Week 6.1 - Setting up a model (Electronic enclosure)

Aim: To perform the flow and thermal simulation on a power board assembly.

Objective:

• The first step is to simplify and convert the given CAD geometry from Space-Claim to ICEPK objects. After converting, we properly mesh the board in ICEPK.
• In which the above two steps have already been done in the 3rd and 4th challenges.
• Then we have to set up and post-process these results

GIVEN GEOMETRY

The image attached below shows the given CAD geometry of an electronic enclosure. A total of 11 assemblies are created for the model The enclosure is divided into separate assembly for the model depending on the meshing technique and the slack is set to zero since the enclosure are attached the slack causes an overlap of assembling.

Procedure: - 
The given CAD model of an electronic enclosure assembly is imported into SpaceClaim where the following steps are carried out:

• The bodies which have no effect on the focus bodies are removed from the geometry.
• Using Icepack commands, the CAD shapes in the geometry are converted into Icepack primitive shapes.

Types of bodies:

The thermal analysis of the electronic component is a crucial part of the design. The CAD model does not describe the function of each component in the system. Thus, the components in the system are assigned the function of heat generation for the processor in the PCB (Printed circuit board). The components in the CAD model of the electronic component are initially classified according to their thermal effect on the system. The components are classified as focus bodies, necessary bodies, peripheral bodies, and dispensable bodies. The components are converted by Icepack objects such that they are detected in the Icepack thermal management software. The objects that are not detected as the Icepack objects are simplified such that the software detects them as the electronics component.

1. Focus bodies - The bodies which will emit some heat or obstruct the flow of the system.
2. Necessary bodies - The bodies which will have some effects on the focus bodies.
3. Peripheral bodies - These bodies may or may not affect the focus bodies.
4. Dispensable bodies - The small bodies on the assembly which has no effect on the physics of the system, these bodies are completely neglected.

Classification of the electronics components:
1. Focus bodies: These are of greatest interest. Processor, PCB, Fins

2. Necessary bodies: Affect focus bodies. Resistor and capacitors

2. Peripheral bodies: Influence on focus bodies is uncertain.
   Power ports
   1. Dispensable bodies: No effect on focus bodies.
   Bolts, nuts

Delete Curvature - The curvature is used to increase the strength of the body which has no effect on flow or thermal analysis & these surfaces create complexity during the mesh which affects the final solution. Select the fillet & click on selection on the left column which finds all the similar fillet edges & these are deleted using the delete option.
To Delete the rounds/chamfers and Fills the Hole

The geometry required for performing thermal analysis using Icepak can often be directly prepared in Icepak. However, in some cases, the designer may choose some other CAD software to prepare the geometry. In such cases, the CAD geometry must first be converted into primitive Icepak shapes using the commands available in SpaceClaim.

The following steps are used to simplify the CAD geometry (shown above) into Icepak Objects:
This part is divided into multiple parts by using the Split Body command with the top and bottom planes of the PCB. This separates most of the components from each other. Identify Objects command is used to identify and convert CAD geometries of the bodies into Icepak Objects. The image attached below shows the different parts identified for conversion to Icepak Objects. (The parts are highlighted in red)

1. Level 0 - Bounding box
   
2. CAD Before and After Simplication

In this type of simplification, the object is converted to a cuboidal block irrespective of its shape. In the present study, the Processor and PCB board are given the Level 0 simplification

2. Level 1 - Non-polygon shapes
   In this simplification, the component is converted into a collection of blocks. In this analysis Fin, all the ports are converted to level 1 simplification.

2. Level 2 - Polygonal
   The geometry takes the polygonal shape.

2. Level 3 - CAD block
   The simplification takes place according to the shape of the component.

Mesh Generation

Assemble 1

• Max element size X - 0.4mm.
• Max element size Y - 3.5mm.
• Max element size Z - 2.5mm.
• Min Gap X - 0.08 mm.
• Min Gap Y - 1 mm.
• Min Gap Z - 0.5 mm.

Assemble 2

• Max element size X - 0.4mm.
• Max element size Y - 8.5mm.
• Max element size Z - 2.5mm.
• Min Gap X - 0.08 mm.
• Min Gap Y - 4 mm.
• Min Gap Z - 0.5 mm.

