GRAPHICS CARD CONJUGATE HEAT TRANSFER ANALYSIS

GRAPHICS CARD CONJUGATE HEAT TRANSFER ANALYSIS

Computational Fluid Dynmaics (CFD)and more specifically Conjugate Heat Transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes, for example: conduction through solids, free and forced convection in the gases/fluids and thermal radiation.

The CHT approach has an advantage over FE Thermal analyses in that wall heat transfer coefficients and their local variations on surfaces are directly calculated within the model rather than based on simplified empirical calculations. The CHT approach therefore has benefits for those applications where heat transfer is either non-uniform or difficult to calculate empirically.

The heat transfer projects performed covered a wide range of aerodynamic and hydrodynamic industrial applications but projects typically had objectives such as:

1. Temperature distribution analysis.
2. Heat flux rate analysis – calculation of wall heat flux rates or heat transfer coefficients.
3. Visualization of heat transfer features for improved understanding of system flow phenomena.
4. Identification of localized ‘hot spots’ or heat sinks in checking against specified requirements.
5. Evaluating variation in temperature peaks for different operating conditions/ failure modes.
6. Assessing insulation or heat shield effectiveness and optimizing of material selections.
7. Coupling CHT with FE analysis to evaluate thermally induced stresses, expansion or fatigue.
8. Temperature field analysis
9. CFD thermal analysis

In this simulation the type of cooling system that was used is air cooling system. The processor was assumed in idle condition. Analytical setup for CHT simulation:

The analysis was performed for two types of mesh:-

Case 1) Base line mesh

Case 2) Refined mesh

STEP 1-

The geometry was setup in ANSYS Space-Claim. Then using share topology feature, all the components like processor, base ,fins and enclosure were shared together to form conformal mesh. Due to this share feature a conformal mesh was formed between all the domains. The formation of conformal was very important to see heat transfer effects at the surface of the solid boundary.an enclosure was formed to capture effects of convection that takes place over graphic card.

STEP 2-

For refining mesh the Hex Dominant Mesh method as used for the enclosure and for the graphic card further mesh size was reduced. The overall mesh size was reduced to 1.10 mm

STEP 3 -

The solver that was used to simulate model was fluent, Pressure based solver are used and turbulent K-E MODEL of viscosity was used and for convection condition-

Initial boundary conditions are-

1. Inlet velocity is 15 m/s
2. Thermal Design Power is the maximum power dissipation in processor assumed to be 20 Watts.
3. PROCESSOR is main and only heat generation source.
4. Temperature inlet is consider 300 K.
5. Heat generated rate at Processor is approximated at =TDP/VOLUME (w/m³)=1953601.953 w/m³

For solid -

Cell Zones-Processor-Source term –No of source-

-Heat Generation Rate-1953601.953 w/m³

For air (fluid)-

Boundaries-Inlet Condition-Velocity-15 m/s and Temperature -300 K

GRAPHICS CARD-

It consist of following components with respected manufactured material -

1. Fins- Aluminum
2. Processor-Gold
3. Base- Copper

Geometry structure –

CASE 1 -BASE MESH

Element Size- 10.2mm

Element-85645

Mesh –

Result-

Residual Plot

From above graph we see that the solution is converging around 100 Iteration.

Temperature plot

Velocity plot

Wall heat transfer coefficient plot

From above graph we say that wall heat coefficient for base mesh varies and accurate value can\'t be determined.

CASE 2 -REFINED MESH

Element size-1.10 mm

Element-457302

Mesh

Result-

Residual Plot

From above graph we see that the solution is converging around 200 Iteration.

Temperature plot

Velocity plot

Wall heat transfer coefficient plot

Global Heat Transfer Coefficient-

Local Heat Transfer Coefficient-

Hotspot in potential hotspot in graphic card is PROCESSOR since it’s generate heat due to power dissipation shown in below figure.

OBSERVATION

Refined mesh gets more accurate result better output and secondly we notice that base mesh have variance result with refined mesh.