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strong temperature gradient in Conjugate Heat Transfer CFD

Hello experts,

I'm trying to perform Conjugate Heat Transfer CFD analysis of PCB mounted on a Heat sink which is cooled by forced air. I'm getting an adverse temperature gradient at a particular region in heat sink. I haven't specified any boundary condition to it so its automatically assigned as default wall.

Is this an Ill posed problem? what could be done to prevent this.

Thanks

ecu_cfd.2.Log

ecu_cfd.inp

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HyperMesh CFD

v2022.2

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acupro

The list of boundaries indicates there are 7 geometric faces/surfaces in the Slip set. Does that number make sense? Is it possible one of the surfaces that shows the odd temperature has been inadvertently placed in the Slip BC set? (You can right-click on Slip and select Isolate)

Is it possible that solid has been assigned incorrect material and/or body force?

Jagan

The list of boundaries indicates there are 7 geometric faces/surfaces in the Slip set. Does that number make sense? Is it possible one of the surfaces that shows the odd temperature has been inadvertently placed in the Slip BC set? (You can right-click on Slip and select Isolate)

Is it possible that solid has been assigned incorrect material and/or body force?

Yes those 7 slip walls are the outer region of air domain. I think that would be the reason.

And I have specified thermal conductivities in x y z direction of PCB using Constant Anisotropic. And Could you please confirm if this is appropriate?

Thanks.

Community-Pasted-Attachment-1679713307598.png

acupro

Yes those 7 slip walls are the outer region of air domain. I think that would be the reason.

And I have specified thermal conductivities in x y z direction of PCB using Constant Anisotropic. And Could you please confirm if this is appropriate?

Thanks.

The anisotropic entries you show would be the conductivity in the X, Y, and Z directions.

Are all of those solids assigned the same - materials, boundary conditions, etc? Is the meshing also the same? Just thinking of possible differences.

Jagan

The anisotropic entries you show would be the conductivity in the X, Y, and Z directions.

Are all of those solids assigned the same - materials, boundary conditions, etc? Is the meshing also the same? Just thinking of possible differences.

No, There are 7 different materials in total. Changing slip wall to default no slip wall solved it. Thank you.