Unsteady problem with volumetric heat source

Jonathan94 · July 13, 2018, 03:09

Hi !
I want to conduct the simulation about cooling server by using PCM (Phase Change Material).
For this, I put the server at the center(Center have volumetric heat source option with 50W/m^3), and surround it with walls and PCM.
And air atmosphere is surrounding this structure.

For Continua model,
Air: implicit unsteady/segregated flow/segregated fluid enthalpy/ideal gas/turbulent/k-epsilon/....
Wall,Server: implicit unsteady/segregated solid energy/constant density/...
PCM: implicit unsteady/eulerian multiphase/ volume of fluid/segregated multiphase temperature/multiphase interaction/melting-solidification/constant density/....

Actually when I run this project with implicit unsteady solver, it shows like below image. There is color bar for temperature but, there shows no temperature difference.

So here is my question....
1. Actually when I solve this problem with steady option, it shows understandable solution (Hot at the center, cooler as it goes outside).

How can I get understandable solution with unsteady option?
I mean that I want to get temperature profile like steady solution that shows center is hot and the vicinity is cooler than it.
2. I also tried with simple geometry with just two attached block giving volumetric heat source to one block. When I run this problem with unsteady option, there shows no temperature difference even there is volumetric heat source. (Both blocks' initial temperature option is 300K. )
Is there any special condition that I should check before using volumetric heat source??

ping · July 21, 2018, 03:26

it should just work so you need to debug it by simplifying progressively eg run just the air in unsteady mode with a heated wall at the pcm interface likewise for the other regions alone
could be time step related too
ensure you have some reports of point probe temperatures
set solid energy urf to .99999 to speed convergence in solids
probably dont need ideal gas either - more stable etc with Boussinesq but remember to set the thermal expansion coef of air to a reasonable value

July 13, 2018, 03:09	Unsteady problem with volumetric heat source	#1
Jonathan94 New Member Yonadan Choi Join Date: Jul 2018 Posts: 1 Rep Power: 0	Hi ! I want to conduct the simulation about cooling server by using PCM (Phase Change Material). For this, I put the server at the center(Center have volumetric heat source option with 50W/m^3), and surround it with walls and PCM. And air atmosphere is surrounding this structure. For Continua model, Air: implicit unsteady/segregated flow/segregated fluid enthalpy/ideal gas/turbulent/k-epsilon/.... Wall,Server: implicit unsteady/segregated solid energy/constant density/... PCM: implicit unsteady/eulerian multiphase/ volume of fluid/segregated multiphase temperature/multiphase interaction/melting-solidification/constant density/.... Actually when I run this project with implicit unsteady solver, it shows like below image. There is color bar for temperature but, there shows no temperature difference. So here is my question.... 1. Actually when I solve this problem with steady option, it shows understandable solution (Hot at the center, cooler as it goes outside). How can I get understandable solution with unsteady option? I mean that I want to get temperature profile like steady solution that shows center is hot and the vicinity is cooler than it. 2. I also tried with simple geometry with just two attached block giving volumetric heat source to one block. When I run this problem with unsteady option, there shows no temperature difference even there is volumetric heat source. (Both blocks' initial temperature option is 300K. ) Is there any special condition that I should check before using volumetric heat source??

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July 21, 2018, 03:26		#2
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	it should just work so you need to debug it by simplifying progressively eg run just the air in unsteady mode with a heated wall at the pcm interface likewise for the other regions alone could be time step related too ensure you have some reports of point probe temperatures set solid energy urf to .99999 to speed convergence in solids probably dont need ideal gas either - more stable etc with Boussinesq but remember to set the thermal expansion coef of air to a reasonable value