U in radial direction and the material property as Orthotropic with high thermal conductivity in the U radial direction and very low in the tangential directions V,W. This way the incident heat flux is not redistributed by conduction camouflaging the problem.

*CONDUCTIVITY, TYPE=ORTHO

**Following line for TYPE=ORTHO:

**• κ11.

**• κ22.

**• κ33.

**• Temperature.

10000,0,0,0

10000,0,0,5000

The pictures show the temperature and heat magnitude of where the view factors could be failing. Seems like radiation is not homogeneous and areas close to the main axis are cooling faster and reach higher transfer rates.

Thanks

After refining x2,

All the flux looks perfectly radial but clearly drops on areas where surface normal are close to 45º .
I think that could be some issue with the Euler Angles representation.

Hi,

did you check that the viewfactors add up to 1? You can force that by specifying a negative environment temperature on the Kelvin scale (cf. Documentation on *RADITATE). Due to numerical roundoff viewfactors are not exact.

If this does not solve the problem you may send the complete input deck to me.

Best Greetings,

Guido

Thank for your kind response Mr.Dhondt and congratulations to the full equip for the new ccx 2.20.
I sent you an E-Mail but maybe was not the right channel ¿? . Just wanted to confirm. Files were way too large. I hope it is ok with you.

Regards
Disla