Week 5.3 - Forced convection Analysis

AIM

The objective of the project is convert CAD shapes into Icepak primitive shapes in Spaceclaim & modify the components in Icepak & define the correct physics.

Procedure

Total number of bodies in the CAD model is calculated. The depending on the functionality of individual bodies or groups of bodies the objects are segregation of the bodies. The properties of the bodies for analysis for the thermal and flow analysis is provided.

Types of bodies

Focus bodies - The bodies which will emit some heat or obstruct the flow of the system.

Necessary bodies - The bodies which will have some effects on the focus bodies.

Peripheral bodeis - These bodies may or may not affect the focus bodies.

Dispensable bodies - The small bodies on the assembly which has no effect on the physics of the system, these bodies are completely neglected.

CAD Geometry

The workbench is used for the geometry simplification and Space claim is used to convert CAD objects into Icepak objetcs and open the dme.stp file.

     

The enclosure, the grille and the fan closure are hide to view the interior objects of the model.

Tools used

Split body - The split body is used to separate a single body into two or delete the uncessary parts from the body. The plane of separation or the face must be chosen for the body separation.

Before split

       

After split

                 

The 

Delete Curvature - The curvature are used to increase the strength of the body which has no effect on flow or thermal analysis & these surface create complexity during the mesh which affect 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.

                     

  

Combine - It is used to make combinations of objects. You can add (or merge) objects together and you can subtract (or split) objects from each other. These actions are also known as Boolean operations.

Before Combine                                                                                                                                                     After Combine                                                                      

                                                       

Fill gaps - It is used to fill in the selected region with the surrounding surface or solid. The Fill tool can also be used to simplify surface edges and cap surfaces to form solids. You can select a combination of faces and edges to replace them with a single new face.

 

 

Fan

Workbench --> fan - This command is used to convert Fan CAD model to Icepak model.

  

Grille

Workbench --> Grille - This command is used to create a grille on the inlet side of the model. The Face of the grille is selected & the grille surface is created for the cooling of the PCB board.

 

           

               

The PCB board has more than 100 components but only the Mosfet, Capacitor, heat sink & processor are used for the simulation so the other small components are deleted.

The components may overlap during the model conversion but these problems must be solved using the split command.

The sketch tool is used to create line & pull command is used to create a surface which acts the plane of separation between the bodies.

                

                 

The final model of the PCB in which the connectors and dispensable bodies are deleted. 

The next step is to convert the CAD model into icepak objects.

Workbench --> Identify objects - This option converts automatically CAD objects into Icepak objects and other objects are converted using Icepak Simplify option.

 

Icepak Simplify - It has four different levels to simplify the model.

Level 0 - In this level the space claim create a bounding box depending on the minimum and maximum coordinate of CAD geometry. The preserve original option is used to preserve the CAD model after the Icepak object conversion.

                                 

Level 1 - In this level, the geometry gets splits into different levels & it create a primitive shapes to fit the CAD geometry. The allow splitting is used to divide the geometry into small parts to capture the model & randomize color is used to differentiate the splitting the model. The cleanup model is used to simplify the model for the simplification.

                                     

Level 2 -  In this level, the polygon are used to capture the CAD model with much more detail to Icepak objects. The Points on arc depicts the division of the line along the curve. 

                                   

Level 3 - The object is directly converted from CAD model to Icepak object. The quality of the icepak object depend on the facet quality we set. Higher value we set higher quality of the Icepak object can be converted.

                                    

Depending on the requirement the level of simplification & the required level of the model are created.

Level 0 Conversion

 

Level 1 Conversion

      

           

 

Level 3 Conversion

       

By this method all the object are converted into the Icepak objects.

Icepak

     

The model is further simplified by removing the fan opening, grille objects and 3D fan is replaced by a 2D fan.

Fan parameters

Fan type - Internal.

Flow direction - Normal --> positive.

Fan flow --> flow type --> Non linear.

