Conjugate Heat Transfer Analysis on a graphics card.
Introduction:
In this project, we will see the conjugate heat transfer analysis of a Graphic Card. Graphic Card is very essential component in different types at computers. Graphic Cards are very efficient for running software and also plays very important role for different kinds of graphics in computers. And for this type of work, it consumes power. And during consumption of power and running for different purposes, it generates heat. This heat generation must be within certain limit for keeping them safe, and for that, always there is a cooling system to maintain its temperature level. Otherwise they may fail. Now, for better product, it is necessary to do an analysis and then based on that report, one can build a graphic card of good quality, which can run so long and keep system running at their optimum condition.
About CHT (Conjugate Heat Transfer) Analysis:
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Conjugate heat transfer represents combination of heat transfer in both solid and liquids simultaneously. The mode of heat transfer in solids is conduction and in case of liquid it is convection.
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Heat transfer in solids is calculated by Fourier's law, which involves heat transfer only by means of conduction.
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For liquids, it is difficult to determine heat transfer because the heat is transported along with the flow of liquid. Sometimes conductive mode of heat transfer dominated the convective heat transfer.
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In viscous models, a viscous effect contributes for heat transfer.
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In compressible flow, heat generation is fluctuating due to variations in thermal properties of fluid
About Analysis :
A Graphic card model is used on which heat will be applied as heat generation source with enclosure placed around it. Air as a fluid will pass over model at certain velocity and heat generation through processor and heat dissipation through fins will be observed. Also temperature of hotspot will be noted down. Heat transfer through processor is also evaluated.
Graphic card model:
Fins:
Processor:
Base:
Material with its specifications used for different components during Analysis:
|
Components |
Material |
Density (Kg/ms) |
Cp (J/Kg-K) |
K (N/ m-K) |
|
Processor |
Silicon |
2330 |
705 |
148 |
|
Fins |
Aluminum |
2719 |
871 |
202.4 |
|
PCB |
Thermoplastic -ABS (Acrynitrile Butadiene Styrene) |
1050 |
1390 |
0.25 |
Fluid Material : Air
Density = 1.223 kg/m3 , Cp= 1006.43 J/kg-k , K= 0.0242 N-m-k
Geometry:
Model is imported in spaceclaim and shared topology options is apply to share each component of model.
Meshing:
Firstly , a baseline mesh is generated to get an overview of model and to generate some results from it. Then an Refined mesh is generated to get better results.
Base Mesh:
Refined mesh:
A good quality mesh is generated to obtain better result for analysis with lowest element quality lies around 18% which is good for this simulation.
Model setup:
- Solver type : Pressure based
- Steady state
- Viscous Turbulent model : K- omega SST
- Model method : SIMPLEC
- Material of each components is assigned in cell zone
Boundary conditions:
In order to provide energy source for heat generation , Processor is used and energy source is assigned to it.
Assume 10 watt as power consumption of heat generation of Processor, volume of processor = 8*8*1 mm3 = 64 * 10-9 m3
So , for Volumetric Heat Source , Source term = power/ volume w/m3 = 10 /(64*10-9) = 156250000 w/m3
For enclosure , Inlet = variable velocities , Outlet = pressure outlet , walls = symmetry .
Case 1 : Baseline mesh
Residual plots:
Solution converged around 375 iterations.
Average area weighted of total temperature:
Total temperature:
Temperature along plane:
Velocity along plane:
Velocity along plane is 4.758 m/s
Velocity streamline:
Fin Temperature:
Temperature obtained on fin is 406.106 K
Processor Temperature:
Temperature obtained on processor is 413.171 k
Base Temperature:
Temperature obtained on base is 319.655 k
Hotspot obtained during Analysis:
Fin wall heat transfer coefficient:
Wall HTC obtained on fin is 146.427 w/m2k1
Processor wall heat transfer coefficient:
Wall HTC obtained on prcocessor is 217.657 w/m2k1
Base wall heat transfer coefficient:
Wall HTC obtained on base is 156.754 w/m2k1
Case 2 : Refined mesh
(a) Velocity 1 m/s.
