Conjugate Heat Transfer (CHT) Analysis on an Graphics Card using Ansys Fluent
Objective: Perform Conjugate Heat Transfer (CHT) Analysis on an Graphics Card using Ansys Fluent and write a detailed report explaining the results obtained.
Question:
Perform a steady-state conjugate heat transfer analysis on a model of a graphics card. You can use appropriate materials of your choice for the simulation. Make sure to properly define the correct solid and fluid zones. Refer the video for further clarification and the model is provided below the video.
Run the simulation for best possible mesh with combination of coarse and refined mesh in different regions. Explain the reason for choosing the particular mesh settings.
Your Objectives:
- Run the simulation by varying the velocity from 1m/sec to 5m/sec for at least 3 velocities and discuss the results.
- Find out the maximum temperature and heat transfer coefficient attained by the processor.
- Prove that the simulation has achieved convergence with appropriate images and plots.
- Identify potential hotspots on the model.
From above information, the following cases can be analysed for expected results.
Case-1: Grip Dependency Test
Case-1A: Default Mesh
Case-1B: Refined Mesh
Case-2: Run the simulation by varying the velocity from 1m/sec to 5m/sec for at least 3 velocities and discuss the results.
Case-2A: velocity - 3m/sec
Case-2B: velocity - 5m/sec
Velocity of 1m/sec is applied in Case-1.
Case Setup and Execution:
Geometry: Geometry is setup in Ansys Space Claim.
Share topology feature applied so that 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.
Named Selections: Named selections has been created for boundaries as shown below.
Materials:
Fins: Aluminium
Density- 2719 Kg/m^3
Heat capacity- 871 J/KgK
Thermal conductivity- 202.4 W/mK
Processer: Silicon
Density- 2000 Kg/m^3
Heat capacity- 710 J/KgK
Thermal conductivity- 150 W/mK
PCB: FR4 (glass-reinforced epoxy laminate material)
Density- 1850 Kg/m^3
Heat capacity- 950 J/KgK
Thermal conductivity- 0.29 W/mK
Fluid: Air
Density- 1.225 Kg/m^3
Heat capacity- 1006.43 J/KgK
Thermal conductivity- 0.0242 W/mK
Viscosity- 1.7894e-05 Kg/m-s
Solver Settings:
- Pressure Based Solver.
- Energy eqn on
- Viscous model - k eps 2 eqn.
- Time : Steady
- Source Term in Processor : 11718750000 w/m^3.
Case-1: Grip Dependency Test
Boundary Conditions:
Inlet:
Velocity: 1m/s
Temparature: 300K
Case-1A: Default Mesh
Mesh: Mesh generated using default element size (10.289mm)
Solution is run for 1000 iterations.
Results:
Residuals: Number of iterations to converge - 150.
Temparature Contour:
Temparature Contour on a cut plane:
Temparature of Processor: Max. Temparature- 6937°C
Heat Transfer Coefficient Contour:
Heat Transfer Coefficient Contour on a Cut Plane:
Heat Transfer Coefficient of Processor: Max- 94.53
Velocity Contour on a cut plane:
Velocity Vector Contour on a cut plane:
Case-1B: Refined Mesh
Mesh:
Element size - 4mm.
Body Sizing:
Fins & PCB - 0.65mm
Processor - 0.25mm
Solution is run for 1000 iterations.
Results:
Residuals: Number of iterations to converge - 400.
Temparature Contour:
Temparature Contour on a cut plane:
Temparature of Processor: Max. Temparature- 8569 °C
Heat Transfer Coefficient Contour:
Heat Transfer Coefficient Contour on a Cut Plane:
Heat Transfer Coefficient of Processor: Max- 1070
Velocity Contour on a cut plane:
Velocity Vector Contour on a cut plane:
Case-2: Run the simulation by varying the velocity from 1m/sec to 5m/sec for at least 3 velocities and discuss the results.
All Settings, Geometry and Mesh will be same as Case-1B except inlet velocity
Case-2A: velocity - 3m/sec
Solution is run for 1000 iterations.
Results:
Residuals: Number of iterations to converge - 200.
Temparature Contour:
Temparature Contour on a cut plane:
Temparature of Processor: Max. Temparature- 8569 °C
Heat Transfer Coefficient Contour:
Heat Transfer Coefficient Contour on a Cut Plane:
Heat Transfer Coefficient of Processor: Max- 1070
Velocity Contour on a cut plane:
Velocity Vector Contour on a cut plane:
Case-2B: velocity - 5m/sec
Solution is run for 1000 iterations.
Results:
Residuals: Number of iterations to converge - 200.
Temparature Contour:
Temparature Contour on a cut plane:
Temparature of Processor: Max. Temparature- 8569 °C
Heat Transfer Coefficient Contour:
Heat Transfer Coefficient Contour on a Cut Plane:
Heat Transfer Coefficient of Processor: Max- 1070
Velocity Contour on a cut plane:
Velocity Vector Contour on a cut plane:
Conclusion:
| CASE | Max. Temparature of Processor (°C) | Max. Heat Transfer Coefficient of Processor (Wm^-2k^-1) | Max. Velocity(m/s) |
| 1A | 6937 | 94.53 | 1.136 |
| 1B | 8569 | 1070 | 1.208 |
| 2A | 8569 | 1070 | 3.644 |
| 2B | 8569 | 1070 | 6.061 |
- The max temperature, heat transfer coefficient attained by the processor will not vary when veocity of air is changed, as the max temperature attained is the max temperature generated by the processor itself but as the velocity is increased the temparature of fins and pcb which are connected to processor is decreased.
- The max temperature, heat transfer coefficient attained by the processor, fins and pcb will vary when mesh is refined.
- From the temperature contour, it is clear that the temperature on the fins is almost equal to the temperature on the processor. This is because fins takes most of the heat generated from the processor.
- The end of the fins plate is relatively hotter away from those in the air inlet than the rest of the area and the end of the fins plate nearer to the inlet is relatively cooler.
- The potential hotspots on the model are the processor, fins and the contact region between processor and base.
- Simulation has achieved convergence and appropriate plots attached.