Hello everybody, I am trying to solve a heat transfer problem(conjugate heat transfer )by the fluent, which is a heat transfer enhancement in a rectangular channel with baffles. I left the computer solving the problem for about 24 hours and it performed about 4774 iterations. I need to know whether I have reached to the convergence and the results are reliable or not. The residuals for the equations reached to the values as they appear in the captured photos of the screen and the value of the net mass transfer rate is 4.0530945e-06 and the net heat transfer rate is
-0.0058049306Watt. Also, I used monitors for variables such as a mass-weighted average at the outlet temperature, Area -weighted average for lower plate surface heat transfer coefficient and the Area -weighted average of all heat fluxes from all entities, but I am confused about the monitor for the surface heat transfer coefficient as the curve fluctuated up and down as shown in the figure. Is this enough for convergence knowing that the under relaxation factors(URFs) are the default values?
Some detailed information about my model:
The problem is a rectangular channel with a 1 m length and there is heating by constant heat flux from the above and lower plates in the channel and there are solid baffles in a staggered arrangement on the lower and upper plates. I used SIMPLE discretisation scheme with second-order upwind and used the default under relaxation factors. The turbulence model is k-epsilon(RNG) equations with enhanced wall treatment and the air properties are constant.
Thanks in advance.
Hello,
From the attached figures, it seems to me that your solution does not converge yet as the residuals in the continuity is still higher than 1e-3, which is the default error is fluent in case you did not change it. Also, I recommend to refine your mesh as the errors do not decrease steadily. This could help. Best,
Dear Dr.@ Ramy H Mohammed
Thank you very much for your kind response. The mesh consists of about 4.4 million elements, I think this huge number of elements causes a massive load on my computer capabilities. Do you think that there is another mesh technique which is better in quality and can count lower than the aforementioned number of elements? Also, you have mentioned that the residual in the continuity equation is high, I relied on my judging that the net mass transfer rate is of the sixth order of magnitude e-6 and I checked whether the net mass transfer rate is lower than 1%of the smallest mass transfer rate at any boundary, Do you think that is not a proof for a convergence in the continuity equation?
Best regards.
The point is the balance between the heat transferred from and to the fins has to be achieved. Number of elements is just one factor to do this. I recommend to change one of the boundary conditions. If it works, so your problem is in the mesh. Relaxation factor could solve this problem. But this will not help much in parametric study.
Ramy H Mohammed
Do you mean the value of the boundary condition or the type of the boundary condition?
Thank you very much ,Dr Hayder I. Mohammed
I really need to reduce the number of mesh elements because the computation takes about one day to be accomplished. The computational resources are limited and this is the biggest problem that I face. I think the refinement will enlarge the number of elements (the current number is 4.4 million elements).
@ Ramy H Mohammed
Frankly, this run is the second one after changing the velocity value. I didn't face any problem at the first value of the inlet velocity.
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