Residual plots:
Solution converged at 400 iterations.
Average area weighted of total temperature:
Total temperature:
Temperature along plane:
Velocity along plane:
Velocity along plane is 0.949 m/s
Velocity streamline:
Fin Temperature:
Temperature obtained on fin is 587.666 K
Processor Temperature:
Temperature obtained on processor is 594.367 k
Base Temperature:
Temperature obtained on base is 392.116 k
Hotspot obtained during Analysis:
Fin wall heat transfer coefficient:
Wall HTC obtained on fin is 308.1966 w/m2k1
Processor wall heat transfer coefficient:
Wall HTC obtained on prcocessor is 1794.96 w/m2k1
Base wall heat transfer coefficient:
Wall HTC obtained on base is 306.398 w/m2k1
(b) Velocity 3 m/s.
Residual plots:
Average area weighted of total temperature:
Solution converged at 550 iterations. After seeing both residual and avg area weighted of total temperature we can see that solution is constant for avg area weighted of total temperature at around 550 so we can say that solution converges around 550 iteration.
Total temperature:
Temperature along plane:
Velocity along plane:
Velocity along plane is 2.8371 m/s
Velocity streamline:
Fin Temperature:
Temperature obtained on fin is 437.602 K
Processor Temperature:
Temperature obtained on processor is 444.303 k
Base Temperature:
Temperature obtained on base is 328.747 k
Hotspot obtained during Analysis:
Fin wall heat transfer coefficient:
Wall HTC obtained on fin is 309.231 w/m2k1
Processor wall heat transfer coefficient:
Wall HTC obtained on prcocessor is 1794.97 w/m2k1
Base wall heat transfer coefficient:
Wall HTC obtained on base is 307.536 w/m2k1
(c) Velocity 5 m/s.
Residual plots:
Average area weighted of total temperature:
Solution converged at 500 iterations. After seeing both residual and avg area weighted of total temperature we can see that solution is constant for avg area weighted of total temperature at around 500 so we can say that solution converges around 550 iteration.
Total temperature:
Temperature along plane:
Velocity along plane:
Velocity along plane is 4.728 m/s
Velocity streamline:
Fin Temperature:
Temperature obtained on fin is 399.572 K
Processor Temperature:
Temperature obtained on processor is 406.199 k
Base Temperature:
Temperature obtained on base is 318.227 k
Hotspot obtained during Analysis:
Fin wall heat transfer coefficient:
Wall HTC obtained on fin is 311.911 w/m2k1
Processor wall heat transfer coefficient:
Wall HTC obtained on prcocessor is 1794.98 w/m2k1
Base wall heat transfer coefficient:
Wall HTC obtained on base is 310.637 w/m2k1
Comparing the results of cases:
| Cases | Elements | Temperature of Processor K | Wall HTC w/m2k1 |
| Baseline mesh | 175712 | 413.171 | 217.657 |
| Refine mesh velocity 1 m/s | 1411268 | 594.367 | 1794.96 |
| Refine mesh velocity 3 m/s | 1411268 | 444.303 | 1794.97 |
| Refine mesh velocity 5 m/s | 1411268 | 406.199 | 1794.98 |
Comparing results of different cases with Temperature and Wall HTC of processor , we can see that huge difference in temperature and wall htc for baseline and refined mesh cases. But with change in velocity for refine mesh case we see that only temperature of processor is decreased with increase in velocity but wall htc value changes only in decimal .
Conclusion:
- We can conclude from above analysis that conjugate heat transfer gives us results of heat distribution in different components
- We increase mesh quality by doing refine mesh from baseline mesh we can see that large change in terms of temperature and wall htc of each components.
- Increase in velocity , decreases the temperature of components.
- No large change is observed in wall htc of processor , base and fins with increase in velocity.
- For processor , wall htc is observe only on side walls as conduction takes place on faces which are connected with fins and base.