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Hex-dominant parametric (Multi Region for CHT): Electronics cooling

Overview:

In this tutorial, the meshing process for a geometry used for cooling electronic device using the conjugate heat transfer (CHT) technique is carried out using the “Hex-dominant parametric” approach. The “Hex-dominant parametric (only CFD)” is the semi-automatic meshing option that uses hexahedral cells and allows full flexibility in meshing parameters with all type of refinements options. The objective is to get a good quality mesh that resolves the geometry and domain well.

This tutorial will highlight some essential points of the meshing process that would help in getting better simulation results.

Link to tutorial project containing the geometry:

Import tutorial project into workbench

Getting started

  • To start this tutorial, you have to import the tutorial project “Tutorial_lectronics cooling using CHT” into your ‘Dashboard’ via the link above.
  • Once imported, the ‘Work bench’ is open and you will be in the ‘Mesh creator’ tab.
  • Click on the CAD model “Heat sink - Electronic cooling” to load the CAD model in the viewer.
CHT1_Mesh0

Geometry requirement

Important

Please note that, the CAD should contain non-overlapping solid and fluid parts. Further, the boundary (interface) must be overlapping faces of the same area. The user should ensure the CAD meets these requirements.

In this case of electronic cooling sink the uploaded geometry has three solids, two representing the FB-4 chips and one for heat sink, and one fluid region which represents the air domain.

Mesh Generation

  • To create a new mesh from this CAD model, click the New Mesh button while selecting the geometry.
CHT1_Mesh1
  • Automatically, a new mesh called “Heat sink - Electronic cooling mesh” is created and a default mesh operation called “Operation 1”.
  • To specify how exactly the mesh shall be generated, click on the operation itself (currently called Operation 1, you may rename it to ‘HexaMesh’) and select the meshing type as: ‘Hex-dominant parametric (only CFD)’, set the meshing parameters like Bounding Box Discretization and Number of computing cores. Now scroll down to set the parameter “Min cell volume” and click save.

Important

Make sure the ‘Create multiregion mesh’ option is set to “true”. This will mesh the parts separately, and create individual regions with interfaces.

CHT1_Mesh2
CHT1_Mesh3
  • After saving, a sub-tree will be generated with “Geometry Primitives” and “Mesh Refinements” as shown below. This will be used to define the meshing parameters and refinements.
MeshTree

1) Geometry Primitives and Main Settings

Here we will specify the settings and primitives for the ‘Base Mesh’ and other refinements that will be applied later.

  • We start with “BaseMeshBox”, under Geometry Primitives. Here we specify the extents of the box for the Base Mesh. It is suggested to maintain the automatic bounding box generated when a geometry is imported, since this is an important factor to split the different faces. Hence the following “BaseMeshBox” and “Material Point” settings can be left default for any other simulations you want to perform using conjugate heat transfer problem.

Important

For a good quality mesh, it is recommended to have near cube cells for the base mesh. Refer Hex-dominant parametric documentation for details.

Important

For an intended fine mesh ( around or more than 5 million cells ), please select 16 or 32 compute core machine to meet the memory requirements.

2) Mesh Refinements

This operation provides option to refine the mesh in critical regions.

i) Refine fluid region

  • Click on ‘Mesh Refinements’ and then click ‘Add mesh refinement’ button as shown.
CHT1_Mesh4
  • Rename it to ‘Fluid’ and select a Type ‘Surface refinement’ to specify the parameters as shown in figure below. The fluid domain has to be selected under entities.
CHT1_Mesh5

ii) Refine solid regions

  • To generate the solid regions click on ‘Mesh Refinements’ and then click ‘Add mesh refinement’ button.
  • Rename it to ‘Solid’ and select a Type ‘Surface refinement’ to specify the parameters as shown in figure below. The remaining 3 solids have to be selected as entities.
CHT1_Mesh6
  • That is all !
  • Now click on “Operation_1” (under Mesh Operations) in the tree and start the meshing operation by clicking ‘Start’ button in the center panel at the top.
CHT1_Mesh7

Important

All operations are computed on the remote cloud (not on your computer). Once an operation is started you can simply move on to another project/operation or start multiple other operations or even logout.

  • After some minutes of computing, there will appear a ‘Meshing Log’ tree item below our mesh operation.
  • Once the mesh operation is finished, the mesh can now be viewed in the viewer.
CHT1_Mesh8

Important

Once the meshing finishes, inspect the mesh log to see if the interfaces are made correctly. In case the log shows no or fewer interfaces, make sure the CAD has overlapping faces at interfaces. Also visually inspect the geometry for solid and fluid regions. There must be as many individual meshed regions as number of parts in the CAD.

CHT1_Mesh12
  • The figures below show highlights of the generated mesh for illustration.

The mesh of FB-4 chips are shown in this image.

CHT1_Mesh9

The heat sink mesh is shown as follows.

CHT1_Mesh10

The following image shows all the 4 parts, which are meshed into 4 regions.

CHT1_Mesh11