Week 6 - CHT Analysis on a Graphics card

Aim – To conduct a conjugate heat transfer analysis on a graphics card and analyse the overall temperature of the components and the heat transfer coefficient of the processor

Solving and Modelling Approach –

1. Firstly, the step file of the entire graphics card was imported into Spaceclaim.
2. The graphics card consists of a processor, base and fins as 3 major components.
3. As the graphics card runs, it generates heat that can considerably damage other components in the vicinity due to high temperatures.
4. The fins of the graphics card is designed to increase the surface area for heat transfer thereby resulting in a lowered average temperature.
5. For this particular simulation, the base, processor, and fins were considered as solid bodies.
6. An enclosure, as shown below, was created around the graphics card for simulation purposes.
7. One end of the enclosure will be considered as an inlet for air to flow on the graphics card, thus cooling the overall component.
8. To obtain a conformal mesh between the solid and fluid boundaries, “share topology” option was enabled to share.
9. The model was then imported into the mesh interface for mesh generation

Base:

Fins base:

Processor:

Section plane:

Meshing –

Baseline mesh:

Number of nodes -15708

Number of elements -83711

Refined mesh:

Number of nodes -39283

Number of elements -216725

Overall global size=5mm

Body sizing of processor=0.5mm

Body sizing of fins=0.8mm

Setting up the case in Ansys Setup –

1. Since the velocities considered for this particular problem are 1, 3, and 5m/s which is very small as compared to the velocity of sound, the Mach number is <<< 0.3.
2. Hence, a pressure-based solver was used since there are low chances of compression.
3. The problem was analysed in a steady state manner since we are only analysing the end results
4. Since this problem statement requires to calculate the wall heat transfer coefficient, a K-omega SST viscous turbulence model was used since this model is more accurate at capturing wall effects as compared to other models such as the k-epsilon model.
5. Then, materials were added for the solid domains.
6. plastic(polystyrene), copper, and silicon were used for the base, fins, and processor respectively.
7. The materials for each component were taken from several articles from the internet.
8. Afterwards, all the domains were assigned to either solid or fluid in the cell zone conditions, the enclosure being the only fluid domain, and the components represented the solid domains.
9. The respective material for each component was added in the cell zone conditions.
10. Since this problem involves the processor being a source of heat generation, an energy source term was applied to the processor domain
11. The processor is component which exists between the base and fins.
12. As the usage increases, the processor produces heat and the base is used to support the overall assembly.
13. Let the thermal design power of the processor be considered as 10W from various sources on the net.
14. Next the volume of the processor is calculated
15. Heat generated by the processor = Power (W)/Volume of the processor = 10/64e-9

= 1.5625e8 W/m^3

16. The above value was inserted as a single source term of energy in the cell zone conditions of the processor
17. For boundary conditions, the velocity inlet value was given as per iteration and the outlet was considered as a pressure outlet.
18. Afterwards, report definitions of maximum temperature and area weighted average temperature of the heat transfer coefficient will be giving.
19. Furthermore, the solution was initialised using hybrid initialisation.
20. Then create contour of temperature and run the simulation for 500 iterations

Results –

Inlet velocity = 3m/s

• A baseline mesh was created and simulated for checking whether the simulation runs properly without any errors

Hotspot region:

Refined mesh results

For velocity=1m/s

Hot spot region:

For velocity=3m/s

For velocity=5m/s

Global hot region:

For Refined mesh

Velocity maximum temperature(K) Heat transfer coefficient(W/m2K)

1 m/s 623.926 6.5205

3 m/s 456.699 12.212

5m/s 414.54 18.1336

Conclusion:

From above table As Velocity Increases,because of increase in heat transfer coefficient ,the maximum temperature decreases. This is because as increasing velocity more convection takes from fins the heat loss takes place fastly as a result temperature decreases.