Wall flux – coupled heat transfer

[sjohn]

 

I’m modeling combustion inside a fluid domain with solid walls. The thermal boundary condition at the solid walls is mixed, i.e.  convection and radiation. 

 

This is a coupled heat transfer problem. The fluid surface and the shadow surface next to the solid wall have been assigned internal emissivity of 1 and that of the solid, respectively.

 

I’m using the P1 radiation model. The number of bands equal to zero in the non-grey model box the solar load model is off.

 

I created contour plots of temperature, radiation heat flux, and total heat flux for all three surfaces. 

 

These are the results seen in the contour plots:

• External wall: temperature ranges from 33° to 1121° C, seems to be as expected. The total surface heat flux ranges from 57,000 to -187,000 W/m2. The radiation heat flux is zero, which is surprising.

 

• Shadow surfaces: temperature ranges from 33° C to 1129 C, as expected. The total surface heat flux ranges from 955,642 to -463,962 W/m2. The radiation flux is zero, which is surprising.

 

• Fluid surfaces: temperature ranges from 30 C to 1129° C, as expected. The total surface heat flux ranges from 463,962 to -955,640 W/m2. Radiation heat flux ranges from 101,909 to -120,938 W/m2.

 

Can someone explain why the radiation flux at the shadow surface and the external wall are zero? The emissivity of the wall was assigned a number between 0 and 1.