Learning Forum

[eugenio benedetti]

I have the model in the picture. These are 3 blocks:
there's a temperature on a face of the rightmost block, label A
there's radiation between the faces B and C
there's radiation between faces D and E
there's an heat flux on the face F
there are contacts on the blocks there are in contact
all is structural steel

this simulation doesn't work. I don't understand why. the simulation doesn't converge, and stop because it reach the maximum limit operation. there's should be an equilibrium temperature for all the other 3 blocks. there's a power out and there's a power in by radiation from the block at fixed temperature.

i tried also to put perfect isolate on all the surface without condition.

the heat flux on face F is very low, 1W, there's no problem due to a too high flux

[Sampat Kumar]

 

Hi eugenio, 
Will you please right-click on the steady state and perform clear generated data? What is the error that you have received? For how many steps has it converged?

regards,
Sampat

 

[eugenio benedetti]

Hi Sampat, thank you so much for your reply
I alway clear my generated data :)
I don't have any error. The simulation reach the iteration limit and do not converge.
Today I tried with a smaller heat flux. In the picture there's 1W on face F, I tried with 0.01W and it works. So maybe it's because the power out is much higher than the power the radiation can give.
I tried also with 0.05W and I had negative temperature in Kelvin.

[Sampat Kumar]

Hi eugenio, 
Sorry for the delayed reply. 
Yes, it might be the reason in your case. I think the power that you want to extract from Face F may not be possible so that’s why your problem converged at lower output heat of 0.01W but not on 1W. If the temperature is negative in kelvin on the wall, it means that it is approaching absolute zero. If you extract heat from the solid wall and the temperature indicates the negative in kelvin, then it might be a possibility that the wall has reached absolute zero and the entropy of the system is zero.

Generally, we refer to kelvin as an absolute zero, which means the vibration of the molecules in the system has stopped. We generally don’t go lower than zero kelvin. In some research cases, they talked about the negative kelvin temperature, but here I don’t think it’s applicable in your case. We keep this discussion simple here and I think your assumption may be correct about the power output is much higher than the power radiation can give. You should probably try to change the temperature value of the wall and heat flow, and then you can verify the behaviour.
My above observation depends upon the data that you have provided. Please let me know what you have observed in this simulation. 

Regards,
Sampat

 

 

[eugenio benedetti]

Hi Sampat
I tried several simulation with different boundary condition. First I used the same model but with higher dimensions to have more radiation.
I also obtained temperature of 10^6 K, depending on the value of the heat flux. With Higher heat flux the simulation gives not coerent results.
I think that a boundary condition of heat flux on a high surface as in my model (high surface relative on the dimensions of the problem) is "too rigid". So this gives numerical problem on the simulation.