Conjugate Heat Transfer Analysis on a Graphics Card
Introduction
Heat is an inevitable byproduct of work. It’s generated when you start a car’s engine, go for a brisk walk or anything else that generates friction. Heat is also prevalent in electronics where it can be more difficult to manage and can be detrimental to their continued operation. When it comes to graphics cards there are many ways to manage heat, from passive cooling, to fans and even water.
When GPU takes on a heavy workload, such as gaming, it generates a load of heat. When the cooling solution can no longer dissipate heat fast enough to keep temperatures within a safe range, graphics card starts to dump performance to shed heat.
Objective
To calculate heat transfer coefficient of a graphics card processor by running a steady state conjugate heat transfer simulation.
Simulation
The graphics card model was created using 3D CAD modeller and enclosed inside a block of dimensions 20cm*7cm*4cm .The heat generated by the processor is assumed to `10^8 W/m^3`.In order to simulate the graphics card,different materials were assigned to the different components of the graphics card.
| Component | Material | Density (`(kg)/m^3`) | Specific Heat (J/kg-K) | Thermal Conductivity(W/m-K) |
| Motherboard | ABS | 1050 | 1390 | 0.25 |
| Processor | Silicon | 2533 | 0.71 | 145 |
| Fins | Aluminiun | 2719 | 871 | 202.4 |
| Enclosure | Air |
1.225 |
1006.43 | 0.0242 |
The mesh size of 1mm is set for the graphics card where as 5mm mesh size is given to the enclosed volume with share prep turned on.
A pressure based steady state simulation is used to perform the conjugate heat transfer analysis.Realizable K-Epsilon turbulenced model is selected for this simulation as we don't need near wall analysis.Leftmost face of the enclosed is set as velocity inlet with magnitudes of 1m/,3m/s and 5m/s whereas the rightmost face is the pressure outlet. All the other faces of the enclosure is set as no-slip walls.The processor cell zone is given a heat source so as to replicate the heat released by an actual graphics card.
Results
- Velocity 1m/s
- Residuals
- Velocity Contour
- Temperature Contour
- Hotpspots
- Velocity 3m/s
- Residuals
- Velocity Contour
- Temperature Contour
- Hotpspots
- Velocity 5m/s
- Residuals
- Velocity Contour
- Temperature Contour
- Hotpspots
Results
| Inlet Velocity (m/s) | Maximum Temperature (K) | Surface Heat Transfer Coefficient (`w/(m^2-k)`) |
| 1 | 484 | 471 |
| 3 | 413 | 744 |
| 5 | 388 | 931 |
From the above table we can see that as the velocity increases, the temperature of the processor wall decereases. This decrease in temperature is due to increase in the rate of heat transfer due to convection to the surrounding air.Since heat flux is directly proportional to change in temperature of the processor and the surrounding and the surface heat transfer coefficient,the surface heat transfer coefficient increases with the decrease in the temperature of the processor surface as the heat flux remains constant.