From the non linear curve use load option is used to import the fan curve.

The Rpm value of the fan under the swirl is provided as 4000.

The total of 15 assembly are created for the model. 

The enclosure are divided into separate assembly for the model depending on the meshing technique and slack is set to zero since the enclosure are attached the slack causes overlap of assemble.

The 6 assemble are created for the Mosfet model. 

Assemble -1

i) Slack setting 

Min X - 1 mm.

Max X - 0.

Min Y - 1 mm.

Max Y - 1 mm.

Min Z - 1 mm.

Max Z - 1 mm.

ii) Mesh type

Max element size X  - 1.5 mm.

Max element size Y - 3 mm.

Max element size Z - 3 mm.

Min Gap X - 0.1 mm.

Min Gap Y - 0.15 mm.

Min Gap Z - 0.15 mm.

Assemble -2

i) Slack setting 

Min X - 0.

Max X - 1 mm.

Min Y - 1 mm.

Max Y - 1 mm.

Min Z - 0.

Max Z - 1 mm.

ii) Mesh type

Max element size X  - 0.6 mm.

Max element size Y - 0.6 mm.

Max element size Z - 2 mm.

Min Gap X - 0.06 mm.

Min Gap Y - 0.06 mm.

Min Gap Z - 0.2 mm.

Fan Assemble

i) Slack setting 

Min X - 1 mm.

Max X - 1 mm.

Min Y - 1 mm.

Max Y -  0.

Min Z - 1 mm.

Max Z - 1 mm.

ii) Mesh type

Max element size X  - 1 mm.

Max element size Y - 1 mm.

Max element size Z - 1 mm.

Min Gap X - 0.1 mm.

Min Gap Y - 0.1 mm.

Min Gap Z - 0.1 mm.

Assemble - 4

i) 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.

ii) Mesh type

Max element size X  - 3 mm.

Max element size Y - 3 mm.

Max element size Z - 3 mm.

Min Gap X - 0.75 mm.

Min Gap Y - 0.3175 mm.

Min Gap Z - 0.0635 mm.

Assemble -5

i) 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.

ii) Mesh type

Max element size X  - 2.5 mm.

Max element size Y - 2 mm.

Max element size Z - 2.5 mm.

Min Gap X - 0.15 mm.

Min Gap Y - 1 mm.

Min Gap Z - 0.35 mm.

Assemble -5

i) Slack setting 

Min X - 0.5 mm.

Max X - 0.5 mm.

Min Y - 1 mm.

Max Y - 1 mm.

Min Z - 0.

Max Z - 1 mm.

ii) Mesh type

Max element size X  - 8 mm.

Max element size Y - 8 mm.

Max element size Z - 1 mm.

Min Gap X - 2 mm.

Min Gap Y - 2 mm.

Min Gap Z - 0.15875 mm.

Final Model

Macros --> Productivity --> Validation --> Automatic case check tool - This option check for the model on various criteria.

The CAD model is successfully converted into Icepak object & the different errors in the model are corrected.

Mesh Control

Y Cut plane

       

Physics Setup

The Mosfet and the Coil are the two heat generating sources in the model & the Heat generated value is provided as input.

Total power generated - 2W for all the Mosfet & the coil also generate 2 W of heat.

 

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 equation are solved for the turbulent model.

The natural convection are not consider for this model & also gravity vector are not consider.                      

The defaults value of the parameters are set to default.

Transient Setup

• Time variation - Steady

Solution Initialization

X velocity - 0.

Y velocity - 0.

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

 

The maximum temperature is around 41.06 deg C & the mim temp is at the ambient temp. The heat conduction near the mosfet is high so the temp at the fins is also around 40 deg C and heat transfer through convection is low.

Velocity plot

The velocity is maximum around the fan & the heat source which causes heat transfer.

Conclusion

The CAD model is converted into Icepak objects using spaceclaim and the further refinement of the model is done in Icepak and the model is meshed and physics has been successfully setup for the model.