SimScale CAE Forum

Maximum number of iterations reached: for CHT


#1

Hi, I want to conduct a CHT simulation with a model of a simple heat exchanger, there is hot water entering in the inlet that heats up the internal chamber (which is separated by a stainless steel sheet).

My mesh has no errors, and the simulation can run, but after about 80-90 mins it gives the error “Maximum number of iterations reached”

My solution doesn’t seem to be converging either. What can I do to fix this?

Link:
https://www.simscale.com/projects/abhalekar/heat_jacket_t/


#2

Actually, those residuals do not seem to be converging to me:

If you also monitor one of your results parameters, you will see that seems to start diverging as early as 30 iterations:

You could try to increase the ‘Maximum Run Time’ in ‘Simulation Control’ but I believe that would just waste core hours as those residuals look pretty stuck to me…

What you might try is set ‘Simulation Control’>‘End time’ and ‘Write interval’ to 50 and make other adjustments, perhaps in ‘Numerics’, to fix the divergence. After it has no signs of diverging at 50, then you can try running it to full convergence and stable result values. I have found that this approach saves both real time and core hours.

I have little experience in CHT, so someone else might give you a better guide to CHT convergence…

EDIT: Actually, I see that the error message given by SimScale seems a little misleading as the simulation ended at 151 iterations, which is less than the 1000 you asked it to go to. Also your real time limit was not reached either.

If you look in your solver log, you can see the real OpenFoam reason that the simulation ended:

I am unfamiliar with this error but my suggestions are still valid and should still help you out…


#4

I tried lowering the simulation end time and changing the numerical values, but the solution arent converging still. Is there anything you can recommend in terms of what my numerics should be adjusted to?


#5

I do not, perhaps someone with more CHT experience can jump in here please…


#6

Hey,

Are you still working on this project?
I’m not an SimScale expert but I think you should change the setting in Material Water “equation of state” from “perfect gas” to “rho constant equation” maybe that would help.


#7

Yes I am! My CHT simulations haven’t been working out still, but I’ll try doing this, perhaps it will help