Week 6 - CHT Analysis on a Graphics card

Aim: CHT analysis o n a graphics card

Objectives:

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.

Introduction:

Conjugate Heat Transfer Analysis (CHT):

The Conjugate Heat Transfer (CHT) analysis type allows for the simulation of heat transfer between solid and fluid domains by exchanging thermal energy at the interfaces between them. conjugate heat transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes.

Application:

1. The simulation of heat exchangers
2. Cooling of electronic equipment
3. General-purpose cooling and heating systems.
4. conduction through solids
5. Free and forced convection in the gases/fluids
6. Thermal radiation

Advantages:

The CHT approach has an advantage over FE thermal analyses in that wall heat transfer coefficients and their local variations on surfaces are directly calculated within the model rather than based on simplified empirical calculations. The CHT approach therefore has benefits for those applications where heat transfer is either non-uniform or difficult to calculate empirically.

Graphics card:

Graphics card is a hardware which is used to increase the video memory of a computer, and make its display quality more high-definition. It makes the computer more powerful and gives it the capacity to do more high-level works. The quality of the image depends on the quality of the graphics card. It is very much important for gaming and video editing on a PC. Every game needs a graphics memory to start and it depends on the type of the game, and the requirements are mentioned on the game box.

Model of graphics carf we used for simulation:

It has four parts namely:

1.Fins : These are placed above the graphics card processor to dissipate heat produced by the processor, Fins increase the surface area of contact with air this increases the amount of heat dissipation.

2.Processor: This is the main hardware in the graphics card that takes the input and gives desired output to get best image quality. Image quality depends upon how powerful this processor is.

3.Base : This is where all circuit and other small electronic components are present it has less thermal conductivity compared to fins as a result most of the heat disspation only occurs through fins.

Problem statement:

To carry out CHT analysis on grahics card and observe the amount of heat generated on processor with increase in incoming velocity of air and also the rate at which heat is dissipated from the fins.

Preparation:

Space claim:

• In space claim we import the graphics card STEP file and set topology to share.
• Reason to set share topology is to conformal mesh in meshing.

Meshing:

Naming:

Name the components of the graphics card and also name the wall and fluid regions

• Fins

• Processor

• Base

• Fluid

• Inlet

• Outlet

• symmetry

After the naming is done add body sizing to processor,fins and base.

For base give element size as 0.5mm

For fins give element size as 0.5mm

For processor give element size as 0.2mm

Give gloabl element size as 5mm

We have:

1. No of elements = 842552

2. No of nodes = 150685

Setup:

Solver:

• Steady state
• Pressure based

Turbulance model:

• Energy term ON
• k-omega SST model

Solution method:

• SIMPLE

Materials:

• Fins: Aluminum

• Processor:
• Base:

Energy Source term :

• volume of the processor = `64mm^3`
• Assumed power = `16W`
• Source value = Assumed power/Volume of the processor
• Source value = `250000000 W/m^3`

Initialization and number of iterations:

• Hybrid initialization
• 300 iterations

Definations:

• Surface heat transfer coefficient at fins
• Maximum temperature at processor

Reference values:

Case 1:

Inlet velocity: 1m/s

Inlet temperature: 25 C

Results:

Residuals:

Surface heat transfer coefficient:

Processor temperature:

temperature contour:

Velocity contour:

Hotspot:

Values of surface heat transfer coefficient and maximum temperature at processor surface:

Case 2:

Inlet velocity: 2.5m/s

Inlet temperature: 25 C

Results:

Residuals:

Surface heat transfer coefficient:

Processor temperature:

temperature contour:

Velocity contour:

Hotspot:

Values of surface heat transfer coefficient and maximum temperature at processor surface:

Case 3:

Inlet velocity: 5m/s

Inlet temperature: 25 C

Results:

Residuals:

Surface heat transfer coefficient:

Processor temperature:

temperature contour:

Velocity contour:

Hotspot:

Values of surface heat transfer coefficient and maximum temperature at processor surface:

Comparing surface heat transfer coefficient and maximum temperature attained in each case:

Conclusion:

• Increase in inlet velocity increases the amount of heat transfered from fins to air.
• Increase in Surface heat transfer coefficient means increase in heat transfer from fins to fluid.
• Increases in Surface heat transfer coefficient increases the amount of heat generated on the surface of the processor as more amount of heat is dissipated to air
• Global hotspot is present at the region where the processor is present.
• Velocity increasw after passing through the graphics card because of the heat transfered from the fins the kinetic energy of the air molecule increaces and this in turn increase teh velocity.
• Since increase in velocity increase the heat dissipated from processor most modern day processors asre provided with fan.