Conjugate Heat Transfer Analysis on a graphics card

Description

The whole setup consist of a processor,a fin and a base. The processor releases heat during its operation. Fins are used to increase the surface area of the setup,so that the heat passes over it and gets cooled by the passing air at room temperature. Cooling takes place due to forced convection as a result of passing of air.

Objective

To perform steady-state CHT Analysis on the model of Graphics Card.

fig.Graphics Card

Assumptions

1. The power output of the processor is assumed as 5 W.

2. The processor is the only heat source in the Graphics Card.

3. The volume of the processor are (8*8*1) mm.

4. The processor is in idle condition.

• Geometry

The model is placed in a fluid enclosure of air to mimic a wind tunnel. This is done as the flow is simulated around the model. Shared topology is applied on the entire setup to create a conformal mesh where the surfaces share a common face.

fig. The geometry of setup (Base and Processor)

fig. The geometry of setup (Fin)

• Meshing

The simulation is run on 2 cases :

1. a baseline mesh where the default elemental size of 10.289 mm is used(precalculated by Ansys based on the geometry).
2. a refined mesh where different sizes are given to different components using Body Sizing.

BASELINE

No of elements = 85020

fig. Baseline Mesh details (Base and Fins)

fig.Baseline Mesh details (Processor)

Conformal Mesh

Mesh Quality

REFINED

No of elements = 203658

Enclosure - a tetrahedral mesh of 4mm element size

Base - 1.5 mm

Fins - 1 mm

Processor - 0.5 mm

fig. Refined Mesh details (Base and Fins)

fig. Refined Mesh details (Processor)

Conformal Mesh

Mesh Quality

• Simulation

*Solver : Steady state,pressure based solver

*Viscous model : k-ε turbulence model with standard wall functions

*Energy equation is enabled.

*Relevant materials are assigned to each components such as

1. Base = copper
2. Fins = aluminium
3. Processor = gold

*Boundary condition :

1. Velocity-inlet & pressure-outlet(Velocity - 5 m/s,Temperature - 300K,Pressure = 0 Pa)
2. Side walls = symmetry BC
3. Base wall = no slip wall BC

*The processor is taken as the source term with a power output of 5W.

*Hybrid initialization is used and the simulation is run for 200 iterations.

BASELINE

at iteration=0

at iteration=200

From the above residual plot, residuals start making repetitive profile after the 100th iteration. Hence, the solution has converged at the 100th iteration.

REFINED

at iteration=0

at iteration=200

From the above residual plot, residuals start making repetitive profile after the 120th iteration. Hence, the solution has converged at the 120th iteration.

• Post-processing

BASELINE

Temperature Contour(cut plane)

Temperature Contour(base,fin,processor)

REFINED

Temperature Contour(cut plane)

Temperature Contour(base,fin,processor)

Conclusion

1.The maximum temperature attained by a processor in Case I is 341.487 K and in Case II
is 335.013 K.

2.The potential hotspots in the graphics card are the processor, fins and the contact region
between the base and processor.