Conjugate Heat Transfer Analysis on a graphics card

Aim:

• To Perform a steady-state conjugate heat transfer analysis on a model of a graphics card.
• To Run the simulation for best possible mesh with combination of course and refined mesh in different regions.

Objective:

1. Run the simulation by varying the velocity from 1m/sec to 5m/sec for at least 3 velocities and discuss the results.
2. Find out the maximum temperature and heat transfer coefficient attained by the processor.
3. Prove that the simulation has achieved convergence with appropriate images and plots.
4. Identify potential hotspots on the model.

Theory:

Graphics processing unit:

1. A graphics processing unit (GPU) is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobile phones, personal computers, workstations, and game consoles. Modern GPUs are very efficient at manipulating computer graphics and image processing. Their highly parallel structure makes them more efficient than general-purpose central processing units (CPUs) for algorithms that process large blocks of data in parallel.
2. The GPU, under usage generates heat. They have to kept in optimum temperature range to function efficiently. Thus, they require an appropriate cooling in order to perform the required tasks efficiently. This exercise is to simulate a working environment and study the heat transfer properties used to keep GPUs at optimum temperature.
3. The GPU has a compact processor that does not have the required surface area to cool itself to maintain optimum operating temperature range. Therefore, they require an external component mounted on the processor to increase the surface area in order for it to cool down under use. The GPU is a device that generally consists following components.

• Processor
• Printed circuit board (PCB)
• Fins (Made out of a good heat conducting material)
• Holder (To mount the GPU)

In this study, the above-mentioned components are put through heat transfer analysis to find out the temperature attained by the processor and to definitively derive the optimum velocity of the cooling fluid (Air in this case) that is practical for real life operation.

Procedure:

Geometry:

The geometry is setup in Ansys Space claim. The model for the same is shown below. This model is enclosed in an enclosure.

After Using the share topology feature in the space claim, all the components viz the PCB, the processor and the fins, and the enclosure are shared together so as to get the conformal mesh. The conformality of mesh is very important to see the heat transfer effects at the surface of the solid boundary.

Case setup :-

1. Solver time = steady state
2. Solver type = pressure based
3. Viscous model = k-epsilon and energy equation is solved
4. Adding materials to the components of graphic card
5. Base = Steal
6. fins = Aluminium
7. processor = Copper

Case 1:-

Baseline Mesh with velocity 1/s ,Temp =300 k :

Num of iteration = 750

Scaled residuals :

Contour temperature :-

Temperature distribution in base :-

Velocity distribution :-

Wall heat transfer coefficient :-

Case 2:

Refined mesh:

Inlet velocity: 3m/s temperature: 300k

Num of iteration : 250

Scaled residuals:-

Contour Temperature :-

Temperature distribution:-

Velocity distribution:-

Wall heat transfer coefficient :-

The heat transfer taking place from solid to fluid. Where the fluid passes over the graphic card it takes heat from the solid. The given picture shows that, heat transfer coefficient on the wall. As we can see that the wall heat transfer coefficient is higher at places where velocity is higher.

Case :- 2(2)

Inlet velocity: 5m/s temperature: 300k

Num of iteration : 200

Scaled residuals :-

Temperature contour:-

Temperature distribution:-

Velocity distribution:-

Wall heat transfer coefficient:-

The heat transfer taking place from solid to fluid. Where the fluid passes over the graphic card it takes heat from the solid. The given picture shows that, heat transfer coefficient on the wall. As we can see that the wall heat transfer coefficient is higher at places where velocity is higher.

CONCLUSION:

maximum temperature and heat transfer coefficient attained by the processor.

	Number of elements	Max Temp (K)
Baseline (1m/s)	84390	408.341
Refined(5m/s)	451317	396.300

• The refined mesh gives more accurate results than that of the coarse mesh.
• The number of elements increased the more accurate results of temperature distribution on the components were obtained and enhanced values of maximum temperature
• From the temperature contours, we can say that the temperature on the fins is approximately equal to to the temperature of the processor. This is an ideal behaviour for the graphic card since fins takes most of the heat generated by the processor. Usually the surface area of the fins is larger which improves the cooling of the graphic card.
• The potential hotspots on the model are processor, fins and the contact region between processor and base.
• Therefore, higher velocity of the cooling fluid is recommended.