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Heat exchanger with PCM.

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Old   May 6, 2017, 17:19
Default Heat exchanger with PCM.
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abdulhamit
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Hi friends.
my english is google translate. sorry
I'm trying to do a pcm analysis. But I have not been able to do it until now. I made some solutions but it was always diverting. I have added some pictures of the results. I used different commands each time. But it did not.
http://imageresim.com/images/58588884045835199054.png
http://imageresim.com/images/79235627896774529537.png
http://imageresim.com/images/20884217028920206034.png

I made a mistake in the analysis above. I corrected my mistake, but still did not solve it. The end result and the video are down. I think The result is false. Please slow down the setting.

http://imageresim.com/images/97555723968852594088.png
https://www.youtube.com/watch?v=X6Sf...ature=youtu.be

I think the problem is timestep. "time-step" needs to be reduced. But this is a big problem for time-related problems. Because the experiment I have done is one hour (3600 seconds). In the ANSYS training file, it is necessary to set "time step" as follows.
http://imageresim.com/images/52029361928234405599.png
Characteristic length= min. element size
According to this formula my time step in my tutorial is 0.001. I think impossible because 3 600 000 time step is 3600 second. And 10 iterations at each time step. 36 000 000 iteration

My problem is at below.
http://imageresim.com/images/21237057014294932401.png
http://imageresim.com/images/14036083610042285437.png
http://imageresim.com/images/93399837100234001895.png
http://imageresim.com/images/16941704906234095570.png

The simulation is laminar, Gravity is downward but flow upward I think it is false. the picture is at 20 second
http://imageresim.com/images/72994045873690356067.png
http://imageresim.com/images/20766371701911633990.png

inlet=0.09337 m/s 60C
outlet=pressure-outlet
pcm wall; h=20 w/m2K temp=25C wallthickness 0.007m and iron
solidwall; h=20 w/m2K temp=25C
I use symetry.
PCM specificition is OK. solution metod= simple, coupled, simplec but Fluent did not solve. I usually use simplec. Standart initilization.

@Tapeworm
I think you should use laminar, you should look https://www.cfd-online.com/Wiki/Turbulence_intensity
What is Reynold number your problem in the inlet?
My guess is that the time step should be very low in PCMs.
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Old   May 8, 2017, 04:19
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Hi,

Thank you for linking this one to my thread!

As I also mentioned in my thread, I will use laminar flow as well.
I also have some troubles with the time steps. I think you should use the adaptive settings as well. The problem is that the simulation is taking way too long... With a time step size (s) of ~0.01 it will take days/weeks to fulfill a simulation. That is only for the discharge process, which takes roughly about 1.5h in real time to complete. The charging process takes about 5-6h real time to complete...
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Old   May 8, 2017, 08:00
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It seems like the mesh of the PCM was a critical point for my problem. I haven't been ablr to run the full simulation yet, but the beginning of the simulation looks much better after increasing the number of cells in the PCM.

I suggest you try do the same, focus on the PCM!

Will get back later on when I got some more information.
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