Assemble 3

• Max element size X - 6mm.
• Max element size Y - 8.5mm.
• Max element size Z - 0.4mm.
• Min Gap X - 3 mm.
• Min Gap Y - 4 mm.
• Min Gap Z - 0.08 mm.

Assemble 4

• Max element size X - 3.5 mm.
• Max element size Y - 0.4 mm.
• Max element size Z - 2.5 mm.
• Min Gap X - 1 mm.
• Min Gap Y - 0.08 mm.
• Min Gap Z - 0.5 mm.

Assemble 5

• Max element size X - 6mm.
• Max element size Y - 8.5 mm.
• Max element size Z - 0.4 mm.
• Min Gap X - 3 mm.
• Min Gap Y - 4 mm.
• Min Gap Z - 0.08 mm.

Assemble 6

• Max element size X - 3.5mm.
• Max element size Y - 0.4 mm.
• Max element size Z - 2.5 mm.
• Min Gap X - 1 mm.
• Min Gap Y - 0.08 mm.
• Min Gap Z - 0.5 mm.

Assemble 7

• Max element size X - 4 mm.
• Max element size Y - 10 mm.
• Max element size Z - 3 mm
• Min Gap X - 1 mm.
• Min Gap Y - 5 mm.
• Min Gap Z - 0.5 mm.

Assemble 8 Slack setting

• Min X - 1 mm. Max X - 1 mm.
• Min Y - 1 mm. Max Y - 1 mm.
• Min Z - 0. Max Z - 1 mm.

1. ii) Mesh type

• Max element size X - 1 mm.
• Max element size Y - 1 mm.
• Max element size Z - 5 mm.
• Min Gap X - 0.05 mm.
• Min Gap Y - 0.05 mm.
• Min Gap Z - 1 mm.

Assemble 9 Slack setting

• Min X - 1 mm. Max X - 1 mm.
• Min Y - 1 mm. Max Y - 1 mm.
• Min Z - 0. Max Z - 1 mm.

1. ii) Mesh type

• Max element size X - 1 mm.
• Max element size Y - 1 mm.
• Max element size Z - 5 mm.
• Min Gap X - 0.05 mm.
• Min Gap Y - 0.05 mm.
• Min Gap Z - 1 mm.

Assemble 10

• Max element size X - 4.5 mm.
• Max element size Z - 2 mm.
• Min Gap X - 0.5 mm.
• Min Gap Y - 1.25 mm.
• Min Gap Z - 0.08 mm.

After the interfering geometries are moved apart from each other manually in Icepak, the Macros Automatic Case Check Tool is applied. The image attached below shows the output of the Macros.

Mesh Quality:

• Face alignment: For current mesh setting the face alignment is 0.137651 which is preferrable value.
• Volume: Minimum value is 2.89*10^-13 which is greater than preferable 10^-14.
• Skewness: minimum skewness is 0.00017 and around 150 elements have less than 0.2 skewness.

Solver

 The three-dimensional steady-state Navier stokes equations for the model are solved within the computational domain.

General Setup

• Variables solved - flow and temperature.
• Radiation - Off.
• Flow regime - Turbulent - The zero equations are solved for the turbulent model.
• Natural convection is not considered for this model & also gravity vectors are not considered.
• The default value of the parameters is set to default.
• Transient Setup Time variation - Steady

Solution Initialization

• X velocity - 0.
• Y velocity - 0 5 m/s
• Z velocity -0.
• Temperature - ambient.

Basic settings

• No of iterations - 100.
• Convergence criteria Flow - 0.001.
• Energy - 1e-7.
• Joule heating - 1e-7.

Parallel Settings

• Configuration - parallel.
• Parallel options - 2 processors.

Advance Solver Setup

Results and Discussion

Residual plot:
The residuals for the following equations are plotted against the number of iterations:

• Continuity equation
• X-Momentum equation
• Y-Momentum equation
• Z-Momentum equation
• Energy

The image attached below shows the residuals plotted against the number of iterations.

Monitor Points

Temperature Contours

Conclusion

In this project, the given model of the Electronic enclosure was meshed using ANSYS Icepak using the non-conformal meshing, per-object meshing parameters, and multi-level meshing. The three-dimensional steady-state governing equations for the model were solved for flow and temperature within the computational domain in the Icepak. 

• The maximum temperature within the computational domain is 27.6 deg.C.
• The maximum air velocity within the computational domain is 4.75 m/s.